PMC

Three examples of inspiratory capacity (IC) maneuvers performed during exercise. (a) Correctly performed maneuver where the individual initiates the IC maneuver at the appropriate end-expiratory lung volume (EELV), denoted by the dashed line. (b) Individual initiating the IC maneuver prior to reaching the appropriate EELV. The absolute volume of the IC breath will be underestimated if it is not anchored to the appropriate EELV. (c) Individual initiating the IC maneuver after surpassing the appropriate EELV. The absolute volume of the IC breath will be overestimated if it is not anchored to the appropriate EELV.

Dynamic hyperinflation can be evaluated as the linear slope relating inspiratory capacity and minute ventilation []. Dynamic hyperinflation is typically assessed at a single time point during an exercise test. The slope method accounts for all inspiratory capacity measurements during an exercise test and takes into account possible changes in ventilation that can occur with various interventions (e.g., hyperoxia, heliox, bronchodilators, exercise training, etc.).

(a) Example of a resting and peak exercise tidal breath superimposed within a maximum flow-volume loop (thick black line). Modified from []. The position of the tidal breaths along the x-axis is based on the measurement of end-expiratory lung volume (determined from inspiratory capacity maneuvers). (b) Operating lung volume plot versus cycle work rate. Inspiratory capacity maneuvers are performed at rest (0 W) and every 20 W throughout exercise. TLC, total lung capacity; IRV, inspiratory reserve volume; EILV, end-inspiratory lung volume; EELV, end-expiratory lung volume; V _T, tidal volume; IC, inspiratory capacity; V _FL, volume of the tidal breath that is flow limited on expiration; %EFL, percentage of expiratory flow limitation; ERV, expiratory reserve volume; MFVL, maximum flow-volume loop; DH, dynamic hyperinflation.

Operating lung volume plots during constant work rate cycle exercise in COPD patients following acute high-dose anticholinergic therapy versus placebo (a) and hyperoxia versus room air (b). The operating lung volumes (i.e., end-expiratory and end-inspiratory lung volumes) were reduced at rest (0 min) following anticholinergic therapy and resulted in a downward shift in operating lung volumes throughout exercise. The magnitude of dynamic hyperinflation at peak exercise (calculated as the difference in EELV from resting values) did not change following bronchodilation. The magnitude of dynamic hyperinflation was also similar at peak exercise (~0.2 L) during hyperoxia compared with room air in hypoxemic patients with COPD. Data for these graphs are based on previously published studies from our laboratory [, ]. IRV, inspiratory reserve volume; V _T, tidal volume; DH, dynamic hyperinflation; TLC, total lung capacity.

Inspiratory capacity (IC), inspiratory reserve volume (IRV), tidal volume (V _T), and breathing frequency (F _b) responses versus minute ventilation during constant work rate exercise across the continuum of health and COPD severity. The IC at rest and throughout exercise progressively decreases with advancing disease. Note the clear inflection (plateau) in the V _T-ventilation relationship, which coincides with a simultaneous inflection in the IRV-ventilation relationship. After this point, further increases in ventilation are accomplished by accelerating F _b. Data from Normal subjects and GOLD stage I (i.e., mild COPD) are from Ofir et al. []. Quartiles (Q) of COPD severity are based on forced expiratory volume in 1 second (FEV₁) expressed as percent predicted (ranges: Q1 = 54.5–85.1; Q2 = 43.8–54.1; Q3 = 34.9–43.6; Q4 = 16.5–34.9) from O'Donnell et al. []. VC, vital capacity; TLC, total lung capacity; GOLD, Global Initiative for Obstructive Lung Disease.