Parametric spectral analysis of the phrenic neurogram during hypercapnia, carotid nerve stimulation, and gasping using autoregressive method

The modified Yule-Walker (MYW) autoregressive (AR) method was used to analyze the frequency characteristics of the phrenic neurogram during gasping, hypercapnia, carotid sinus nerve (CSN) stimulation, and eupnea. The results of the analysis indicate that the transition from eupnea to gasping is characterized by loss of a midfrequency peak in the phrenic power spectrum and the appearance of a low-frequency peak which was not apparent during eupnea. Similar changes in phrenic nerogram frequency spectra were not seen during hypercapnia or CSN stimulation, suggesting that phrenic stimulation per se is not the cause of the spectral changes seen during gasping. These findings suggest that the spectral characteristics of gasping, loss of MFO peak, and appearance of a new peak at 25 Hz are unique to gasping. These findings are consistent with the idea that there is a synchronization of neural firing at a frequency of 20-25 Hz during gasping. This frequency is low compared to maximal firing rates achievable during eupnea but may represent the maximum neuronal firing rate achievable under the severe hypoxic conditions of these experiments