The respiratory pattern of gasping has been characterized on the phrenic nerve as rapidonset, rapid-rise, large-amplitude bursts of neural activity. Furthermore, medullary sites critical for the neurogenesis of gasping have been identified and are not the sites of identified respiratory neurons, such as the dorsal and ventral respiratory groups. I classified envelopes of phrenic nerve activity as eupneic breaths, or gasps based on the time-domain features of duration, shape, and amplitude. Gasps were elicited by hypoxia and low blood pressure in 9 of 12 decerebrate cats. Inspiratory times were 1.15 +/- 0.43 (SD) for eupneic breaths and 0.55 +/- 0.18s for gasps. The high-frequency peaks in the power spectra of phrenic nerve activity were at 80 +/- 13 Hz for eupneic breaths and at 120 +/- 21 Hz for gasps. Three of the 12 cats developed a breathing pattern that began as a normal breath and terminated in a gasp. Power spectra of the normal portion had eupneic spectral peaks (75 +/- 24 Hz); power spectra of the gasp portion had the high peaks at 110 +/- 23 Hz, a value 1.5 times higher than that for the normal peaks. Although this analysis of peripheral nerve activity cannot distinguish between two central pattern generators at two distinct anatomical sites or one pattern generator operating in two distinct modes, the fact that gasps were much shorter in duration and had markedly higher spectral peaks than control breaths supports the idea that the central pattern generator for gasping is not the central pattern generator for eupnea.