Instantaneous cardiac acceleration in the cat elicited by peripheral nerve stimulation

The short-latency effect of peripheral nerve stimulation on heart rate was studied in decerebrate cats. Stimulus trains (100 Hz) of 1-s duration were given to the tibial nerve or to muscle nerves with an intensity yielding a maximal force of isometric contraction of the triceps surae muscle. The first detectable sign and the maximum of cardiac cycle length shortening were found at 0.5-0.6 and 2.1 +/- 0.4 (SD) s, respectively, after the onset of stimulation. A positive correlation exists between the basic cycle length (i.e., before nerve stimulation) and the stimulation-induced shortening of cycle length. The average maximum shortening was found to be 6.7% of basic cycle length. Atropine (0.05-0.1 mg/kg) or bilateral vagotomy suppresses the heart rate response almost completely, whereas the administration of propranolol (2 mg/kg) leaves the response intact. When the nerve is cut proximal to the site of stimulation, the response disappears. Paralysis of the muscle diminishes the response upon nerve stimulation. It is concluded that the short-latency response studied here can be considered as a muscle-heart reflex that is similar to the one previously found in humans.