Bulbar respiratory neurons during artificial lung distension or collapse in spontaneously breathing rabbits.

Lung volume was altered setting the mean air pressure within a closed spirometer system to +5, +10, -5 or -10 cm H2O. In many respiratory modulated neurons (RMN) the duration of discharge changed in the same direction as the duration of the corresponding half cycle, but changes of duration of neuronal discharge were often larger. This was the case in many EI neurons for the duration of discharge during expiration, in many I units at high lung volume for the duration during inspiration and in many IE and E cells at low lung volume for the duration of discharge during expiration. The responses to inflation or collapse, however, differed in magnitude. At all lung volumes in part of the IE and E neurons and at low lung volume in part of the I units the duration of discharge during inspiration changed in opposite direction as the duration of inspiration. Neuronal desactivation at high lung volume or activation at low volume was termed alpha-type response; it occurred in many I neurons at high lung volume and for the inspiratory part of discharge of many EI units. Neuronal activation at high lung volume or desactivation at low volume was denoted as beta-type response; it was observed in many I neurons at low lung volume and in E, EI and IE cells for the expiratory part of discharge. In a large majority of all phase types of RMN, incidence of maximum spike density within the burst discharge was delayed in time when the corresponding half cycle was prolonged and vice versa; the shift of time incidence often exceeded the change of duration of inspiration or expiration.