Figures
- FIGURE 1.
Schematic representations of alveolar units a) in health and b) in chronic obstructive pulmonary disease (COPD), and their corresponding flow versus volume profiles in c) health and d) COPD. In COPD, expiratory flow limitation (EFL) occurs because of the combined effects of increased airway resistance and reduced lung recoil: alveolar emptying is therefore critically dependent on expiratory time, which, if insufficiently long, results in lung over-inflation (reduction in inspiratory capacity (IC)). The presence of EFL is suggested in COPD by the encroachment of tidal expiratory flows on the forced maximal expiratory flow envelope over the tidal operating lung volume range. In contrast to health, hyperinflation occurs in COPD during exercise, as indicated by the shift in end-expiratory lung volume to the left, i.e. reduced IC. PL: lung recoil pressure; V′: gas flow; V′max: maximal expiratory flow. Solid, circular lines: tidal volume at rest; dashed, circular lines: tidal volume during exercise. Reproduced and modified from [1], with permission from the publisher.
- FIGURE 2.
Pressure (P)–volume (V) relationships of the total respiratory system a) in normal and b) in chronic obstructive pulmonary disease (COPD). Tidal P–V curves during rest (▪) and exercise (▓) are shown. In COPD, because of resting and dynamic hyperinflation (a further increased end-expiratory lung volume (EELV)), exercise tidal volume (VT) encroaches on the upper, alinear extreme of the respiratory system's P–V curve where there is increased elastic loading. In COPD, the ability to further expand VT is reduced, i.e. inspiratory reserve volume (IRV) is diminished. In contrast to health, the combined recoil pressure of the lungs and chest wall in hyperinflated patients with COPD is inwardly directed during both rest and exercise; this results in an inspiratory threshold load on the inspiratory muscles. RV: residual volume; TLC: total lung capacity.
- FIGURE 3.
The distribution of the extent of change in inspiratory capacity (IC) during exercise is shown in moderate-to-severe chronic obstructive pulmonary disease (COPD; n = 534). A reduction (negative change, i.e. from the dotted zero line to −2.0) in IC reflects dynamic hyperinflation (DH) during exercise. Each bar width corresponds to a change in IC range of 0.10 L. The majority of patients with COPD experienced significant DH during exercise. Graph represents cumulative data taken from references [17, 35, 36]. Reproduced from [41], with permission from the publisher.
- FIGURE 4.
Changes in operating lung volumes are shown as ventilation increases with exercise in a) age-matched normal subjects (n = 25) and b) chronic obstructive pulmonary disease (COPD; n = 105). “Restrictive” constraints on tidal volume (VT; ▪) expansion during exercise are significantly greater in the COPD group from both below (reduced inspiratory capacity (IC)) and above (minimal inspiratory reserve volume (minimal IRV). □: IRV. In normal subjects, vital capacity (VC) occurred at 62% predicted and in COPD patients it occurred at 42% pred. EELV: end-expiratory lung volume; EILV: end-inspiratory lung volume; TLC: total lung capacity. Reproduced and modified from reference [17], with permission from the publisher.
- FIGURE 5.
Tidal pressure–volume loops (i.e. Campbell diagrams) during rest and exercise in a patient with very severe chronic obstructive pulmonary disease. Note the increased elastic (░) and inspiratory threshold loads (ITL; ▒) resulting from dynamic hyperinflation (change in inspiratory capacity (ΔIC)). Total lung capacity (TLC) occurred at 9.25 L. CL,dyn: dynamic lung compliance; Cw: chest wall compliance; Poes: oesophageal pressure.
