Exercise in COPD: damned if you do and damned if you don’t

In this issue of Thorax Aliverti et al¹ present the most complete description of the effect of bronchodilators in chronic obstructive pulmonary disease (COPD) to date. Surprisingly, they found that the patient population separated cleanly into two groups: those whose exercise endurance was improved and those whose exercise endurance decreased. This unexpected adverse effect was not trivial: endurance time at constant workload decreased on average by 34%, while endurance time in those who improved increased by 86%. They called this group the “improvers”, and those whose exercise performance became worse the “non-improvers”; a more accurate moniker for the non-improvers would be “worseners”. Both groups dynamically hyperinflated to the same extent during exercise after placebo, whereas following bronchodilation the improvers hyperinflated more than the worseners so that, at the limit of endurance, inspiratory reserve volume was considerably larger in the latter.

In a previous paper Aliverti et al² studied patients with stable COPD during incremental exercise and found that 60% dynamically hyperinflated while 40% did not. The latter group (which they called “euvolumics”) decreased end expiratory volume during exercise, just as healthy subjects do. The euvolumics had significantly better resting lung function but, paradoxically, significantly worse exercise performance.

The implication of these two papers is that, in COPD, it is better to hyperinflate dynamically because it improves exercise performance than to use a breathing pattern which mimics that used by healthy subjects. What on earth is going on here? According to many experts, dynamic hyperinflation is supposed to be the most important factor limiting exercise in COPD.

In a study of 105 patients with COPD, O’Donnell et al³ found dynamic hyperinflation occurred in 80% of patients during incremental exercise. These researchers measured inspiratory capacity by integrating flow at …