Characteristics of pre‐inspiratory and decoupled activities of the upper airway motoneurons in the rat

Abstract

Inspiratory activities of the upper airway motor nerves (UAWMN) commence before phrenic burst. These pre-inspiratory (Pre-I) activities of the UAWMN may play an important role in the stabilization of UAW patency. To get insight into the mechanism for this preceding onset of the UAW motoneurons, we investigated influence of different level of positive end-expired pressure (PEEP) on pre-I activities of UAWMN in the first part of the current study. Activities of UAWMN, including the facial, hypoglossal, and superior laryngeal nerves, and the phrenic nerve were recorded simultaneously in anesthetized and artificially ventilated rats. Our results showed that Pre-I activities of UAWMN were all increased and even decoupled from phrenic burst (a response activity during phrenic cessation) by the increase of PEEP to a level between 6–12 cmH2O. Further increased PEEP to a level of 15 cmH2O produced, however, an inhibition on Pre-I and decoupled activities. In the second part, we monitored single fiber activities on each of the UAWMN and found that decoupled activity was primarily due to the persistence of activities of expiratory-inspiratory (EI) motoneurons during phrenic burst cessation. Our data suggest that signals from changes in PEEP might induce either excitation or inhibition on Pre-I and decoupled activities of UAWMN. They might also indicate that rhythmic activities of UAWMN could be uncoupled from the phrenic nerve burst by increasing PEEP.