Respiratory pattern changes produced by intercostal muscle/rib vibration

Large-amplitude vibration of the intercostal muscles/ribs has an inhibitory effect on inspiratory motor output. This effect has been attributed, in part, to the stimulation of intercostal muscle tendon organs. Intercostal muscle/rib vibration can also produce a decrease or increase in respiratory frequency. Studies were conducted 1) to determine whether, in addition to intercostal tendon organs, costovertebral joint mechanoreceptors (CVJR's) contribute to the inspiratory inhibitory effect of intercostal muscle/rib vibration (IMV) and 2) to explain the different respiratory frequency responses to IMV previously reported. Phrenic (C5) activity was monitored in paralyzed thoracotomized, artificially ventilated cats. Vibration (125 Hz) at amplitudes greater than 1,200 micron of one T6 intercostal space in decerebrated vagotomized rats reduced phrenic activity. This response was still present but weaker in some animals after denervation of the T6 intercostal muscles. Subsequent denervation of the T6 CVJR's by dorsal root sections eliminated this effect. Respiratory frequency decreased during simultaneous vibration (greater than 1,200 micron) of the T5 and T7 intercostal spaces in vagotomized cats. Respiratory frequency increased during IMV of two intercostal spaces (greater than 1,300 micron) in vagal intact cats. The use of different anesthetics (pentobarbital, allobarbital) did not alter these results. We conclude that CVJR's may contribute to the inhibitory effect of IMV on medullary inspiratory activity. The presence or absence of pulmonary vagal afferents can account for the different respiratory frequency responses to IMV, and different anesthetics did not influence these results.