Purpose: Whether dyspnea, chest wall dynamic hyperinflation, and abnormalities of rib cage motion are interrelated phenomena has not been systematically evaluated in patients with chronic obstructive pulmonary disease (COPD). Our hypothesis that they are not interrelated was based on the following observations: (i) externally imposed expiratory flow limitation is associated with no rib cage distortion during strenuous incremental exercise, with indexes of hyperinflation not being correlated with dyspnea, and (ii) end-expiratory chest wall volume may either increase or decrease during exercise in patients with COPD, with those who hyperinflate being as breathless as those who do not.
Methods: Sixteen patients breathed either room air or 50% supplemental O2 at 75% of peak exercise in randomized order. We evaluated the volume of chest wall (Vcw) and its compartments: the upper rib cage (Vrcp), lower rib cage (Vrca), and abdomen (Vab) using optoelectronic plethysmography; rib cage distortion was assessed by measuring the phase angle shift between Vrcp and Vrca.
Results: Ten patients increased end-expiratory Vcw (Vcw,ee) on air. In seven hyperinflators and three non-hyperinflators, the lower rib cage paradoxed inward during inspiration with a phase angle of 63.4° ± 30.7° compared with a normal phase angle of 16.1° ± 2.3° recorded in patients without rib cage distortion. Dyspnea (by Borg scale) averaged 8.2 and 9 at the end of exercise on air in patients with and without rib cage distortion, respectively. At iso-time during exercise with oxygen, decreased dyspnea was associated with a decrease in ventilation regardless of whether patients distorted the rib cage, dynamically hyperinflated, or deflated the chest wall.
Conclusions: Dyspnea, chest wall dynamic hyperinflation, and rib cage distortion are not interrelated phenomena.