Journal of Applied Physiology, Vol 66, Issue 3 1297-1303, Copyright © 1989 by American Physiological Society
Phrenic afferents and ventilatory control at increased end-expiratory lung volumes in cats
S. Iscoe
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
The role of phrenic afferents in controlling inspiratory duration (TI) at
elevated end-expiratory lung volume (EEV) has been studied in
pentobarbital-anesthetized, spontaneously breathing cats with intact vagi.
Responses to increases in EEV, induced by imposition of an expiratory
threshold load (ETL) of 10 cmH2O, were monitored before and after section
of cervical dorsal roots C3-C7. The immediate (first-breath) effect of
application of ETL was a prolongation of both TI and expiratory duration
(TE). After 10 min of breathing against the ETL, average TI returned to
control values but TE remained prolonged. Abolishing feedback from the
diaphragm did not affect these responses. When steady-state responses to
ETL were compared with those elicited by inhalation of 5-6% CO2 in O2,
changes in EEV had, on average, no independent effect on respiratory drive
(rate of rise of integrated phrenic activity), although phrenic activity
increased greatly in some cats despite little or no change in arterial
partial pressure of CO2. These data indicate that diaphragmatic receptors
do not contribute to either the immediate (first-breath) or steady-state
responses of phrenic motoneurons to increases in EEV in intact cats.
