Journal of Applied Physiology, Vol 60, Issue 5 1524-1534, Copyright © 1986 by American Physiological Society
Transient ventilatory and heart rate responses to moderate nonabrupt pseudorandom exercise
E. C. Greco, H. Baier and A. Saez
Dynamic responses of inspired minute ventilation, CO2 and O2 end-tidal gas
fractions, and heart rate were obtained from six normal human volunteers in
response to a complex dynamic exercise challenge. Subjects pedalled a chair
ergometer at constant frequency. The retarding torque applied to the
ergometer pedals was controlled by a low-pass-filtered pseudorandom binary
sequence (fPRBS), which provided a complex, nonanticipatory exercise
stimulus containing sufficient high- and low-frequency energy to excite the
small signal, broadband ventilatory response. The exercise range was chosen
to produce a mean level of O2 consumption at or below 50% maximum O2
consumption. Cross-covariant analysis of the fPRBS exercise with
breath-by-breath ventilation provided an estimate of the dynamic (impulse)
response to exercise, which contained both fast phase 1 and slow phase 2
components. The initial, phase one, hyperpnea occurred within the same
breath as the exercise transition and preceded a hypocapnic response. The
phase one hyperpnea represented 26% of the total ventilatory response. The
secondary, phase 2, hyperpnea was delayed several breaths from the onset of
phase 1. It contained slower dynamics and followed a hypercapnic response.
Heart rate increased abruptly during phase 1, peaked near the phase 1-to-2
boundary, and then decreased rapidly. The experimental protocol was
designed to minimize the subjective response and provide an adequate
stimulus for the faster time constants. Results obtained from these
experiments were consistent with a nonhumoral induced phase 1 exercise
hyperpnea.
