Spatiotemporal regulation of the cough motor pattern

Cough is an important airway defensive behavior. It is characterized by coordinated ballistic-like bursts of activity in inspiratory and expiratory muscles. Airflows during intensive coughs can reach 12 L/s in humans [1]. Although it has been proposed that cough and breathing share a common neurogenic control system [2], significant regulatory differences exist between the two behaviors. For example, during eupnea, there are well-known relationships between inspiratory volume (VI) and inspiratory time (TI) and between expiratory volume (VE) and expiratory time (TE). Smaller VI or VE are associated with longer TI or TE durations during breathing [3]. This volume timing behavior is mediated by slowly adapting pulmonary stretch receptors (PSR) However, Romaniuk et al [4] suggested that phasic PSR afferent feedback does not play an important role in the development of cough. This suggestion was supported by our previous study in which we found that there was no relationship between volume and phase durations during repetitive tracheobronchial coughing in spontaneously breathing cats [5]. These observations indicate that the regulation of cough motor pattern is fundamentally different than that of breathing. It follows that presumptions of how the cough motor pattern is controlled that are based on our knowledge of the control of the pattern of breathing may be subject to significant error.In preliminary experiments, we observed that a period of expiratory motor quiescence existed between the end of the expiratory motor burst and the onset of the next inspiration during repetitive cough, consistent with the existence of two subphases within the cough expiratory period [4,6], as first proposed by Romaniuk et al [4]. The presence of two subphases within the expiratory interval of cough is consistent with the control of the expiratory interval during breathing, and if substantiated, would be consistent with the synaptic network model of Shannon and coworkers for cough [2] w