Central integration of pulmonary stretch receptor input in the control of expiration

The dynamics of the central processing of the discharge pattern from vagal pulmonary afferents that mediate the expiratory facilitatory reflex have been investigated. These studies involved the development of mathematical models based on analogs of neurophysiological principles such as temporal summation and threshold crossing. These models, which are capable of predicting the expiratory duration for arbitrary discharge patterns, were verified through comparison of their prediction with experimentally obtained relationships between expiratory duration (TE) and waveform parameters of various input patterns. These relationships were obtained by electrical activation of the largest vagal afferent fibers in bilaterally vagotomized, pentobarbital-anesthetized dogs. A parallel two-component model with long time constants (ca. 0.8 and 18 s) was best able to describe the experimental responses. This model suggests that 1) central integration of pulmonary stretch receptor (PSR) input is similar to long time-constant temporal summation; 2) central inspiratory inhibition (no vagal input) may share a common mechanism with vagal processing; 3) PSR-induced inhibition is a linear function of discharge frequency; and 4) TE depends on both the trajectory of lung deflation and the tonic activity at functional residual capacity. These characteristics embody information regarding specific neural arrangements and properties within the respiratory centers.