The inhibitory effects of positive end-expiratory pressure (PEEP) on phrenic motoneuronal activity in cats.

Abstract

We examined the effects of positive end-expiratory pressure (PEEP) on phrenic single motoneuronal activity (SMA) in anesthetized, paralyzed, and mechanically ventilated cats. SMA was isolated and recorded from the right C-5 phrenic root. Phrenic nerve compound activity was also recorded simultaneously from the contralateral C-5 phrenic root in each preparation. With the vagus nerve intact, phrenic SMA significantly decreased to 91.5, 76.2, 45.3, and 21.6% of control when PEEP was loaded to levels of 2.5, 5, 7.5, and 10 cm H2O, respectively. Compound activity also decreased. Moreover, not only phrenic single postinspiratory inspiratory activity (PIIA) but also the ratio of PIIA to the inspiratory SMA significantly decreased with increments of PEEP. In contrast, with the vagus nerve sectioned, phrenic nerve activity, including PIIA, remained unchanged when loading PEEP. These results suggest that 1) SMA might be inhibited in lung volume-dependent manner by PEEP, and that 2) the vagal nerve afferents are essential for the inhibition of SMA by PEEP.