Effect of asphyxia on the frequency and amplitude modulation of synchronized renal nerve activity in the cat.

A computerized peak detection algorithm was used to retrieve new information about changes in the characteristics of renal nerve activity (RNA) with asphyxia in anesthetized cats. The algorithm scanned the series of RNA voltages for significant increases followed by significant decreases in a small cluster of voltage values. Once each synchronized RNA peak had been detected, its corresponding amplitude, width, and peak-to-peak interval were calculated. The peak-to-peak interval showed two rhythms of synchronized discharge: one between 200-500 ms accounting for 38 +/- 3% of intervals and a higher 20-180 ms frequency (52 +/- 5% of intervals). Asphyxia did not change the periodicity distribution despite increases in arterial pressure. The peak amplitude of RNA, reflecting the number of active fibers, was unimodally distributed and was increased 39 +/- 9% with asphyxia. The shape of the distribution was unchanged. The width of the synchronized activity was also unimodally distributed, mean 79 +/- 3 ms, and increased by asphyxia to 99 +/- 5 ms. The results indicate that the control of the periodicity and amplitude of synchronized discharge appear to be independent and are differentially affected by chemoreceptor input.