AIRFLOW LIMITATION AND REGULATION OF END EXPIRATORY LUNG VOLUME DURING EXERCISE 522

Increases in end expiratory lung volume (EELV) during exercise have been noted in patients, fit elderly subjects and some highly fit young athletes. Elevation seems to occur with the onset of expiratory air flow limitation(AFL). To test the hypothesis that AFL influences the regulation of EELV during exercise, eleven subjects with normal lung function performed steady state (SS) exercise on an ergometer, with and without AFL. AFL was achieved by increasing the density of inspired air in a hyperbaric chamber, at a depth of 3 atmospheres (3 ATA). SS exercise also was performed with the same apparatus at atmospheric pressure (SL). Six subjects achieved AFL, and 5 did not achieve AFL during the 3 ATA phase, none of the subjects had AFL during SL exercise. EELV was significantly higher during exercise at 3 ATA compared with SL exercise in the subjects with AFL at 3 ATA (SL=46+6%; 3 ATA-AFL=53+9%; (% of TLC) BTPS; p=0.012). However, in subjects with no AFL during exercise at 3 ATA, EELV was not different from that seen at SL (SL=43+6%; 3 ATA = 44+4%; p=0.74). End inspiratory lung volume also was significantly elevated during exercise at 3 ATA compared with SL, but only in those subjects with AFL at 3 ATA (SL=81+6%; 3 ATA-AFL=86+5%; p=0.01; in subjects without AFL, SL=82+4%; 3 ATA=83+4%; p=0.65). Tidal volume and ventilation were not different for either group. These data suggest that the occurrence of AFL influences the regulation of EELV during SS exercise.