In the in vivo anesthetized adult cat model, multiple patterns of inspiratory motor discharge have been recorded in response to chemical stimulation and focal hypoxia of the pre-Botzinger complex (pre-BotC), suggesting that this region may participate in the generation of complex respiratory dynamics. The complexity of a signal can be quantified using approximate entropy (ApEn) and multiscale entropy (MSEn) methods, both of which measure the regularity (orderliness) in a time series, with the latter method taking into consideration temporal fluctuations in the underlying dynamics. The current investigation was undertaken to examine the effects of pre-BotC-induced excitation of phasic phrenic nerve discharge, which is characterized by high-amplitude, rapid rate of rise, short-duration bursts, on the complexity of the central inspiratory neural controller in the vagotomized, chloralose-anesthetized adult cat model. To assess inspiratory neural network complexity, we calculated the ApEn and MSEn of phrenic nerve bursts during eupneic (basal) discharge and during pre-BotC-induced excitation of phasic inspiratory bursts. Chemical stimulation of the pre-BotC using DL-homocysteic acid (DLH; 10 mM; 10-20 nl; n=10) significantly reduced the ApEn from 0.982±0.066 (mean±SE) to 0.664±0.067 (p < 0.001) followed by recovery (~1-2 minute after DLH) of the ApEn to 1.014±0.067; a slightly enhanced magnitude reduction in MSEn was observed. Focal pre-BotC hypoxia (induced by sodium cyanide; NaCN; 1 mM; 20 nl; n=2) also elicited a reduction in both ApEn and MSEn, similar to those observed for the DLH-induced response. These observations demonstrate that activation of the pre-BotC reduces inspiratory network complexity, suggesting a role for the pre-BotC in regulation of complex respiratory dynamics.