Journal of Applied Physiology, Vol 47, Issue 4 778-786, Copyright © 1979 by American Physiological Society
Ventilatory responses to elastic loading at constant PACO2 hypercapnic hyperpnea
J. A. Daubenspeck
Elastic loads of 9 cmH2O/1 were suddenly applied to the external airways of
four normal human subjects during hypercapnic hyperpnea of 20-32 1/min
using a closed-circuit breathing apparatus that permitted alveolar carbon
dioxide pressure (PACO2) to be held nearly constant in spite of loading
induced changes in ventilation. Transient depression of minute ventilation
(V) and mean inspiratory flow (VT/TI) was observed immediately on loading;
both these variables increased progressively to steady levels less than
control without significant changes in alveolar chemistry. Two subjects
increased VT (volume compensators) whereas the other two chose to increase
f (frequency compensators). The net result in V and VT/TI compensation was
not different between these groups. Load removal always resulted in an
overshooting response of V lasting for several breaths and due entirely to
an overshoot in VT because f transiently fell to or below control at once.
Elastic loading always resulted in a steeper plot of V-VT in the steady
state; in three of the subjects, the transition to this steeper line was
immediate. The steady-state responses were qualitatively though not
quantitatively consistent with pattern adaptation appropriate to minimize
the work-rate of breathing.
