Effect on Left Ventricular Performance of Stimulation of an Afferent Nerve from Muscle

The effect on left ventricular performance of electrical stimulation of the cut central end of the quadriceps nerve was studied in open-chest dogs. Stimulation of the nerve at 2 to 4 times threshold for the flexion reflex, which presumably activated intermediate-sized afferent fibers, caused a decrease in heart rate and arterial pressure. Stimulation at 5 to 25 times threshold, which presumably activated small-sized, high-threshold afferent fibers, increased heart rate, arterial pressure, and cardiac output. When heart rate, arterial pressure, and cardiac output were controlled, activation of high-threshold afferent fibers caused a significant increase in the maximal rate of pressure rise, stroke power, and mean rate of ejection of the left ventricle without an increase in the end-diastolic pressure. These same fibers may in some way be activated during muscular exercise and be partially responsible for the increase in left ventricular contractility that occurs during that time.