Airflow limitation and regulation of end expiratory lung volume during exercise

Abstract

Fourteen subjects with normal lung function performed steady state, submaximal exercise on a cycle ergometer, with and without expiratory air flow limitation (AFL) to test the hypothesis that the presence of AFL influences the regulation of end expiratory lung volume (EELV) during exercise. AFL was achieved by increasing the density of inspired air via a hyperbaric chamber during exercise. Three subjects were excluded from analysis due to equipment failure while six subjects achieved AFL, and 5 did not achieve AFL. This appeared to be because increased resistance decreased ventilatory response to exercise independent of AFL. To further examine the influence of AFL on the regulation of EELV, a 5 cmH20 threshold expiratory load was imposed during exercise, with and without AFL. EELV was significantly higher during exercise at 3 atmospheres pressure (3 ATA; AFL) than when compared with sea level (SL; non-AFL) exercise (SL- non AFL= 46+6% (% of TLC) BTPS; 3 ATA-AFL= 52+9% BTPS; p=0.0001). There also was a similar, significant difference in EELV at rest (SL= 52+6%; 3 ATA-non-AFL= 55+7%; P=0.0001). There was no significant change in EELV during exercise when expiratory loading was applied during non-AFL, SL exercise (unloaded EELV, SL=46+6%; loaded SL= 45+6%; p>0.05). Subjects also had no significant change in EELV with exercise at 3 ATA (AFL) with loading, compared with no loading (unloaded 3 ATA= 53+9%; loaded 3 ATA= 55+9; p>0.05). Thus, when subjects incur AFL during exercise in a hyperbaric environment, EELV is increased. These data suggest that the occurrence of AFL in subjects with normal lung function has an influence on EELV.