Journal of Applied Physiology, Vol 81, Issue 2 530-540, Copyright © 1996 by American Physiological Society
Autoregressive spectral analysis of phrenic neurogram during eupnea and gasping
M. Akay, J. E. Melton, W. Welkowitz, N. H. Edelman and J. A. Neubauer
Department of Medicine, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Brunswick 08903-0019, USA.
During hypoxic gasping, the phrenic neurogram (PN) has a steeper rate of
rise, an augmented amplitude, and a shorter duration than is seen during
eupnea. Because hypoxia reduces neuronal activity, we hypothesized that
gasping would be characterized in the frequency domain by enhanced
low-frequency power compared with eupnea. Autoregressive (AR) spectral
analysis of the PN in chloralose-anesthetized, vagotomized, peripherally
chemodenervated cats was performed during eupnea and hypoxic gasping.
During eupnea, significant spectral peaks were seen at 41 +/- 2 and 93 +/-
2 (SE) Hz. In all cats, the 41-Hz spectral peak disappeared during hypoxic
gasping and was replaced by a high-power, low-frequency peak at 26 +/- 1
Hz. No consistent change in the frequency or power of the high-frequency
spectral peak was seen during gasping. To determine whether changes in the
AR spectrum of the PN during gasping result from augmented respiratory
output, we compared the AR spectra of the PN during gasping, hypercapnia
(end-tidal CO2 fraction = 0.09), and carotid sinus nerve stimulation.
Unlike during gasping, there was no shift in power toward lower frequencies
during hypercapnia and carotid sinus nerve stimulation. We conclude that
the spectral characteristics of gasping, loss of the medium-frequency peak
and the appearance of low-frequency (< 30-Hz) power, are unique to this
respiratory pattern.
