Respiratory and sympathetic activity during recovery from hypoxic
depression and gasping in the cat.
Melton, J. E., S. C. Kadia, Q. P. Yu, J. A. Neubauer, and N. H.
Edelman.
Division of Pulmonary and Critical Care Medicine, Department of
Medicine, UMDNJ-Robert Wood Johnson Medical School, New Brunswick,
N.J. 08903-0019
APStracts 3:0063A, 1996.
In peripherally chemodenervated, vagotomized, chloralose-anesthetized
cats, hypoxia can produce central cardiorespiratory depression or
excitation depending on severity. We monitored phrenic and cervical
sympathetic neurograms during either hypoxic depression or gasping
and 30 min. of subsequent isocapnic reoxygenation to determine if the
response of these outputs during hypoxia predicts their activity
during recovery. Three levels of hypoxic response were produced in
cats: (1) reduction of phrenic neurogram amplitude (PNA) by 30%
(FIO2=14-18%); (2) production of phrenic apnea (FIO2=9-10%); (3)
hypoxic gasping (FIO2=6-8%). Recovery from the milder levels of
hypoxia was characterized by transient (<10 min.) depression of
PNA and inspiratory-synchronous sympathetic activity (ISSA).
Respiratory frequency (f) was unaffected or only transiently
depressed. Tonic sympathetic activity (TSA) was unaffected. During
reoxygenation following gasping, both PNA and ISSA were initially
increased by 80% over control levels and f was depressed. TSA
increased during hypoxia but returned to control levels after a brief
undershoot upon reoxygenation. All variables returned to control
levels within 15 min. Measurement of medullary extracellular
potassium ([K+]ec) in a separate group of cats indicated that a
significant increase in this variable was associated with hypoxic
gasping but was not correlated with PNA augmentation during
reoxygenation. We hypothesize that increased [K+]ec coincident with
gasping may trigger a post-anoxic potentiation of respiratory
premotor neurons similar to that described in hippocampus.
Received 17 July 1995; accepted in final form 5 January 1996.
APS Manuscript Number A767-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96