Racial differences in cardiovascular reactivity to mental stress in essential hypertension

Racial differences in cardiovascular and non-cardiovascular sympathetic nervous system (SNS) activity were studied at rest and during an aversive reaction-time task in established hypertensives, borderline hypertensives and normotensive controls. White and black subjects of each group were subjected to 16 signalled reaction time tasks where a 110 decibel (dB) white noise was delivered contingent upon poor performance. During 16 signalled foreperiods (35 s) the following measurements were taken: systolic and diastolic blood pressures, heart rate, respiration-rate and muscle and skin blood flow. Muscle and skin vascular resistances were calculated. Skin conductance activity was recorded as an index of non-cardiovascular SNS-activation. Resting cardiovascular activity was similar in black and white hypertensives and controls, whereas skin conductance activity was greater in white compared to black hypertensives and controls. During the reaction-time task both quantitative and qualitative differences between the races tended to emerge. Heart rate and systolic blood pressure increased less in black patients and controls than in whites. Muscle and skin vascular resistance increased in blacks but was unaffected by behavioural demands in whites. Skin conductance reactivity was attenuated in black patients and controls. Thus, blacks compared to whites show lesser cardiac sympathomimetic responses but enhanced vascular responses to mental stress.     

Structural skin capillary rarefaction in essential hypertension

A reduction in the density of capillaries (rarefaction) is known to occur in many tissues in patients with essential hypertension. This rarefaction may play a role in increasing peripheral resistance. However, the mechanism underlying this capillary rarefaction is not understood. The aim of this study was to assess the extent of structural versus functional capillary rarefaction in the skin of dorsum of fingers in essential hypertension. The capillary microcirculation was examined with video microscopy before and after maximizing the number of perfused capillaries by venous congestion. The study group comprised 17 patients with essential hypertension (mean supine blood pressure, 155/96 mm Hg) and 17 closely matched normotensive controls (mean blood pressure, 127/77 mm Hg). We used intravital video microscopy with an epi-illuminated microscope to examine the skin of the dorsum of left middle phalanx before and after venous congestion at 60 mm Hg for 2 minutes. A significantly lower mean capillary density occurred at baseline in hypertensive subjects versus normotensive subjects. With venous occlusion, capillary density increased significantly in both groups; however, maximal capillary density remained significantly lower in the hypertensive subjects than in the normotensive subjects. The study strongly suggests that much of the reduction in capillary density in the hypertensive subjects is caused by structural (anatomic) absence of capillaries rather than functional nonperfusion.     

Role of cardiovascular reactivity to mental stress in predicting future hypertension

Hypertension (HT) has been known since times immemorial to be one of the major causes of morbidity and mortality. It contributes to atherosclerotic cardiovascular disease, increasing its risk 2-3 times and is also associated with dyslipidemia, insulin resistance, glucose intolerance and obesity (1). The age of onset of hypertension is now earlier than before, making it essential that early detection of people who could be future hypertensives is done. Therefore, cardiovascular reactivity to stress in predicting future hypertension becomes important. In this fast paced age most people are exposed to mental stress which is the most common and prevalent form of stress. Increase in blood pressure (BP) in response to emotional arousal is well known, but support for this hypothesis of reactivity in predicting future hypertension is limited. We are attempting here to put forth a review of the various endeavours done so far to support this hypothesis.     

Cognitive stress and cardiovascular reactivity. I. Relationship to hypertension

This report reviews the current literature relating cognitive stress and cardiovascular reactivity to the development of hypertension. Cardiovascular reactivity may refer to a change in one or several cardiovascular parameters as a function of exposure to a cognitive stressor, e.g., systolic BP, HR, etc. The cognitive stressors involve laboratory-based mental tasks such as mental mathematics, choice reaction time, and stressful interviews. The current findings suggest that the reactivity literature may have something unique to contribute to the study of hypertension. Prospective studies linking clinical hypertension to early reactivity are few in number. However, reactivity appears to be reliable within individuals over short periods of time (3 months), and individuals at the upper end of the reactivity distribution may have a higher incidence of future hypertension than those at the lower end. Reactivity may also contribute to two other dimensions of hypertension. Subjects with positive family histories of hypertension may be expected to be among the most reactive to cognitive stress, and among established hypertensive individuals, the reactivity to stress may be correlated with casual BP lability. Several avenues have been suggested through which a hyperresponsiveness to mental stress may be implicated in the development of hypertension. Repeated stressor episodes might influence vascular rigidity, through direct alteration of smooth muscle morphology and downregulation of the alpha receptor or through a process of autoregulation of CO, blood volume, and changes in renal regulation of water and sodium balance.     

Blood rheology in men with essential hypertension and capillary rarefaction

The pathophysiological significance of hyperviscosity and capillary rarefaction in untreated essential hypertension is unknown. Fifty untreated hypertensive men with capillary rarefaction (intravital capillaroscopy) and 20 age- and sex-matched normotensive controls underwent full haemorheological profiling (blood viscosity at high and low shear, haematocrit, platelet and leukocyte counts, fibrinogen and total protein concentrations, P-selectin levels, erythrocyte and leukocyte filterability rates and erythrocyte deformability and aggregation indexes). Subjects with skin capillary density below the group median had younger age, higher diastolic pressure, higher blood viscosity at low shear, higher P-selectin levels, higher erythrocyte and leukocyte filterability rates, and higher erythrocyte aggregation indexes (all P < 0.01). In contrast, patients with greater skin capillary density had a greater plasma viscosity (P < 0.05). The conclusions were that in untreated hypertensive men, capillary rarefaction and hyperviscosity are associated to an increased diastolic blood pressure and to an adverse haemorheological profile.     

Abnormal thiol reactivity of tropomyosin in essential hypertension and its association with abnormal sodium-lithium countertransport kinetics

OBJECTIVES: To identify a thiol protein that is abnormal in a subgroup of essential hypertensive (EHT) patients who have a strong family history of hypertension and cardiovascular disease and have a low Km of erythrocyte Na/Li countertransport (CT). METHODS: To detect biotin maleimide labelling of a key thiol protein to investigate its reaction with N-ethylmaleimide (NEM) in normal and EHT erythrocytes. RESULTS: The thiol protein of 33 kDa apparent molecular weight (p33) identified by the loss of labelling with biotin maleimide was identified as tropomyosin due to its retarded running in 6 mol/l urea gels and immunoblotting. The NEM reaction with p33 detected by loss of subsequent biotin maleimide labelling is biphasic in normal control erythrocytes with the rate in the first 30 s double that after 30 s. In EHT erythrocytes NEM reaction (1) after 30 s is faster than normal and (2) in the first 30 s causes a paradoxical increase in apparent biotin maleimide labelling. In normal control erythrocytes, the loss of biotin maleimide labelling with NEM reaction or the faster phenylmaleimide reaction follows the same time course as the decrease in Km of Na/Li CT. CONCLUSIONS: NEM reaction with p33 requires two thiols. Only the cytoskeletal form of tropomyosin from the TM3 gene has more than one thiol group and agrees with SDS-PAGE mobility. Tropomyosin is a strong candidate to explain the familial abnormality in EHT with abnormal Na/ Li CT and it could explain many of the characteristics of this disease.     

Mechanism of action of ketanserin: studies on cardiovascular reactivity in essential and diabetes-associated hypertension

Ketanserin is a selective serotonin-S2 receptor antagonist with alpha 1-adrenoceptor inhibiting activity. The relative contribution of the latter mechanism to antihypertensive efficacy was studied in a group comprising eight normal subjects, 10 patients with essential hypertension and eight diabetics with arterial hypertension. Ketanserin treatment administered over a period of 8 weeks, decreased arterial pressure in patients with essential hypertension and, to a lesser extent, in diabetics, but not in normal subjects. In all three groups, exchangeable sodium, blood volume, the activity of the adrenergic and renin-angiotensin-aldosterone systems and the pressor responsiveness to norepinephrine (NE) or angiotensin II (Ang II) were unaltered, while the pressor reactivity to phenylephrine showed a significant decrease in normal subjects only. This suggests that the antihypertensive mechanism of ketanserin does not involve a modification of the physiological relationship between endogenous noradrenergic and pressor reactivity to NE. Moreover, ketanserin does not interfere with Ang II-dependent mechanisms.     

Family history of hypertension and cardiovascular reactivity to mental stress--effects of stimulus intensity and environment

Normotensives with hypertensive parents have been reported to exhibit enhanced cardiovascular reactions to mental stress. We have examined the question of why this result was not confirmed in all studies. In addition we have investigated whether appropriate tests can be performed under clinical rather than laboratory conditions. Healthy male subjects were examined. In experiment I, under laboratory conditions, a standard stress test was intensified (n = 30). In experiment II the same test was used in a simplified version which did not require special equipment (n = 19). Blood pressure, heart rate and stroke volume (by impedance cardiography) were measured. In contrast to the results with the standard test, subjects with at least one hypertensive parent exhibited enhanced responses of systolic and diastolic blood pressure and heart rate. We conclude that cardiovascular hyper-reactivity in subjects with hypertensive parents is only apparent using sufficiently intense stimuli. Although less pronounced, these differences can also be observed under clinical conditions.     

Hypertriglyceridaemia in mild hypertension: impact on cardiovascular and hormonal reactivity under different stress tests.

OBJECTIVES: We investigated the significance of hypertriglyceridaemia (HTG) for associated components of the metabolic syndrome and stress reactivity in subjects with mild hypertension. METHODS: Seventeen asymptomatic subjects with mild hypertension assessed by 24-h blood pressure (BP) measurement plus HTG (TG >2.3 mmol/l) were recruited and compared with age- and sex-matched subjects with hypertension alone and healthy controls. Cardiovascular and hormonal stress reactivity were tested in a standardised programme consisting of 6 min mental stress, 3 min finger grip and a submaximal bicycle ergometry. RESULTS: The hypertensive patients with HTG exhibited significantly higher fasting insulin, uric acid and gamma-GT levels and lower HDL-cholesterol. The cardiovascular reactivity was similar in all three tests with respect to brachial and peripheral BP in the groups. Peripheral BP during the tests was found to be higher particularly in subjects with hypertension alone. The correlations between BP parameters were disturbed in hypertensives with HTG. Latter group showed significantly higher dopamine, noradrenaline, as well as ACTH levels and an increased ACTH/cortisol ratio. CONCLUSION: HTG in mild hypertension is indicative for insulin resistance accompanied by a modified vascular reactivity as well as elevated catecholamines and ACTH.     

强化干预对社区中老年高血压或伴有脂代谢异常人群心血管事件的作用

目的了解强化干预对社区中老年高血压或伴有脂代谢异常人群心血管事件(CVD)的影响。方法采用整群抽样南宁市两个社区的1215人为研究对象,随机分成强化干预组和对照组。干预组按照是否患有高血压及其相关疾病分别采取不同的强化治疗方案进行干预;对照组人员维持志愿就诊和志愿服药的正常医疗状态,随访43.5个月,记录CVD发生情况。结果随访43.5个月后,单纯高血压患者及高血压伴血脂异常患者干预组和对照组收缩压和舒张压均较干预前明显降低(P0.01);两组CVD合计43例(4.0%),患有高血压者明显高于非高血压患者(6.9%vs2.9%,χ2=9.004,P=0.003,OR值2.492,95%CI 1.349-4.601);(3)干预组无论高血压或非高血压者CVD均明显低于对照组(其中2χ=4.729和6.822,和P=0.03和0.009,OR值2.645和3.438,95%CI为1.006-6.562和1.296-9.118)。结论高血压是社区中老年人CVD的高危因素,强化干预或普通干预均可明显降低社区高血压患者及伴有脂代谢异常人群血压水平。强化干预改变多重风险因子的作用较非强化干预能够更多的减少社区中老年人CVD的发生。     

Sodium-volume factor, cardiovascular reactivity and hypotensive mechanism of diuretic therapy in mild hypertension associated with diabetes mellitus

Diabetes mellitus is often associated with excess body sodium and frequently accompanied by hypertension. Relationships among blood pressure and various regulatory factors were studied before and after six weeks of diuretic therapy with chlorthalidone, 100 mg/day, in 17 diabetic subjects (aged 32 to 75 years) with borderline to moderate hypertension. Following a four-week placebo phase, mean supine blood pressure was 165/93 ± 26/15 (±SD) mm Hg and exchangeable sodium was increased (49 ± 4 versus 45 ± 4 meq/kg lean body mass in 90 normal subjects; p < 0.01). Blood volume, and supine and upright plasma renin, aldosterone, norepinephrine, epinephrine or dopamine levels were comparable to normal values. Measurements in eight diabetic subjects revealed an increased cardiovascular reactivity, as evidenced by decreased (p < 0.001) pressor doses of norepinephrine (68 ± 42 versus 151 ± 52 ng/kg/min) or angiotensin II (3.9 ± 1.2 versus 10.3 ± 5.5 ng/kg/min). Chlorthalidone decreased blood volume by 11 per cent, lowered body sodium (by 9 per cent) and cardiovascular sensitivity to norepinephrine (by 48 per cent) or angiotensin II (by 60 per cent) towards normal and reduced blood pressure by 11 per cent to 145/82 ± 13/12 mm Hg (11 per cent). Plasma renin and aldosterone were markedly increased by chlorthalidone, whereas plasma and urinary catecholamine levels were not significantly altered. These findings suggest that hypertension in patients with diabetes mellitus may partly depend on increased body sodium and/or an exaggerated cardiovascular reactivity to norepinephrine and angiotensin II. The blood pressure-lowering effect of diuretic therapy may be due to removal of excess sodium and the restoration of norepinephrine pressor sensitivity towards normal without an equivalent increase in adrenergic nervous activity.     

Normal and abnormal aging of cardiovascular system

Studies of normal aging in the cardiovascular system in humans are affected by the study population. Besides intrinsic biological aging, extrinsic factors including overt or latent cardiovascular diseases as well as life style variables such as physical activity, diet, alcohol and smoking may influence the age-related changes of cardiovascular function. We have recruited "normal" elderly subjects from community-dwelling volunteers by extensive health screening procedures including treadmill maximum exercise tests. Some of their cardiovascular functions, such as various cardiovascular regulatory functions, were altered compared to normal young subjects, while others such as resting hemodynamics were not. Interrelationships among various autonomic functions in the elderly were not recognized. Although general effects of life styles on circulatory regulatory functions were not clearly indicated, variables such as sodium intake or body mass index appeared to affect some of the sympathetic nervous functions. Furthermore, hypertension in the elderly had much less impact on cardiovascular functions than is generally expected, based on the results from young or middle-aged subjects. To identify factors which either modify (accelerate) or do not affect the aging of the cardiovascular functions is important not only to achieve a good aging process but also to establish therapeutic goals in elderly subjects.     

Race and cardiovascular reactivity. A replication

In a previous study, we reported that black children demonstrated greater cardiovascular reactivity than did white children to the psychological stress of a television video game. Reliance on urban volunteers and the wide age range of the children may have limited conclusions concerning the generalizability of those results. In the present study, 481 of 484 children enrolled in the third grade of the public schools of an entire rural county in Tennessee were examined with the same video game procedure used previously. Results indicated greater heart rate and blood pressure reactivity among black children than among white children. Thus, the previous results were replicated. The greater prevalence of hypertension among black adults may relate to the greater reactivity among black children; reactivity may be either a marker or a mechanism in the development of hypertension.