Functional versus structural changes of forearm vascular resistance in hypertension

Association of ambulatory heart rate and atherosclerosis risk factors with blood pressure in young non-hypertensive adults

OBJECTIVE

The study objective was to assess the association between 24 h ambulatory heart rate (HR), atherosclerosis risk factors and blood pressure (BP) in young non-hypertensive patients.

METHODS

We recruited 186 participants aged 18-45 years from a large urban academic Family Medicine outpatient practice, serving 40 000 individuals for this observational study. The main analyses were based on multiple linear regression, with mean 24 h BP (systolic BP (SBP) or diastolic BP (DBP)) as the outcomes, mean 24 h HR as the main predictor of interest, and controlling for age, gender, race, insulin sensitivity/resistance and endothelial function measured by strain gauge venous occlusion plethysmography.

RESULTS

HR was independently associated with mean 24 h SBP and DBP (SBP and DBP: p=0.042 and 0.001, respectively). In our analyses, associations were markedly stronger for ambulatory compared with office BP measurements. Endothelial dysfunction was associated with higher SBP (p=0.013); plasminogen activator inhibitor-1 was significantly associated with both SBP and DBP (p=0.041 and 0.015, respectively), while insulin resistance was not associated with either SBP or DBP. Insulin resistance and C reactive protein were significant predictors of HR (p=0.013 and 0.007, respectively).

CONCLUSIONS

These findings suggest that HR may be a potential marker of elevated cardiovascular risk in young asymptomatic individuals, prior to the development of clinical hypertension or cardiovascular disease.

The effect of microvascular pattern alterations on network resistance in spontaneously hypertensive rats

Structural microvascular rarefaction, defined by a loss of vessels, is a common characteristic of hypertension and has been associated with elevated microvascular resistance. However, determining the causal relationship between microvascular network structure and resistance requires a consideration of all pattern changes throughout a network. The objectives of this study were to determine whether microvascular rarefaction is associated with other network pattern alterations and to evaluate whether pattern alterations in hypertension necessarily contribute to increased microvascular resistance. Mesenteric tissues from age-matched (15-16 weeks) male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were harvested and immunolabeled for PECAM. SHR networks displayed a decreased microvascular area, arteriolar-venular (AV) length, number of AV branches, and number of capillary segments. In addition, SHR networks displayed increased AV connections per network compared to WKY networks. Based on network geometries, resistance per network was calculated using a computational model. For simulations with equal vessel diameter and with relative diameters based on reported intravital measurements, SHR microvascular network resistance was not elevated compared to the WKY level. Our results suggest that microvascular pattern alterations associated with hypertension are more complex than vessel loss, and that these combined alterations do not necessarily lead to elevated resistance.

Alterations in capillary morphology are found in mild blood pressure elevation

OBJECTIVES

Remodeling of small resistance arteries is an early sign of target organ damage in hypertension. Peripheral capillary morphology abnormalities in hypertension are not well studied. The study objective was to determine whether altered capillary morphology is associated with SBP, DBP, or both in individuals without and with mild blood pressure elevation (SBP = 130-160 mmHg). Another objective was to determine whether capillary morphology is associated with minimum forearm vascular resistance, a measure of altered resistance artery structure.

METHODS

Participants included 115 nonpregnant, nondiabetic individuals 23-55 years of age. A five-component morphology score (distribution, tone, configuration, hypertrophy, and extravasates) was developed to describe fingernail bed capillaries visualized using venous congestion in digital photomicrographs. Multiple linear regression models adjusted for age, sex, race, tobacco use, hyperglycemia, dyslipidemia, and renal function were used to analyze the relationship between SBP, DBP, and minimum forearm vascular resistance with the morphology score.

RESULTS

The total morphology score was significantly associated with SBP and DBP as well as minimum forearm vascular resistance (P < 0.005 for all). Among the five individual morphology score components, hypertrophy was significantly associated with SBP and DBP (P = 0.002 and 0.001, respectively), whereas extravasates were significantly associated with SBP only (P = 0.002).

CONCLUSION

A five-component capillary morphology score is associated with SBP, DBP, and altered resistance artery structure in individuals with and without mild blood pressure elevation. These observations suggest that target organ damage at the level of the microcirculation can be detected using capillary morphology.

Functional capillary rarefaction in mild blood pressure elevation

Capillary rarefaction is described in patients with moderate to severe hypertension. The study objective was to determine if structural and/or functional capillary rarefaction is detectable and associated with endothelial dysfunction in patients with mild blood pressure elevation (HBP: Systolic blood pressure 130 - 160 mm Hg). Capillary density was quantified by direct capillaroscopy in 110 nondiabetic black and non-black subjects. Endothelial function was quantified by plethysmographic measures of flow-mediated vasodilation. Compared to normotensives (NBP: N = 90), functional capillary rarefaction was detected in HBP (N = 20; P<0.001). Functional capillary density measures correlated with endothelial function (P<0.001). Functional, but not structural, capillary rarefaction is detectable and associated with endothelial dysfunction in both black and non-black individuals with mild blood pressure elevation.

Forearm plethysmography in the assessment of vascular tone and resistance vasculature design: new methodological insights

AIM

High peripheral resistance and structural alteration in resistance arteries are central phenomena in essential hypertension and have been widely examined by forearm venous occlusion plethysmography; at rest for studying vascular tone, and during reactive hyperaemia for studying vascular structure. This work concerns the influence of venous pressure on hyperaemic vascular resistance (Rmin), the reproducibility of hyperaemic and resting vascular resistances (Rrest) and the relation between forearm and total peripheral vascular resistance (TPR).

METHODS

In four healthy subjects, intravenous and intra-arterial blood pressures were measured simultaneously with plethysmographic recordings of hyperaemic and resting forearm blood flows. Reproducibility was examined in 15 young and 14 middle-aged healthy subjects and in 21 untreated hypertensive patients.

RESULTS

Rmin remained low in the first recorded cardiac cycle, but rose in the second, even though corrected for the venous pressure rise, suggesting vascular tone recovery along with venous congestion. Between-day reproducibility of Rmin was high in middle-aged normotensive (8.7%) and hypertensive subjects (10.6%), but Rmin fell significantly between successive days in the young subjects. Rrest correlated with TPR, but required up to 40 min to reach steady state and showed high day-to-day variation in young (21.8%) and hypertensive subjects (16.2%).

CONCLUSIONS

During hyperaemia, vascular resistance should be measured in the first cardiac cycle following venous occlusion to minimize influences of venous pressure rise and possible tone recovery. Rrest seems to reflect TPR. About 20 subjects may be needed to detect 15% changes between days in Rrest, fewer when concerning Rmin and TPR.

The lord of the ring: mandatory role of the kidney in drug therapy of hypertension

Strong evidence supports the idea that total peripheral resistance (TPR) is increased in all forms of human and experimental hypertension. Although the etiological participation of TPR in the origin and long-term maintenance of hypertension has been extensively debated, it now seems clear that the renal, nonadaptive, infinite gain-working, pressure-sensitive natriuresis and diuresis is the main mechanism of blood pressure control in the long term. The tissue, cellular, biochemical, and genetic sensors and executors of this process have not been fully identified yet, but the role of the renal medulla has gained growing attention as the physiopathological scenario in which the key regulatory elements reside. Specifically, the functionality of the renomedullary vasculature seems to be highly responsible for blood pressure control. The vasculature of the renal medulla becomes a new and more specific target for the therapeutic intervention of hypertension. Recent data on the effect of baroreceptor-controlled renal sympathetic activity on the long-term regulation of blood pressure are integrated. The renomedullary effects of the main antihypertensive drugs are discussed, and new perspectives for the therapeutic intervention of hypertension are outlined. Comparison of the genetic program of the renal medulla before and after the development of hypertension in spontaneously hypertensive and experimentally induced animal models might provide a mechanism for identifying the key genes that become activated or suppressed in the development of high blood pressure. These genes, their encoded proteins, or other elements related to their signalling and genetic pathways might serve as new and more specific targets for the pharmacological treatment of abnormally elevated blood pressure. Besides, proteins specifically located to the luminal side of the renomedullary vascular endothelium may serve as potential targets for site-directed drug and gene therapy.

Structural remodeling of resistance arteries in uremic hypertension

BACKGROUND

Structural remodeling of the resistance vasculature is present in many forms of human and experimental hypertension. In particular, an increase in the ratio of wall thickness to lumen diameter develops, and might in itself maintain hypertension by increasing vascular resistance. Because uremia is associated with raised peripheral resistance, hypertension, and histologic changes suggestive of vascular remodeling, we sought to formally examine the structural and mechanical (elastic) properties of isolated pressurized resistance arteries in uremic hypertension.

METHODS

Cremaster, cerebral and mesenteric arteries from subtotally nephrectomised Wistar-Kyoto rats, normotensive control Wistar-Kyoto rats, and spontaneously hypertensive rats were mounted on a pressure myograph and relaxed in calcium-free buffer. Wall thickness and lumen diameter were measured at increasing lumen pressures from 10 to 200 mm Hg, and from this wall:lumen ratio, wall cross-sectional area, and an index of elasticity were derived.

RESULTS

In uremic hypertensive animals increased wall:lumen ratio and decreased lumen diameter was seen in cremaster and mesenteric arteries, although no significant changes were observed in cerebral arteries, compared to normotensive controls. In spontaneously hypertensive animals increased wall thickness and wall:lumen ratio was seen in cerebral and mesenteric arteries, decreased lumen diameter in cremaster and mesenteric arteries, and increased wall cross-sectional area in cerebral arteries, compared to normotensive controls. Elasticity of the arterial wall in uremic and spontaneously hypertensive animals did not differ from normotensive controls.

CONCLUSION

Cremaster and mesenteric resistance arteries undergo predominantly eutrophic inward remodeling in uremic hypertension, broadly similar to that seen in spontaneous hypertension.

Noradrenergic vascular hyper-responsiveness in human hypertension is dependent on oxygen free radical impairment of nitric oxide activity

BACKGROUND

Noradrenergic vascular hyper-responsiveness is a hallmark of essential hypertension. To evaluate whether nitric oxide plays a role in the enhanced vascular response to norepinephrine in hypertension, we examined 32 hypertensives and 28 normotensives who were distributed in 3 experimental series.

METHODS AND RESULTS

In the first series, we measured the forearm blood flow (FBF) response to a norepinephrine infusion under control conditions and during the infusion of L-N-monomethylarginine (L-NMMA). Norepinephrine evoked dose-dependent vasoconstriction that was greater in hypertensives than in normotensives (maximum FBF, -61+/-1 versus -51+/-1%; P<0.01). During L-NMMA infusion, norepinephrine vasoconstriction was not modified in hypertensives; however, it was potentiated in normotensives (maximum FBF, -64+/-2%; P<0.01). In the second series, we tested whether norepinephrine vasoconstriction could be affected by an antioxidant such as ascorbic acid. Norepinephrine vasoconstriction was blunted by ascorbic acid administration only in hypertensives (maximum FBF, -49+/-3 versus -63+/-2%; P<0.01); the vasoconstriction became similar to that observed in normotensives. During ascorbic acid plus L-NMMA administration, the vascular response to norepinephrine increased to a similar extent in both study groups. To rule out the possibility that the effect of ascorbic acid on norepinephrine vasoconstriction could depend on adrenergic receptor-induced nitric oxide release, in the last series we inhibited endogenous nitric oxide and replaced it with an exogenous nitric oxide donor (sodium nitroprusside). Even in these conditions, ascorbic acid attenuated norepinephrine vasoconstriction only in hypertensives (maximum FBF, -50+/-2 versus -62+/-1%; P<0.01).

CONCLUSIONS

Our data demonstrate that noradrenergic vascular hyper-responsiveness in hypertension is dependent on an impairment of nitric oxide activity that is realized through norepinephrine-induced oxygen free radical production.

Effects of alpha 1-blockade on maximal vascular conductance in young borderline hypertensives

This study was conducted to determine if reducing sympathetic tone with alpha 1-adrenergic receptor blockade affected the maximal forearm vascular conductance (FVCmax, reactive hyperemia) responses in young borderline hypertensives and normotensive controls. The FVC response following ischemia (14 min arterial occlusion with 3 min of hand exercise) was determined after systemic alpha 1-blockade (5 mg prazosin in preceding 24 h) in hypertensives (n = 11, MAP = 110 +/- 1, age = 24.5 +/- 1.1, mean +/- SEM) and normotensives (n = 13, MAP = 82 +/- 1, age = 22.5 +/- 0.3). During the placebo trial, resting FVC was lower in the hypertensives than the normotensives (.0472 +/- .0073 vs .0755 +/- .0095 units; P < .05). During alpha 1-blockade, FVC did not differ between the groups. Within each group, FVCmax did not differ significantly between either trial. During placebo, FVCmax was lower (P < .05) in the hypertensives (.3485 +/- .0335 vs .5641 +/- .0503 units) and remained so during alpha 1-blockade (.4048 +/- .0520 vs .5286 +/- .0275 units; P < .05). These data suggest that alpha 1-blockade does not increase FVCmax in borderline hypertensives and that both functional and structural changes in the peripheral vasculature are involved in the blood pressure elevations seen in this group.

Dietary salt restriction increases vascular insulin resistance

BACKGROUND

Recent studies have shown that insulin has a direct vasodilator effect and that vascular sensitivity to insulin is impaired in hypertension. How the vasodilator effect of insulin is regulated physiologically is unknown. It has been appreciated that salt restriction may have adverse effects on glucose and lipid metabolism--processes regulated by insulin. To determine whether dietary salt restriction might affect vascular sensitivity to insulin, we studied 13 subjects (including eight borderline hypertensive subjects and five normotensive subjects) after 1 week of a normal sodium diet (240 mEq/day) and after 1 week of a low-sodium diet (20 mEq/day) with a randomized, double-blind crossover design.

METHODS AND RESULTS

Vascular sensitivity to insulin was assessed with the dorsal hand vein linear variable differential transformer technique. When the "normal" salt diet was given, vascular sensitivity for insulin was significantly less (i.e., dose that produced the half-maximal response [ED50] insulin was higher) in hypertensive subjects (ED50 insulin for hypertensive subjects, 5.75 milliunits (mU)/min; ED50 insulin for normotensive subjects, 0.23 mU/min; p < 0.05). Vascular sensitivity to insulin was inversely correlated with mean arterial pressure and plasma norepinephrine concentration. When the low salt diet was given, vascular sensitivity to insulin decreased in both the normotensive and hypertensive groups, paralleling an increase in plasma norepinephrine. Blood pressure was not significantly decreased by reducing salt intake.

CONCLUSION

In these younger normotensive and hypertensive subjects, dietary salt restriction increases resistance to the vasodilating effects of insulin.

Evidence for a multifactorial process involved in the impaired flow response to nitric oxide in hypertensive patients with endothelial dysfunction

The assessment of endothelial function in hypertensive patients receiving acetylcholine has revealed conflicting results. Whether an impaired flow response to acetylcholine is explained solely by a diminished endothelial synthesis of nitric oxide (NO) remains unclear as yet. In the present study, we tested the hypothesis that mechanisms other than reduced NO synthesis contribute to the hypertension-associated impairment of endothelium-dependent vasodilation. Therefore, the dilatory response to endogenous and exogenous NO was measured in resistance arteries and cutaneous microvessels in the forearm circulation of 12 normotensive individuals and 17 hypertensive patients. In addition, the overall dilatory capacity was assessed by peak flow during reactive hyperemia after 3 minutes of ischemia. Forearm blood flow was quantified by venous occlusion plethysmography at rest, during application of the NO donor sodium nitroprusside, and during stimulation of endogenous NO synthesis by acetylcholine and bradykinin. Blood flow velocity in the cutaneous microvasculature was measured with laser-Doppler flowmetry in parallel. Resting forearm flow was comparable in both groups (3.1 +/- 0.2 and 3.4 +/- 0.2 mL.min-1.100mL-1 tissue), whereas blood pressure and thus peripheral vascular resistance was significantly elevated in hypertensive compared with normotensive subjects. Hyperemic peak flow was significantly blunted in hypertensive patients. Sodium nitroprusside, acetylcholine, and bradykinin increased flow in a dose-dependent manner to a comparable extent in the control group (13.3 +/- 0.8, 13.6 +/- 1.3, and 14.6 +/- 0.7 mL.min-1.100mL-1 tissue, respectively). In contrast, in hypertensive patients maximum increase in resting flow was significantly reduced (sodium nitroprusside, -36%; acetylcholine, -44%; and bradykinin, -56%). The flow response after stimulation of endogenous NO synthesis by bradykinin was significantly more blunted compared with that of exogenous NO after application of sodium nitroprusside. In the cutaneous microvasculature, bradykinin-induced increases in blood flow velocity were selectively impaired in hypertensive patients, whereas flow response to acetylcholine was preserved. Thus, we conclude that in arterial hypertension endothelium-dependent, NO-mediated dilation of resistance arteries and cutaneous microvessels of the forearm vasculature is heterogeneously impaired, depending on the type of endothelial receptor stimulated. Furthermore, the present data suggest that in hypertensive patients the impairment of NO-dependent dilation of resistance arteries is caused by at least three different mechanisms: (1) a reduced endothelial synthesis of NO due to either a disturbed signal-transduction pathway and/or a reduced activity of NO synthase, (2) an accelerated NO degradation within the vessel wall, and (3) alterations in the vessel architecture resulting in an overall reduced dilatory capacity of resistance arteries.

Computerized evaluation of the peripheral blood flow during maximal vasodilatation in humans using venous occlusion plethysmography

Forearm blood flow was studied with venous occlusion plethysmography after ischaemic exercise in 10 healthy volunteers and 10 hypertensive patients. The peak blood flow was calculated by three methods: the manual conventional graphic technique and by fitting of a tangent to the inflow curve with the help of a computer. In addition a computer-aided derivation of an exponential curve adapted to the initial part of the inflow curve was used for the calculation of the maximal blood flow. With the two tangential techniques the peak mean blood flow values did not differ significantly and were 58 ml min-1 100 ml-1 tissue while the exponential derivation procedure gave in both groups about 40% higher maximal flow values. The effect of venous occlusion on the linear velocity of the brachial arterial blood flow blood was studied with Ultrasound Doppler Flowmetry. The maximal flow velocity after ischaemic exercise decreased by about 18% during 50 mmHg venous occlusion; the influence of the venous stasis was least during the first heart beats after the onset of the venous occlusion. The effect of the venous stasis was similar but less pronounced in the hypertensive patients. In conclusion, forearm blood flow during maximal vasodilatation is reduced by venous occlusion and the best estimate of the flow is obtained from the earliest part of the venous occlusion inflow curve, as indicated by the use of the computer-aided exponential derivation technique.

Relationship between vitamin D3 and the peripheral circulation in moderate arterial primary hypertension

Although altered cellular calcium handling plays a critical role in the pathophysiology of hypertension, little attention has been focused on the impact of calcium regulating hormones on target-organs (e.g. vascular tissue). Therefore the relationship between calcium, phosphorus, parathyroid hormone, 25- and 1,25-(di) hydroxyvitamin D3, blood pressure (BP) and regional circulation was examined in 25 patients (44 +/- 2.5 years) with moderate hypertension (systolic BP 164 +/- 4 mmHg, diastolic BP 105 +/- 2 mmHg). Calf and finger blood flow were measured simultaneously using ECG-triggered plethysmography at rest and after 3 min arterial occlusion (reactive hyperemia). Systolic and diastolic BP were inversely correlated with 25-hydroxyvitamin D3 (r = -0.511 and r = -0.445, p < 0.002). Calf vascular resistance at rest (r = -0.46, p = 0.02) and after 3 min arterial occlusion (r = -0.78, p = 0.0001) was related to 25-hydroxyvitamin D3 concentration. Only calf vascular resistance during reactive hyperemia was significantly related to 1,25-dihydroxyvitamin D3 (r = -0.44, p = 0.03). After correction for blood pressure calf vascular resistance after 3 min arterial occlusion remained significantly and inversely related with 25-hydroxyvitamin D3. There was no relation between finger (skin) circulation and vitamin D3. All other calcium regulating factors were unrelated to the parameters of peripheral circulation. Our results indicate that among the calcium regulating factors, particularly vitamin D3 seems to inversely influence muscle, but not skin vascular tone-independently of blood pressure in mild to moderate hypertension.

The influence of antihypertensive therapy on the structural arteriolar changes in essential hypertension: different effects of enalapril and hydrochlorothiazide

OBJECTIVES

To assess the peripheral and central haemodynamics, in particular the effect on minimal resistance in the hand, with an ACE inhibitor in comparison with a diuretic.

DESIGN

Double-blind randomized parallel group study.

SUBJECTS

Twenty-eight previously untreated men with essential hypertension (supine diastolic blood pressure > 95 mmHg repeatedly on placebo). METHODS/INTERVENTION: Causal and intra-arterial blood pressure, dye-dilution technique, water plethysmography at rest and at ischaemia, enalapril (n = 14), hydrochlorothiazide (n = 14).

RESULTS

After 6 months the mean arterial pressure was reduced from 112.7 to 96.9 mmHg (change -15.9 mmHg; 95% confidence interval (CI) -21.9, -9.8) on enalapril and from 110.1 to 101.5 mmHg (change -8.6 mmHg; CI -14.4, -2.8). Heart rate did not change on any of the therapies. Enalapril reduced blood pressure mainly through a reduction in total peripheral resistance (delta -3.0 PRU100; CI -5.6, -0.4) while hydrochlorothiazide reduced blood pressure mainly through a reduction in cardiac output (delta -0.8 l/min-1; CI -1.5, -0.07). Minimal vascular resistance (mean of right and left hand) displayed a significant time x treatment interaction indicating a different trend with enalapril than hydrochlorothiazide with a change of -0.12 PRU100 (CI -0.33, 0.05) on enalapril and a change of 0.14 (CI -0.29, 0.56) on hydrochlorothiazide. The resistance level after 6 months was significantly higher on hydrochlorothiazide than on enalapril (P = 0.0105).

CONCLUSION

Enalapril reduced blood pressure through vasodilatation and hydrochlorothiazide through decreased cardiac output. The two therapies also affected minimal vascular resistance (an indirect measure of vascular wall thickness) differently; with enalapril showing a favourable response in contrast to hydrochlorothiazide.

Resting and maximal forearm skin blood flows are reduced in hypertension

To find whether the vasodilator capacity of nonacral skin is reduced in hypertension, we measured forearm blood flow by venous occlusion plethysmography in 10 seated normotensive (mean +/- SD mean arterial pressure, 94 +/- 5 mm Hg) and 10 hypertensive (112 +/- 9 mm Hg) men at rest for 39 minutes while the forearm was heated with water at 42 degrees C, a maneuver known to selectively and maximally vasodilate skin. Blood pressure, measured every 5 minutes, did not change with heating. We found that in the normotensive group resting forearm blood flow was higher (3.64 +/- 1.12 versus 2.48 +/- 0.58 ml/100 ml tissue per minute, p less than 0.001; normotensive group versus hypertensive group) and resting forearm vascular resistance lower (30.17 +/- 10.99 versus 48.88 +/- 17.37 mm Hg.min.100 ml tissue per minute, p less than 0.05; normotensive group versus hypertensive group), and maximal forearm blood flow with local heating was higher (29.32 +/- 11.99 versus 18.19 +/- 4.50 ml/100 tissue per minute, p less than 0.018; normotensive group versus hypertensive group and vascular resistance lower (4.07 +/- 1.04 versus 6.54 +/- 1.17 mm Hg.min.100 ml tissue per minute, p less than 0.005; normotensive group versus hypertensive group). To find whether this degree and duration of local warming maximally vasodilated the skin in hypertensive subjects (as it does in normotensive subjects), we measured forearm skin blood flow before and during local heating plus 10 minutes of ischemia using a laser Doppler flowmeter.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated arterial blood pressure in cardiac tamponade

BACKGROUND

In cardiac tamponade cardiac output falls, but peripheral vascular resistance increases, so that systemic blood pressure may be maintained at normal or near-normal levels. We recently observed a patient with cardiac tamponade whose blood pressure was markedly elevated.

METHODS

To determine the frequency of elevated blood pressure in patients with cardiac tamponade and their hemodynamic characteristics, we studied 18 consecutive patients with cardiac tamponade from a variety of causes using right heart catheterization.

RESULTS

Six of the 18 patients had systolic arterial blood pressures ranging from 150 to 210 mm Hg (mean [+/- SD], 176 +/- 26) and diastolic pressures ranging from 100 to 130 mm Hg (mean, 113 +/- 14). All six had previously been hypertensive. After pericardiocentesis there was a significant decrease in blood pressure (to 139 +/- 13 mm Hg systolic, P less than 0.05; and 83 +/- 6 mm Hg diastolic, P less than 0.01) and peripheral vascular resistance (from 2150 +/- 588 to 1207 +/- 345 dyn.sec.cm-5, P less than 0.01). Cardiac output increased in all six. The other 12 patients, 3 of whom had a history of hypertension, had significant increases in cardiac output and systolic blood pressure (from 119 +/- 13 to 127 +/- 7 mm Hg, P less than 0.05) after pericardiocentesis, whereas peripheral vascular resistance decreased. Both groups had similar degrees of cardiac tamponade, as indicated by measurements of cardiac output and intrapericardial, right atrial, and pulmonary-artery wedge pressures.

CONCLUSIONS

Elevated blood pressure may occur in some patients with cardiac tamponade who have preexisting hypertension. Moreover, blood pressure may fall after pericardiocentesis in patients who have elevated blood pressure associated with tamponade.

The relationship between systolic blood pressure and microvascular resistance in non-diabetic and diabetic subjects

Skin blood flow and microvascular resistance were measured in the feet of hypertensive and normotensive subjects by the non-invasive transient thermal clearance method. Skin blood flow decreased and microvascular resistance increased as a function of systolic brachial blood pressure for the non-diabetic subjects who were not treated by vasoactive medication. The relationship between blood flow and systolic blood pressure for diabetic patients and for patients who were treated by enalapril was poor. The average resistance for non-diabetic patients treated by enalapril was lower than that of untreated non-diabetic subjects. For diabetic patients no significant difference in resistance between enalapril treated and untreated patients was found. The results demonstrate that for non-diabetic patients the role of microvascular resistance in hypertension is significant while it is less important in diabetic patients.

Abnormalities of resistance vessel structure in essential hypertension: are these important?

1. The relationship between essential hypertension and abnormalities of the proximal resistance vessels (small arteries) is reviewed, with particular emphasis on their structure. 2. There seems to be good evidence that the media: lumen ratio of these vessels is increased, and this may account for the increased pressor response. 3. Whether there is also growth is not clear, and it is possible that the altered structure is due to redistribution of existing cells. 4. Regardless of the basis for the altered structure, it appears that in essential hypertension the altered vascular structure is in itself sufficient to explain the increased peripheral resistance. 5. Paradoxically, the altered vascular structure does not seem to be the main determinant of blood pressure, but the altered vascular structure appears to allow it to perform its function in the most convenient fashion. 6. It is suggested that the interest in vascular structure lies in connection with therapy, for correction of blood pressure without correction of vascular structure will probably not prevent all the consequences of the disease. 7. Current therapies do not appear to be able, in the short-term, to normalize vascular structure, indicating that there is a need to find other more specific ways of correcting vascular structure.

"White coat" versus "sustained" borderline hypertension in Tecumseh, Michigan

During a survey of young subjects not receiving treatment for hypertension in Tecumseh, Michigan, clinic and self-monitored blood pressures taken at home (14 readings in 7 days) were obtained in 737 subjects (387 men, 350 women, average age 31.5 years). Hypertension in the clinic was diagnosed if the clinic blood pressure exceeded 140 mm Hg systolic or 90 mm Hg diastolic. In the absence of firm criteria for what constitutes hypertension at home, subjects whose average home blood pressure was in the upper decile of the whole population were considered to have hypertension at home. By these criteria, 7.1% of the whole population had "white coat" hypertension (i.e., high clinic but not elevated home readings). The prevalence of "sustained" hypertension (i.e., high readings in the clinic and at home) was 5.1%. Subjects with white coat and sustained borderline hypertension in Tecumseh were very similar. Both groups showed, at previous examinations (at ages 5, 8, 21, and 23 years), significantly higher blood pressure readings than the normotensive subjects. As young adults (average age 33.3 years), the parents of both hypertensive groups had significantly higher blood pressure readings than the parents of normotensive subjects. Both hypertensive groups had faster heart rates, higher systemic vascular resistance, and higher minimal forearm vascular resistance. Both hypertensive groups were more overweight, had higher plasma triglycerides, insulin, and insulin/glucose ratios than normotensive subjects. The white coat hypertensive group also had lower values of high density lipoprotein than the normotensive group. White coat hypertension is a frequent condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Does combined kidney and pancreas transplantation reverse functional diabetic microangiopathy?

Using videophotometric capillaroscopy and laser Doppler fluxmetry, we have investigated skin microvascular reactivity in the fingers of 14 diabetic patients with severe, late complications 20 months after combined kidney and pancreas transplantation. The results were compared with those obtained in 20 diabetic patients awaiting pancreas transplantation and in 19 healthy subjects. The capillary blood cell velocity at rest (P less than 0.01) and during postocclusive reactive hyperemia (P less than 0.05) was significantly lower in both patient groups than in the healthy controls. However, the time to peak capillary blood cell velocity during hyperemia was normal in the post-transplantation group (NS) but significantly prolonged in the pretransplantation group (P less than 0.01). The ability to decrease flow during venous stasis-the so called venoarte-riolar reflex--was strongly impaired in the pretransplantation group (P less than 0.001) but less so in the post-transplantation group (P less than 0.05) as compared to healthy controls. It may be concluded that diabetic patients, after combined kidney and pancreas transplantation, show a tendency towards better microvascular reactivity than those awaiting transplantation.

[Effect of bradykinin on systemic and pulmonary hemodynamics in the human]

In our studies we investigated the vasodepressor effects of bradykinin in vivo in normotensive and hypertensive subjects. Bradykinin was injected intravenously and intraarterially (40-6050 pM/kg) respectively was infused intraarterially (40-6050 pM/kg/min). The investigations were performed in 21 normotensives and 15 hypertensives. Bradykinin injections were performed after the following pharmacological interventions: salt restriction (10 mmol Na/d), salt loading (300 mmol Na/d), captopril (50 mg), ramipril (5 mg), lisinopril (20 mg), ketotifen (2 x 1 mg), indomethacin (2 x 50 mg), and propranolol (80 mg). The results show that bradykinin lowers blood pressure dose related by marked reduction in peripheral vascular resistance. The blood pressure reduction was strongly correlated with the increase in kinin concentration. This effect of bradykinin appears to be independent of changes in sodium metabolism, of beta adrenoceptors, of histamine-1 receptors, and of prostaglandins. ACE-inhibitors potentiate the blood pressure lowering effect of bradykinin about 20- to 50-fold. In case of an intraarterial injection of bradykinin in only 2-5% o the intravenously used dose of bradykinin are needed to produce an identical fall in blood pressure. From this experiments a pulmonary clearance rate of bradykinin over 95% can be calculated. In the pulmonary arteries bradykinin has no effect on the vascular resistance. In patients suffering from primary or renovascular hypertension the blood pressure response to bradykinin was enhanced. The bradykinin potentiating effect of the ACE-inhibitors was not altered in the hypertensives. In patients suffering from bradykinin hypertension or primary hyperaldosteronism bradykinin developed the same blood pressure lowering effect as in the normotensives.