The baroreceptor reflex and the cardiovascular changes associated with sustained muscular contraction in the cat.

In decerebrate unanaesthetised cats the cardiovascular effects of raising the pressure in a blind sac preparation of a carotid sinus on one side were examined at rest and during sustained contractions of hind-limb muscles. During a tetanic contraction the absolute value of the blood pressure and heart-rate components of the baroreceptor reflex response were not significantly changed from those at rest. The curve relating heart-rate and mean blood pressure, during carotid sinus distension, was similar at rest and when the muscles of the hind-limb were contracting tetanically, although each value of heart-rate was greater, suggesting a resetting of the baroreceptor reflex. By contrast, in the same experiments, suppression of the baroreceptor reflex changes in heart-rate and blood pressure could be demonstrated during the increases of blood pressure and heart-rate elicited by the afferent discharge from muscles during sustained contraction are buffered to some extent by the baroreceptors, though their inhibitoru effect is incomplete under these conditions.