Effects of postural changes and vestibular lesions on diaphragm and rectusabdominis activity in awake cats

Changes in posture can affect the resting length of the diaphragm, requirin g alterations in the activity of both the abdominal muscles and the diaphra gm to maintain stable ventilation. To determine the role of the vestibular system in regulating respiratory muscle discharges during postural changes, spontaneous diaphragm and rectus abdominis activity and modulation of the firing of these muscles during nose-up and ear-down tilt were compared befo re and after removal of labyrinthine inputs in awake cats. In vestibular-in tact animals, nose-up and ear-down tilts from the prone position altered re ctus abdominis firing, whereas the effects of body rotation on diaphragm ac tivity were not statistically significant. After peripheral vestibular lesi ons, spontaneous diaphragm and rectus abdominis discharges increased signif icantly (by similar to 170%), and augmentation of rectus abdominis activity during nose-up body rotation was diminished. However, spontaneous muscle a ctivity and responses to tilt began to recover after a few days after the l esions, presumably because of plasticity in the central vestibular system. These data suggest that the vestibular system provides tonic inhibitory inf luences on rectus abdominis and the diaphragm and in addition contributes t o eliciting increases in abdominal muscle activity during some changes in b ody orientation.