Different Methods of Analysis to Study Oscillations of Peripheral Arterial Chemoreceptor Discharges in the Anaesthetized Cat

Abstract

Different methods have been used to establish that the frequency of sinus and aortic nerve chemoreceptor activity oscillates in response to respiration. Some authors, however, still consider chemoreceptor discharges as a random process. Different methods of analysis of chemoreceptor discharges have been carried out, one of them (Band et al., 1971) based on dividing each respiration into equal time bins and averaging counts/bin over 40 to 70 respirations. Respiratory oscillations will appear if the number of spikes in different phases is significantly different. This method does not give positive results of analysis, however, when the frequency of chemoreceptor oscillation is subharmonic to respiration. Another method (O’Regan and Przybyszewski, 1987) was obtained by applying a power spectral analysis to the instantaneous frequency of the chemoreceptor discharges. By averaging many power spectra it was shown that first or even higher subharmonics of respiration are dominating in a great number of fibers. Even more interesting was the fact that in most of the fibers these dominating oscillations were not stable, but jumped spontaneously from one subharmonic to another with periods of 20 to 60 s. In this report we propose other methods of analysis which demonstrate that the chemoreceptor discharges do not always oscillate in a simple, stable manner, but their discharges are rather similar to the transition between quasiperiodicity and chaos, as could be observed in a driven nonlinear oscillator.