PHRENIC AFFERENT STIMULATION BY BRADYKININ AND THE DISTRIBUTION OF THE INSPIRATORY MOTOR DRIVE

Activation of thin-fiber (groups III and IV) afferents from the diaphr agm using capsaicin or ischemia increases the respiratory muscle activ ity. To assess whether bradykinin causes similar effects, we injected boluses of bradykinin into the phrenic artery of in situ, isolated and innervated left hemi-diaphragm preparations in 8 alpha-chloralose ane sthetized, vagotomized, mechanically ventilated dogs. Inspiratory moto r drive during spontaneous breathing attempts was assessed from the in tegrated EMG activity of several inspiratory muscles. Fifty mug of bra dykinin increased peak integrated EMG activities of alae nasi to 110%, genioglossus to 189%, left diaphragm to 115% (P<0.05) and parasternal to 109% (P<0.01) of baseline activity 60 sec after the injection. Ins piratory time decreased by 10% (P<0.01). The mean arterial blood press ure increased by about 10 mmHg. Responses were similar with 10, 25 and 100 mug of bradykinin. After left phrenicotomy, bradykinin did not af fect inspiratory muscle EMG or respiratory timing. In conclusion, thin -fiber phrenic afferent activation by bradykinin exerts an excitatory but disproportionate influence on the inspiratory motor drive.