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Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and The University of Texas Southwestern Medical Center, Dallas, Texas 77231
Received 27 November 1995; accepted in final form 14 October 1996.
Babb, T. G. Ventilatory response to exercise in
subjects breathing CO2 or
HeO2.
J. Appl. Physiol. 82(3): 746-754, 1997.
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-balance
N2; and once while breathing HeO2 (79% He and 21%
O2). Minute 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, at ventilatory threshold (VTh),
and at maximal exercise. When the subjects were breathing 3%
CO2, there was an increase
(P < 0.001) in
E at rest and at VTh but not during
maximal exercise. When the subjects were 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 the subjects were breathing 3% CO2
(P < 0.05). Above VTh, the
ventilatory response when the subjects were breathing
HeO2 was greater than when
breathing 3% CO2
(P < 0.01). Flow limitation, as
percent of tidal volume, during maximal exercise was greater
(P < 0.01) when the subjects were
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 the subjects were 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.
mechanical ventilatory limitations to exercise; control of breathing during exercise; exercise in the aged; ventilatory capacity in the aged
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