Does impaired O2 delivery during exercise accentuate central and peripheral fatigue in patients with coexistent COPD-CHF?

Can Non-invasive Ventilation Modulate Cerebral, Respiratory, and Peripheral Muscle Oxygenation During High-Intensity Exercise in Patients With COPD-HF?

Aim

To evaluate the effect of non-invasive positive pressure ventilation (NIPPV) on (1) metabolic, ventilatory, and hemodynamic responses; and (2) cerebral (Cox), respiratory, and peripheral oxygenation when compared with SHAM ventilation during the high-intensity exercise in patients with coexisting chronic obstructive pulmonary disease (COPD) and heart failure (HF).

Methods and Results

On separate days, patients performed incremental cardiopulmonary exercise testing and two constant-work rate tests receiving NIPPV or controlled ventilation (SHAM) (the bilevel mode—Astral 150) in random order until the limit of tolerance (Tlim). During exercise, oxyhemoglobin (OxyHb+Mb) and deoxyhemoglobin (DeoxyHb+Mb) were assessed using near-infrared spectroscopy (Oxymon, Artinis Medical Systems, Einsteinweg, The Netherlands). NIPPV associated with high-intensity exercise caused a significant increase in exercise tolerance, peak oxygen consumption (V·O2 in mlO₂·kg⁻¹·min⁻¹), minute ventilation peak (V·E in ml/min), peak peripheral oxygen saturation (SpO₂, %), and lactate/tlim (mmol/s) when compared with SHAM ventilation. In cerebral, respiratory, and peripheral muscles, NIPPV resulted in a lower drop in OxyHb+Mb (p < 0.05) and an improved deoxygenation response DeoxyHb+Mb (p < 0.05) from the half of the test (60% of Tlim) when compared with SHAM ventilation.

Conclusion

Non-invasive positive pressure ventilation during constant work-rate exercise led to providing the respiratory muscle unloading with greater oxygen supply to the peripheral muscles, reducing muscle fatigue, and sustaining longer exercise time in patients with COPD-HF.

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.

Residual Exertional Dyspnea in Cardiopulmonary Disease

In cardiopulmonary medicine, residual exertional dyspnea (RED) can be defined by the persistence of limiting breathlessness in a patient who is already under the best available therapy for the underlying heart and/or lung disease. RED is a challenge to the pulmonologist because the patient (and the referring physician) assumes that the "lung doctor" should invariably provide a successful plan to fight the symptom. After presenting a simplified framework to understand the neurobiological underpinnings of dyspnea in cardiorespiratory disease, I discuss the seeds of RED associated with 1) increased metabolic cost of work, 2) increased inspiratory constraints, 3) diaphragm dysfunction, 4) impaired right ventricle preload, 5) increased central and/or peripheral chemosensitivity, 6) increased physiological dead space, 7) increased pulmonary venous and/or high left ventricle filling pressures, 8) impaired chronotropic response to exertion, and 9) increased activation of the cortical-limbic circuits. I finalize by outlining the following two common coexistence of diseases in which these multiple mechanisms interact to produce severe RED: chronic obstructive pulmonary disease-heart failure with reduced ejection fraction and chronic pulmonary fibrosis-emphysema. RED exposes the important limitations of the current reductionist approach focused only on the (over)treatment of the poorly reversible cardiopulmonary disease(s). Conversely, recognizing the existence of RED sets the stage for a more holistic approach toward one of the most devastating symptoms known to man.

Simultaneous Measurement of Perfusion and T2* in Calf Muscle at 7T with Submaximal Exercise using Radial Acquisition

Impairments in oxygen delivery and consumption can lead to reduced muscle endurance and physical disability. Perfusion, a measure of microvascular blood flow, provides information on nutrient delivery. T₂* provides information about relative tissue oxygenation. Changes in these parameters following stress, such as exercise, can yield important information about imbalance between delivery and consumption. In this study, we implemented novel golden angle radial MRI acquisition technique to simultaneously quantify muscle perfusion and T₂* at 7T with improved temporal resolution, and demonstrated assessment of spatial and temporal changes in these parameters within calf muscles during recovery from plantar flexion exercise. Nine healthy subjects participated the studies. At rest, perfusion and T₂* in gastrocnemius muscle group within calf muscle were 5 ± 2 mL/100 g/min and 21.1 ± 3 ms respectively. Then the subjects performed plantar flexion exercise producing a torque of ~8ft-lb. Immediately after the exercise, perfusion was elevated to 79.3 ± 9 mL/100 g/min and T₂* was decreased by 6 ± 3%. The time constants for 50% perfusion and T₂* recovery were 54.1 ± 10 s and 68.5 ± 7 s respectively. These results demonstrate successful simultaneous quantification of perfusion and T₂* in skeletal muscle using the developed technique.

Characterization of performance fatigability during a self-paced exercise

Pacing during a high-intensity cycling time trial (TT) appears to prevent premature task failure, but the performance fatigability during a self-paced exercise is currently unknown. Therefore, the current study characterized the time course of performance fatigability during a 4-km TT. Eleven male cyclists performed three separated TTs in a crossover, counterbalanced design. The TTs lasted until the end of the fast-start (FS; 600 ± 205 m), even-pace (EP; 3,600 ± 190 m), and end-spurt (ES; 4,000 m) phases. Performance fatigability was characterized by using isometric maximal voluntary contractions (IMVCs), whereas the muscle activation [i.e., voluntary activation (VA)] and contractile function of knee extensors [e.g., peak torque of potentiated twitches (TwPt)] were evaluated using electrically evoked contractions performed before and 1 min after each specific part of the trial. Gas exchange, power output (PO), and electromyographic activity (EMG) were also recorded. EMG/PO showed an abrupt increase followed by a continuous decrease toward the end of FS, resulting in a drop in IMVC (−12%), VA (−8%), and TwPt (−23%). EMG/PO was stable during EP, with no additional drop on IMVC, VA, or TwPt (−12%, −6%, and −22%, respectively). EMG/PO increased abruptly during the ES, but there was no change in IMVCs, VA, or TwPt (−13%, −8%, and −26%, respectively). These findings demonstrate that the performance fatigability during a self-paced exercise is characterized by a large drop in contractile function and muscle activation at the beginning of the trial (i.e., FS), without additional change during the middle and end phases (i.e., EP and ES).

NEW & NOTEWORTHY The time course of performance fatigability throughout a self-paced exercise is currently unknown. The results showed that a large amount of muscle activation and contractile function impairments are attained early on a self-paced exercise (first ∼15% of the total time trial distance) and maintained throughout the test. This novel finding characterizes the performance fatigability from a contractile function and muscle activation perspective, which brings new insights for future studies focused on real-world exercise training and competition.

Cardiopulmonary and Muscular Interactions: Potential Implications for Exercise (In)tolerance in Symptomatic Smokers Without Chronic Obstructive Pulmonary Disease

Smoking and physical inactivity are important preventable causes of disability and early death worldwide. Reduced exercise tolerance has been described in smokers, even in those who do not fulfill the extant physiological criteria for chronic obstructive pulmonary disease (COPD) and are not particularly sedentary. In this context, it is widely accepted that exercise capacity depends on complex cardio-pulmonary interactions which support oxygen (O₂) delivery to muscle mitochondria. Although peripheral muscular factors, O₂ transport disturbances (including the effects of increased carboxyhemoglobin) and autonomic nervous system unbalance have been emphasized, other derangements have been more recently described, including early microscopic emphysema, pulmonary microvascular disease, ventilatory and gas exchange inefficiency, and left ventricular diastolic dysfunction. Using an integrative physiological approach, the present review summarizes the recent advances in knowledge on the effects of smoking on the lung-heart-muscle axis under the stress of exercise. Special attention is given to the mechanisms connecting physiological abnormalities such as early cardio-pulmonary derangements, inadequate oxygen delivery and utilization, and generalized bioenergetic disturbances at the muscular level with the negative sensations (sense of heightened muscle effort and breathlessness) that may decrease the tolerance of smokers to physical exercise. A deeper understanding of the systemic effects of smoking in subjects who did not (yet) show evidences of COPD and ischemic heart disease - two devastating smoking related diseases - might prove instrumental to fight their ever-growing burden.

Exercise intolerance in comorbid COPD and heart failure: the role of impaired aerobic function

Impaired aerobic function is a potential mechanism of exercise intolerance in patients with combined cardiorespiratory disease. We investigated the pathophysiological and sensory consequences of a low change in oxygen uptake (ΔV'_O2 )/change in work rate (ΔWR) relationship during incremental exercise in patients with coexisting chronic obstructive pulmonary disease (COPD) and systolic heart failure (HF).After clinical stabilisation, 51 COPD-HF patients performed an incremental cardiopulmonary exercise test to symptom limitation. Cardiac output was non-invasively measured (impedance cardiography) in a subset of patients (n=18).27 patients presented with ΔV'_O2 /ΔWR below the lower limit of normal. Despite similar forced expiratory volume in 1 s and ejection fraction, the low ΔV'_O2 /ΔWR group showed higher end-diastolic volume, lower inspiratory capacity and lower transfer factor compared to their counterparts (p<0.05). Peak WR and peak V'_O2 were ∼15% and ∼30% lower, respectively, in the former group: those findings were associated with greater symptom burden in daily life and at a given exercise intensity (leg discomfort and dyspnoea). The low ΔV'_O2 /ΔWR group presented with other evidences of impaired aerobic function (sluggish V'_O2 kinetics, earlier anaerobic threshold) and cardiocirculatory performance (lower oxygen pulse, lower stroke volume and cardiac output) (p<0.05). Despite similar exertional hypoxaemia, they showed worse ventilatory inefficiency and higher operating lung volumes, which led to greater mechanical inspiratory constraints (p<0.05).Impaired aerobic function due to negative cardiopulmonary-muscular interactions is an important determinant of exercise intolerance in patients with COPD-HF. Treatment strategies to improve oxygen delivery to and/or utilisation by the peripheral muscles might prove particularly beneficial to these patients.

Faster oxygen uptake, heart rate, and ventilatory kinetics in stepping compared with cycle ergometry in patients with COPD during moderate-intensity exercise

Step tests are a stressful and feasible cost-effective modality to evaluate aerobic performance. However, the eccentric in addition to concentric muscle contractions of the legs on stepping emerge as a potential speeding factor for cardioventilatory and metabolic adjustments towards a steady-state, since eccentric contractions would prompt an earlier and stronger mechanoreceptor activation, as well as higher heart rate/cardiac output adjustments to the same metabolic demand. Moreover, shorter tests are ideal for exercise-limited subjects. Nine subjects with chronic obstructive pulmonary disease were invited to participate in comprehensive lung function tests and constant work tests performed on different days at a 90% gas exchange threshold for 6 min, in single-step tests or cycle ergometry. After careful monoexponential regression modelling, statistically relevant faster phase II time constants for oxygen uptake (45 ± 18 s vs 53 ± 17 s, p = 0.017) and minute ventilation (61 ± 13 s vs 74 ± 17 s, p = 0.027) were observed in the 6-min step tests compared with cycle ergometry, respectively. Despite an absence of heart rate time constant difference (43 ± 20 s vs 69 ± 46 s, p = 0.167), there was a significantly faster rate constant toward a steady state for heart rate (p = 0.02). In addition, 4-min compared with 6-min analysis presented similar results (p > 0.05), providing an appropriate steady-state. We conclude that step tests might elicit faster time constants compared with cycle ergometry, at the same average metabolic level, and 4-min analysis has similar mean errors compared with 6-min analysis within an acceptable range. New studies, comprising mechanisms and detailed physiological backgrounds, are necessary.

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.

Does peripheral arterial occlusive disease influence muscle strength and exercise capacity in COPD patients?

Background

The pathophysiology of chronic obstructive pulmonary disease (COPD) is complex and understanding of it has been changing in recent years, with regard to its multisystemic manifestations, especially peripheral dysfunction and its influence on intolerance to exercise.

Objectives

To evaluate the relationship between peripheral arterial occlusive disease (PAOD) and peripheral muscle strength and exercise capacity in COPD patients.

Methods

We conducted a cross-sectional study of 35 patients with COPD who were evaluated with the Ankle-Brachial Index, handgrip strength test, 1 repetition maximum (1RM) of knee extensors and flexors, and distance covered in the incremental shuttle walking test (dISWT).

Results

COPD patients with coexisting PAOD had lower dominant handgrip strength test results (33.00 vs. 26.66 kgf, p = 0.02) and worse performance in the dISWT (297.32 vs. 219.41 m, p = 0.02) when compared to the COPD patients without PAOD. Strong correlations were found between the result of the handgrip strength test and both the dISWT (r = 0.78; p < 0.001) and the 1RM/knee extension (r = 0.71; p = 0.03); and also between the dISWT and both the 1RM/knee extension (r = 0.72; p = 0.02) and the 1RM/knee flexion (r = 0.92; p < 0.001). The linear regression model showed that the dISWT variable alone explains 15.3% of the Ankle-Brachial Index result (p = 0.01).

Conclusion

COPD patients with PAOD exhibit reduced muscle strength and lower exercise capacity than COPD patients without PAOD.

Handgrip and functional capacity in Chronic Obstructive Pulmonary Disease patients

Abstract Introduction: In the Chronic Obstructive Pulmonary Disease (COPD) both pulmonary and systemic condition increase dyspnea, intolerance to exercise and inactivity. Objective: To evaluate possible association between Hand Grip Strength (HGS) and the distance covered in the Six-Minute Walk Test (6MWT) in patients with Chronic Obstructive Pulmonary Disease (COPD). Methods: A cross-sectional study that evaluated 34 patients with COPD from moderate to very severe stages. The HGS test was performed with a manual hydraulic dynamometer (Jamar®, California, USA) with three bilateral measures, allowing 60-seconds rest time in-between measurements. Afterwards, the patients were submitted to the 6MWT along a 30-meters level corridor following the rules of the American Thoracic Society. Results: Average age 62.7±7.2 years old, body mass index 26.7±6.9 Kg/m². The value of the HGS in the dominant hand was 28.0±8.7 Kgf and in the non-dominant hand was 26.7±7.7 Kgf (99.2% of the predicted value and 106.3% of the predicted value, respectively). The subjects covered in average 421.0±110.4 meters in the 6MWT and there has been detected direct and significant correlation between the distance covered and the HGS of the dominant hand (r=0,430; p=0,011) and non-dominant (r=0,502; p=0,002). The patients with COPD that presented lower HGS also covered less distance in the 6MWT. Conclusion: The hand grip strength was directly associated with the functional capacity assessed through the distance covered in the Six-Minute Walk Test in the evaluated trial.

Moderate Aerobic Training Improves Cardiorespiratory Parameters in Elastase-Induced Emphysema

Aim: We investigated the therapeutic effects of aerobic training on lung mechanics, inflammation, morphometry and biological markers associated with inflammation, and endothelial cell damage, as well as cardiac function in a model of elastase-induced emphysema.

Methods: Eighty-four BALB/c mice were randomly allocated to receive saline (control, C) or 0.1 IU porcine pancreatic elastase (emphysema, ELA) intratracheally once weekly for 4 weeks. After the end of administration period, once cardiorespiratory impairment associated with emphysema was confirmed, each group was further randomized into sedentary (S) and trained (T) subgroups. Trained mice ran on a motorized treadmill, at moderate intensity, 30 min/day, 3 times/week for 4 weeks.

Results: Four weeks after the first instillation, ELA animals, compared to C, showed: (1) reduced static lung elastance (Est,L) and levels of vascular endothelial growth factor (VEGF) in lung tissue, (2) increased elastic and collagen fiber content, dynamic elastance (E, in vitro), alveolar hyperinflation, and levels of interleukin-1β and tumor necrosis factor (TNF)-α, and (3) increased right ventricular diastolic area (RVA). Four weeks after aerobic training, ELA-T group, compared to ELA-S, was associated with reduced lung hyperinflation, elastic and collagen fiber content, TNF-α levels, and RVA, as well as increased Est,L, E, and levels of VEGF.

Conclusion: Four weeks of regular and moderate intensity aerobic training modulated lung inflammation and remodeling, thus improving pulmonary function, and reduced RVA and pulmonary arterial hypertension in this animal model of elastase-induced emphysema.

Respiratory muscle strength effect on linear and nonlinear heart rate variability parameters in COPD patients

Introduction

Chronic obstructive pulmonary disease (COPD) is recognized as a multisystemic inflammatory disease associated with extrapulmonary comorbidities, including respiratory muscle weakness and cardiovascular and cardiac autonomic regulation disorders. We investigated whether alterations in respiratory muscle strength (RMS) would affect cardiac autonomic modulation in COPD patients.

Methods

This study was a cross-sectional study done in ten COPD patients affected by moderate to very severe disease. The heart rate variability (HRV) signal was recorded using a Polar cardiofrequencimeter at rest in the sitting position (10 minutes) and during a respiratory sinus arrhythmia maneuver (RSA-M; 4 minutes). Linear analysis in the time and frequency domains and nonlinear analysis were performed on the recorded signals. RMS was assessed using a digital manometer, which provided the maximum inspiratory pressure (PImax) and the maximum expiratory pressure (PEmax).

Results

During the RSA-M, patients presented an HRV power increase in the low-frequency band (LFnu) (46.9±23.7 vs 75.8±27.2; P=0.01) and a decrease in the high-frequency band (HFnu) (52.8±23.5 vs 24.0±27.0; P=0.01) when compared to the resting condition. Significant associations were found between RMS and HRV spectral indices: PImax and LFnu (r=−0.74; P=0.01); PImax and HFnu (r=0.74; P=0.01); PEmax and LFnu (r=−0.66; P=0.01); PEmax and HFnu (r=0.66; P=0.03); between PEmax and sample entropy (r=0.83; P<0.01) and between PEmax and approximate entropy (r=0.74; P=0.01). Using a linear regression model, we found that PImax explained 44% of LFnu behavior during the RSA-M.

Conclusion

COPD patients with impaired RMS presented altered cardiac autonomic control, characterized by marked sympathetic modulation and a reduced parasympathetic response; reduced HRV complexity was observed during the RSA-M.

Exercise intolerance in pulmonary hypertension: mechanism, evaluation and clinical implications

INTRODUCTION

Exercise intolerance in pulmonary hypertension (PH) is a major factor affecting activities of daily living and quality of life. Evaluation strategies (i.e., non-invasive and invasive tests) are integral to providing a comprehensive assessment of clinical and functional status. Despite a growing body of literature on the clinical consequences of PH, there are limited studies discussing the contribution of various physiological systems to exercise intolerance in this patient population.

AREAS COVERED

This review, through a search of various databases, describes the physiological basis for exercise intolerance across the various PH etiologies, highlights the various exercise evaluation methods and discusses the rationale for exercise training amongst those diagnosed with PH. Expert commentary: With the growing importance of evaluating exercise capacity in PH (class 1, Level C recommendation), understanding why exercise performance is altered in PH is crucial. Thus, the further study is required for better quality evidence in this area.