Mechanisms by Which COPD Affects Exercise Tolerance

Abstract

In view of the recent advances in our understanding of the pathophysiology of COPD, we felt that it would be appropriate to examine the contribution of several abnormalities, not hitherto examined, to exercise limitation in this disease. These included: (1) The ability to exceed maximum expiratory flow (determined during forced maneuvers from TLC) during partial expiratory maneuvers. This is referred to as deltaFEV1. (2) Shape of the flow-volume curve (Shape). (3) Susceptibility to develop dynamic hyperinflation (dynamic hyperinflation index, DHI). (4) Ventilatory response to exercise (VEmax/VEpred). Twenty-four COPD patients (FEV1 = 42 +/- 13% pred) underwent symptom-limited progressive exercise. DeltaFEV1, shape, DHI and VEmax/VEpred were determined. All values were normalized to eliminate the effects of age, sex, and body size. Shape had no impact on peak VO2 (r = 0.8). DeltaFEV1 (r = 0.50), DHI (r = 0.50) and VEmax/VEpred (r = 0.46) correlated significantly with peak VO2 with all three exceeding FEV1 (r = 0.43). DHI and deltaFEV1 correlated significantly with each other (r = 0.43) suggesting that the latter exerts its beneficial effects by reducing the tendency to develop DH. We conclude that variability among patients in ventilatory response to exercise and in deltaFEV1 (likely an expression of extent of regional mechanical heterogeneity) contribute importantly to variability of exercise tolerance in COPD.

Comparação das variáveis fisiológicas no teste de caminhada de seis minutos e no teste da escada em portadores de doença pulmonar obstrutiva crônica

“…The six-minute walk test (TC6') has been used in the dynamic evaluation of the COPD patients, in an attempt to express the exercise capacity. In this test, the distance completed is used as the main parameter for performance evaluation 3,4 . In the stair climbing test (SCT), the work against gravity and the use of muscular groups not frequently used in the daily life makes the metabolic and ventilatory demands more intense, with maximal thresholds being frequently reached in parameters such as heart rate (HR), systemic blood pressure (BP), scores of dyspnea perception and oxygen saturation, measured by wrist oximetry (SpO 2 ) 5 .…”

Effects of Lung Volume Reduction Surgery on Gas Exchange and Breathing Pattern During Maximum Exercise

“…Emphysema causes decreased lung elastic recoil, which increases expiratory airflow resistance and leads to dynamic hyperinflation. [1][2][3] During exercise, dynamic hyperinflation progresses rapidly, decreasing chest wall compliance and impairing respiratory muscle function. [3][4][5][6][7][8][9] Dynamic hyperinflation and an elevated work of breathing precipitate breathlessness, thereby decreasing exercise tolerance and quality of life.…”

Role of inspiratory capacity on exercise tolerance in COPD patients with and without tidal expiratory flow limitation at rest

“…In most previous studies, it was found that forced expiratory volume in one second (FEV1) was a poor predictor of exercise capacity [1±3]. Recently, however, it has been shown that indices related to dynamic hyperinflation, such as the inspiratory capacity (IC), are more closely related to exercise tolerance than FEV1 [4,5].Even at rest, patients with COPD often exhibit tidal expiratory flow limitation (FL) [6,7], promoting an increase in end-expiratory lung volume (EELV) due to dynamic hyperinflation with a concomitant decrease in inspiratory capacity and inspiratory reserve volume (IRV) [8,9]. During exercise, normal subjects increase the tidal volume (VT) at the expense of both the IRV and the expiratory reserve volume [8,9].…”

“…In most previous studies, it was found that forced expiratory volume in one second (FEV1) was a poor predictor of exercise capacity [1±3]. Recently, however, it has been shown that indices related to dynamic hyperinflation, such as the inspiratory capacity (IC), are more closely related to exercise tolerance than FEV1 [4,5].…”