Impaired cerebral oxygenation and exercise tolerance in patients with severe obstructive sleep apnea syndrome

Effect of high-intensity interval training on obstructive sleep apnea severity: A randomized controlled trial

Vigorous physical activity has been associated with a reduced risk of developing obstructive sleep apnea (OSA). However, whether high-intensity interval training (HIIT) reduces OSA severity remains unclear. Thus, this study aimed to investigate the impact of 12 weeks of HIIT on the apnea-hypopnea index (AHI) and sleep parameters in participants with moderate-severe OSA. In this randomized controlled trial, 36 adults (19 males; 52.2 ± 9.8 years; body mass index = 34.2 ± 5.8) with moderate to severe OSA (AHI = 42.0 ± 22.9 e/h) were randomly assigned to HIIT [5 periods of 4 min of walking or running on a treadmill at 90-95 % of maximum heart rate (HRmax) interspersed with 3 min of walking at 50-55 % of HRmax performed three times per week for 12 weeks] or a control group (CG; stretching exercises performed two times per week for 12 weeks). Sleep parameters were assessed at baseline and after 12 weeks through overnight polysomnography. Generalized estimated equations assessed differences between groups over time. There was not group × time interaction for body mass index between groups (p = 0.074). However, significant group × time interactions were observed for AHI (CG change = 8.2 ± 3.7, HIIT change = -8.6 ± 4.8; p = 0.005), SaO2 minimum (CG change = -1.6 ± 1.6 %, HIIT change = 0.4 ± 2.3 %; p = 0.030), total sleep time (CG change = -31.5 ± 19.5 min, HIIT change = 33.7 ± 19.3 min; p = 0.049), and sleep efficiency (CG change = -3.2 ± 4.4 %, HIIT change = 9.9 ± 3.5 %; p = 0.026). Moreover, there was a significant time × group interaction for maximum oxygen consumption (VO2max; CG change = -1.1 ± 1.0 mL/kg/min, HIIT change = 4.8 ± 0.9 mL/kg/min; p < 0.001)]. However, In patients with OSA, 12 weeks of HIIT decreases sleep apnea severity, improves sleep quality, and cardiorespiratory fitness. CLINICAL TRIAL REGISTRATION: (Registro Brasileiro de Ensaios Clínicos [ReBec]): # RBR-98jdt3.

Cerebral oxygenation during cardiopulmonary exercise testing in cardiorespiratory diseases: A systematic review

BACKGROUND

Cardiopulmonary exercise testing (CPET) is the gold standard for analyzing cardiorespiratory fitness and integrating physiological responses. However, the presence of chronic diseases may compromise cerebral hemodynamic responses during CPET. In addition, the acute response of cerebral oxygenation during incremental CPET may identify abnormal behavior and ensure greater safety for patients with cardiovascular, respiratory, and metabolic diseases.

OBJECTIVE

To summarize the cerebral oxygenation acute response during CPET of patients with cardiovascular, metabolic, or respiratory diseases.

METHODS

From inception to 23rd September 2022, five databases (PubMed, SCOPUS, Web of Science, Embase and CINAHAL) were searched for cross-sectional studies performing incremental CPET and measuring the cerebral oxygenation acute response in cardiovascular, metabolic, or respiratory diseases compared with healthy individuals. The Downs and Black tool assessed the risk of bias of the studies.

RESULTS

We included seven studies with 428 participants (305 men and 123 women), aged 43 to 70 years. Of these, 101 had heart failure NYHA II and III; 77 idiopathic dilated cardiomyopathy; 33 valvular disease; 25 coronary heart disease; 22 pulmonary arterial hypertension; 15 had severe obstructive sleep apnea (OSA) and 166 were apparently healthy. There was no eligible article with metabolic disease. There was a lower magnitude increase in cerebral oxygenation of cardiovascular patients compared with the healthy individuals during the CPET. Furthermore, pulmonary arterial hypertension patients presented increased cerebral oxygen extraction, differently to those with severe OSA.

CONCLUSION

Considering the heterogeneity of the included studies, patients with cardiovascular disease may suffer from reduced cerebral oxygen supply, and individuals with OSA presented lower brain oxygen extraction during the CPET. Future studies should aim for strategies to improve cerebral oxygenation to ensure greater safety at CPET of cardiovascular and OSA patients. An acute response pattern for metabolic and other respiratory diseases was not established.

Quantifying leg muscle deoxygenation during incremental cycling in hypoxemic patients with fibrotic interstitial lung disease

BACKGROUND

Hypoxaemia and cardiocirculatory abnormalities may impair muscle oxygen (O₂ ) delivery relative to O₂ requirements thereby increasing the rate of O₂ extraction during incremental exercise in fibrotic interstitial lung disease (f-ILD). Using changes in deoxyhaemoglobin concentration ([HHb]) by near-infrared spectroscopy (NIRS) as a proxy of O₂ extraction, we investigated whether a simplified (double-linear) approach, previously tested in heart failure, would provide useful estimates of muscle deoxygenation in f-ILD.

METHODS

A total of 25 patients (23 men, 72 ± 8 years; 20 with idiopathic pulmonary fibrosis, lung diffusing capacity for carbon monoxide = 44 ± 11% predicted) and 12 age- and sex-matched healthy controls performed incremental cycling to symptom limitation. Changes in vastus lateralis [HHb] assessed by NIRS were analysed in relation to work rate (WR) and O₂ uptake throughout the exercise.

RESULTS

Patients showed lower exercise capacity than controls (e.g., peak WR = 67 ± 18% vs. 105 ± 20% predicted, respectively; p < 0.001). The [HHb] response profile was typically S-shaped, presenting three distinct phases. Exacerbated muscle deoxygenation in patients versus controls was evidenced by: (i) a steeper mid-exercise [HHb]-WR slope (0.30 ± 0.22 vs. 0.11 ± 0.08 μmol/W; p = 0.008) (Phase 2), and (ii) a larger late-exercise increase in [HHb] (p = 0.002) (Phase 3). Steeper [HHb]-WR slope was associated with lower peak WR (r = -0.70) and greater leg discomfort (r = 0.77; p < 0.001) in f-ILD.

CONCLUSION

This practical approach to interpreting [HHb] during incremental exercise might prove useful to determine the severity of muscle deoxygenation and the potential effects of interventions thereof in hypoxemic patients with f-ILD.

High-intensity interval training to promote cerebral oxygenation and affective valence during exercise in individuals with obesity

Left/right prefrontal cortex (PFC) activation is linked to positive/negative affects, respectively. Besides, larger left PFC oxygenation during exercise relates to higher cardiorespiratory fitness (CRF). High-intensity interval training (HIIT) is superior to moderate-intensity continuous training (MICT) in improving CRF. The influence of training on PFC oxygenation and affects during exercise in individuals with obesity is, however, currently unknown. Twenty participants with obesity (14 males, 48 ± 8 years, body-mass index = 35 ± 6 kg·m^-2) were randomised to MICT [50% peak work rate (WR_peak)] or HIIT (1-min bouts 100% WR_peak; 3 sessions/week, 8 weeks). Before/after training, participants completed an incremental ergocycle test. Near-infrared spectroscopy and the Feeling Scale assessed PFC oxygenation and affects during exercise, respectively. Improvements in CRF (e.g., WR_peak: 32 ± 14 vs 20 ± 13 W) were greater after HIIT vs MICT (p < 0.05). Only HIIT induced larger left PFC oxygenation (haemoglobin difference from 7 ± 6 to 10 ± 7 μmol) and enhanced affective valence (from 0.7 ± 2.9 to 2.2 ± 2.0; p < 0.05) at intensities ≥ second ventilatory threshold. Exercise-training induced changes in left PFC oxygenation correlated with changes in CRF [e.g., WR_peak (% predicted), r = 0.46] and post-training affective valence (r = 0.45; p < 0.05). HIIT specifically improved left PFC oxygenation and affects during exercise in individuals with obesity. Implementing HIIT in exercise programmes may therefore have relevant implications for the management of obesity, since greater affective response to exercise is thought to be associated with future commitment to physical activity.

Abnormal Cerebral Blood Flow and Volumetric Brain Morphometry in Patients With Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a serious breathing disorder, leading to myocardial infarction, high blood pressure, and stroke. Brain morphological changes have been widely reported in patients with OSA. The pathophysiological mechanisms of cerebral blood flow (CBF) changes associated with OSA are not clear. In this study, 20 patients with OSA and 36 healthy controls (HCs) were recruited, and then pseudo-continuous arterial spin labeling (pCASL) and voxel-based morphometry (VBM) methods were utilized to explore blood perfusion and morphological changes in the patients with OSA. Compared with the HC group, the OSA group showed increased CBF values in the right medial prefrontal cortex (mPFC), left precentral gyrus, and right insula and showed decreased CBF values in the right temporal pole (TP) and the right cerebellum_Crus2. Compared with the HC group, the patients with OSA showed decreased gray matter volume (GMV) in the right dorsal lateral prefrontal cortex (DLPFC), the right occipital pole, and the vermis. There were no significantly increased GMV brain regions found in patients with OSA. Pearson correlation analysis showed that the reduced GMV in the right DLPFC and the right occipital pole was both positively correlated with Mini-Mental State Examination (MMSE) (r = 0.755, p < 0.001; r = 0.686, p = 0.002) and Montreal Cognitive Assessment (MoCA) scores (r = 0.716, p = 0.001; r = 0.601, p = 0.008), and the reduced GMV in the right occipital pole was negatively correlated with duration of illness (r = -0.497, p = 0.036). Patients with OSA have abnormal blood perfusion metabolism and morphological changes in brain regions including the frontal lobe and the cerebellum and were closely related to abnormal behavior, psychology, and cognitive function, which play an important role in the pathophysiological mechanism of OSA.

The Exercising Brain: An Overlooked Factor Limiting the Tolerance to Physical Exertion in Major Cardiorespiratory Diseases?

“Exercise starts and ends in the brain”: this was the title of a review article authored by Dr. Bengt Kayser back in 2003. In this piece of work, the author highlights that pioneer studies have primarily focused on the cardiorespiratory-muscle axis to set the human limits to whole-body exercise tolerance. In some circumstances, however, exercise cessation may not be solely attributable to these players: the central nervous system is thought to hold a relevant role as the ultimate site of exercise termination. In fact, there has been a growing interest relative to the “brain” response to exercise in chronic cardiorespiratory diseases, and its potential implication in limiting the tolerance to physical exertion in patients. To reach these overarching goals, non-invasive techniques, such as near-infrared spectroscopy and transcranial magnetic stimulation, have been successfully applied to get insights into the underlying mechanisms of exercise limitation in clinical populations. This review provides an up-to-date outline of the rationale for the “brain” as the organ limiting the tolerance to physical exertion in patients with cardiorespiratory diseases. We first outline some key methodological aspects of neuromuscular function and cerebral hemodynamics assessment in response to different exercise paradigms. We then review the most prominent studies, which explored the influence of major cardiorespiratory diseases on these outcomes. After a balanced summary of existing evidence, we finalize by detailing the rationale for investigating the “brain” contribution to exercise limitation in hitherto unexplored cardiorespiratory diseases, an endeavor that might lead to innovative lines of applied physiological research.

Sleep deprivation reduces vagal tone during an inspiratory endurance task in humans

STUDY OBJECTIVES

Sleep deprivation alters inspiratory endurance by reducing inspiratory motor output. Vagal tone is involved in exercise endurance. This study aimed to investigate the effect of sleep deprivation on vagal tone adaptation in healthy subjects performing an inspiratory effort.

METHODS

Vagal tone was assessed using Heart Rate Variability normalized units of frequency domain component HF (high frequency) before, at the start, and the end of an inspiratory loading trial performed until exhaustion by 16 volunteers after one night of sleep deprivation and one night of normal sleep, where sleep deprivation reduced the inspiratory endurance by half compared to the normal sleep condition (30 min vs 60 min).

RESULTS

At rest, heart rate was similar in sleep deprivation and normal sleep conditions. In normal sleep condition, heart rate increased during inspiratory loading task; this increase was greater in sleep deprivation condition. In normal sleep condition, vagal tone increased at the beginning of the trial. This vagal tone increase was absent in sleep deprivation condition.

CONCLUSIONS

Sleep deprivation abolished vagal tone response to inspiratory load, possibly contributing to a higher heart rate during the trial and to a reduced inspiratory endurance.

CLINICAL TRIAL REGISTRATION

NCT02725190.

A randomized sham-controlled trial on the effect of continuous positive airway pressure treatment on gait control in severe obstructive sleep apnea patients

To determine the effect of continuous positive airway pressure (CPAP), the gold standard treatment for obstructive sleep apnea syndrome (OSAS), on gait control in severe OSAS patients. We conducted a randomized, double-blind, parallel-group, sham-controlled monocentric study in Grenoble Alpes University Hospital, France. Gait parameters were recorded under single and dual-task conditions using a visuo-verbal cognitive task (Stroop test), before and after the 8-week intervention period. Stride-time variability, a marker of gait control, was the primary study endpoint. Changes in the determinants of gait control were the main secondary outcomes. ClinicalTrials.gov Identifier: (NCT02345694). 24 patients [median (Q1; Q3)]: age: 59.5 (46.3; 66.8) years, 87.5% male, body mass index: 28.2 (24.7; 29.8) kg. m⁻², apnea–hypopnea index: 51.6 (35.0; 61.4) events/h were randomized to be treated by effective CPAP (n = 12) or by sham-CPAP (n = 12). A complete case analysis was performed, using a mixed linear regression model. CPAP elicited no significant improvement in stride-time variability compared to sham-CPAP. No difference was found regarding the determinants of gait control. This study is the first RCT to investigate the effects of CPAP on gait control. Eight weeks of CPAP treatment did not improve gait control in severe non-obese OSAS patients. These results substantiate the complex OSAS-neurocognitive function relationship.

Muscle and cerebral oxygenation during cycling in chronic obstructive pulmonary disease: A scoping review

To synthesize evidence for prefrontal cortex (PFC), quadriceps, and respiratory muscle oxygenation using near-infrared spectroscopy (NIRS) during cycling in individuals with chronic obstructive pulmonary disease (COPD). A scoping review was performed searching databases (inception-August 2020): Ovid MEDLINE, EMBASE, Cochrane Systematic Reviews, Cochrane Central Register of Controlled Clinical Trials, CINAHL, SPORTDiscus and Pedro. The search focused on COPD, cycling, and NIRS outcomes. 29 studies (541 COPD participants) were included. Compared to healthy individuals (8 studies), COPD patients at lower cycling workloads had more rapid increases in vastus lateralis (VL) deoxygenated hemoglobin (HHb); lower increases in VL total hemoglobin (tHb) and blood flow; and lower muscle tissue saturation (StO₂). Heliox and bronchodilators were associated with smaller and slower increases in VL HHb. Heliox increased VL and intercostal blood flow compared to room air and supplemental oxygen in COPD patients (1 study). PFC oxygenated hemoglobin (O₂Hb) increased in COPD individuals during cycling in 5 of 8 studies. Individuals with COPD and heart failure demonstrated worse VL and PFC NIRS outcomes compared to patients with only COPD-higher or more rapid increase in VL HHb and no change or decrease in PFC O₂Hb. Individuals with COPD present with a mismatch between muscle oxygen delivery and utilization, characterized by more rapid increase in VL HHb, lower muscle O₂Hb and lower muscle StO₂. PFC O₂Hb increases or tends to increase in individuals with COPD during exercise, but this relationship warrants further investigation. NIRS can be used to identify key deoxygenation thresholds during exercise to inform PFC and muscle oxygenation.

Inspiratory muscle strength training lowers blood pressure and sympathetic activity in older adults with OSA: a randomized controlled pilot trial

Previous work has shown lowered casual blood pressure after just 6 wk of inspiratory muscle strength training (IMST), suggesting IMST as a potential therapeutic in the prevention/treatment of hypertension. In this study, we assessed the effects of IMST on cardiovascular parameters in older, overweight adults diagnosed with moderate and severe obstructive sleep apnea (OSA). Subjects were randomly assigned to one of two interventions 1) high-intensity IMST (n = 15, 75% maximal inspiratory pressure), or 2) a control intervention (n = 10, 15% maximum inspiratory pressure). Subjects in both groups trained at home completing 30 training breaths/day, 5 days/wk for 6 wk. Pre- and posttraining measures included maximal inspiratory pressure, casual and ambulatory blood pressures, spontaneous cardiac baroreflex sensitivity, and muscle sympathetic nerve activity. Men and women in the high-intensity IMST group exhibited reductions in casual systolic (SBP), diastolic (DBP), and mean arterial blood pressures (MAP) [SBP: -8.82 ± 4.98 mmHg; DBP: -4.69 ± 2.81 mmHg; and MAP: -6.06 ± 1.03 mmHg; P < 0.002] and nighttime SBP (pre: -12.00 ± 8.20 mmHg; P < 0.01). Muscle sympathetic nerve activities also were lower (-6.97 ± 2.29 bursts/min^-1; P = 0.01 and -9.55 ± 2.42 bursts/100 heartbeats; P = 0.002) by week 6. Conversely, subjects allocated to the control group showed no change in casual blood pressure or muscle sympathetic nerve activity and a trend toward higher overnight blood pressures. A short course of high-intensity IMST may offer significant respiratory and cardiovascular benefits for older, overweight adults with OSA. For Clinical Trial Registration, see https://www.clinicaltrials.gov (Identifier: NCT02709941).NEW & NOTEWORTHY Older, obese adults with moderate-severe obstructive sleep apnea who perform 5 min/day high-intensity inspiratory muscle strength training (IMST) exhibit lowered casual and nighttime systolic blood pressure and sympathetic nervous outflow. In contrast, adults assigned to a control (low-intensity) intervention exhibit no change in casual blood pressure or muscle sympathetic nerve activity and a trend toward increased overnight blood pressure. Remarkably, adherence to IMST even among sleep-deprived and exercise-intolerant adults is high (96%).

New Directions in Exercise Prescription: Is There a Role for Brain-Derived Parameters Obtained by Functional Near-Infrared Spectroscopy?

In the literature, it is well established that regular physical exercise is a powerful strategy to promote brain health and to improve cognitive performance. However, exact knowledge about which exercise prescription would be optimal in the setting of exercise–cognition science is lacking. While there is a strong theoretical rationale for using indicators of internal load (e.g., heart rate) in exercise prescription, the most suitable parameters have yet to be determined. In this perspective article, we discuss the role of brain-derived parameters (e.g., brain activity) as valuable indicators of internal load which can be beneficial for individualizing the exercise prescription in exercise–cognition research. Therefore, we focus on the application of functional near-infrared spectroscopy (fNIRS), since this neuroimaging modality provides specific advantages, making it well suited for monitoring cortical hemodynamics as a proxy of brain activity during physical exercise.

ERS International Congress, Madrid, 2019: highlights from the Sleep and Clinical Physiology Assembly

The 2019 European Respiratory Society (ERS) International Congress took place in Madrid, Spain, and served as a platform to find out the latest advances in respiratory diseases research. The research aims are to understand the physiology and consequences of those diseases, as well as the improvement in their diagnoses, treatments and patient care. In particular, the scientific sessions arranged by ERS Assembly 4 provided novel insights into sleep-disordered breathing and new knowledge in respiratory physiology. This article, divided by session, will summarise the most relevant studies presented at the ERS International Congress. Each section has been written by Early Career Members specialising in the different fields of this interdisciplinary assembly.

Fatigue in Chronic Respiratory Diseases: Theoretical Framework and Implications For Real-Life Performance and Rehabilitation

Fatigue is a primary disabling symptom in chronic respiratory diseases (CRD) with major clinical implications. However, fatigue is not yet sufficiently explored and is still poorly understood in CRD, making this symptom underdiagnosed and undertreated in these populations. Fatigue is a dynamic phenomenon, particularly in such evolving diseases punctuated by acute events which can, alone or in combination, modulate the degree of fatigue experienced by the patients. This review supports a comprehensive inter-disciplinary approach of CRD-related fatigue and emphasizes the need to consider both its performance and perceived components. Most studies in CRD evaluated perceived fatigue as a trait characteristic using multidimensional scales, providing precious information about its prevalence and clinical impact. However, these scales are not adapted to understand the complex dynamics of fatigue in real-life settings and should be augmented with ecological assessment of fatigue. The state level of fatigue must also be considered during physical tasks as severe fatigue can emerge rapidly during exercise. CRD patients exhibit alterations in both peripheral and central nervous systems and these abnormalities can be exacerbated during exercise. Laboratory tests are necessary to provide mechanistic insights into how and why fatigue develops during exercise in CRD. A better knowledge of the neurophysiological mechanisms underlying perceived and performance fatigability and their influence on real-life performance will enable the development of new individualized countermeasures. This review aims first to shed light on the terminology of fatigue and then critically considers the contemporary models of fatigue and their relevance in the particular context of CRD. This article then briefly reports the prevalence and clinical consequences of fatigue in CRD and discusses the strengths and weaknesses of various fatigue scales. This review also provides several arguments to select the ideal test of performance fatigability in CRD and to translate the mechanistic laboratory findings into the clinical practice and real-world performance. Finally, this article discusses the dose-response relationship to training and the feasibility and validity of using the fatigue produced during exercise training sessions in CRD to optimize exercise training efficiency. Methodological concerns, examples of applications in selected diseases and avenues for future research are also provided.