Nonlinearities of the human carotid baroreceptor-cardiac reflex.

Abstract

Carotid baroreceptors of nine healthy young men and women were stretched or compressed with neck suction or pressure, before and after beta-adrenergic and cholinergic blockade, to evaluate several nonlinearities of sinus node baroreflex responses. Sinus node inhibition was related linearly to the intensity of brief baroreceptor stimuli over a range extending from carotid-distending pressures of about 101 +/- 5 (mean +/- SE) to 160 +/- 6 mm Hg (the subject's average systolic pressure was 108 +/- 2 mm Hg). Sinus node response to sustained (5 seconds) neck suction or pressure were strikingly asymmetrical. Responses were abolished by atropine, or by atropine and propranolol. Propranolol alone augmented sinus node responses to both neck suction and pressure. These results suggest that, in normal human subjects, sinus node responses to abrupt alterations of afferent baroreceptor traffic are nonlinear and are mediated by fluctuations of efferent cholinergic activity. Most of the observed nonlinear behavior of the integrated reflex can be explained on the basis of known properties of afferent and central portions of the baroreflex arc.

Asymmetric features of short-term blood pressure variability

“…Heart rate changes induced by blood pressure are mediated by baroreflex, which has also asymmetrical properties. 1,[3][4][5][6][7]9,14,16,[18][19][20][21]27,31 The baroreflex sensitivity is different for blood pressure increases and reductions, which is evident by comparing phenylephrine with nitroprusside infusion, or neck pressure with neck suction methods. [18][19][20] Heart rate asymmetry, although independent of blood pressure asymmetry, is probably related to baroreflex, which is supported by the observation that heart rate asymmetry is correlated with measures of baroreflex function.…”

“…However, in most physiological and clinical studies continuous noninvasive recordings of blood pressure signal at the finger level are most commonly used. [4][5][6][7][8][9]14,[18][19][20][21]27,35 Studies on blood pressure asymmetry can develop in different directions. First, the explanation of the mechanisms responsible for this phenomenon like the influence of respiration, autonomic provocations or blockade is necessary.…”

“…9,[18][19][20][21] As both HRV and baroreflex function are asymmetric, it can be expected that a similar phenomenon may be found in BPV. The primary aim of this study is to establish the existence of asymmetric features of short-term blood pressure asymmetry, in short, blood pressure asymmetry, by separately analyzing the information from systolic blood pressure (SBP) increases and reductions.…”

A model for the genesis of arterial pressure Mayer waves from heart rate and sympathetic activity

“…1991) It is interesting to note that stimulation of carotid sinus baroreceptive afferents, either directly (Borst, ct a!. 1983) or by neck suction (Eckberg 1980) results in changing arterial pressure after a delay of2-3 sec. This is similar to the consistent lead fcrund in our subjects which may reflect the narrow range oflatcncies in the human heart rate-pressure closed loop.…”

The effect of enalapril on baroreceptor mediated reflex function in normotensive subjects.

“…Then, each RR-interval value was plotted as a function of the preceding systolic blood pressure value. Baroreflex set-point was defined as the highest (during activation by phenylephrine) or lowest (during deactivation by nitroglycerin) systolic blood pressure value inducing no variation in RR-interval (Eckberg, 1980). The analysis was then performed beat by beat beginning only after the first noticeable change in RR-interval.…”