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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Chemical activation of pre-Bötzinger complex in vivo reduces respiratory network complexity

Departments of ¹Biomedical Engineering and ²Physiology and Biophysics, State University of New York at Stony Brook

Submitted 22 September 2004 ; accepted in final form 6 January 2005

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-Bötzinger complex (pre-BötC), 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-BötC-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-BötC-induced excitation of phasic inspiratory bursts. Chemical stimulation of the pre-BötC 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 min after DLH) of the ApEn to 1.014 ± 0.067; a slightly enhanced magnitude reduction in MSEn was observed. Focal pre-BötC 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-BötC reduces inspiratory network complexity, suggesting a role for the pre-BötC in regulation of complex respiratory dynamics.

approximate entropy; network dynamics; inspiratory motor discharge; control of breathing

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