Functional asymmetry in carotid sinus cardiac reflexes in humans

Abstract

The reflex cardiac response to activation (CBA) and inactivation (CBI) of the left and right carotid baroreceptors was studied in 30 healthy subjects, aged between 24 and 38 years. The CBA was evoked by applying negative pressure (from -20 to -60 mmHg) for 10 s to the left and right carotid sinus regions separately or both together, using two small neck capsules. The CBI was produced by applying left and right positive neck pressure (from 20 to 60 mmHg) for 10 s. The blood flow velocity was measured non-invasively with a Doppler scanner placed in the suprasternal notch. Blood flow acceleration was calculated and used as an indication of left cardiac contractility. Heart rate was measured continuously. Differences were found between right and left carotid sinus responses to CBA and CBI. The maximal response of the R-R interval was significantly greater during right CBA than during left CBA (the average gain: R-R.mmHg-1 2.69 ms.mmHg-1 and 1.75 ms.mmHg-1, respectively). Also, the reflex CBI response was significantly greater for the right (3.16 ms.mmHg-1) than for the left (2.22 ms.mmHg-1). The reflex decrease/increase in blood-flow acceleration in response to CBA/CBI was significantly greater during left than during right-sided activation/inactivation. It is suggested that the functional asymmetry was related to differences in right/left-sided cardiac innervation as well as to central ipsilateral projection of the carotid baroreceptor afferents to the nuclei tractus solitarii.

Effects of Unilateral and Bilateral Carotid Baroreflex Stimulation on Cardiac and Neural Sympathetic Discharge Oscillatory Patterns

“…A functional asymmetry in HR response to unilateral carotid sinus reflex stimulation, that is, maximal changes during rightside baroreceptor activation/deactivation similar to the results of the present study, has been described by Bernardi and colleagues 23 and others 9 in humans, although not consistently, 10 and has been related to differences in the right-/left-side innervation of the heart. In fact, in animals, right cardiac efferent fibers, both sympathetic 24 and vagal, 25 elicited greater chronotropic effects than the left-side fibers, and a right-side vagotomy induced a more pronounced increase of HR than left vagal transection.…”

“…5,6 However, the use of unilateral neck stimulation to evaluate possible asymmetry in carotid-cardiac and carotid-sympathetic baroreflex modulation has provided conflicting results. Indeed, animal studies have consistently reported that right carotid perturbation induced greater effects on HR than left-sided stimulation, 7,8 whereas human investigations have found the right carotid-cardiac reflex response to be either greater 9 or similar to the left. 10 In humans, a sustained left-sided carotid baroreceptor unloading resulted in a more pronounced MSNA activation than the contralateral perturbation, 11 whereas in anesthetized rabbits, the carotid baroreflex modulation of the cardiac efferent sympathetic activity did not show lateralization.…”

Psychophysiology of arterial baroreceptors and the etiology of hypertension

“…This reduction was obtained regardless of whether the heart rate had increased (as in the biofeedback study), showed no phasic change (under norfenefrin) or decreased as a consequence of the baroreflex elicited by cervical suction or PRES 3 . This impact of baroreceptors on the cortex is lateralized: stimulation of the receptors on the right produces a more pronounced change in heart rate than stimulation on the left, whereas the left carotid sinus was found to alter cardiac contractility to a higher degree than the sinus on the right side (Tafil-Klawe et al, 1988). We replicated these effects and demonstrated that stimulation of the left side reduces negativity to a greater extent over the left than over the right hemisphere (Elbert et al, 1991).…”

“…Modulation of the firing rate of the right carotid sinus nerve produced more pronounced changes in heart rate, while the baroreceptors located in the left carotid sinus were found to evoke changes in cardiac contractility to a somewhat greater extent than those on the right (Tafil-Klawe et al, 1988). In the study of Elbert et al (1991), nine out of the ten subjects displayed more pronounced chronotropic effects from pressure manipulation over the right than for those over the left carotid sinus region.…”

“…The neck cuff procedure was modified by Tafil-Klawe et al (1988), Elbert et al, 1991) with the construction of smaller cuffs which allow the application of a lateralized positive or negative cuff pressure. A negative pressure is used to evoke baroreceptor activation in one of two separate small pressure chambers with a kidney-like shape (about 5 cm in diameter).…”