Spectral analysis of the phrenic neurogram during eupnea and gasping

In this study, the frequency characteristics of the phrenic neurograms of seven cats were determined during normal respiration (eupnea) and hypoxic gasping using the Modified Yule-Walker (MYW) Autoregressive (AR) technique. The power spectral density function of the eupneic phrenic neurogram resulting from this analysis was arbitrarily divided into three frequency bandwidths: 1. 10–30 Hz; 2. 30–60 Hz; 3. 60–120 Hz. The eupneic phrenic neurogram was characterized by frequency peaks in the two higher bandwidth bins (38.7∓2.2 and 94.9∓1.9Hz, respectively; x∓SD). During gasping, however, a significant power peak in the lowest frequency bandwidth (24.7∓1.1Hz) was noted and the peak seen in the midfrequency range during eupnea was lost suggesting a shift of signal from the mid-to the low frequency range. The high frequency power peak seen during eupnea was also present during gasping. These observations suggest that hypoxic gasping is characterized by synchronous discharge of respiratory neurons at 20–25 Hz.