Increased venous PCO2 enhances dynamic responses of avian intrapulmonary chemoreceptors
Hempleman, S.C.; Bebout, D.E.
American Journal of Physiology 266(1 Pt 2): R15-R19
1994
ISSN/ISBN: 0002-9513 PMID: 8304535 Document Number: 429252
We quantified the neural discharge of intrapulmonary chemoreceptors (IPC) innervating the left lungs of anesthetized Pekin ducks. Right and left lungs were separately unidirectionally ventilated. Alternating steps in CO-2 concentration (0-6%, 11-s period) were delivered to the left lung under control conditions (mixed venous P-CO-2, (P hivin v-CO-2) 43 +- 4 Torr) and under venous CO-2 load conditions (P hivin V-CO-2 79 +- 6 Torr). During venous CO-2 loading the right lung was ventilated with 10-20% CO-2, while the left lung was ventilated with a sufficient flow of gas containing 0% CO-2 to maintain normal expired P-CO-2 (indicated by constant IPC discharge rate). Venous loading increased the peak-to-peak amplitude of the oscillation in IPC discharge by 4.3 +- 1.8 s-1 (n = 11, P lt 0.05), left lung ventilation was increased 2.6 old. and the IPC step response became more prompt. The mean IPC discharge rate during the CO-2 stepping cycle was not significantly affected (11.8 +- 1.4 during control vs. 10.3 +- 1.3 s-1 during venous loading). Increased IPC discharge oscillations were due to enhancement of the dynamic overshoot in receptor discharge after the 6-0% downstep in inspired CO-2 and to a depression of discharge during 6% inspired CO-2. We propose that the phasic enhancement of IPC discharge oscillations during venous CO-2 loading may cause feedback inhibition of ventilatory drive.