Evaluation of Dynamic Respiratory Mechanical Abnormalities During Conventional CPET

Abstract

Assessment of the ventilatory response to exercise is important in evaluating mechanisms of dyspnea and exercise intolerance in chronic cardiopulmonary diseases. The characteristic mechanical derangements that occur during exercise in chronic respiratory conditions have previously been determined in seminal studies using esophageal catheter pressure-derived measurements. In this brief review, we examine the emerging role and clinical utility of conventional assessment of dynamic respiratory mechanics during exercise testing. Thus, we provide a physiologic rationale for measuring operating lung volumes, breathing pattern, and flow-volume loops during exercise. We consider standardization of inspiratory capacity-derived measurements and their practical implementation in clinical laboratories. We examine the evidence that this iterative approach allows greater refinement in evaluation of ventilatory limitation during exercise than traditional assessments of breathing reserve. We appraise the available data on the reproducibility and responsiveness of this methodology. In particular, we review inspiratory capacity measurement and derived operating lung volumes during exercise. We demonstrate, using recent published data, how systematic evaluation of dynamic mechanical constraints, together with breathing pattern analysis, can provide valuable insights into the nature and extent of physiological impairment contributing to exercise intolerance in individuals with common chronic obstructive and restrictive respiratory disorders.

Keywords: cardiopulmonary exercise test; dyspnea; inspiratory capacity; respiratory mechanics; respiratory physiology.

Figure 1

Representative changes in (A) inspiratory capacity, (B) inspiratory reserve volume, (C) tidal volume, and (D) breathing frequency in COPD, ILD, and healthy controls during incremental exercise. Note the reduced IC and early critical reduction in IRV with corresponding V_T plateau in COPD and ILD subjects. Values are mean ± SEM. *p < 0.05 for ILD vs. control, ^†p < 0.05 for COPD vs. control. Representative flow–volume loop observed in COPD (E) demonstrating operating lung volumes, dynamic hyperinflation, and expiratory flow limitation. COPD, chronic obstructive pulmonary disease; DH, dynamic hyperinflation; EELV, end-expiratory lung volume; EFL, expiratory flow limitation; EILV, end-inspiratory lung volume; ERV, expiratory reserve volume; Fb, breathing frequency; FRC, functional residual capacity; IC, inspiratory capacity; ILD, interstitial lung disease; IRV, inspiratory reserve volume; MFVL, resting maximal flow–volume loop; TLC, total lung capacity; V_FL, volume of tidal breath that is flow limited; V_T, tidal volume. Reprinted with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society. All rights reserved Faisal et al. (11). The American Journal of Respiratory and Critical Care Medicine is an official journal of the American Thoracic Society (11). Adapted from Guenette et al. (10).

Figure 2

Representative volume–time, pressure–volume, flow–volume, and operating lung volume relationships during exercise observed in (A) healthy controls, (B) COPD, and (C) ILD. COPD, chronic obstructive pulmonary disease; EELV, end-expiratory lung volume; EILV, end-inspiratory lung volume; IC, inspiratory capacity; ILD, interstitial lung disease; IRV, inspiratory reserve volume; RV, residual volume; TLC, total lung capacity. Reprinted from O'Donnell et al. (12). Copyright (2019), with permission from Elsevier (12). Reprinted with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society. All rights reserved. O'Donnell et al. (13). Proceedings of the American Thoracic Society* is an official journal of the American Thoracic Society. *Now titled Annals of the American Thoracic Society (13).