Ventilatory response to exercise when breathing co2 or heo2.
Babb, T. G.
Institute for Exercise and Environmental Medicine, Presbyterian
Hospital of Dallas and The University of Texas Southwestern Medical
Center, Dallas, TX 77231
APStracts 3:0475A, 1996.
To investigate the effects of mechanical ventilatory limitation on the
ventilatory response to exercise, eight older subjects with normal
lung function were studied. Each subject performed graded cycle
ergometry to exhaustion, once while breathing room air, once while
breathing 3%CO2, 21%O2, and balance N2, and once while breathing HeO2
(79% He & 21%O2). Ventilation (E) and respiratory mechanics were
measured continuously during each 1 min increment in work rate (10 or
20 W). Data were analyzed at rest, ventilatory threshold (VTh), and
maximal exercise. When breathing 3% CO2, there was an increase (p
< 0.001) in E at rest and at VTh, but not during maximal
exercise. When breathing HeO2, E was increased (p < 0.05) only
during maximal exercise (24 +/- 11%). The ventilatory response to
exercise below VTh was greater only when breathing 3% CO2 (p <
0.05). Above VTh, the ventilatory response when breathing HeO2 was
greater than when breathing 3% CO2 (p < 0.01). Flow
limitation, as %tidal volume, during maximal exercise was greater (p
< 0.01) when breathing CO2 (22 +/- 12%) than when breathing
room air (12 +/- 9%) or when breathing HeO2 (10 +/- 7%) (n=7). End
-expiratory lung volume during maximal exercise was lower when
breathing HeO2 than when breathing room air or when breathing CO2 (p
< 0.01). These data indicate that older subjects have little
reserve for accommodating an increase in ventilatory demand and
suggest that mechanical ventilatory constraints influence both the
magnitude of E during maximal exercise and the regulation of E and
respiratory mechanics during heavy-to-maximal exercise.
Received 27 November 1995; accepted in final form 14 October
1996.
APS Manuscript Number A1225-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996