Baroreflex sensitivity modulates vasodepressor response to nitroprusside.

Abstract

SUMMARY Baroreflex activity is a determinant of the homeostatic response to alteration in blood pressure. We examined the factors that determine the magnitude of the vasodepressor response to sequential incremental intravenous infusions of sodium nitroprusside (NP), 0.05 to 6.4 yug/kg/min, in eight male patients with essential hypertension. Each infusion level was of 10 minutes' duration. Change from control values of mean arterial pressure (AMAP), heart rate (AHR) and plasma norepinephrine (ANE) were obtained at the end of each infusion level. Significant correlations were found between AMAP vs log dose NP, AHR vs AMAP and ANE vs AMAP for each patient (p < 0.05). However, the slopes of these relationships varied widely between subjects and were significantly correlated with the control blood pressure of each patient. In addition, the sympathetic responsiveness, as measured by ANE vs AMAP, was inversely correlated with the degree of vasodepressor response seen. Thus, the magnitude of the vasodepressor response was determined by two major factors: 1) the predrug blood pressure, possibly reflecting altered vascular geometry with hypertension; 2) the degree of sympathetic response, which probably acts by mediating the degree of reflex alpha-adrenergic-mediated arteriolar vasoconstriction. (Hypertension 5: 79-85, 1983) KEY WORDS * plasma norepinephrine • hypertension • heart rate • humans T HE level of baroreceptor activity, acting by way of the sympathetic nervous system, is a major determinant of the homeostatic response to perturbation of blood pressure. Changes in sensitivity of the baroreflex arc occur in hypertension, 1 " 5 sleep, 6 and with aging. Baroreflex sensitivity (BRS) is usually expressed in terms of the change in heart rate (HR), or R-R interval, for each unit of change in blood pressure.' 2 7~9 However, there are practical and theoretical limitations to this approach. First, in subjects receiving beta-adrenoceptor antagonists, the relationship between HR response and the level of sympathetic activity may change. Second, HR is controlled by a balance between the level of activity of the vagal and the sympa-

Asymmetric features of short-term blood pressure variability

“…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. 32 Porta et al 33 showed that asymmetrical features of HRV change during sympathetic provocation like head-up tilting and that heart rate asymmetry expression increases during the day compared with night, both in healthy people and patients with congestive heart failure.…”

“…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.…”

Captopril modifies the hemodynamic and neuroendocrine responses to sodium nitroprusside in hypertensive patients.

“…Baroreflex sensitivity was calculated by linear regression analysis of AHR versus AMAP during a nitroprusside infusion test, 25 and significant linear correlations were noted in each subject before and during 2.74±0.80t MAP = mean arterial pressure; HR = heart rate; NE = plasma norepinephrine concentration; EPI = plasma epinephrine concentration; PRA = plasma renin activity; ANG I = angiotensin I.…”

“…25 By relating changes in HR (AHR) to the changes in MAP (AMAP) during the infusion of each dose of sodium nitroprusside, baroreflex sensitivity was calculated. In addition, the responsiveness of the sympathetic nervous system was assessed by relating the changes in plasma norepinephrine concentration (ANE) to AMAP.…”