Abnormalities in baroreflex control of heart rate in canine heart failure

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Abstract
The mechanism of the attenuated arterial baroreceptor control of heart rate in heart failure was studied in 18 unanesthetized dogs after the development of chronic right-heart failure and compared to 12 control animals. The change in heart rate and arterial pressure in response to increases in right carotid sinus pressure during isolated carotid sinus perfusion was markedly reduced in heart failure (P < 0.05). After vagotomy the difference in heart rate responses persisted, but was less pronounced (P = 0.065). The chronotropic response to perfusion of the sinus node artery acetylcholine in heart-failure dogs showed a selectively depressed response, compared to norepinephrine and hypertonic saline. The ratio of the change in heart rate in heart failure vs. control dogs was 57% for acetylcholine but was not diminished for hypertonic saline (114%). The effect of direct vagal nerve stimulation on changes in heart rate was markedly reduced in heart-failure dogs. The alterations in baroreceptor control of heart rate in heart failure apparently involve the parasympathetic and sympathetic baroreflex efferent limbs. There is a depressed responsiveness of the sinus node to cholinergic stimuli.

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