Fatiguing inspiratory muscle work causes reflex reduction in resting leg blood flow in humans

Influence of an inspiratory muscle fatigue protocol on older adults on respiratory muscle strength, muscle oxygen saturation, and functional capacity: a randomized controlled trial

BACKGROUND

The fatigue of the inspiratory musculature, particularly the diaphragm, has been demonstrated to exert systemic effects on the body, impacting cardiovascular and performance outcomes. This study aimed to evaluate the influence of an inspiratory muscle fatigue protocol on respiratory muscle strength, functionality, and muscle oxygen saturation in older adults.

METHODS

A single-blinded randomized controlled clinical trial was conducted on twenty-four older adults aged over 60 years, who met inclusion criteria were physically independent in terms of gait and functionality. Participants were randomly assigned to one of three groups: control group, inspiratory muscle fatigue group, or activation group. Diaphragmatic ultrasonography (diaphragmatic thickness, thickening fraction, diaphragm movement curve), maximal inspiratory mouth pressure, muscle oxygen saturation, and functionality (timed up and go test, for five times sit to stand test) were used to measure the study variables at two time points: pre-intervention (T1) and post-intervention (T2).

RESULTS

In the maximum inspiratory pressure variable in the activation group an increase was found between baseline and post-treatment of 3.00 ± 0.93 cmH2O (P < 0.01), while in the inspiratory muscle fatigue a decrease of -6.75 ± 2.66 cmH2O (P < 0.01) was found. In addition, the inspiratory muscle fatigue group showed lower scores for respiratory and functional variables after performing the diaphragmatic fatigue intervention than the activation and control group (P < 0.05), on the other hand, the activation group showed more positive values for functional and respiratory capacity variables after performing the inspiratory muscle activation training (P < 0.05).

CONCLUSIONS

Fatigue of the inspiratory musculature appears to negatively impact inspiratory muscle strength, peripheral muscle strength, muscular oxygenation, and functionality in older adults. Activation of the inspiratory musculature could contribute to improved respiratory muscle strength and function in these individuals.

TRIAL REGISTRATION

ClinicalTrials.gov ID: NCT06266013.

Decreased Work Capability Related to High-Altitude Exposure

Background

The unique environment of high altitude can affect the work capacity of those not accustomed to it, and in some cases, it can even endanger their lives. Studying the effect of high-altitude exposure on work capacity is important. Still, there are few reviews on this topic. We aimed to summarize the parameters used to evaluate work capability in a high-altitude environment, the potential pathophysiological mechanisms, and the available pharmacological and non-pharmacological strategies for improvement.

Methods

We conducted searches on PubMed, Google Scholar, and China National Knowledge Infrastructure to explore the existing literature including basic and clinical studies from 1968 to 2023, using keywords such as "work capability/performance and high-altitude hypoxia" or "work/exercise at high altitude". Conference proceedings, notes, and case reports were excluded. The CiteSpace 6.1.R3 was used for de-duplication.

Results

A total of 727 papers were identified through search terms from the database. 486 papers were eliminated following the de-duplication process, lacking full text and deemed irrelevant to this article. Among the remaining 241 papers, 21 investigate the underlying mechanisms of reduced work capability due to altitude exposure, and 94 papers discuss measures to improve work capability when exposed to high altitudes.

Conclusion

In conclusion, this review summarizes the evaluation of indicators, pathomechanisms, and improvement measures for high-altitude exposure-related changes in work capability. More basic research on its mechanisms and large-sample, randomized controlled clinical studies to validate its effects are needed.

Sex-based differences in the blood pressure responses to muscle metaboreflex activation are consistent between limb and respiratory muscle

The purpose of this study was to compare sex-based differences in the mean arterial blood pressure (MAP) response to limb and inspiratory metaboreflex activation, during relative and absolute workloads. Healthy males (n = 9) and females (n = 8) completed pulmonary function testing, forearm volume and circumference measurements, and bouts of limb and inspiratory muscle exercise. The exercises performed included bouts of rhythmic handgrip exercise (RHG) and inspiratory pressure threshold loading (PTL) to task failure, performed in a randomized order and separated by 30 minutes of rest. Participants performed both RHG and PTL at predetermined relative (R) and absolute (A) workloads, while cardiopulmonary measurements were recorded continuously. A time-dependent rise in MAP was observed in all participants, regardless of sex, muscle, or workload (P < 0.001). MAP was greater in males than females during all exercise bouts regardless of muscle group or workload (P < 0.001). The change in MAP from baseline was also greater in males (R-RHG: Δ31 ± 12 mmHg; R-PTL: Δ31 ± 9; A-RHG: Δ35 ± 6; and A-PTL: Δ30 ± 7) than females (R-RHG: Δ21 ± 7 mmHg; R-PTL: Δ13 ± 7; A-RHG: Δ21 ± 7; and A-PTL: Δ14 ± 3) (P < 0.001). Results from this study show that when the forearm and diaphragm perform the same relative or absolute work, the blood pressure response is statistically similar, and both responses are greater in males than females. The findings from the present study suggest that the sex-based difference in the response to metaboreflex activation is similar between the limb and respiratory musculature.NEW & NOTEWORTHY With rhythmic handgrip exercise and inspiratory pressure threshold loading there was a time-dependent rise in the blood pressure that was significantly lower in females than males. The blunted blood pressure response in females was present whether handgrip or inspiratory workload was relative or absolute. An attenuated cardiovascular response to high levels of limb or respiratory muscle work may have implications for whole body exercise in health and disease.

Recruitment of the diaphragm and sternocleidomastoid muscle during increasing inspiratory pressure loads in healthy young adults

BACKGROUND

Inspiratory muscle training (IMT) is often employed to enhance improvement in inspiratory muscle strength. However, the relationship between inspiratory muscle recruitment patterns and increasing inspiratory load remains unclear. Furthermore, the effect of breathing instructions on diaphragm activity at various inspiratory loads is unknown.

OBJECTIVE

To investigate the recruitment activity of the diaphragm and sternocleidomastoid (SCM) muscle under increased inspiratory pressure loading, with and without diaphragmatic breathing instructions, in healthy young adults.

METHODS

Participants were invited to breathe, in random order, 6 sets of 10 breaths at inspiratory loads of 30 % to 80 % maximal inspiratory pressure (MIP), in 10 % increments. The measurement process was repeated with a specific focus of diaphragmatic descent during inspiration. During each targeted breath, recordings of surface electromyography of the right SCM muscle and thickness of the right hemi-diaphragm measured by ultrasonography were undertaken concurrently.

RESULTS

Sixty-two adults (31 males, age: 23±3 years) participated in the study. Irrespective of breathing instructions, computed diaphragm thickening fraction (DTf) increased with increasing inspiratory load but peaked at 50 % MIP and declined with increasing load to 80 % MIP. SCM recruitment increased with increasing inspiratory load to 80 % MIP. Forced inspiration with diaphragmatic breathing was associated with a higher DTf and lower SCM muscle activity. The above pattern was similar for both male and female participants. Female participants produced higher SCM activity compared with males but only at inspiration loads below 50 % MIP.

CONCLUSIONS

In a cohort of young healthy adults, magnitude of diaphragmatic effort was greatest at 50 % MIP but declined with increasing inspiratory load to 80 % MIP. Forced inspiration combined with focused diaphragmatic breathing accentuated diaphragm contraction and reduced SCM muscle contribution. Our findings show that diaphragmatic muscle recruitment is non-linear and that the generic clinical prescription of an IMT program may need to be reconfigured.

Effects of inspiratory muscle training on pulmonary function, diaphragmatic thickness, balance and exercise capacity in people after stroke: a systematic review and meta-analysis

PURPOSE

To examine the effects of inspiratory muscle training (IMT) on pulmonary and diaphragmatic function, exercise capacity, balance and quality of life (QOL), in post-stroke individuals.

METHODS

A literature search was conducted using MEDLINE, CINAHL, EMBASE, PubMed, PEDro, Web of Science and China Biological Medicine databases. Randomized controlled trials (RCTs) with a PEDro score ≥6 focusing on the effects of IMT were included. The GRADE system was used to determine the certainty of evidence for each outcome.

RESULTS

Nine studies (255 participants) were included. IMT significantly increased forced expiratory volume in one second (FEV1) (4 studies, 112 participants, mean difference (MD)=0.18 litre, 95% confidence interval (CI): 0.14-0.23); maximal inspiratory pressure (MIP) (8 studies, 226 participants, MD = 6.37 cm H2O, 95% CI: 1.26-11.49); and diaphragm thickness fraction (DTf) on both sides (MD of affected side vs. unaffected side: 51 vs. 37%). The evidence certainty for diaphragmatic function was moderate. No significant change was observed in forced vital capacity (FVC), balance function, exercise capacity and QOL.

CONCLUSION

This review reveals moderate evidence certainty in support of IMT improving diaphragmatic function. It appears that a training intensity between 30 and 50% MIP results in a significantly improved MIP.

Correlation between handgrip strength and air trapping in patients with stable chronic obstructive pulmonary disease

Background

Chronic obstructive pulmonary disease (COPD) often presents with dyspnea resulting from the condition of air trapping, assessed by lung volume measurement studies. This study aimed to investigate the relationship between handgrip strength (HGS) and air trapping in COPD patients.

Methods

Cross-sectional research was conducted in COPD patients at Thammasat University Hospital, Thailand between May 2022 and December 2023. HGS was assessed using the Jamar® Smart Hand Dynamometer, and air trapping was measured using a body plethysmograph. Air trapping was defined as a ratio of residual volume (RV) to total lung capacity (TLC) greater than 40%. Receiver operator characteristic (ROC) curves, sensitivity, and specificity values were calculated to determine the optimal cutoff value of HGS for predicting air trapping.

Results

A total of 72 patients (90.3% male) were included, with an average age of 72.4±9.7 years. The body mass index was 23.5±4.3 kg/m2. The smoking history was 23.2±14.8 pack-years. Common comorbidities included hypertension (36.1%) and diabetes (22.2%). Post-bronchodilator forced expiratory volume in 1 second (FEV1) was 72.1%±21.2%. Air trapping was found in 55.6%. A negative correlation was found between HGS and RV/TLC (R=-0.399, P=0.001). The best cutoff value for HGS to predict air trapping was 28.3 kg, with 71.9% sensitivity and 65.0% specificity. The area under the ROC curve for identifying air trapping was 0.681 (95% CI: 0.554 to 0.808, P=0.009).

Conclusions

Air trapping is common in COPD patients, and HGS is significantly correlated with air trapping. Thus, HGS may serve as an alternative tool for assessing air trapping.

The influence of low resistance respiratory muscle training on pulmonary function and high intensity exercise performance

Background/objectives

Respiratory muscle training (RMT) was recognized as an effective means to improve respiratory muscle (RM) strength and enhance exercise performance. The purpose of this study was to examine the effect of low-intensity RMT on RM strength, pulmonary function, and performance.

Methods

Fourteen healthy active adults were assigned randomly to either a training or placebo group. The training group completed six weeks of RMT, which consisted of a first week, 1 set of 15 min/d, 5 d/wk at 10-25% of maximal inspiratory pressure (PImax), and the remaining 5 weeks, 2 sets of 15 min/d, 5 d/wk, at 30% PImax. The placebo group followed the same protocol but with almost no additional ventilatory resistance. Measurement of RM strength and endurance, spirometry, and endurance exercise performance were obtained before and after the RMT program.

Results

In the training group, PImax (+14%) and maximal expiratory pressure (PEmax, +27%), forced vital capacity (FVC, +3.6%), maximal oxygen uptake (VO2max, +11%), and time to exhaustion (Tlim90%, +25%) increased significantly from baseline values (P < 0.05). No significant changes were observed in the placebo group. Also, no significant interaction in maximum voluntary ventilation (MVV12), minute ventilation (VE), and respiratory rate (RR) were detected.

Conclusions

These data suggest that low-intensity RMT is an effective tool to improve RM strength, pulmonary elastic properties and endurance exercise performance.

Differential effects of exercise intensity and tolerable duration on exercise-induced diaphragm and expiratory muscle fatigue

We investigated the effect of exercise intensity and tolerable duration on the development of exercise-induced diaphragm and expiratory muscle fatigue. Ten healthy adults (25 ± 5 yr; 2 females) cycled to intolerance on three separate occasions: 1) 5% below critical power ( 0.05). In conclusion, the magnitude of exercise-induced diaphragm fatigue was greater after longer-duration severe exercise than after shorter-duration severe and heavy exercise. By contrast, the magnitude of exercise-induced expiratory muscle fatigue was unaffected by exercise intensity and tolerable duration.NEW & NOTEWORTHY Exercise-induced respiratory muscle fatigue contributes to limiting exercise tolerance. Accordingly, better understanding the exercise conditions under which respiratory muscle fatigue occurs is warranted. Although heavy-intensity as well as short- and long-duration severe-intensity exercise performed to intolerance elicit diaphragm and expiratory muscle fatigue, we find, for the first time, that the relationship between exercise intensity, exercise duration, and the magnitude of exercise-induced fatigue is different for the diaphragm compared with the expiratory muscles.

Effects of High-Intensity Inspiratory Muscle Warm-Up on High-Intensity Exercise Performance and Muscle Oxygenation

PURPOSE

An inspiratory muscle warm-up (IMW) improves inspiratory muscle function, but the effects of high-intensity exercise are inconsistent. We aimed to determine the effects of high-intensity IMW on high-intensity exercise performance and muscle oxygenation.

METHODS

Ten healthy men (maximal oxygen uptake [V˙O2max] 52.2 [5.0] mL·kg-1·min-1) performed constant-load exercise to exhaustion on a cycle ergometer at V˙O2max under 2 IMW conditions: a placebo condition (PLA) and a high-intensity IMW condition (HIGH). The inspiratory loads were set at 15% and 80% of maximal inspiratory pressure, respectively. Maximal inspiratory pressure was measured before and after IMW. Oxyhemoglobin was measured in the vastus lateralis by near-infrared spectroscopy during exercise. Rating of perceived exertion (RPE) for a leg was measured after 1 and 2 minutes of exercise.

RESULTS

Exercise tolerance was significantly higher under HIGH than PLA (228 [49] s vs 218 [49] s, P = .003). Maximal inspiratory pressure was significantly increased by IMW under HIGH (from 125 [20] to 136 [25] cm H2O, P = .031). Oxyhemoglobin was significantly higher under HIGH than PLA at 80% of the total duration of exercise (P = .048). RPE for the leg was significantly lower under HIGH than PLA after 2 minutes of exercise (P = .019).

CONCLUSIONS

Given that oxyhemoglobin is an index of local oxygen supply, the results of this study suggest that high-intensity IMW increases the oxygen supply to active limbs. It may also reflect a reduction in RPE in the leg. In addition, high-intensity IMW may improve exercise performance.

Respiratory training effects in Long COVID-19 patients: a systematic review and meta-analysis

INTRODUCTION

To date, it is unknown whether respiratory training interventions can benefit Long COVID-19 patients. The main objective was to analyze the effects of respiratory training on patients with Long COVID-19, concretely on respiratory muscle strength, lung function, dyspnea, and functional capacity.

METHODS

We performed a systematic review following PRISMA statement using PubMed, Scopus, and PEDro (last search November 2023). The risk of bias was assessed using the Cochrane tool. We included randomized controlled trials testing the effect of respiratory training interventions in Long COVID-19 patients versus no intervention, control, or placebo intervention. The data was pooled, and a meta-analysis was complete.

RESULTS

We selected 7 studies, which included 572 patients. Meta-analysis results show significant differences in favor of respiratory training in respiratory muscle strength (MD = 13.71; 95% CI = 5.41; 22; p = 0.001), dyspnea (SDM = 1.39; 95% CI = 0.33; 2.46; p = 0.01) and functional capacity (SDM = 0.90; 95% CI = 0.37; 1.43; p = 0.0009), but not in lung function (MD = 0.28; 95%CI = -0.27; 0.83; p = 0.32).

CONCLUSION

The results of this systematic review with meta-analysis suggest that respiratory training improves respiratory muscle strength and functional capacity in Long COVID-19 patients, as well as dyspnea if combined with therapeutic exercise. However, respiratory training does not improve lung function in these patients.

REVIEW REGISTRATION PROSPERO IDENTIFIER

CRD42022371820.

Load carriage physiology in normoxia and hypoxia

PURPOSE

To determine the effects of load carriage in normoxia and normobaric hypoxia on ventilatory responses, hemodynamics, tissue oxygenation, and metabolism.

METHODS

Healthy males (n = 12) completed 3 randomly ordered baseline graded exercise tests in the following conditions: (1) unloaded normoxic (U: FIO2 = 20.93%), (2) loaded (~ 30 kg) normoxic (LN), and (3) loaded hypoxic simulating ~ 3650 m (LH: FIO2 =  ~ 13%). Thereafter, experimental exercise trials were completed in quasi-randomized order (i.e., U completed first) consisting of 3 × 10 min of walking (separated by 5 min seated rest) with stages matched with the U condition (in ascending order) for relative intensity, absolute oxygen consumption ([VO2]; 1.7 L min-1), and walking speed (1.45 ± 0.15 m s-1).

RESULTS

Load carriage increased perceived exertion and reduced VO2max (LN: - 7%; LH: - 32%; p < 0.05). At matched VO2, stroke volume and tidal volume were reduced and maintained with LN and LH vs. U, respectively (p < 0.05). Increases in cardiac output and minute ventilation at matched VO2 (with LH) and speed (with LN and LH), were primarily accomplished via increases in heart rate and breathing frequency (p < 0.05). Cerebral oxygenated hemoglobin (O2HHb) was increased at all intensities with LN, but deoxygenated hemoglobin and total hemoglobin were increased with LH (p < 0.05). Muscle oxygen kinetics and substrate utilization were similar between LN and U, but LH increased CHO dependence and reduced muscle O2HHb at matched speed (p < 0.05).

CONCLUSION

Load carriage reduces cardiorespiratory efficiency and increases physiological strain, particularly in hypoxic environments. Potential load carriage-induced alterations in cerebral blood flow may increase the risk for altitude illnesses and requires further study.

Breathing a low-density gas reduces respiratory muscle force development and marginally improves exercise performance in master athletes

INTRODUCTION

We tested the hypothesis that breathing heliox, to attenuate the mechanical constraints accompanying the decline in pulmonary function with aging, improves exercise performance.

METHODS

Fourteen endurance-trained older men (67.9 ± 5.9 year, [Formula: see text]O2max: 50.8 ± 5.8 ml/kg/min; 151% predicted) completed two cycling 5-km time trials while breathing room air (i.e., 21% O2-79% N2) or heliox (i.e., 21% O2-79% He). Maximal flow-volume curves (MFVC) were determined pre-exercise to characterize expiratory flow limitation (EFL, % tidal volume intersecting the MFVC). Respiratory muscle force development was indirectly determined as the product of the time integral of inspiratory and expiratory mouth pressure (∫Pmouth) and breathing frequency. Maximal inspiratory and expiratory pressure maneuvers were performed pre-exercise and post-exercise to estimate respiratory muscle fatigue.

RESULTS

Exercise performance time improved (527.6 ± 38 vs. 531.3 ± 36.9 s; P = 0.017), and respiratory muscle force development decreased during inspiration (- 22.8 ± 11.6%, P < 0.001) and expiration (- 10.8 ± 11.4%, P = 0.003) with heliox compared with room air. EFL tended to be lower with heliox (22 ± 23 vs. 30 ± 23% tidal volume; P = 0.054). Minute ventilation normalized to CO2 production ([Formula: see text]E/[Formula: see text]CO2) increased with heliox (28.6 ± 2.7 vs. 25.1 ± 1.8; P < 0.001). A reduction in MIP and MEP was observed post-exercise vs. pre-exercise but was not different between conditions.

CONCLUSIONS

Breathing heliox has a limited effect on performance during a 5-km time trial in master athletes despite a reduction in respiratory muscle force development.

The relationship between inspiratory muscle strength, venous refilling time, disease severity, and functional capacity in patients with chronic venous insufficiency

BACKGROUND

Our aim is to evaluate the relationship between inspiratory muscle strength and venous refilling time, disease severity, and functional capacity in patients with chronic venous insufficiency (CVI).

METHODS

Sixty-one patients (49 female, aged 20-65 ) were enrolled in the study. The demographic characteristics of the patients were questioned. All patients were assessed with maximum inspiratory and expiratory pressure (MIP/MEP) for inspiratory and expiratory muscle strength, photoplethysmography for venous refilling time (VRT), venous clinical severity score (VCSS) for disease severity, and 6-min walk test (6-MWT) for functional capacity.

RESULTS

The mean age of the patients was 49.48 ± 13.19 years, and the mean duration of disease was 9.18 ± 6.57 years. There was statistically significant positive association between MIP and VRT(r: 0.331, p: 0.009), 6-MWT (r: 0.616, p < 0.001) values, and there was negative association between MIP and VCSS(r: -0.439 p < 0.001) scores.

CONCLUSION

Evaluation of inspiratory muscle strength and elimination of its deficiency, providing interventions to approach normative values have the potential to contribute positively to the treatment of the patient.

Consequences of group III/IV afferent feedback and respiratory muscle work on exercise tolerance in heart failure with reduced ejection fraction

Exercise intolerance and exertional dyspnoea are the cardinal symptoms of heart failure with reduced ejection fraction (HFrEF). In HFrEF, abnormal autonomic and cardiopulmonary responses arising from locomotor muscle group III/IV afferent feedback is one of the primary mechanisms contributing to exercise intolerance. HFrEF patients also have pulmonary system and respiratory muscle abnormalities that impair exercise tolerance. Thus, the primary impetus for this review was to describe the mechanistic consequences of locomotor muscle group III/IV afferent feedback and respiratory muscle work in HFrEF. To address this, we first discuss the abnormal autonomic and cardiopulmonary responses mediated by locomotor muscle afferent feedback in HFrEF. Next, we outline how respiratory muscle work impairs exercise tolerance in HFrEF through its effects on locomotor muscle O2 delivery. We then discuss the direct and indirect evidence supporting an interaction between locomotor muscle group III/IV afferent feedback and respiratory muscle work during exercise in HFrEF. Last, we outline future research directions related to locomotor and respiratory muscle abnormalities to progress the field forward in understanding the pathophysiology of exercise intolerance in HFrEF. NEW FINDINGS: What is the topic of this review? This review is focused on understanding the role that locomotor muscle group III/IV afferent feedback and respiratory muscle work play in the pathophysiology of exercise intolerance in patients with heart failure. What advances does it highlight? This review proposes that the concomitant effects of locomotor muscle afferent feedback and respiratory muscle work worsen exercise tolerance and exacerbate exertional dyspnoea in patients with heart failure.

Acute upper and lower limb hemodynamic responses during single sessions of low- versus high-intensity inspiratory muscle strength training

Inspiratory muscle strength training (IMST) has shown potential to improve both respiratory and cardiovascular function in health and disease. Less is known about acute hemodynamic responses to a single IMST session, therefore we assessed upper and lower limb blood flow via Doppler ultrasound in the brachial and popliteal arteries, respectively. Mean, anterograde, and retrograde blood flow (BF) and shear rate (SR) were assessed relative to baseline during low-intensity (15% maximal inspiratory pressure - PImax) and high-intensity (75% PImax) IMST. During low-intensity IMST, popliteal BF and SR were reduced by ∼10%, and brachial BF and SR were reduced by ∼40%. During high-intensity IMST, popliteal BF and SR were reduced by ∼20%, and brachial BF and SR were reduced by ∼35%. BF and SR responses were not statistically different between low-intensity and high-intensity training for either blood vessel (P > 0.05). In addition, anterograde BF and SR were significantly decreased in the brachial artery for both low-intensity and high-intensity training (P < 0.05), but not the popliteal artery (P > 0.05). Finally, during IMST retrograde BF and SR were significantly increased in both the upper and lower limbs during low-intensity and high-intensity training (P < 0.05). These data provide novel insight into the acute BF and SR responses to a single bout of IMST and may enhance our understanding of the mechanism(s) by which IMST imparts its beneficial chronic effects on cardiovascular function.NEW & NOTEWORTHY Herein, we demonstrate for the first time that upper and lower limb blood flow and shear rate patterns are altered during a single bout of IMST, at low- and high-intensity training. Specifically, anterograde blood flow and shear rate are significantly reduced in the brachial artery, whereas retrograde blood flow is significantly elevated in both the brachial and popliteal arteries. These findings provide insight into the vascular impact of IMST, which may inform future mechanistic studies.

The therapeutic role of inspiratory muscle training in the management of asthma: a narrative review

Asthma is a disorder of the airways characterized by chronic airway inflammation, hyperresponsiveness, and variable recurring airway obstruction. Treatment options for asthma include pharmacological strategies, whereas nonpharmacological strategies are limited. Established pharmacological approaches to treating asthma may cause unwanted side effects and do not always afford adequate protection against asthma, possibly because of an individual's variable response to medications. A potential nonpharmacological intervention that is most available and cost effective is inspiratory muscle training (IMT), which is a technique targeted at increasing the strength and endurance of the diaphragm and accessory muscles of inspiration. Studies examining the impact of IMT on asthma have reported increases in inspiratory muscle strength and a reduction in the perception of dyspnea and medication use. However, because of the limited number of studies and discordant methods between studies more evidence is required to elucidate in individuals with asthma the efficacy of IMT on inspiratory muscle endurance, exercise capacity, asthma control, symptoms, and quality of life as well as in adolescents with differing severities of asthma. Large randomized controlled trials would be a significant step forward in clarifying the effectiveness of IMT in individuals with asthma. Although IMT may have favorable effects on inspiratory muscle strength, dyspnea, and medication use, the current evidence that IMT is an effective treatment for asthma is inconclusive.

Role of the Inspiratory Muscles on Functional Performance From Critical Care to Hospital Discharge and Beyond in Patients With COVID-19

OBJECTIVE

The role of inspiratory muscle performance in functional performance in patients with coronavirus disease 2019 (COVID-19) is poorly understood. The purpose of this study was to perform a longitudinal examination of inspiratory and functional performance from intensive care unit (ICU) discharge (ICUD) to hospital discharge (HD) and symptoms at HD and 1 month after HD in patients with COVID-19.

METHODS

Thirty patients (19 men, 11 women) with COVID-19 were included. Examination of inspiratory muscle performance at ICUD and HD was performed with an electronic manometer, which provided the maximal inspiratory pressure (MIP) and several other inspiratory measures. Examination of dyspnea and functional performance was performed at ICUD and HD with the Modified Borg Dyspnea Scale and the 1-minute sit-to-stand test (1MSST), respectively.

RESULTS

The mean age was 71 (SD = 11) years, the mean length of ICU stay was 9 (SD = 6) days, and the mean length of hospital stay was 26 (SD = 16) days. Most of the patients were diagnosed with severe COVID-19 (76.7%) and had a mean Charlson Comorbidity Index of 4.4 (SD = 1.9), reflecting high comorbidity. The mean MIP of the entire cohort increased minimally from ICUD to HD (from 36 [SD = 21] to 40 [SD = 20] cm H2O), reflecting predicted values for men and women at ICUD and HD of 46 (25%) to 51 (23%) and 37 (24%) to 37 (20%), respectively. The 1MSTS score increased significantly from ICUD to HD (9.9 [SD = 7.1] vs 17.7 [SD = 11.1]) for the entire cohort but remained far below population-based reference values (2.5th percentile) for the majority of patients at ICUD and HD. At ICUD, MIP was found to be a significant predictor of a favorable change in 1MSTS performance (β = 0.308; odds ratio = 1.36) at HD.

CONCLUSION

A significant reduction in inspiratory and functional performance exists in patients with COVID-19 at both ICUD and HD, with a greater MIP at ICUD being a significant predictor of a greater 1MSTS score at HD.

IMPACT

This study shows that inspiratory muscle training may be an important adjunct after COVID-19.

Respiratory issues in patients with multiple sclerosis as a risk factor during SARS-CoV-2 infection: a potential role for exercise

Coronavirus disease-2019 (COVID-19) is associated with cytokine storm and is characterized by acute respiratory distress syndrome (ARDS) and pneumonia problems. The respiratory system is a place of inappropriate activation of the immune system in people with multiple sclerosis (MS), and this may cause damage to the lung and worsen both MS and infections.The concerns for patients with multiple sclerosis are because of an enhance risk of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The MS patients pose challenges in this pandemic situation, because of the regulatory defect of autoreactivity of the immune system and neurological and respiratory tract symptoms. In this review, we first indicate respiratory issues associated with both diseases. Then, the main mechanisms inducing lung damages and also impairing the respiratory muscles in individuals with both diseases is discussed. At the end, the leading role of physical exercise on mitigating respiratory issues inducing mechanisms is meticulously evaluated.

Short-Term L-Citrulline Supplementation Does Not Affect Inspiratory Muscle Oxygenation and Respiratory Performance in Older Adults

In sports nutrition, nitric oxide (NO^•) precursors such as L-citrulline are widely used to enhance NO^• bioavailability, which is considered an ergogenic aid. Our study aimed to examine the effect of short-term L-citrulline supplementation on respiratory muscles' performance, fatigue, and oxygenation in older adults. Fourteen healthy older males took 6 g of L-citrulline or a placebo for seven days in a double-blind crossover design. Pulmonary function via spirometry (i.e., forced expired volume in 1 s (FEV₁), forced vital capacity (FVC), and their ratio)), fractional exhaled nitric oxide (NO^•), maximal inspiratory pressure (MIP), rate of perceived exertion, and sternocleidomastoid muscle oxygenation (i.e., oxyhemoglobin (Δ[O₂Hb]) and de-oxyhemoglobin (Δ[HHb]), total hemoglobin concentration (Δ[tHb]), and tissue saturation index (TSI%)) were evaluated at baseline, after seven days of L-citrulline supplementation, and after incremental resistive breathing to task failure of the respiratory muscles. The exhaled NO^• value was only significantly increased after the supplementation (26% p < 0.001) in the L-citrulline condition. Pulmonary function, MIP, rate of perceived exertion, and sternocleidomastoid muscle oxygenation were not affected by the L-citrulline supplementation. In the present study, although short-term L-citrulline supplementation increased exhaled NO^•, no ergogenic aids were found on the examined parameters at rest and after resistive breathing to task failure in older adults.

Minimal Clinically Important Differences in Inspiratory Muscle Function Variables after a Respiratory Muscle Training Programme in Individuals with Long-Term Post-COVID-19 Symptoms

OBJECTIVE

To establish the minimal clinically important difference (MCID) for inspiratory muscle strength (MIP) and endurance (IME) in individuals with long-term post-COVID-19 symptoms, as well as to ascertain which of the variables has a greater discriminatory capacity and to compare changes between individuals classified by the MCID.

DESIGN

Secondary analysis of randomised controlled trial of data from 42 individuals who performed an 8-week intervention of respiratory muscle training programme.

RESULTS

A change of at least 18 cmH₂O and 22.1% of that predicted for MIP and 328.5s for IME represented the MCID. All variables showed acceptable discrimination between individuals who classified as "improved" and those classified as "stable/not improved" (area under the curve ≥0.73). MIP was the variable with the best discriminative ability when expressed as a percentage of prediction (Youden index, 0.67; sensitivity, 76.9%; specificity, 89.7%). Participants classified as "improved" had significantly greater improvements in quality of life and lung function compared with the participants classified as "stable/not improved".

CONCLUSION

In individuals with long-term post-COVID-19 symptoms, the inspiratory muscle function variables had an acceptable discriminative ability to assess the efficacy of a respiratory muscle training programme. MIP was the variable with the best discriminative ability, showing better overall performance when expressed as a percentage of prediction.

The effect of proportional assist ventilation on the electrical activity of the human diaphragm during exercise

NEW FINDINGS

What is the central question of this study? What is the effect of lowering the normally occurring work of breathing on the electrical activity and pressure generated by the diaphragm during submaximal exercise in healthy humans? What is the main finding and its importance? Ventilatory assist during exercise elicits a proportional lowering of both the work performed by the diaphragm and diaphragm electrical activity. These findings have implications for exercise training studies using proportional assist ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

ABSTRACT

We hypothesized that when a proportional assist ventilator (PAV) is applied in order to reduce the pressure generated by the diaphragm, there would be a corresponding reduction in electrical activity of the diaphragm. Healthy participants (five male and four female) completed an incremental cycle exercise test to exhaustion in order to calculate workloads for subsequent trials. On the experimental day, participants performed submaximal cycling, and three levels of assisted ventilation were applied (low, medium and high). Ventilatory parameters, pulmonary pressures and EMG of the diaphragm (EMGdi ) were obtained. To compare the PAV conditions with spontaneous breathing intervals, ANOVA procedures were used, and significant effects were evaluated with a Tukey-Kramer test. Significance was set at P < 0.05. The work of breathing was not different between the lowest level of unloading and spontaneous breathing (P = 0.151) but was significantly lower during medium (25%, P = 0.02) and high (36%, P < 0.001) levels of PAV. The pressure-time product of the diaphragm (PTPdi ) was lower across PAV unloading conditions (P < 0.05). The EMGdi was significantly lower in medium and high PAV conditions (P = 0.035 and P < 0.001, respectively). The mean reductions of EMGdi with PAV unloading were 14, 22 and 39%, respectively. The change in EMGdi for a given lowering of PTPdi with the PAV was significantly correlated (r = 0.61, P = 0.01). Ventilatory assist during exercise elicits a reduction in the electrical activity of the diaphragm, and there is a proportional lowering of the work of breathing. Our findings have implications for exercise training studies using assisted ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

Home-based respiratory muscle training on quality of life and exercise tolerance in long-term post-COVID-19: Randomized controlled trial

OBJECTIVE

To evaluate the effects of a home-based respiratory muscle training programme (inspiratory [IMT] or inspiratory/expiratory muscles [RMT]) supervised by telerehabilitation on quality of life and exercise tolerance in individuals with long-term post-COVID-19 symptoms. The secondary objective was to evaluate the effects of these programmes on respiratory muscle function, physical and lung function, and psychological state.

METHODS

88 individuals with long-term symptoms of fatigue and dyspnoea after COVID-19 diagnosis were randomly (1:1 ratio) assigned to IMT, IMT_sham, RMT or RMT_sham groups for an 8-week intervention (40min/day, 6 times/week). Primary outcomes were quality of life (EuroQol-5D questionnaire) and exercise tolerance (Ruffier test). Secondary outcomes were respiratory muscle function (inspiratory/expiratory muscle strength; inspiratory muscle endurance), physical function (lower and upper limb strength [1-min Sit-to-Stand and handgrip force]), lung function (forced spirometry), and psychological status (anxiety/depression levels and post-traumatic stress disorder). All outcomes were measured pre-, intermediate- (4^th week), and post-intervention.

RESULTS

At post-intervention, there was a statistically significant and large (d>0.90) improvement in quality of life, but not in exercise tolerance, in the RMT group compared with the RMT_sham group. Both of the real training groups produced a statistically significant and large increase in inspiratory muscle strength and endurance (d≥0.80) and in lower limb muscle strength (d≥0.77) compared with the 2 sham groups. Expiratory muscle strength and peak expiratory flow showed a statistically significant and large (d≥0.87) increase in the RMT group compared with the other 3 groups.

CONCLUSION

Only an 8-week supervised home-based RMT programme was effective in improving quality of life, but not exercise tolerance, in individuals with long-term post-COVID-19 symptoms. In addition, IMT and RMT programmes were effective in improving respiratory muscle function and lower limb muscle strength, but had no impact on lung function and psychological status.

Dietary nitrate supplementation enhances heavy load carriage performance in military cadets

PURPOSE

To determine the effects of dietary nitrate (NO₃^-) supplementation on physiological responses, cognitive function, and performance during heavy load carriage in military cadets.

METHODS

Ten healthy males (81.0 ± 6.5 kg; 180.0 ± 4.5 cm; 56.2 ± 3.7 ml·kg·min^-1 VO_2max) consumed 140 mL·d^-1 of beetroot juice (BRJ; 12.8 mmol NO₃^-) or placebo (PL) for six d preceding an exercise trial, which consisted of 45 min of load carriage (55% body mass) at 4.83 km·h^-1 and 1.5% grade, followed by a 1.6-km time-trial (TT) at 4% grade. Gas exchange, heart rate, and perceptual responses were assessed during constant-load exercise and the TT. Cognitive function was assessed immediately prior to, during, and post-exercise via the psychomotor vigilance test (PVT).

RESULTS

Post-TT HR (188 ± 7.1 vs. 185 ± 7.4; d = 0.40; p = 0.03), mean tidal volume (2.15 ± 0.27 vs. 2.04 ± 0.23; p = 0.02; d = 0.47), and performance (770.9 ± 78.2 s vs. 809.8 ± 61.4 s; p = 0.03; d = 0.63) were increased during the TT with BRJ versus PL. There were no effects of BRJ on constant-load gas exchange or perceptual responses, and cognitive function was unchanged at all time points.

CONCLUSION

BRJ supplementation improves heavy load carriage performance in military cadets possibly as a result of attenuated respiratory muscle fatigue, rather than enhanced exercise economy.

A short course of high-resistance, low-volume breathing exercise extends respiratory endurance and blunts cardiovascular responsiveness to constant load respiratory testing in healthy young adults

Our objective was to evaluate the effects of 6-weeks high-resistance, low-volume inspiratory muscle strength training (IMST) on respiratory endurance, blood pressure (BP) and heart rate (HR) responsiveness to high respiratory workloads. Ten healthy young adults completed two constant-load resistive breathing tests to exhaustion (T_lim) (target pressure =65 % maximal inspiratory pressure [PI_max]; duty cycle = 0.7; breathing frequency matched to eupnea) separated by 6-weeks high-resistance (75 % maximal inspiratory pressure, PI_max), low-volume (30 inspiratory efforts/day, 5 days/week) IMST. Throughout resistive breathing trials we measured beat-to-beat changes in BP and HR, mouth pressure, inspiratory muscle work and perceived exertion. POST resistive breathing tests revealed significant gains in endurance (PRE: 362.0 ± 46.6 s vs. POST: 663.8 ± 110.3 s, p = 0.003) and increases in respiratory muscle work (PRE: -9445 ± 1562 mmHg.s vs. POST: -16648 ± 3761 mmHg.s, p = 0.069). Conversely, systolic and diastolic BP responses, HR and ratings of perceived exertion all declined. Consistent with previous observations, 6 weeks high resistance, low volume IMST lowered casual resting SBP (p = 0.002), DBP (p = 0.007) and mean arterial pressure (p = 0.001) and improved static inspiratory pressure. High resistance, low volume inspiratory muscle strength training extends respiratory endurance and attenuates BP responsiveness in healthy, recreationally-active young adults. The outcomes have implications for improved athletic performance and for attaining and/or maintaining cardiorespiratory fitness.

The effects of cloth face masks on cardiorespiratory responses and VO2 during maximal incremental running protocol among apparently healthy men

We aimed to determine the effects of wearing a cloth face mask on cardiorespiratory response, peak oxygen uptake (Vo₂), respiratory muscle effort, and exercise tolerance during incremental exercise. The study had a randomized crossover design: 11 apparently healthy young men performed the Bruce protocol treadmill test in two conditions, wearing a cloth face mask (CFM) and without CFM (CON), in random order. Minute ventilation and oxygen uptake were measured using a mass spectrometry metabolic analyzer; cardiac output (CO) was measured using an impedance CO monitor; and mouth pressure (P_m) was measured and calculated as an integral P_m to assess respiratory muscle effort. Maximal minute ventilation was 13.4 ± 10.7% lower in the CFM condition than in the CON condition (P < 0.001). The peak Vo₂ (52.4 ± 5.6 and 55.0 ± 5.1 mL/kg/min in CFM and CON, respectively) and CO were not significantly different between the two conditions. However, the integral value of P_m was significantly higher (P = 0.02), and the running time to exhaustion was 2.6 ± 3.2% lower (P = 0.02) in the CFM condition than in the CON condition. Our results suggest that wearing a cloth face mask increased respiratory muscle effort and decreased ventilatory volume in healthy young men; however, Vo₂ remained unchanged. Exercise tolerance also decreased slightly.

Sex differences in blood pressure and inactive limb blood flow responses during dynamic leg exercise with increased inspiratory muscle work

We hypothesized that, compared with young males, young females have a smaller decrease in blood flow to the inactive limb, accompanied by a smaller increase in arterial blood pressure, during dynamic exercise with increased inspiratory muscle work. Young males and females performed dynamic knee-extension and -flexion exercises for 10 min (spontaneous breathing for 5 min and voluntary hyperpnoea with or without inspiratory resistance for 5 min). Mean arterial blood pressure (MAP) and mean blood flow (MBF) in the brachial artery were continuously measured by means of finger photoplethysmography and Doppler ultrasound, respectively. No sex differences were found in the ΔMAP and ΔMBF (Δ: from baseline) during exercise without inspiratory resistance. In contrast, the ΔMAP during exercise with inspiratory resistive breathing was greater (P < 0.05) in males (+31.3 ± 2.1 mmHg, mean ± SE) than females (+18.9 ± 3.2 mmHg). The MBF during exercise with inspiratory resistance did not change in males (-4.4 ± 10.6 mL/min), whereas it significantly increased in females (+25.2 ± 15.4 mL/min). These results suggest that an attenuated inspiratory muscle-induced metaboreflex in young females affects blood flow distribution during submaximal dynamic leg exercise.

Inspiratory and leg muscle blood flows during inspiratory muscle metaboreflex activation in heart failure with preserved ejection fraction

The purpose of this study was to determine the cardiovascular consequences elicited by activation of the inspiratory muscle metaboreflex in patients with heart failure with preserved ejection fraction (HFpEF) and controls. Patients with HFpEF (n = 15; 69 ± 10 yr; 33 ± 4 kg/m2) and controls (n = 14; 70 ± 8 yr; 28 ± 4 kg/m2) performed an inspiratory loading trial at 60% maximal inspiratory pressure (PIMAX) until task failure. Mean arterial pressure (MAP) was measured continuously. Near-infrared spectroscopy and bolus injections of indocyanine green dye were used to determine the percent change in blood flow index (%ΔBFI) from baseline to the final minute of inspiratory loading in the vastus lateralis and sternocleidomastoid muscles. Vascular resistance index (VRI) was calculated. Time to task failure was shorter in HFpEF than in controls (339 ± 197 s vs. 626 ± 403 s; P = 0.02). Compared with controls, patients with HFpEF had a greater increase from baseline in MAP (16 ± 7 vs. 10 ± 6 mmHg) and vastus lateralis VRI (76 ± 45 vs. 32 ± 19%) as well as a greater decrease in vastus lateralis %ΔBFI (-32 ± 14 vs. -17 ± 9%) (all, P < 0.05). Sternocleidomastoid %ΔBFI normalized to absolute inspiratory pressure was higher in HFpEF compared with controls (8.0 ± 5.0 vs. 4.0 ± 1.9% per cmH2O·s; P = 0.03). These data indicate that patients with HFpEF exhibit exaggerated cardiovascular responses with inspiratory muscle metaboreflex activation compared with controls.NEW & NOTEWORTHY Respiratory muscle dysfunction is thought to contribute to exercise intolerance in heart failure with preserved ejection fraction (HFpEF); however, the underlying mechanisms are unknown. In the present study, patients with HFpEF had greater increases in leg muscle vascular resistance index and greater decreases in leg muscle blood flow index compared with controls during inspiratory resistive breathing (to activate the metaboreflex). Furthermore, respiratory muscle blood flow index responses normalized to pressure generation during inspiratory resistive breathing were exaggerated in HFpEF compared with controls.

Effects of Inspiratory Muscle Training and High-Intensity Interval Training on Lung Function and Respiratory Muscle Function in Asthma

BACKGROUND

Asthma is a heterogeneous disease, usually characterized by chronic airway inflammation. Although inspiratory muscle training (IMT) and high-intensity interval training (HIIT) are beneficial for patients with asthma, controversies persist. Therefore, we aimed to investigate the effects of IMT and HIIT on lung function and respiratory muscle function of subjects with asthma.

METHODS

We searched PubMed, Embase, Web of Science, and the Cochrane Library databases up to May 2021. Inclusion criteria were randomized controlled trials (RCTs) of subjects with asthma who received either IMT or HIIT. The outcome measures were changes in lung function and respiratory muscle function.

RESULTS

A total of 13 RCTs (10 in IMT and 3 in HIIT) were included, with a total of 598 subjects. The meta-analysis showed a significantly improved FEV1 of the expected value (FEV1%pred) (mean difference [MD] 4.49% [95% CI 2.31-6.67], P < .001; I2 = 13%), FVC of the expected value (FVC % pred) (MD 5.72% [95% CI 3.56-7.88], P < .001; I2 = 0%), FEV1/FVC % (MD 5.01% [95% CI 2.45-7.58], P < .001; I2 = 25%), FVC (L) (MD 0.21 L [95% CI 0.03-0.40], P = .02; I2 = 0%), maximum inspiratory pressure (PImax) (MD 27.62 cm H2O [95% CI 6.50-48.74], P = .01; I2 = 96%), and PImax (%pred) (MD 27.35% [95% CI 6.94-47.76], P = .009; I2 = 83.5%) in the IMT group. There was no statistical significance in maximum expiratory pressure.

CONCLUSIONS

IMT improved pulmonary function (FEV1%pred, FVC) and inspiratory muscle strength in subjects with stable asthma. Due to the small number of RCT studies included and the limited outcome measures involving HIIT, we were unable to draw conclusions about whether HIIT was beneficial in this meta-analysis. Moreover, clinical heterogeneity exists in different areas such as population and training programs; the above conclusions still need to be confirmed in future studies.

Blood pressure and celiac artery blood flow responses during increased inspiratory muscle work in healthy males

NEW FINDINGS

What is the central question of this study? Increased work of breathing and the accumulation of metabolites have neural and cardiovascular consequences through a respiratory muscle-induced metaboreflex. The influence of respiratory muscle-induced metaboreflex on splanchnic blood flow in humans remains unknown. What is the main finding and its importance? Celiac artery blood flow decreased gradually during inspiratory resistive breathing, accompanied by a progressive increase in arterial blood pressure. It is possible that respiratory muscle-induced metaboreflex contributes to splanchnic blood flow regulation.

ABSTRACT

The purpose of this study was to clarify the effect of increasing inspiratory muscle work on celiac artery blood flow. Eleven healthy young males completed the study. The subjects performed voluntary hyperventilation with or without inspiratory resistance (loading or non-loading trial) (tidal volume of 40% of vital capacity and breathing frequency of 20 breaths/min). The loading trial was conducted with inspiratory resistance (40% of maximal inspiratory pressure) and was terminated when the subjects could no longer maintain the target tidal volume or breathing frequency. The non-loading trial was conducted without inspiratory resistance and was the same length as the loading trial. Arterial blood pressure was recorded using finger photoplethysmography, and celiac artery blood flow was measured using Doppler ultrasound. Mean arterial blood pressure (MAP) increased gradually during the loading trial (89.0±10.8 to 103.9±17.3 mmHg, mean ± SD) but not in the non-loading trial (88.7±5.9 to 90.4±9.9 mmHg). Celiac artery blood flow and celiac vascular conductance decreased gradually during the loading trial (601.2±155.7 to 482.6±149.5 mL/min and 6.9±2.2 to 4.8±1.7 mL/min/mmHg, respectively), but were unchanged in the non-loading trial (630.7±157.1 to 635.6±195.7 mL/min and 7.1±1.8 to 7.2±2.9 mL/min/mmHg, respectively). These results show that increasing inspiratory muscle work affects splanchnic blood flow regulation, and we suggest that it is possibly mediated by the inspiratory muscle-induced metaboreflex. This article is protected by copyright. All rights reserved.

THE EFFECTS OF INSPIRATORY MUSCLE TRAINING VERSUS CALF MUSCLE TRAINING ON QUALITY OF LIFE, PAIN, VENOUS FUNCTION AND ACTIVITY IN PATIENTS WITH CHRONIC VENOUS INSUFFICIENCY

OBJECTIVE

The aim of this study was to evaluate the effect of inspiratory muscle training(IMT) and calf muscle exercise training(ETC) in addition to compression therapy(CT) on quality of life, venous refilling time, disease severity, pain, edema, range of motion, muscle strength and functionality in patients with chronic venous insufficiency (CVI) compared to compression treatment alone.

METHODS

Thirty-two participants diagnosed with CVI were randomly divided into three groups. IMT in addition to compression therapy, Group 1, exercise training for the calf muscle in addition to compression therapy, Group 2, and compression therapy alone, Group 3. All the patients were assessed with the Chronic Venous Insufficiency Quality of Life Questionnaire-20, Nottingham Health Profile, photoplethysmography, venous clinical severity score, visual analog scale, intraoral pressure measurements, dynamometer, digital goniometer, 6-minute walk test and lower extremity functional scale.

RESULTS

After treatment, Group 2 improved more than groups 1 and 3 in terms of quality of life, venous refilling time, pain, edema, range of motion, muscle strength and functionality scores; Group 1 improved more than groups 2 and 3 in terms of disease severity, inspiratory and expiratory muscle strength values(p<0.05). Only physical mobility and right leg venous refilling time increased in group 3(p<0.05).

CONCLUSIONS

IMT and ETC improve venous function in both legs in patients with CVI while CT alone improves venous function only in the right leg of patients with CVI.

CO2-Enriched Air Inhalation Modulates the Ventilatory and Metabolic Responses of Endurance Runners During Incremental Running in Hypobaric Hypoxia

Cao, Yinhang, Naoto Fujii, Tomomi Fujimoto, Yin-Feng Lai, Takeshi Ogawa, Tsutomu Hiroyama, Yasushi Enomoto, and Takeshi Nishiyasu. CO₂-enriched air inhalation modulates the ventilatory and metabolic responses of endurance runners during incremental running in hypobaric hypoxia. High Alt Med Biol. 23:125-134, 2022. Aim: We measured the effects of breathing CO₂-enriched air on ventilatory and metabolic responses during incremental running exercise under moderately hypobairc hypoxic (HH) conditions. Materials and Methods: Ten young male endurance runners [61.4 ± 6.0 ml/(min·kg)] performed incremental running tests under three conditions: (1) normobaric normoxia (NN), (2) HH (2,500 m), and (3) HH with 5% CO₂ inhalation (HH+CO₂). The test under NN was always performed first, and then, the two remaining tests were completed in random and counterbalanced order. Results: End-tidal CO₂ partial pressure (55 ± 3 vs. 35 ± 1 mmHg), peak ventilation (163 ± 14 vs. 152 ± 12 l/min), and peak oxygen uptake [52.3 ± 5.5 vs. 50.5 ± 4.9 ml/(min·kg)] were all higher in the HH+CO₂ than HH trial (all p < 0.01), respectively. However, the duration of the incremental test did not differ between HH+CO₂ and HH trials. Conclusion: These data suggest that chemoreflex activation by breathing CO₂-enriched air stimulates breathing and aerobic metabolism during maximal intensity exercise without affecting exercise performance in male endurance runners under a moderately hypobaric hypoxic environment.

Exploring relationships between inspiratory muscle strength and functional capacity in childhood cancer survivors: a pilot study

Childhood cancer survivors (CCS) experience short- and long-term side effects from cancer treatment that often impair functional capacity. Inspiratory muscle weakness is a potential mechanism for reduced functional capacity. The objective of this pilot study was to examine the relationship between inspiratory muscle strength and functional capacity in 10 CCS. Inspiratory muscle strength was measured by maximal inspiratory pressure (MIP) while functional capacity was measured by the two-minute walk test (2MWT), the physiological cost index and hemodynamic response to exercise according to changes in heart rate, blood pressure and rate-pressure product (RPP). Overall, MIP and 2MWT distance were below predicted values. Hemodynamic responses to the 2MWT were consistent with little variation, except for elevated diastolic blood pressure (DBP) response. MIP had significant relationships with resting DBP (Spearman's rank correlation coefficient [r_s] = -0.70; p = 0.03) and DBP response (r_s = 0.72; p = 0.02). Time since completion of cancer treatment had a significant positive relationship with RPP response (r_s = 0.67; p = 0.03). Inspiratory muscle weakness in childhood cancer could be an indicator of skeletal muscle dysfunction and should be considered when symptoms of dyspnea or poor functional capacity arise. Inspiratory muscle strength was found to be related to changes in blood pressure in CCS. Future studies should further investigate these relationships and the impact of inspiratory muscle training on hemodynamics and functional capacity in CCS.

Influence of High Hemoglobin-Oxygen Affinity on Humans During Hypoxia

Humans elicit a robust series of physiological responses to maintain adequate oxygen delivery during hypoxia, including a transient reduction in hemoglobin-oxygen (Hb-O₂) affinity. However, high Hb-O₂ affinity has been identified as a beneficial adaptation in several species that have been exposed to high altitude for generations. The observed differences in Hb-O₂ affinity between humans and species adapted to high altitude pose a central question: is higher or lower Hb-O₂ affinity in humans more advantageous when O₂ availability is limited? Humans with genetic mutations in hemoglobin structure resulting in high Hb-O₂ affinity have shown attenuated cardiorespiratory adjustments during hypoxia both at rest and during exercise, providing unique insight into this central question. Therefore, the purpose of this review is to examine the influence of high Hb-O₂ affinity during hypoxia through comparison of cardiovascular and respiratory adjustments elicited by humans with high Hb-O₂ affinity compared to those with normal Hb-O₂ affinity.

Sex differences in the effect of acute intermittent hypoxia on respiratory modulation of sympathetic activity

Sex-related differences in respiratory modulation of sympathetic activity have been observed in rodent models of sleep apnea [intermittent hypoxia (IH)]. In light of sex disparities in the respiratory response to acute IH in humans as well as changes in respiratory modulation of muscle sympathetic nerve activity (MSNA) in clinical sleep apnea, we examined sex-related differences in respiratory modulation of MSNA following acute IH. We hypothesized that respiratory modulation of MSNA would be altered in both male and female participants after IH; however, the respiratory patterning of MSNA following IH would be sex specific. Heart rate, MSNA, and respiration were evaluated in healthy male (n = 21, 30 ± 5 yr) and female (n = 10, 28 ± 5 yr) participants during normoxic rest before and after 30 min of IH. Respiratory modulation of MSNA was assessed by fitting polynomials to cross-correlation histograms constructed between sympathetic spikes and respiration. MSNA was elevated after IH in male (20 ± 6 to 24 ± 8 bursts/min) and female (19 ± 8 to 22 ± 10 bursts/min) participants (P < 0.01). Both male and female participants exhibited respiratory modulation of MSNA (P < 0.01); however, the pattern differed by sex. After IH, modulation of MSNA within the breath was reduced in male participants (P = 0.03) but increased in female participants (P = 0.02). Both male and female adults exhibit changes in respiratory patterning of MSNA after acute IH; however, this pattern differs by sex. These data support sex disparities in respiratory modulation of MSNA and may have implications for conditions such as sleep apnea.

Respiratory muscle training improves exercise tolerance and respiratory muscle function/structure post-stroke at short term: A systematic review and meta-analysis

BACKGROUND

Previous reviews relating to the effects of respiratory muscle training (RMT) after stroke tend to focus on only one type of training (inspiratory or expiratory muscles) and most based the results on poor-quality studies (PEDro score ≤4).

OBJECTIVES

With this systematic review and meta-analysis, we aimed to determine the effects of RMT (inspiratory or expiratory muscle training, or mixed) on exercise tolerance, respiratory muscle function and pulmonary function and also the effects depending on the type of training performed at short- and medium-term in post-stroke.

METHODS

Databases searched were MEDLINE, PEDro, CINAHL, EMBASE and Web of Science up to the end of April 2020. The quality and risk of bias for each included study was examined by the PEDro scale (including only high-quality studies) and Cochrane Risk of Bias tool.

RESULTS

Nine studies (463 patients) were included. The meta-analysis showed a significant increase in exercise tolerance [4 studies; n = 111; standardized mean difference [SMD] = 0.65 (95% confidence interval 0.27-1.04)]; inspiratory muscle strength [9 studies; n = 344; SMD = 0.65 (0.17-1.13)]; inspiratory muscle endurance [3 studies; n = 81; SMD = 1.19 (0.71-1.66)]; diaphragm thickness [3 studies; n = 79; SMD = 0.9 (0.43-1.37)]; and peak expiratory flow [3 studies; n = 84; SMD = 0.55 (0.03-1.08)] in the short-term. There were no benefits on expiratory muscle strength and pulmonary function variables (forced expiratory volume in 1 s) in the short-term.

CONCLUSIONS

The meta-analysis provided moderate-quality evidence that RMT improves exercise tolerance, diaphragm thickness and pulmonary function (i.e., peak expiratory flow) and low-quality evidence for the effects on inspiratory muscle strength and endurance in stroke survivors in the short-term. None of these effects are retained in the medium-term. Combined inspiratory and expiratory muscle training seems to promote greater respiratory changes than inspiratory muscle training alone.

The association of breathing pattern with exercise tolerance and perceived fatigue in women with systemic lupus erythematosus: an exploratory case-control study

The aims of the study were to (1) to characterize the breathing pattern and work of breathing during peak exercise in patients with SLE; (2) to examine the extent to which the breathing pattern and work of breathing impact the exercise capacity and fatigue. Forty-one women participated in the study (SLE: n = 23, median = 35, range = 21-57 years, control: n = 18, median = 38, range = 22-45 years). Each subject performed a treadmill cardiopulmonary exercise test (a modified Bruce treadmill protocol) ending with volitional exhaustion. Breathing mechanic was characterized by measures of expired minute volume (V_E), tidal volume (Vt), respiratory rate (f), work of breathing, and cardiorespiratory fitness was quantified by measures of peak oxygen consumption (VO₂) and time to exhaustion. Data presented as median and interquartile range (IQR). Women with SLE had lower Vt {1221 [488.8] mL/min vs. 1716 [453.1] mL; p = .006}, V_E {58.9 [18.9] L/min vs 70 [28.1] L/min, p = 0.04} and increased breathing frequency {51.5 [10.8] vs 43.6 [37.8] bpm, p = 0.01} compared to the control group. The time to exhaustion and peak VO₂ during the CPET were significantly reduced in those with SLE compared to controls {13.3 [10.2] vs 16.1 [2.2] min; p = 0.004}, {20 [6.1] mL/kg/min vs 26.6 [7] mL/kg/min p < 0.001}, respectively. Differences remained when the analyses were controlled for the observed differences in peak VO₂. When the regression model adjusted for the peak VO₂, it had been shown that Vt, WOB and f were explained variances in the fatigue severity by 64% [p < 0.001]. The decline in V_E and Vt coupled with a decreased peak VO_2, and work of breathing may have contributed to low cardiorespiratory fitness and fatigue in patients with systemic lupus erythematosus.

Adjunctive inspiratory muscle training for patients with COVID-19 (COVIDIMT): protocol for randomised controlled double-blind trial

INTRODUCTION

A significant number of patients with COVID-19 may experience dyspnoea, anxiety, depression, pain, fatigue and physical impairment symptoms, raising the need for a multidisciplinary rehabilitation approach, especially for those with advanced age, obesity, comorbidities and organ failure. Traditional pulmonary rehabilitation (PR), including exercise training, psychosocial counselling and education, has been employed to improve pulmonary function, exercise capacity and quality of life in patients with COVID-19. However, the effects of inspiratory muscle training (IMT) in PR programmes remain unclear. This study aimed to determine whether the addition of a supervised IMT in a PR is more effective than PR itself in improving dyspnoea, health-related quality of life and exercise capacity in symptomatic patients with post-COVID-19.

METHODS AND ANALYSIS

This parallel-group, assessor-blinded randomised controlled trial, powered for superiority, aimed to assess exercise capacity as the primary outcome. A total of 138 are being recruited at two PR centres in Brazil. Following baseline testing, participants will be randomised using concealed allocation, to receive either (1) standard PR with sham IMT or (2) standard PR added to IMT. Treatment effects or differences between the outcomes (at baseline, after 8 and 16 weeks, and after 6 months) of the study groups will be analysed using an ordinary two-way analysis of variance.

ETHICS AND DISSEMINATION

This trial was approved by the Brazilian National Ethics Committee and obtained approval on 7 October 2020 (document number 4324069). The findings will be disseminated through publications in peer-reviewed journals and conference presentations.

TRIAL REGISTRATION NUMBER

NCT04595097.

Effects of the Elevation Training Mask® 2.0 on dyspnea and respiratory muscle mechanics, electromyography, and fatigue during exhaustive cycling in healthy humans

OBJECTIVES

Examine the effects of the Elevation Training Mask® 2.0 (ETM) on dyspnea, and respiratory muscle function and fatigue during exercise.

DESIGN

Randomized crossover.

METHODS

10 healthy participants completed 2 time-to-exhaustion (TTE) cycling tests while wearing the ETM or under a sham control condition. During the sham, participants were told they were breathing air equivalent to "9000 ft" (matched to the selected resistance valves on the ETM according to the manufacturer), but they were breathing room air. Dyspnea and leg discomfort were assessed using the modified 0-10 category-ratio Borg scale. Qualitative dyspnea descriptors at peak exercise were selected from a list of 15. Crural diaphragmatic electromyography (EMG_di) and transdiaphragmatic pressure (P_di) were measured via a multipair esophageal electrode balloon catheter. Participants performed maximal respiratory maneuvers before and after exercise to estimate the degree of respiratory muscle fatigue.

RESULTS

Exercise with the ETM resulted in a significant decrease in TTE (p = 0.015), as well as increased dyspnea at baseline (p = 0.032) and during the highest equivalent submaximal exercise time (p = 0.0001). The increase in dyspnea with the ETM was significantly correlated with the decrease in exercise time (r = 0.73, p = 0.020). EMG_di and P_di were significantly increased with the ETM at all time points (all p < 0.05). There was a significant increase in the selection frequency of "my breath does not go in all the way" at peak exercise with the ETM (p = 0.02). The ETM did not induce respiratory muscle fatigue.

CONCLUSIONS

Exercising with the ETM appears to decrease exercise performance, in part, by increasing the sensation of dyspnea.

Current limits for flowmeter resistance in metabolic carts can negatively affect exercise performance

PURPOSE

To investigate whether a metabolic cart using a flowmeter in the upper range of accepted resistance to airflow (<1.5 cmH2 O∙L-1 ∙s-1 for flows up to 14 L∙s-1 , American Thoracic Society) negatively impacts exercise performance in healthy individuals.

METHODS

16 recreationally active males (age 25 ± 1 years, height 180 ± 6 cm, weight 73.5 ± 5.8 kg, all mean ± SD) performed two incremental tests on a bicycle ergometer on each of two visits, using a metabolic cart with a flowmeter of either low (Oxycon Pro) or high (Innocor) airflow resistance. Mouth pressures, gas exchange, blood lactate concentration [La- ], perception of breathlessness, respiratory, and leg exertion were assessed throughout the tests.

RESULTS

Tests performed with the Innocor were significantly shorter (15.3 ± 3.2 vs. 15.8 ± 3.3 min, p < 0.0001) and showed higher maximal flow resistance (1.3 ± 0.2 vs. 0.3 ± 0.0 cmH2 O∙L-1 ∙s-1 , p < 0.0001). At end-exercise, peak oxygen consumption (-200 ± 220 ml.min-1 , p < 0.0001), minute ventilation (-19.9 ± 10.5 L.min-1 , p < 0.0001), breathing frequency (-5.4 ± 5.2 breaths.min-1 , p < 0.0001), heart rate (-2.1 ± 3.6 bpm, p = 0.002) and [La- ] (-0.7 ± 1.0 mmol.L-1 , p < 0.0001), but not tidal volume (-0.1 ± 0.2 L, p = 0.172) were lower with the Innocor, while the perception of breathlessness was higher (+3.8 ± 5.1 points, p < 0.0001).

CONCLUSIONS

Airflow resistance in the upper range of current guidelines can significantly affect exercise performance and respiratory pattern in young, healthy males during incremental exercise. The present results indicate the need to revisit guidelines for devices used in ergospirometry.

Systolic reserve maintains left ventricular-vascular coupling when challenged by adverse breathing mechanics and hypertension in healthy adults

Augmented negative intrathoracic pressures (nITP) and dynamic hyperinflation (DH) are adverse breathing mechanics (ABM) associated with chronic obstructive pulmonary disease (COPD) that attenuate left ventricular (LV) preload and augment afterload. In COPD, hypertension (elevated systemic arterial load) commonly adds additional afterload to the LV. Combined ABM and hypertension may profoundly challenge ventricular-vascular coupling and attenuate stroke volume (SV), particularly if LV systolic reserve is limited. However, even in the healthy heart, the combined impact of ABM and systemic arterial loading on LV function and ventricular-vascular coupling has not been fully elucidated. Healthy volunteers (10 M/9 F, 24 ± 3 yr old) were challenged with mild (-10 cmH₂O nITP and 25% DH) and severe (-20 cmH₂O nITP and 100% DH) ABM, without and with postexercise ischemia (PEI) at each severity. LV SV, chamber geometry, end-systolic elastance (E_es), arterial elastance (E_a), and ventricular-vascular coupling (E_es:E_a) were quantified using echocardiography. Compared with resting control (58 ± 13 mL), SV decreased during mild ABM (51 ± 13 mL), mild ABM + PEI (51 ± 11 mL), severe ABM (50 ± 12 mL), and severe ABM + PEI (47 ± 11 mL) (P < 0.001); similar trends were observed for LV end-diastolic volume. The end-diastolic radius of septal curvature increased, indicating direct ventricular interaction, during severe ABM and severe ABM + PEI (P < 0.001). Compared with control (1.99 ± 0.41 mmHg/mL), E_a increased progressively with mild ABM (2.21 ± 0.47 mmHg/mL) and severe ABM (2.50 ± 0.56 mmHg/mL); at each severity, E_a was greater with superimposed PEI (P < 0.001). However, well-matched E_es increases occurred, and E_es:E_a was unchanged throughout. ABM pose a challenge to ventricular-vascular coupling that is accentuated by superimposed PEI; however, in healthy younger adults, the LV has substantial systolic reserve to maintain coupling.NEW & NOTEWORTHY In healthy younger adults, combined dynamic hyperinflation (DH) and negative intrathoracic pressures (nITP) attenuate left ventricular filling, but through different mechanisms at different severities. DH and nITP contribute to increased left ventricular afterload through mechanical effects in addition to presumed reflexive regulation, which can be further increased by elevated arterial loading. However, within this demographic, the left ventricle has substantial reserve to increase systolic performance, which matches contractility to afterload to preserve stroke volume.

Five-year outcome of respiratory muscle weakness at intensive care unit discharge: secondary analysis of a prospective cohort study

PURPOSE

To assess the association between respiratory muscle weakness (RMW) at intensive care unit (ICU) discharge and 5-year mortality and morbidity, independent from confounders including peripheral muscle strength.

METHODS

Secondary analysis of the prospective 5-year follow-up of the EPaNIC cohort (ClinicalTrials.gov: NCT00512122), limited to 366 patients screened for respiratory and peripheral muscle strength in the ICU with maximal inspiratory pressure (MIP) after removal of the artificial airway, and the Medical Research Council sum score. RMW was defined as an absolute value of MIP <30 cmH₂O. Associations between RMW at (or closest to) ICU discharge and all-cause 5-year mortality, and key measures of 5-year physical function, comprising respiratory muscle strength (MIP), hand-grip strength (HGF), 6 min walk distance (6MWD) and physical function of the SF-36 quality-of-life questionnaire (PF-SF-36), were assessed with Cox proportional hazards and linear regression models, adjusted for confounders including peripheral muscle strength.

RESULTS

RMW was present in 136/366 (37.2%) patients at ICU discharge. RMW was not independently associated with 5-year mortality (HR with 95% CI 1.273 (0.751 to 1.943), p=0.352). Among 156five-year survivors, those with, as compared with those without RMW demonstrated worse physical function (MIP (absolute value, cmH₂O): 62(42-77) vs 94(78-109), p<0.001; HGF (%pred): 67(44-87) vs 96(68-110), p<0.001; 6MWD (%pred): 87(74-102) vs 99 (80-111), p=0.009; PF-SF-36 (score): 55 (30-80) vs 80 (55-95), p<0.001). Associations between RMW and morbidity endpoints remained significant after adjustment for confounders (effect size with 95% CI: MIP: -23.858 (-32.097 to -15.027), p=0.001; HGF: -18.591 (-30.941 to -5.744), p=0.001; 6MWD (transformed): -1587.007 (-3073.763 to -179.253), p=0.034; PF-SF-36 (transformed): 1.176 (0.144-2.270), p=0.036).

CONCLUSIONS

RMW at ICU discharge is independently associated with 5-year morbidity but not 5-year mortality.

The cardiovascular consequences of fatiguing expiratory muscle work in otherwise resting healthy humans

In 11 healthy adults (25 ± 4 yr; 2 female, 9 male subjects), we investigated the effect of expiratory resistive loaded breathing [65% maximal expiratory mouth pressure (MEP), 15 breaths·min^-1, duty cycle 0.5; ERL_Pm] on mean arterial pressure (MAP), leg vascular resistance (LVR), and leg blood flow ([Formula: see text]). On a separate day, a subset of five male subjects performed ERL targeting 65% of maximal expiratory gastric pressure (ERL_Pga). ERL-induced expiratory muscle fatigue was confirmed by a 17 ± 5% reduction in MEP (P < 0.05) and a 16 ± 12% reduction in the gastric twitch pressure response to magnetic nerve stimulation (P = 0.09) from before to after ERL_Pm and ERL_Pga, respectively. From rest to task failure in ERL_Pm and ERL_Pga, MAP increased (ERL_Pm = 31 ± 10 mmHg, ERL_Pga = 18 ± 9 mmHg, both P < 0.05), but group mean LVR and [Formula: see text] were unchanged (ERL_Pm: LVR = 0.78 ± 0.21 vs. 0.97 ± 0.36 mmHg·mL^-1·min, [Formula: see text] = 133 ± 34 vs. 152 ± 74 mL·min^-1; ERL_Pga: LVR = 0.70 ± 0.21 vs. 0.84 ± 0.33 mmHg·mL^-1·min, [Formula: see text] = 160 ± 48 vs. 179 ± 110 mL·min^-1) (all P ≥ 0.05). Interestingly, [Formula: see text] during ERL_Pga oscillated within each breath, increasing (∼66%) and decreasing (∼50%) relative to resting values during resisted expirations and unresisted inspirations, respectively. In conclusion, fatiguing expiratory muscle work did not affect group mean LVR or [Formula: see text] in otherwise resting humans. We speculate that any sympathetically mediated peripheral vasoconstriction was counteracted by transient mechanical effects of high intra-abdominal pressures during ERL.NEW & NOTEWORTHY Fatiguing expiratory muscle work in otherwise resting humans elicits an increase in sympathetic motor outflow; whether limb blood flow ([Formula: see text]) and leg vascular resistance (LVR) are affected remains unknown. We found that fatiguing expiratory resistive loaded breathing (ERL) did not affect group mean [Formula: see text] or LVR. However, within-breath oscillations in [Formula: see text] may reflect a sympathetically mediated vasoconstriction that was counteracted by transient increases in [Formula: see text] due to the mechanical effects of high intra-abdominal pressure during ERL.

Effects of 4-Week Inspiratory Muscle Training on Sport Performance in College 800-Meter Track Runners

Background and objectives: Respiratory muscle fatigue is one of the important factors limiting sports performance due to the metaboreflex. This reflex will cause a decrease in blood flow to the extremities and accelerate exercising limb fatigue. Previous studies found that inspiratory muscle training (IMT) can effectively enhance the respiratory muscle endurance and reduce fatigue during long-duration exercise or aerobic exercise, thereby enhancing athletic performance. However, the mechanism between inspiratory muscle strength, change of limb blood flow and sports performance still requires investigation, especially in short-duration exercise, anaerobic or both aerobic and anaerobic exercise. The purpose of this study was to investigate the effects of 4-week inspiratory muscle training on respiratory muscle strength, limb blood flow change rate and sports performance in recreational 800-m college runners. Materials and Methods: Twenty healthy 800-m college runners randomized into the IMT group (11 subjects) and control group (9 subjects). IMT consisted of 30 inspiratory efforts twice daily, 5 days a week, with intensity at 50%, 60%, 70% and 80% of maximum inspiratory pressure (MIP) for 4 weeks, while a control group kept 50% of MIP for 4 weeks. An 800-m trial test, limb blood flow change rate by using Impedance Plethysmography, and MIP were as the outcome measured variables and be evaluated. All measured variables were assessed before and after 4-week IMT training. Two-way ANOVA was conducted for statistical analysis. Results: The results showed significantly interaction between groups and pre-posttest. IMT group significantly decreased limb blood flow change rate from 19.91 ± 11.65% to 9.63 ± 7.62% after received the IMT training program (p < 0.05). The MIP significantly improved from 112.95 ± 27.13 cmH₂O to 131.09 ± 28.20 cm H₂O in IMT group, and the 800-m trial test also shorted the running time from 162.97 ± 24.96 s to 156.75 ± 20.73 s. But the control group no significantly changed in MIP and 800-m trial test. Conclusions: Our results indicated that the 4-week IMT training (twice a day, 5 days a week) significantly improves participants’ inspiratory muscle strength, 800-m running performance and decreases the limb blood flow change rate.

Age and sex differences in blood pressure responses during hyperpnoea

NEW FINDINGS

What is the central question of this study? Increased respiratory muscle activation is associated with neural and cardiovascular consequences via the respiratory muscle-induced metaboreflex. Does ageing and/or sex influence the arterial blood pressure response during voluntary normocapnic incremental hyperpnoea? What is the main finding and its importance? The increase in blood pressure during hyperpnoea was smaller in younger females than in older females, whereas no difference was found between older males and older females. The blunted respiratory muscle-induced metaboreflex in younger females is normalized with advancing age, whereas ageing has no such effect in males.

ABSTRACT

We hypothesized that older females (OF) have a greater arterial blood pressure response to increased respiratory muscle work compared with younger females (YF) and that no such difference exists between older males (OM) and younger males (YM). To test these hypotheses, cardiovascular responses during voluntary normocapnic incremental hyperpnoea were evaluated and compared between older and younger subjects. An incremental respiratory endurance test (IRET) was performed as follows: target minute ventilation was initially set at 30% of the maximal voluntary ventilation (MVV12) and was increased by 10% of MVV12 every 3 min. The test was terminated when the subject could not maintain the target percentage of MVV12. Heart rate and mean arterial blood pressure (MAP) were recorded continuously. The increase in MAP from baseline (ΔMAP) during the IRET in OM (+24.0 ± 14.7 mmHg, mean ± SD) did not differ (P = 0.144) from that in YM (+24.3 ± 13.4 mmHg), but it was greater (P = 0.004) in OF (+31.2 ± 11.6 mmHg) than in YF (+10.3 ± 5.5 mmHg). No significant difference in ΔMAP during the IRET was observed between OM and OF (P = 0.975). These results suggest that the respiratory muscle-induced metaboreflex is blunted in YF, but it could be normalized with advancing age. In males, ageing has little effect on the respiratory muscle-induced metaboreflex. These results show no sex difference in the respiratory muscle-induced metaboreflex in older adults.

Respiratory impact of a grand tour: insight from professional cycling

PURPOSE

The aim of this study was to evaluate the respiratory function and symptom perception in professional cyclists completing a Grand Tour (GT).

METHODS

Nine male cyclists completed La Vuelta or Tour de France (2018/19). At study entry, airway inflammation was measured via fractional exhaled nitric oxide (FeNO). Respiratory symptoms and pulmonary function were assessed prior to the first stage (Pre-GT), at the second rest day (Mid-GT) and prior to the final stage of the GT (Late-GT). Sniff nasal inspiratory pressure (SNIP) was assessed at pre and late-GT timepoints.

RESULTS

Seven cyclists reported respiratory symptoms during the race (with a prominence of upper airway issues). Symptom severity increased either mid or late-GT for most cyclists. A decline in FEV₁ from pre-to-mid GT (- 0.27 ± 0.24 l, - 5.7%) (P = 0.02) and pre-to-late GT (- 0.27 ± 0.13 l, - 5.7%) (P < 0.001) was observed. Similarly, a decline in FVC (- 0.22 ± 0.17 l, - 3.7%) (P = 0.01) and FEF_25-75 (- 0.49 ± 0.34 l/s, - 11%) (P = 0.02) was observed pre-to-late GT. Overall, eight (89%) and six (67%) demonstrated a clinically meaningful decline (> 200 ml) in FEV₁ and FVC during the GT follow-up, respectively. SNIP remained unchanged pre-to-late GT (n = 5), however, a positive correlation was observed between ΔSNIP and ΔFVC (r = 0.99, P = 0.002).

CONCLUSION

GT competition is associated with a high prevalence of upper respiratory symptoms and a meaningful decline in lung function in professional cyclists. Further research is now required to understand the underpinning physiological mechanisms and determine the impact on overall respiratory health and elite cycling performance and recovery.

No Evidence That Hyperpnea-Based Respiratory Muscle Training Affects Indexes of Cardiovascular Health in Young Healthy Adults

Introduction

The chronic effects of respiratory muscle training (RMT) on the cardiovascular system remain unclear. This investigation tested to which degree a single sessions of RMT with or without added vibration, which could enhance peripheral blood flow and vascular response, or a 4-week RMT program could result in changes in pulse wave velocity (PWV), blood pressure (systolic, SBP; diastolic, DBP) and other markers of cardiovascular health.

Methods

Sixteen young and healthy participants (8 m/8f) performed 15 min of either continuous normocapnic hyperpnea (RMET), sprint-interval-type hyperpnea (RMSIT) or a control session (quiet sitting). Sessions were performed once with and once without passive vibration of the lower limbs. To assess training-induced adaptations, thirty-four young and healthy participants (17 m/17f) were measured before and after 4 weeks (three weekly sessions) of RMET (n = 13, 30-min sessions of normocapnic hyperpnea), RMSIT [n = 11, 6 × 1 min (1 min break) normocapnic hyperpnea with added resistance] or placebo (n = 10).

Results

SBP was elevated from baseline at 5 min after each RMT session, but returned to baseline levels after 15 min, whereas DBP was unchanged from baseline following RMT. Carotid-femoral PWV (PWV_CF) was elevated at 5 and 15 min after RMT compared to baseline (main effect of time, P = 0.001), whereas no changes were seen for carotid-radial PWV (PWV_CR) or the PWV_CF/PWV_CR ratio. Vibration had no effects in any of the interventions. Following the 4-week training period, no differences from the placebo group were seen for SBP (P = 0.686), DBP (P = 0.233), PWV_CF (P = 0.844), PWV_CR (P = 0.815) or the PWV_CF/PWV_CR ratio (P = 0.389).

Discussion/Conclusion

Although 15 min of RMT sessions elicited transient increases in PWV_CF and SBP, no changes were detected following 4 weeks of either RMET or RMSIT. Adding passive vibration of the lower limbs during RMT sessions did not provide additional value to the session with regards to vascular responses.

Influence of Inspiratory Muscle Training of Various Intensities on the Physical Performance of Long-Distance Runners

The aim of this study was to assess the efficacy of inspiratory muscle training (IMT) at different intensities on the pulmonary function and physiological adaptations of long-distance runners undergoing sports training. This study involved 25 long-distance runners. The subjects were randomly divided into three groups depending on the type of IMT applied: POWERbreathe device (group 1), Threshold IMT device (group 2), and a control group. The following lung variables were evaluated: vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in one second (FEV₁) and peak expiratory flow (PEF). Respiratory muscle strength was assessed by maximum inspiratory pressure (PImax) and maximum expiratory pressure (PE_max). Spiroergometric measures included: heart rate (HR), oxygen uptake (VO_2max), carbon dioxide production (VCO_2max), maximum ventilation (VE) and respiratory exchange rate (RER), which were measured breath by breath using a gas analyser (VYNTUS CPX). Group 1, which used the POWERbreathe device, showed significant increases in all assessed physiological and physical performance variables. In group 2, which used the Threshold device, only VO_2max, VE and tRER ventilation were significantly increased to a similar level as that observed in group 1. In the control group, we only observed a significant reduction in saturation. The use of IMT with a higher intensity resulted in significant improvements in all tested variables of lung ventilation and respiratory muscle strength. Also, after training, lactate accumulation was significantly decreased. Physiological characteristics (VO_2max/kg) and muscle respiratory strength variables were significantly improved in the group that used the POWERbreathe device after 8 weeks of training.

Inspiratory Muscle Training Improves Aerobic Capacity in Amateur Indoor Football Players

Inspiratory muscle training represents a recommended clinical practice to improve physical performance of healthy individuals, athletes, and those with chronic diseases. This study aimed to evaluate whether high- and low-intensity inspiratory muscle training interferes with the aerobic capacity of indoor soccer players. Volunteers were equally and randomly divided into CON (control group, no inspiratory muscle training); HIG (high-intensity group, inspiratory muscle training at 80% of maximal inspiratory pressure, 3 sets of 12 repetitions); and LIG (low-intensity group, inspiratory muscle training at 50% of maximal inspiratory pressure, 2 sets of 20 repetitions). Before and after inspiratory muscle training, maximal inspiratory and expiratory pressures, the incremental shuttle run test, and the 3-min step test were evaluated. Both inspiratory muscle training protocols improved maximal inspiratory and expiratory pressures, and indirect maximal oxygen consumption and distance traveled in the shuttle test compared to CON. However, only HIG achieved significant increases of indirect oxygen consumption and frequency of step rise in the 3-min step test (p<0.05). Inspiratory muscle training is an important tool to enhance maximal inspiratory pressure and exercise tolerance with potential benefits on submaximal aerobic capacity. However, high-intensity inspiratory muscle training improved aerobic capacity in amateur indoor soccer players in both submaximal tests.

Sex differences in diaphragmatic fatigue: Effects of hypoxia during inspiratory loading

KEY POINTS

Under normoxic conditions, both healthy female and male diaphragms fatigue at a similar degree when matched for absolute diaphragmatic work during inspiratory loading. We investigated whether similarities in diaphragm fatigability persist under acute hypoxic conditions. We found that, in acute hypoxia, fatigue of the diaphragm is greater in women compared to men, whereas the magnitude of fatigue in normoxia did not differ between sexes. When matched for maximal diaphragm strength, women and men had a similar pressor response to work-matched inspiratory loading, independent of oxygen availability.

ABSTRACT

In normoxia, women and men display a comparable magnitude of diaphragmatic fatigue (DF) after work-matched inspiratory loading. Whether these sex similarities are maintained under acute hypoxic conditions is unknown. We investigated the influence of acute hypoxia during work-matched inspiratory pressure-threshold loading (PTL) on DF in healthy women (n = 8) and men (n = 8). Two 5 min isocapnic PTL tasks targeting a transdiaphragmatic pressure (P_di ) of 92 cmH₂ O in normoxia and hypoxia (8% O₂ ) were performed on separate days (≥48 h). DF was quantified by twitch P_di (P_di,tw ) via cervical magnetic stimulation post-PTL. Women and men had similar maximal P_di (P_di,max ; women: 171 ± 16, men: 178 ± 20 cmH₂ O) and relative target workload (women: 54 ± 5%, men: 53 ± 6% P_di,max ). The absolute cumulative diaphragmatic work did not differ between sexes in normoxia (women: 12,653 ± 1796 cmH₂ O s^-1 , men: 13,717 ± 1231 cmH₂ O s^-1 ; P = 0.202) or hypoxia (women: 11,624 ± 1860 cmH₂ O s^-1 , men: 12 722 ± 1502 cmH₂ O s^-1 ; P = 0.189). In normoxia, the magnitude of reduction in P_di,tw post-PTL was similar between sexes (women: -21.1 ± 8.4%, men: -22.5 ± 4.9 %; P = 0.193); however, a higher degree of DF was observed in women compared to men following PTL in acute hypoxia (women: -27.6 ± 7.7%, men: -23.4 ± 9.6%, P = 0.019). We conclude that the female diaphragm is more susceptible to fatigue after inspiratory loading under acute hypoxic conditions. This finding may be related to sex differences in diaphragm muscle metabolism, such as fibre type composition, contractile properties, substrate utilisation and blood perfusion.

Physiological sex differences affect the integrative response to exercise: acute and chronic implications

NEW FINDINGS

What is the topic of this review? We review sex differences within physiological systems implicated in exercise performance; specifically, how they integrate to determine metabolic thresholds and fatigability. Thereafter, we discuss the implications that these sex differences might have for long-term adaptation to exercise. What advances does it highlight? The review collates evidence from recent physiological studies that have investigated sex as a biological variable, demonstrating that the physiological response to equivalent 'dosages' of exercise is not the same in males and females; thus, highlighting the need to research diversity in physiological responses to interventions.

ABSTRACT

The anatomical and physiological differences between males and females are thought to determine differences in the limits of human performance. The notion of studying sex as a biological variable has recently been emphasized in the biosciences as a vital step in enhancing human health. In this review, we contend that the effects of biological sex on acute and chronic responses must be studied and accounted for when prescribing aerobic exercise, much like any intervention targeting the optimization of physiological function. Emerging evidence suggests that the response of physiological systems to exercise differs between males and females, potentially mediating the beneficial effects in healthy and clinical populations. We highlight evidence that integrative metabolic thresholds during exercise are influenced by phenotypical sex differences throughout many physiological systems. Furthermore, we discuss evidence that female skeletal muscle is more resistant to fatigue elicited by equivalent dosages of high-intensity exercise. How the different acute responses affect the long-term trainability of males and females is considered, with discussion about tailoring exercise to the characteristics of the individual presented within the context of biological sex. Finally, we highlight the influence of endogenous and exogenous sex hormones on physiological responses to exercise in females. Sex is one of many mediating influences on the outcomes of exercise, and with careful experimental designs, physiologists can advance the collective understanding of diversity in physiology and optimize outcomes for both sexes.