TRACHEAL, CIRCULATORY, AND RESPIRATORY RESPONSES TO FEMORAL NERVE-STIMULATION

Tracheal, circulatory, and respiratory responses to electrical stimula tion of the afferent nerve from the hindlimb were analyzed in decerebr ate, paralyzed, and mechanically ventilated dogs. Tension of the trach eal smooth muscle (TSM), arterial blood pressure, and phrenic nerve ac tivity (PNA) were measured during stimulation of the proximal end of t he transected femoral nerve (FNS) with train pulses (duration; 0.5 ms, frequency; 40 Hz). With low intensity (e.g., 0.62 V) FNS, TSM exhibit ed relaxation, arterial pressure decreased, and neural respiratory out put (NRO) was reduced (3 of 8 dogs) or unchanged (5 of 8 dogs). With i ncreases in stimulus intensity, TSM always exhibited relaxation while arterial pressure and NRO exhibited excitatory responses almost at the same thresholds (similar to 5 V). The TSM relaxation and the excitato ry NRO and arterial responses augmented with increases in stimulus int ensity up to 16 times of threshold of the excitatory NRO response. TSM response was blocked by intravenous atropine but presser response and phrenic response were not. The arterial response disappeared after ad ministration of a ganglionic blocker. These findings suggest that TSM, arterial pressure, and PNA may be controlled by one neuronal mechanis m during high intensity FNS, but that arterial pressure and PNA may be modified by another mechanism in an inhibitory direction when the sti mulus intensity is low. This study suggested the existence of a neural mechanism which controls the airway and cardiorespiratory systems pro perly to execute exercise. Physiological significance of the responses to low intensity femoral nerve stimulation was uncertain.