Respiration and medullary blood flow during sinusoidal hypoxia in
the peripherally chemodenervated cat.
Yu, Q. P., J. E. Melton, J. A. Neubauer, and N. H. Edelman.
Division of Pulmonary and Critical Care Medicine, Department of
Medicine, University of Medicine and Dentistry of New Jersey, Robert
Wood Johnson Medical School, New Brunswick, New Jersey 08903-0019
APStracts 3:0033R, 1996.
The hypothesis that hypoxic respiratory depression is mediated by
changes in medullary blood flow (MBF) was assessed in 18
anesthetized, paralyzed, vagotomized, peripherally chemodenervated,
ventilated cats exposed to sinusoidal hypoxic hypoxia. In 9 cats, the
dynamic response of the central respiratory controller to hypoxia was
studied by varying the cycle time of sinusoidal hypoxia (cycle time =
2.5, 4, 6, 10 and 15 min). Peak phrenic neurogram amplitude (PNA)
followed sinusoidal oscillations in the hypoxic input (SaO2) at all
cycle times. The relationship between PNA and SaO2 was expressed as
the transfer function of the system and was approximated as a first
order differential equation with a time constant of 78 +/- 1 sec, a
value consistent with a previous measurement of the time constant of
the change in respiration following a change in brain blood flow. In
a separate study, MBF was continuously measured during sinusoidal
hypoxia (cycle time = 6 min; n=9) with a laser Doppler flow probe to
directly assess the role of MBF in production of hypoxic respiratory
depression. PNA and MBF followed SaO2 oscillations during sinusoidal
hypoxia. Infusion of sodium nitroprusside (20 [mu]g kg-1 min-1, iv)
increased MBF by 30-40% and abolished MBF oscillations during
subsequent sinusoidal hypoxia but had no effect on PNA oscillations.
We conclude that the increase in brain blood flow seen during
sinusoidal hypoxia is not the primary cause of the accompanying
central hypoxic respiratory depression.
Received 8 June 1995; accepted in final form 23 January 1996.
APS Manuscript Number R346-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96