Journal of Applied Physiology, Vol 52, Issue 1 71-78, Copyright © 1982 by American Physiological Society
Impaired cardiac "acceleration" at the onset of exercise in patients with coronary disease
P. Zimmerman, G. J. Heigenhauser, N. McCartney, J. R. Sutton and N. L. Jones
The responses to two levels of exercise (400 and 800 kpm/min) were studied
in nine untrained healthy subjects and seven patients with coronary artery
disease. Measurements were made over 20-s time intervals to obtain the half
times (t1/2) of the asymptotic rise in cardiac frequency (fc), O2 intake
(VO2), CO2 output (VCO2), and ventilation (VE). Complete data were obtained
in both groups at 400 kpm/min, but only in healthy subjects at 800 kpm/min,
as patients were unable to exercise for longer than 2 min at this power. At
the onset of 400 kpm/min, t1/2 for VO2 was similar, but t1/2 for fc, VCO2,
and VE were all longer in the patients. At 800 kpm/min there was a delay in
VO2 in the patients before stopping exercise. In patients and healthy
subjects t1/2 for VCO2 and VE, but not VO2, were related to t1/2 for fc.
The results emphasized the importance of tissue CO2 storage in attenuating
the delivery of CO2 to the lungs and thus delayed the ventilatory response
to a step increase in power output.
