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John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin-Madison, Madison, Wisconsin 53705
We subjected 29 healthy young women (age: 27 ± 1 yr) with a wide range of fitness levels [maximal oxygen
uptake (
O2 max): 57 ± 6 ml · kg
1 · min1;
35-70
ml · kg1 · min1]
to a progressive treadmill running test. Our subjects had significantly smaller lung volumes and lower maximal expiratory flow rates, irrespective of fitness level, compared with predicted values for age-
and height-matched men. The higher maximal workload in highly fit
(O2 max > 57 ml · kg1 · min1,
n = 14) vs. less-fit
(O2 max < 56 ml · kg1 · min1,
n = 15) women caused a higher maximal
ventilation (E) with increased tidal volume (VT)
and breathing frequency (fb) at
comparable maximal VT/vital
capacity (VC). More expiratory flow limitation (EFL; 22 ± 4% of
VT) was also observed during
heavy exercise in highly fit vs. less-fit women, causing higher
end-expiratory and end-inspiratory lung volumes and greater usage of
their maximum available ventilatory reserves.
HeO2 (79% He-21%
O2) vs. room air exercise trials
were compared (with screens added to equalize external apparatus
resistance). HeO2 increased
maximal expiratory flow rates (20-38%) throughout the range of
VC, which significantly reduced EFL during heavy exercise. When EFL was
reduced with HeO2, VT,
fb, and
E (+16 ± 2 l/min) were
significantly increased during maximal exercise. However, in the
absence of EFL (during room air exercise),
HeO2 had no effect on
E. We conclude that smaller lung
volumes and maximal flow rates for women in general, and especially
highly fit women, caused increased prevalence of EFL during heavy
exercise, a relative hyperinflation, an increased reliance on
fb, and a greater encroachment on
the ventilatory "reserve." Consequently,
VT and
E are mechanically constrained during
maximal exercise in many fit women because the demand for high
expiratory flow rates encroaches on the airways' maximum flow-volume
envelope.
expiratory flow limitation; ventilatory limitation; mechanical constraints; carbon dioxide elimination; hyperinflation; hypoxemia
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