3.4 Pulmonary Disease: COPD, Asthma & Restrictive/Interstitial Disorders

Pulmonary disease limits exercise tolerance primarily through the ventilatory system rather than the cardiovascular system, which changes how the clinical exercise physiologist monitors and paces these patients.

Chronic Obstructive Pulmonary Disease (COPD)

COPD is a progressive, largely irreversible airflow limitation caused by a combination of two overlapping processes: emphysema, in which destruction of alveolar walls and loss of elastic lung recoil causes airways to collapse during exhalation, and chronic bronchitis, in which chronic airway inflammation drives mucus hypersecretion and a productive cough on most days for at least 3 months in 2 consecutive years. The diagnostic hallmark is a post-bronchodilator FEV1/FVC ratio below 0.70, confirming persistent airflow obstruction.

GOLD staging grades the severity of airflow obstruction using percent-predicted FEV1 once the FEV1/FVC threshold is met:

Since the 2023 GOLD update, the older ABCD symptom/exacerbation grid was refined into the ABE assessment tool: Group A (low symptom burden, low exacerbation risk), Group B (higher symptom burden via mMRC >=2 or CAT >=10, low exacerbation risk), and Group E (history of two or more moderate exacerbations, or one or more requiring hospitalization, regardless of symptom level) — reflecting that exacerbation history, not symptom severity alone, most strongly predicts future risk.

COPD Pathophysiology and Exercise Response

Loss of elastic recoil and airway collapse produce expiratory flow limitation: patients cannot exhale a full tidal volume before the next breath begins, causing air trapping. During exercise, faster breathing rates worsen this trapping, producing dynamic hyperinflation — progressive increases in end-expiratory lung volume that push the diaphragm into a mechanically disadvantaged, flattened position and dramatically raise the work of breathing. This mechanical/ventilatory limitation, not cardiovascular limitation, is usually what stops exercise first in COPD, manifesting as severe exertional dyspnea. Ventilation-perfusion (V/Q) mismatch from destroyed alveolar-capillary units causes hypoxemia, and in advanced disease hypercapnia develops as ventilatory reserve is exhausted. Pursed-lip breathing is a compensatory strategy patients use to slow expiration, maintain positive airway pressure, and reduce air trapping.

Asthma

Asthma is characterized by reversible airway obstruction from bronchial smooth-muscle constriction, airway inflammation, and excess mucus production, typically triggered by allergens, irritants, cold air, or exercise itself. Exercise-induced bronchospasm (EIB) describes transient airway narrowing that develops during or, more classically, 5-15 minutes after exercise, especially with breathing cold, dry air; a proper warm-up and, when prescribed, pre-exercise use of a short-acting bronchodilator can blunt this response. Unlike COPD, asthmatic airflow obstruction is substantially or fully reversible with bronchodilator therapy, and baseline lung function between episodes may be near normal.

Restrictive and Interstitial Lung Disease

Restrictive diseases, such as idiopathic pulmonary fibrosis, reduce lung volumes — total lung capacity (TLC) and forced vital capacity (FVC) fall, while the FEV1/FVC ratio remains normal or even elevated (in contrast to the obstructive pattern). Fibrotic thickening of the alveolar-capillary interface impairs gas exchange, reflected in a reduced diffusing capacity for carbon monoxide (DLCO). Because gas exchange is directly impaired at the alveolar membrane, patients with restrictive disease frequently show exercise-induced hypoxemia that is more pronounced, for a given symptom level, than in COPD, and desaturation can occur at relatively low workloads.

Pulmonary Hypertension

Pulmonary hypertension — elevated mean pulmonary artery pressure — increases right ventricular afterload and can progress to right heart failure (cor pulmonale). It may occur as a complication of severe COPD or interstitial lung disease, or as a primary condition. Exercise capacity is limited by the right ventricle's inability to augment output against a fixed elevated afterload, and unsupervised vigorous exercise carries real risk of acute right-heart decompensation, so these patients require close medical guidance before and during exercise programming.

Safety Considerations

Pulse oximetry (SpO2) monitoring during exercise is essential in any patient with known or suspected desaturation risk. Supplemental oxygen should be titrated to keep exercise SpO2 at or above approximately 88-90%, consistent with standard hypoxemia thresholds used across pulmonary rehabilitation. The CEP should watch for excessive dyspnea disproportionate to workload, cyanosis, confusion (a sign of hypercapnia or severe hypoxemia), and should have a rescue bronchodilator plan readily available for patients with reactive airway disease.

Pulmonary Rehabilitation Programming Notes

Beyond aerobic conditioning, effective pulmonary rehabilitation for COPD and restrictive disease typically incorporates interval-style training (shorter, higher-intensity work bouts interspersed with rest) for patients who cannot sustain continuous moderate exercise due to dyspnea, inspiratory muscle training to directly target the increased work of breathing, and upper-body endurance/resistance work, since many activities of daily living involve unsupported arm elevation that is disproportionately dyspnea-provoking in this population. Patients should also be taught to self-monitor dyspnea using a standardized scale (such as the modified Borg or 0-10 dyspnea scale) alongside SpO2, since perceived breathlessness, not heart rate, is usually the primary limiting symptom guiding intensity in ventilatory-limited populations.