Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our ...understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.
Several studies in mild chronic obstructive pulmonary disease (COPD) have shown a higher than normal ventilatory equivalent for carbon dioxide (Formula: see texte/Formula: see textco2) during ...exercise. Our objective was to examine pulmonary gas exchange abnormalities and the mechanisms of high Formula: see texte/Formula: see textco2 in mild COPD and its impact on dyspnea and exercise intolerance.
Twenty-two subjects (11 patients with GOLD Global Initiative for Chronic Obstructive Lung Disease grade 1B COPD, 11 age-matched healthy control subjects) undertook physiological testing and a symptom-limited incremental cycle exercise test with arterial blood gas collection.
Patients (post-bronchodilator FEV1: 94 ± 10% predicted; mean ± SD) had evidence of peripheral airway dysfunction and reduced peak oxygen uptake compared with control subjects (80 ± 18 vs. 113 ± 24% predicted; P<0.05). Arterial blood gases were within the normal range and effective alveolar ventilation was not significantly different from control subjects throughout exercise. The alveolar-arterial O2 tension gradient was elevated at rest and throughout exercise in COPD (P<0.05). Formula: see texte/Formula: see textco2, dead space to tidal volume ratio (Vd/Vt), and arterial to end-tidal CO2 difference were all higher (P<0.05) in patients with COPD than in control subjects during exercise. In patients with COPD versus control subjects, there was significant dynamic hyperinflation and greater tidal volume constraints (P<0.05). Standardized dyspnea intensity ratings were also higher (P<0.05) in patients with COPD versus control subjects in association with higher ventilatory requirements. Within all subjects, Vd/Vt correlated with the Formula: see texte/Formula: see textco2 ratio during submaximal exercise (r=0.780, P<0.001).
High Vd/Vt was the most consistent gas exchange abnormality in smokers with only mild spirometric abnormalities. Compensatory increases in minute ventilation during exercise maintained alveolar ventilation and arterial blood gas homeostasis but at the expense of earlier dynamic mechanical constraints, greater dyspnea, and exercise intolerance in mild COPD.
Key points
Diaphragmatic fatigue (DF) elicits a sympathetically mediated metaboreflex resulting in increased heart rate, blood pressure and limb vascular resistance.
Women may be more resistant to DF ...compared to men, and therefore it was hypothesised that women would experience an attenuated inspiratory muscle metaboreflex during inspiratory pressure‐threshold loading (PTL) performed to task failure.
At the time of PTL task failure, the severity of DF was not different between sexes; however, inspiratory muscle endurance time was significantly longer in women than in men.
For a given cumulative diaphragmatic force output, the severity of DF was less in women than in men.
Women exhibited a blunted cardiovascular response to inspiratory resistance (i.e. metaboreflex) that may have implications for exercise tolerance.
Diaphragmatic fatigue (DF) elicits reflexive increases in sympathetic vasomotor outflow (i.e. metaboreflex). There is some evidence suggesting women may be more resistant to DF compared to men, and therefore may experience an attenuated inspiratory muscle metaboreflex. To this end, we sought to examine the cardiovascular response to inspiratory resistance in healthy young men (n = 9, age = 24 ± 3 years) and women (n = 9, age = 24 ± 3 years). Subjects performed isocapnic inspiratory pressure‐threshold loading (PTL, 60% maximal inspiratory mouth pressure) to task failure. Diaphragmatic fatigue was assessed by measuring transdiaphragmatic twitch pressure (Pdi,tw) using cervical magnetic stimulation. Heart rate (HR) and mean arterial pressure (MAP) were measured beat‐by‐beat throughout PTL via photoplethysmography, and low‐frequency systolic pressure (LFSBP; a surrogate for sympathetic vasomotor tone) calculated from arterial waveforms using power spectrum analysis. At PTL task failure, the degree of DF was similar between sexes (∼23% reduction in Pdi,tw; P = 0.33). However, time to task failure was significantly longer in women than in men (27 ± 11 vs. 16 ± 11 min, respectively; P = 0.02). Women exhibited less of an increase in HR (13 ± 8 vs. 19 ± 12 bpm; P = 0.02) and MAP (10 ± 8 vs. 14 ± 9 mmHg; P = 0.01), and significantly lower LFSBP (23 ± 11 vs. 34 ± 8 mmHg2; P = 0.04) during PTL compared to men. An attenuation of the inspiratory muscle metaboreflex may influence limb and respiratory muscle haemodynamics with implications for exercise performance.
Key points
Diaphragmatic fatigue (DF) elicits a sympathetically mediated metaboreflex resulting in increased heart rate, blood pressure and limb vascular resistance.
Women may be more resistant to DF compared to men, and therefore it was hypothesised that women would experience an attenuated inspiratory muscle metaboreflex during inspiratory pressure‐threshold loading (PTL) performed to task failure.
At the time of PTL task failure, the severity of DF was not different between sexes; however, inspiratory muscle endurance time was significantly longer in women than in men.
For a given cumulative diaphragmatic force output, the severity of DF was less in women than in men.
Women exhibited a blunted cardiovascular response to inspiratory resistance (i.e. metaboreflex) that may have implications for exercise tolerance.
Chronic obstructive pulmonary disease (COPD) is a preventable and treatable lung disease characterized by airflow limitation that is not fully reversible. In a significant proportion of patients with ...COPD, reduced lung elastic recoil combined with expiratory flow limitation leads to lung hyperinflation during the course of the disease. Development of hyperinflation during the course of COPD is insidious. Dynamic hyperinflation is highly prevalent in the advanced stages of COPD, and new evidence suggests that it also occurs in many patients with mild disease, independently of the presence of resting hyperinflation. Hyperinflation is clinically relevant for patients with COPD mainly because it contributes to dyspnea, exercise intolerance, skeletal muscle limitations, morbidity, and reduced physical activity levels associated with the disease. Various pharmacological and nonpharmacological interventions have been shown to reduce hyperinflation and delay the onset of ventilatory limitation in patients with COPD. The aim of this review is to address the more recent literature regarding the pathogenesis, assessment, and management of both static and dynamic lung hyperinflation in patients with COPD. We also address the influence of biological sex and obesity and new developments in our understanding of hyperinflation in patients with mild COPD and its evolution during progression of the disease.
The purpose of this study was to determine if a dissociation existed between respiratory drive, as estimated by diaphragmatic electromyography (EMGdi), and its pressure-generating capacity during ...exercise in mild chronic obstructive pulmonary disease (COPD) and whether this, if present, had negative sensory consequences. Subjects meeting spirometric criteria for mild COPD (n=16) and age and sex-matched controls (n=16) underwent detailed pulmonary function testing and a symptom limited cycle test while detailed ventilatory, sensory and respiratory mechanical responses were measured. Compared with controls, subjects with mild COPD had greater ventilatory requirements throughout submaximal exercise. At the highest equivalent work rate of 60 W, they had a significantly higher: total work of breathing (32±17 versus 16±7 J·min(-1); p<0.01); EMGdi (37.3±17.3 versus 17.9±11.7% of maximum; p<0.001); and EMGdi to transdiaphragmatic pressure ratio (0.87±0.38 versus 0.52±0.27; p<0.01). Dyspnoea-ventilation slopes were significantly higher in mild COPD than controls (0.17±0.12 versus 0.10±0.05; p<0.05). However, absolute dyspnoea ratings reached significant levels only at high levels of ventilation. Increased respiratory effort and work of breathing, and a wider dissociation between diaphragmatic activation and pressure-generating capacity were found at standardised work rates in subjects with mild COPD compared with controls. Despite these mechanical and neuromuscular abnormalities, significant dyspnoea was only experienced at higher work rates.
A cardiopulmonary exercise test (CPET) is ideally suited to quantify exercise tolerance and evaluate the pathophysiological mechanism(s) of dyspnea and exercise limitation in people with chronic ...respiratory disease. Although there are several statements on CPET and many outstanding resources detailing the cardiorespiratory and perceptual responses to exercise, limited information is available to support the health care provider in conducting a practical CPET evaluation. This article provides the health care provider with practical and timely information on how to use CPET data to understand dyspnea and exercise intolerance in people with chronic respiratory diseases. Information on CPET protocol, as well as how to evaluate maximal patient effort, peak rate of oxygen consumption, ventilatory demand, pulmonary gas exchange, ventilatory reserve, operating lung volumes, and exertional dyspnea, is presented. Two case examples are also described to highlight how these parameters are evaluated to provide a clinical interpretation of CPET data.
Women are more resistant to diaphragmatic fatigue (DF) and experience an attenuated inspiratory muscle metaboreflex relative to men. The effects of such sex-based differences on whole body exercise ...tolerance are yet to be examined. It was hypothesized that DF induced prior to exercise would cause less of a reduction in subsequent exercise time in women compared to men. Healthy men ( n = 9, age = 24 ± 3 yr) and women ( n = 9, age = 24 ± 3 yr) completed a maximal incremental cycle test on day 1. On day 2, subjects performed isocapnic inspiratory pressure-threshold loading (PTL) to task failure followed by a constant load submaximal time-to-exhaustion (TTE) exercise test at 85% of the predetermined peak work rate. On day 3, subjects performed the same exercise test without prior induced DF. Days 2 and 3 were randomized and counterbalanced. Magnetic stimulation of the phrenic nerve roots was used to nonvolitionally assess DF by measurement of transdiaphragmatic twitch pressure ( P
). A similar degree of DF was produced in both sexes following PTL P
(% change from baseline): M = -24.6 ± 7.8%, W = -23.1 ± 5.4%; P = 0.54). There was a significant reduction in TTE with prior induced DF compared with the control condition in both men (10.9 ± 3.5 min vs. 13.0 ± 3.2 min, P = 0.05) and women (10.1 ± 2.4 min vs. 12.2 ± 3.3 min, P = 0.03) that did not differ in magnitude between the sexes (M = -15.8 ± 19.5%, W = -14.5 ± 19.2%, P = 0.89). In conclusion, DF negatively and equally impairs exercise tolerance independent of sex. NEW & NOTEWORTHY Women are more resistant to diaphragmatic fatigue (DF) relative to men. The effect of DF on exercise tolerance is currently being debated. Our findings show that DF negatively and equally affects exercise tolerance in healthy men and women. Mechanisms beyond the inspiratory muscle metaboreflex (e.g., dyspnea, central fatigue, breathing pattern) may explain the absence of a sex-based difference.
To minimize transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus responsible for coronavirus disease (COVID-19), the U.S. Centers for Disease Control ...and Prevention and the World Health Organization recommend wearing face masks in public. Some have expressed concern that these may affect the cardiopulmonary system by increasing the work of breathing, altering pulmonary gas exchange and increasing dyspnea, especially during physical activity. These concerns have been derived largely from studies evaluating devices intentionally designed to severely affect respiratory mechanics and gas exchange. We review the literature on the effects of various face masks and respirators on the respiratory system during physical activity using data from several models: cloth face coverings and surgical masks, N95 respirators, industrial respirators, and applied highly resistive or high-dead space respiratory loads. Overall, the available data suggest that although dyspnea may be increased and alter perceived effort with activity, the effects on work of breathing, blood gases, and other physiological parameters imposed by face masks during physical activity are small, often too small to be detected, even during very heavy exercise. There is no current evidence to support sex-based or age-based differences in the physiological responses to exercise while wearing a face mask. Although the available data suggest that negative effects of using cloth or surgical face masks during physical activity in healthy individuals are negligible and unlikely to impact exercise tolerance significantly, for some individuals with severe cardiopulmonary disease, any added resistance and/or minor changes in blood gases may evoke considerably more dyspnea and, thus, affect exercise capacity.
•Dyspnoea persists in many patients following COVID-19 infection.•COVID-19 patients with persistent dyspnoea have impaired spirometry and gas exchange.•COVID-19 patients with persistent dyspnoea have ...reduced exercise performance.
The purpose of this study was to examine the physiological mechanisms of persistent dyspnoea in COVID-19 survivors. Non-critical patients (n = 186) with varying degrees of COVID-19 severity reported persistent symptoms using a standardized questionnaire and underwent pulmonary function and 6-minute walk testing between 30 and 90 days following the onset of acute COVID-19 symptoms. Patients were divided into those with (n = 70) and without (n = 116) persistent dyspnoea. Patients with persistent dyspnoea had significantly lower FVC (p = 0.03), FEV1 (p = 0.04), DLCO (p = 0.01), 6-minute walk distance (% predicted, p = 0.03), and end-exercise oxygen saturation (p < 0.001), and higher Borg 0-10 ratings of dyspnoea and fatigue (both p < 0.001) compared to patients without persistent dyspnoea. We have shown that dyspnoea is a common persistent symptom across varying degrees of initial COVID-19 severity. Patients with persistent dyspnoea had greater restriction on spirometry, lower DLCO, reduced functional capacity, and increased exertional desaturation and symptoms. This suggests that there is a true physiological mechanism that may explain persistent dyspnoea after COVID-19.
ABSTRACT
Background and objective
Despite its clinical and prognostic significance, few studies have evaluated the severity of exertional oxygen desaturation in fibrotic interstitial lung disease ...(ILD). Our objectives were to identify clinical and physiological variables that predict the extent of exertional oxygen desaturation in fibrotic ILD and to quantify the severity of desaturation compared to chronic obstructive pulmonary disease (COPD).
Methods
This retrospective study compared the results of 6‐min walk test (6MWT) performed while breathing room air in fibrotic ILD patients and COPD patients eligible for pulmonary rehabilitation. Outcomes included the oxygen saturation (SpO2) nadir and the change in SpO2 from rest during a 6MWT. Predictor variables were identified on unadjusted analysis, followed by multivariate analysis to identify independent predictors of desaturation.
Results
The study included 134 patients with fibrotic ILD and 274 patients with COPD. The ILD and COPD cohorts had similar age, sex, frequency of major comorbidities, walk distance, baseline SpO2 and baseline Borg dyspnoea scores. DLCO was the strongest predictor of desaturation in both cohorts. Compared to patients with COPD, ILD patients had significantly lower SpO2 nadir values (88.1 ± 6.4 vs 91.0 ± 4.6) and greater decrease in SpO2 from baseline (7.4 ± 5.2 vs 4.5 ± 3.7) after adjusting for demographic features and pulmonary physiology (P < 0.0005), with greater between‐group differences at lower DLCO values.
Conclusion
Patients with fibrotic ILD have greater oxygen desaturation during 6MWT compared to patients with COPD when adjusting for demographic features and pulmonary physiology. These findings suggest the need for disease‐specific studies to evaluate the potential utility of ambulatory oxygen in fibrotic ILD.
See related Editorial
Few studies have evaluated the severity of exertional hypoxemia in fibrotic interstitial lung disease (ILD). We demonstrate that exertional hypoxemia is more common and severe in fibrotic ILD compared to COPD. More ILD‐specific studies are needed to evaluate the potential utility of ambulatory oxygen in fibrotic ILD.
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