Analysis of Interactions Between Central and Vagal Respiratory Control Mechanisms in Cats

In anesthetized cats, regulation of the duration of inspiration (T
_I
) and expiration (T
_e
) has been investigated by analyzing the operation of central inspiratory on-and off-switch mechanisms. Using the tracheal pressure (P) generated during airway occlusion at FRC as a measure of central inspiratory activity, and the end-inspiratory pressure (P
⁰
_max
) as the setting of the off-switch threshold, we considered two indices in the central and lung volume-related control of T
_I
: (a) P/P
⁰
_max
, an index of central inspiratory contribution to inspiratory off-switching, and (b) 1-P/P
⁰
_max
an index of the additional vagal input needed to terminate inspiration. Both indices were found to be independent of P
_aCO2
, varying solely as a function of time from the onset of inspiration. Changes in the relationship between tidal volume (V
_T
) and T
_I
with variation in body temperature and unilateral vagotomy were attributed to separate effects on the 1-P/P
⁰
_max
vs T
_I
and 1P/P
⁰
_max
vs V
_T
relations, respectively. The rapid shallow breathing pattern observed with continuous negative pressure breathing has been explained on the basis of early activation of an inspiratory on-switch mechanism by lung deflation receptors.