PURPOSE: A decreased inspiratory to total lung capacity ratio (IC/TLC) is associated with dynamic hyperinflation, decreased exercise capacity and survival in patients with COPD. The O2 pulse has been a proposed surrogate marker of cardiac function. We hypothesized that low IC/TLC may impair cardiac function during exercise (CPET) as assessed through the O2 pulse.
METHODS: We studied 87 consecutive CPET performed in COPD patients with GOLD category 3 and 4 and compared the response with that of 46 controls. We analyzed maximal work (watts), oxygen consumption, O2 pulse, breathing reserve, inspiratory capacity and hand grip force. COPD patients were classified according to IC/TLC >25% and IC/TLC ≤;25%. Appropriate statistical analysis was used with O2 pulse as the dependent variable.
RESULTS: Patients with IC/TLC ≤;25% (n=45) had significantly lower exercise capacity, peak O2 pulse, ▵O2 pulse, peak IC, peak IC/TLC, and ▵ IC/TLC% compared to patients with IC/TLC >25% and the control group. The rest and peak exercise IC/TLC was associated with O2 pulse (r=0.65, p<0.0001 and r=0.68, p<0.0001). In multivariate analysis the body mass index (BMI), IC/TLC ratio, FEV1 (%) and hand-grip force were associated with peak O2 pulse.
CONCLUSION: Resting hyperinflation (IC/TLC) predicts lower O2 pulse and exercise capacity in patients with COPD stages 3 and 4. This supports the role of hyperinflation on decreased cardiac function as a mechanism contributing to exercise limitation in this group of patients.
CLINICAL IMPLICATIONS: This study supports the concept that cardiac function could be affected at rest and during exercise by the degree of hyperinflation of patients with COPD. Decreasing hyperinflation may improve exercise performance not only by improving pulmonary mechanics but also overall cardiac function.
DISCLOSURE: Felipe Cortopassi, None.