Airflow Limitation and Breathing Strategy in Congestive Heart Failure Patients during Exercise

Abstract

Background: Congestive heart failure (CHF) patients experience dyspnea on exertion and therefore have decreased exercise tolerance. Objective: This study explores the hypothesis that stable New York Heart Association (NYHA) class III CHF patients without a history of pulmonary disease exhibit airflow limitation with increasing exercise. Methods: We characterized flow limitations and breathing reserves at baseline, during exercise before anaerobic threshold (pre-AT), and after anaerobic threshold (post-AT) in CHF patients and normal subjects. Data were collected in the form of maximal flow volume loops and subsequent tidal flow volume loops at baseline and during exercise. Expiratory flow limitation was expressed as percent of tidal volume that corresponded with overlap of the tidal flow volume loops and maximal flow volume loops during expiration. The area directly between the maximum flow volume loops and the tidal flow volume loops during the expiratory phase is expressed as expiratory flow volume reserve (EFVR). Results: CHF patients experienced expiratory flow limitation during exercise (pre-AT and post-AT) that was significantly increased compared to baseline and to normal subjects at similar exercise levels (CHF, baseline 8.5 ± 7, pre-AT 37 ± 10, post-AT 38 ± 8%, n = 9, p < 0.05). Both CHF patients and normal subjects increased EFVR during exercise, but only the normal subjects increased EFVR to a significantly different value at post-AT exercise levels (normal subjects, 9.5 ± 2, 11 ± 2, 32 ± 4%, n = 7, p < 0.05). Both CHF patients and normal subjects increased end inspiratory lung volume (EILV) during exercise, but only the normal subjects significantly increased EILV at post-AT exercise levels (normal subjects, 49 ± 4, 55 ± 5, 76 ± 4%, p < 0.05). Inspiratory capacity (IC)/forced vital capacity (FVC) ratios were increased in CHF patients compared to normal subjects. However, IC/FVC values did not change during exercise in either group. Conclusions: CHF patients cannot utilize their full respiratory capacity during exercise secondary to expiratory flow limitation and an inability to increase EILV and EFVR.