Wall Cross-sectional Area Research Articles

Relation of arterial structure and function to left ventricular geometric patterns in hypertensive adults

Objectives. The present study sought to determine whether conduit artery structure and function vary according to the pattern of left ventricular adaptation to hypertension.Background. Although left ventricular geometric pattern has been shown to predict cardiovascular events in hypertension, the arterial status in patients with the different patterns is unknown.Methods. We evaluated arterial structure and function by carotid ultrasound and applanation tonometry in 271 unmedicated hypertensive patients classified by echocardiography as having normal ventricular geometry (n = 176), concentric remodeling (n = 54), concentric hypertrophy (n = 16) or eccentric hypertrophy (n = 25).Results. All groups were similar in age, gender distribution and body size. Patients with concentric and eccentric hypertrophy had similar blood pressures (mean 173/100 and 171/99 mm Hg, respectively) and left ventricular mass, but compared with patients with normal left ventricular geometry and concentric remodeling, only those with concentric hypertrophy had increased arterial wall thickness (0.96 ± 0.20 vs. 0.80 ± 0.18 mm, p< 0.05), end-diastolic diameter (6.38 ± 0.97 vs. 5.76 ± 0.87 mm, p < 0.05), cross-sectional area (22.1 ± 5.71 vs. 16.6 ± 5.4 mm2, p < 0.05) and elastic modulus (713 ± 265 vs. 471 ± 241 dynes/cm2 × 10−6, p < 0.05). Patients with concentric remodeling and eccentric hypertrophy had similar values for these measures (0.85 ± 0.22 and 0.89 ± 0.21 mm, 5.67 ± 0.77 and 6.04 ± 0.44 mm, 17.2 ± 5.4 and 19.7 ± 5.9 mm2, 558 ± 263 and 614 ± 257 dynes/cm2 × 10−6, respectively), despite lower systolic blood pressures in the former group (156/94 mm Hg, p < 0.001). The prevalence of plaque was comparable in patients with concentric (56%) and eccentric (42%) hypertrophy and significantly greater in those with normal geometry (21%).Conclusions. Among patients with generally mild, uncomplicated systemic hypertension, arterial structure and function are most abnormal when concentric left ventricular hypertrophy is present and may contribute to the more adverse outcome associated with this geometric pattern.

Remodeling of the Radial Artery in Response to a Chronic Increase in Shear Stress

Chronic changes in large artery blood flow rates induce corresponding adjustments in arterial diameter, but little is known about structural adaptations of the vessel wall in humans. We used a high-resolution echo-tracking system to measure radial artery internal diameter, wall thickness, and mean blood flow on both arms of 11 patients with end-stage renal disease. Measurements were performed on the wrist side of the arteriovenous fistula. The contralateral radial artery was investigated as control. Wall cross-sectional area, circumferential wall stress, and mean wall shear stress were calculated. Results indicate a sixfold increase in blood flow on the side of the arteriovenous fistula compared with the control side, with a 1.4-fold increase in internal diameter. The diameter enlargement was sufficient to normalize wall shear stress. Changes in diameter were not associated with arterial wall hypertrophy because wall cross-sectional area was not increased and rather suggest a "remodeling" of the arterial wall. For the same level of blood pressure, circumferential wall stress was increased on the side of the arteriovenous fistula. These results suggest that the structural adaptations of the arterial wall to a chronic increase in blood flow normalize wall shear stress and overcome stretch-induced changes in the particular circumstance of arteriovenous fistula.

Effects of Endothelin Receptor Inhibition on Cerebral Arterioles in Hypertensive Rats

The purpose of this study was to examine the effects of endothelin receptor inhibition on cerebral arterioles in stroke-prone spontaneously hypertensive rats (SHRSP). Structure and mechanics of cerebral arterioles were examined in untreated Wistar-Kyoto rats (WKY) and SHRSP that were either untreated or treated for 3 months with bosentan, an inhibitor of endothelin receptors (100 mg/kg per day). We measured pressure, external diameter, and cross-sectional area of the vessel wall (histologically) in maximally dilated (EDTA) arterioles on the cerebrum. Bosentan reduced but did not normalize arteriolar mean pressure (103 +/- 3 and 81 +/- 5 mm Hg in untreated and treated SHRSP versus 51 +/- 4 mm Hg in WKY, P < .05; mean +/- SEM) and pulse pressure (40 +/- 2 and 33 +/- 2 mm Hg in untreated and treated SHRSP versus 25 +/- 3 mm Hg in WKY, P < .05) in SHRSP. Cross-sectional area of the vessel wall (CSA) was increased in untreated SHRSP (1627 +/- 173 microm2), and CSA in treated SHRSP (1287 +/- 78 microm2) was similar to that in WKY (1299 +/- 65 microm2). Bosentan had no effect on reductions in external diameter (remodeling) of cerebral arterioles (104 +/- 7 and 96 +/- 4 microm in untreated and treated SHRSP compared with 126 +/- 7 microm in WKY, P < .05). Stress-strain curves indicate that bosentan had no significant effect on distensibility of arterioles on the cerebrum in SHRSP. The results suggest that endothelin-1 may contribute to the development of hypertrophy, but not remodeling or changes in distensibility, of cerebral arterioles in SHRSP.

Effects of Increased Pulse Pressure on Cerebral Arterioles

The goal of this study was to examine the hypothesis that increases in pulse pressure produce hypertrophy of cerebral arterioles, even in the absence of increases in mean pressure. Sprague-Dawley rats underwent creation of an arteriovenous fistula and clipping of one carotid artery at 1 month of age. Rats that underwent exposure of the abdominal aorta without fistula production and unilateral carotid clipping served as controls. At about 6 months of age, the mechanics of sham and clipped pial arterioles were examined in vivo in anesthetized rats. Stress-strain relations were calculated from measurements of pial arteriolar pressure (servo null) and diameter and cross-sectional area of the arteriolar wall. Point counting stereology was used to quantify individual components in the arteriolar wall. Before deactivation of smooth muscle with EDTA, cross-sectional areas of the vessel wall and pulse pressures in sham pial arterioles were significantly greater (P < .05) in arteriovenous fistula rats than in control rats (cross-sectional area, 1468 +/- 100 versus 1129 +/- 104 microns 2; pulse pressure, 26 +/- 1 versus 14 +/- 1 mm Hg). In contrast, systolic and mean pressures in sham arterioles were not significantly different and diastolic pressure was significantly less in arteriovenous fistula rats (systolic pressure, 69 +/- 1 versus 67 +/- 4 mm Hg; mean pressure, 52 +/- 2 versus 57 +/- 3 mm Hg; diastolic pressure, 43 +/- 2 versus 53 +/- 3 mm Hg). Carotid clipping normalized cross-sectional area of the vessel wall (1083 +/- 86 microns 2) and pulse pressure (12 +/- 1 mm Hg) in pial arterioles of arteriovenous fistula rats. During maximal dilatation, the stress-strain curve in sham arterioles of arteriovenous fistula rats was shifted to the right of the curve in control rats, which indicates that arteriovenous fistulae increase passive distensibility of cerebral arterioles. The proportion of distensible components in the vessel wall (smooth muscle, elastin, and endothelium) was increased in sham arterioles of arteriovenous fistula rats. These findings (1) suggest that increases in pulse pressure, even in the absence of increases in mean pressure, are sufficient to produce hypertrophy of cerebral arterioles and (2) provide support for the concept that increases in distensibility of cerebral arterioles in association with hypertrophy of the vessel wall may be related to alterations in wall composition.

A Study of the Physical and Mechanical Properties of Wheat Straw

A series of experiments was conducted to measure the physical properties, tensile and shear strengths and elastic moduli of stem between nodes of wheat straw (var Mercia). These stems are referred to subsequently as "stem internodes". Apparatus is described for the measurements of physical properties, strength and elastic moduli. Young's modulus was measured by applying four point loading transversely to the stem; the rigidity modulus was found by subjecting a stem to torque. The principal variables investigated were (a) the effects of four stages of plant maturity for the third stem internode position, (b) position of the stem internode measured downwards from the ear for the fourth stage of plant maturity and (c) stem moisture in the range 8 to 22% w.b., for the third stem internode position at the fourth stage of plant maturity. There was in increase in stem diameter and wall cross-sectional area from the first to the fourth stem internode from the plant ear. Tensile strength was in the range 21·2 to 31·2MPa and shear strength in the range 4·91 to 7·26MPa. Young's modulus was between 4·76 and 6·58 GPa and the rigidity modulus in the range 267 to 547 MPa. Plant maturity had some significant effects on shear strength, which was highest for the first stage of maturity and for Young's modulus which increased with maturity, but had no effect on rigidity modulus. The stem internode position for the fourth stage of maturity had some significant effects on both the strengths and elastic moduli, but consistent trends were not evident. Moisture content for the fourth stage of maturity, at the third stem internode position, affected both shear strength which increased and rigidity modulus which decreased with increasing moisture content. It had no effect on Young's modulus, however, or any consistent influence on tensile strength. Stem conservation by freezing at -20°C had a significant effect on strength and elastic moduli. Young's modulus was larger for samples which had been frozen and shear strength and rigidity modulus were smaller. Storage of stems for 3 months had no significant effect on the elastic moduli.

Prevalence and Determinants of Cardiac and Vascular Hypertrophy in Hypertension

Hypertrophy of the capacitance arteries has recently been documented in hypertensive patients by noninvasive ultrasound techniques. To better define the prevalence and determinants of vascular hypertrophy and its potential association with ventricular hypertrophy in hypertension, we compared carotid and cardiac ultrasound findings in 172 normotensive and 172 unmedicated hypertensive subjects matched for age and sex. Despite similar body size, hypertension was associated with increased left ventricular wall thicknesses, mass, and mass index (89 versus 80 g/m2, P < .0001 for all comparisons) and increased carotid wall thickness (0.82 versus 0.77 mm) and cross-section area (17.1 versus 15.3 mm2, P < .005 for both comparisons). Among the 172 normotensive subjects, left ventricular hypertrophy was noted in 9 (5.2%) and arterial hypertrophy was found in 9 (5.2%), whereas ventricular hypertrophy was found in 21 (12.2%) and arterial hypertrophy in 19 (11%) hypertensive subjects. Arterial hypertrophy was found in 9% of hypertensive subjects with normal ventricular mass and in 24% with left ventricular hypertrophy (P < .05). Among hypertensive subjects carotid wall thickness and cross-sectional area were most strongly related to age and systolic pressure (P < .0001 for all comparisons), with little contribution form body size. Carotid relative wall thickness was only related to increasing age (P < .01). In contrast, left ventricular wall thickness and mass were strongly related to body size and systolic pressure (P < .0001 for comparisons) but not to age (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Distensibility and Structural Changes in Sinoaortic-Denervated Rats

The purpose of the present study was to determine the effects of chronic sinoaortic denervation on the mechanical properties and composition of the abdominal aorta in Wistar rats. We used a high-resolution echotracking system to determine in situ under physiological conditions of blood flow and arterial wall innervation the aortic diameter-, compliance-, and distensibility-pressure curves in 16-week-old anesthetized rats that had been denervated at 10 weeks of age for 6 weeks (n = 8). Compared with sham-operated rats (n = 8) we observed a marked reduction of baroreflex response and increase in overall mean blood pressure variability as measured by standard deviation and spectral analysis in sinoaortic-denervated rats. Mean blood pressure was not affected by sinoaortic denervation in both conscious and anesthetized rats. Sinoaortic denervation significantly shifted the distensibility-pressure curve toward lower levels of distensibility, indicating a decreased aortic distensibility for a given level of arterial pressure. Sinoaortic denervation produced a significant increase of aortic wall cross-sectional area and collagen content, one of the less-distensible components of the arterial wall. These results suggest that intact arterial baroreceptors are necessary for maintaining normal functional and structural properties of large arteries in rats. The reduction in arterial distensibility in chronic sinoaortic-denervated rats may have resulted from different factors, including the initial hypertensive phase, aortic wall hypertrophy, and increase in collagen content. The changes in aortic wall structure and related reduction in aortic distensibility, in addition to other mechanisms, might have been direct consequences of an increased blood pressure variability.

Mechanical and contractile properties of in situ localized mesenteric arteries in normotensive and spontaneously hypertensive rats

An in situ model was developed for studying mechanical properties of mesenteric arteries in rats. A branch of the mesenteric artery was exposed and dissected in normotensive (WKY) and spontaneously hypertensive rats (SHR). A catheter was introduced into the larger branch of the mesenteric artery and connected to a pressure chamber. The artery was submitted to transmural pressures ranging from 0 to 200 mmHg per steps of 25 mmHg and observed using a microscope-video-camera system. The diameter-pressure relations were established under basal conditions, under contraction (phenylephrine 10 −6M), and after abolition of the smooth muscle tone by potassium cyanide (KCN, 0.1 mg/mL). The arterial segment was then fixed (glutaraldehyde 2.5%), and the wall cross-sectional areas were measured in transverse sections. Compliances, distensibility, wall tensions, and wall stresses were calculated from diameter, pressure, and media thickness values under three conditions. Active tension and active stress were defined as differences in wall stresses and wall tensions calculated under passive and active conditions. Comparision of WKY and SHR when arteries were studied at the respective operating pressure indicates (1) thicker and stiffer mesenteric arteries in SHRs than in WKY rats. (2) similar wall stresses in mesenteric arteries from WKY and SHRs despite larger wall tensions in the hypertensive group, and (3) larger contractility to phenylephrine in SHRs than in WKY mesenteric arteries.

Longitudinal strain of canine and porcine aortas

The in situ longitudinal strain of canine and porcine aortas was investigated. Marks of black water-resistant ink were placed on the aortas and the axial lengths between the marks measured in situ and in vitro. When the aortas were cut, the retraction was measured and described by the stretch ratio, which is defined as the length of a segment in situ divided by the length at no-load state. Results show that the stretch ratios of both porcine and canine aortas increase monotonically from 1.2 in the descending region to about 1.5 in abdominal region. Species differences are seen in the middle region. In both animals, the stretch ratio is correlated to the cross-sectional area of the vessel wall.

Is Asthma a Vascular Disorder?

Is Asthma a Vascular Disorder?

Cardiovascular hypertrophy in one-kidney, one clip renal hypertensive rats

To investigate the role of angiotensin II (Ang II) in cardiovascular hypertrophy in the Goldblatt one-kidney, one clip (1-K, 1C) renal hypertensive rat. Six-week-old Wistar-Kyoto (WKY) rats underwent uninephrectomy and left renal artery clipping. After surgery, rats were treated with perindopril, an angiotensin converting enzyme (ACE) inhibitor, or losartan, an Ang II type 1 (AT1) receptor antagonist, for 4 weeks. Untreated 1-K, 1C rats and uninephrectomized (sham) rats served as controls. The rise in systolic blood pressure in the perindopril-treated and losartan-treated rats was not significantly different from that in the untreated 1-K, 1C group throughout the treatment period. At 4 weeks after surgery the heart weight:body weight ratios of the untreated 1-K, 1C and losartan-treated 1-K, 1C groups were significantly greater than for sham-operated normotensive rats and hypertensive perindopril-treated rats. The total number of smooth muscle cells in the thoracic aortae of the 1-K, 1C untreated, losartan-treated 1-K, 1C and sham groups were similar. However, after treatment the aortae of the perindopril-treated group contained significantly fewer smooth muscle cells. The medial cross-sectional wall area and wall: lumen ratio were similar in the 1-K, 1C untreated and perindopril-treated 1-K, 1C groups. These results suggest that Ang II, via its effects on cardiac and vascular AT1 receptors, does not contribute to the development of cardiovascular hypertrophy in the 1-K, 1C rat. Attenuation of cardiac and vascular growth after ACE inhibition appears to be mediated by mechanisms independent of the actions of the renin-angiotensin system.

Elastic modulus of the radial artery wall material is not increased in patients with essential hypertension.

Hypertension is known to decrease arterial distensibility and systemic compliance. However, the arterial tree is not homogeneous, and it has been shown that the medium-size radial artery does not behave like the proximal, elastic, large, common carotid artery. Indeed, radial artery compliance in hypertensive patients (HTs) has been shown to be paradoxically increased when compared with that in normotensive control subjects (NTs) at the same blood pressure level. To determine whether this increase was due to hypertension-related hypertrophy of the arterial wall, radial artery functional and geometric parameters from 22 NTs (mean +/- SD, 44 +/- 11 years) were compared with those from 25 age- and sex-matched never-treated essential HTs (48 +/- 12 years) by using a high-precision ultrasonic, echo-tracking system coupled to a photoplethysmograph (Finapres system), which allows simultaneous arterial internal diameter, intima-media thickness, and finger blood pressure measurements. When the values for HTs were compared with those of NTs at their respective mean arterial pressures, HTs had similar internal diameter (2.50 +/- 0.56 versus 2.53 +/- 0.32 mm, mean +/- SD) and greater intima-media thickness (0.40 +/- 0.06 versus 0.28 +/- 0.05 mm, P < .001) measurements and increased arterial wall cross-sectional areas (3.79 +/- 1.14 versus 2.45 +/- 0.57 mm2, P < .001). Circumferential wall stress was not significantly different between the two groups. Compliance calculated for a given blood pressure, ie, 100 mm Hg (C100), was greater in HTs than NTs (3.46 +/- 2.41 versus 2.10 +/- 1.55 m2.kPa-1 x 10(-8), P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth, Pressure, and Wall Stress in Epidermal Cells of Begonia argenteo- guttata L. Leaves during Development

Conventional growth-turgor analyses of wall yielding do not take into account developmental changes in tissue and cell geometry that could significantly alter the force on and stress borne by expanding walls. To ascertain the role of wall stress in the decline in growth during leaf maturation, we analyzed the relation between leaf elongation and epidermal turgor (Pe), and the leaf and cell wall cross-sectional areas at three different stages of leaf development. As Begonia leaves elongated from 70 to 140 mm (fully expanded), the relative growth rate declined from ca. 20% d-1 to zero. Yet, there was an increase in Pe of 0.15 and 0.10 MPa in epidermal cells over the midvein and lamina, respectively. Characterization of cell wall cross-sectional areas, through image analysis of stained leaf sections, showed that the fraction of the leaf cross-sectional area occupied by cell wall was approximately 10% larger for epidermal cells of the midvein than for midvein parenchyma cells or for epidermal cells of the lam...

Mechanics of large and small cerebral arteries in chronic hypertension.

The goal of this study was to investigate factors that contribute to reductions in internal diameter of large and small cerebral arteries during chronic hypertension. We measured diameter of second- and third-order branches of the posterior cerebral artery in vitro during maximal dilation with EDTA in 6-mo-old stroke-prone spontaneously hypertensive rats (SHRSP, n = 7) and Wistar-Kyoto rats (WKY, n = 7). Cross-sectional area of the vessel wall, measured histologically, was not significantly different at 70 mmHg in SHRSP and WKY in large or small branches of posterior cerebral artery. In large branches of posterior cerebral artery, external and internal diameters were significantly less at 70 mmHg in SHRSP than in WKY, whereas external and internal diameters converged at 0 mmHg in the two groups of rats. In small branches, on the other hand, external and internal diameters were significantly less at all levels of intravascular pressure in SHRSP than in WKY. The stress-strain relation in posterior cerebral artery of SHRSP was shifted to the left in large branches and to the right in small branches, which indicates that distensibility was reduced in large cerebral arteries of SHRSP and increased in small cerebral arteries. These findings suggest that different mechanisms are responsible for impairment of maximal dilator capacity in large and small cerebral arteries of SHRSP: reduced distensibility in large arteries and remodeling with reduced external diameter in small arteries. Furthermore the findings provide additional support for the concept that hypertrophy may not be a primary factor in impaired maximal dilation.

Perindopril inhibits both the development of atherosclerosis in the cholesterol-fed rabbit and lipoprotein binding to smooth muscle cells in culture

The aim of the study was to examine the effect of low doses of perindopril, approximating those used therapeutically and sub-therapeutically in human hypertensives, on the development of atherosclerosis in the cholesterol-fed rabbit. The right carotid artery of 12 week old rabbits was balloon de-endothelialized to induce the formation of a myointimal thickening. After 14 weeks rabbits were placed into 6 groups, 6 rabbits per group. Groups I, II and III were fed a l% cholesterol diet for the following 6 week experimental period, while Groups IV, V and VI received a normolipemic diet. In addition, Groups II and V rabbits received in their drinking water 0.3 mg/kg per day perindopril, and Groups III and VI 0.01 mg/kg per day. At the end of 6 weeks' treatment, the mean arterial pressure (MAP) in Groups II and V decreased by about 12%, while that in Groups III and VI decreased by 13%. Plasma cholesterol levels of rabbits on a normolipemic diet (Groups IV, V, VI) averaged l.3 mmol/l while those on a cholesterol-enriched diet (Groups I, II, III) averaged 10.5 mmol/l. Plasma perindoprilat concentrations and percentage of plasma angiotensin converting enzyme (ACE) inhibition in Groups II and V averaged 14 ng/ml and 92.l% respectively, while in Groups III and VI they were 5.7 ng/ml and 80.5%, respectively. The percentage luminal surface area of the thoracic aorta covered by lipid-filled plaques (as observed by en face staining with Oil-Red-O) averaged 26.3% in Group I, 4.7% in Group II and 20.0% in Group III. No lesions developed in Groups IV, V and VI. Microscopic examination of the right (manipulated) carotid arteries of Group I rabbits revealed lesions of large, lipid-filled cells radially oriented, overlying the pre-formed myointimal thickening. Both doses of perindopril in the cholesterol-fed rabbits (Groups II and Ill) decreased the amount of lipid-filled cells which were oriented circumferentially. More extracellular matrix was present in the lesions of Groups II and III than of Group I. No lesions were observed in the right carotid arteries of Groups IV, V and VI (normal diet) or in the unmanipulated left carotid arteries of all 6 groups. The sizes of the neointima plus lesion in Groups I, II and III were, however, not significantly different, being 42.4%, 48.5% and 46.9% of the cross-sectional area of the artery wall. Culture studies revealed that perindoprilat decreased specific binding of 125I-labelled β-very low density lipoprotein to passaged smooth muscle cells (SMC) from the rabbit aorta in a dose-dependent manner. Perindoprilat had no effect on SMC proliferation, but did increase collagen synthesis. These results indicate that perindopril at low doses has a beneficial effect in decreasing the severity of atherosclerosis in the cholesterol-fed rabbit. The effect is not related to MAP, or to any effect on plasma cholesterol level. Instead, perindopril appears to have a direct effect on the biology of the cells of the artery wall, in particular increasing collagen synthesis by the SMC and decreasing their binding and uptake of atherogenic lipoprotein.

Temporal variability and correlation with geometric parameters in vasospastic angina: a quantitative angiographic study.

Long-term changes in vasocontractility were examined in 23 coronary segments from 20 patients with variant angina using computer-based quantitative coronary angiography and ergonovine provocation tests repeated at an interval of 42 +/- 14 months. Measurements of vasospasticity at the sites of fixed stenoses were compared with values predicted by an elementary geometric theory based on the assumption that the cross-sectional area of a vessel wall is constant regardless of its state of vasoconstriction. While all patients were symptomatic initially, only 11 remained symptomatic at follow-up. At the initial provocation test, the response was correctly predicted in four segments, was lower than expected in one, and was stronger in 18. At follow-up, only one of the four segments in which the response had been initially predicted correctly again showed the predicted response and the remaining three showed a response weaker than expected; the one segment which was initially hypocontractile remained hypocontractile at follow-up; and of the 18 segments which were initially hypercontractile, 12 exhibited hypercontractility again, four had the predicted value and the remaining two showed hypocontractility. In only one of 23 segments did the geometric theory predict the behaviour of vasospasticity at the site of fixed stenosis on both tests. Vasospastic responsiveness is a dynamic process demonstrating temporal variability and is not directly predicted by geometric theory.

Enhanced myogenic activation in skeletal muscle arterioles from spontaneously hypertensive rats

The purpose of this study was to determine whether the vascular myogenic response is enhanced in hypertension. Experiments were conducted in the intact cremaster muscle microcirculation as well as in isolated arterioles of hypertensive (SHR) and normotensive (WKY) rats. Increasing venous pressure in vivo by approximately 5 mmHg had no effect on normotensive first- (1A) or third-order arteriolar (3A) diameters; in contrast, hypertensive 1A diameter decreased 4% (89 +/- 2 to 85 +/- 3 microns) with an 8% decrease in 3A (24 +/- 2 to 22 +/- 2 microns). To further examine this enhanced constriction to elevated intravascular pressure in SHR, diameter was monitored in isolated 1A during step increases and decreases in intraluminal pressure. Normotensive arterioles displayed myogenic responses between pressures of 50 and 170 cmH2O; in contrast, hypertensive arterioles demonstrated myogenic responses over an extended pressure range (50-210 cmH2O). In addition, the change in diameter for each step change in pressure was greater in the arterioles from SHR, indicating an increased myogenic responsiveness. The myogenic reactions were unaffected by alpha-receptor blockade with phentolamine (10(-6) M), indicating that adrenergic hypersensitivity was not involved in the enhanced response to stretch. Morphometric analysis of the vascular wall revealed no differences in wall thickness, cross-sectional wall area, or wall-to-lumen ratio between normotensive and hypertensive rats. The length-tension relationships for normotensive and hypertensive rats demonstrated that peak active tension occurred at nearly the same vascular smooth muscle length. In addition, SHR arterioles were capable of maintaining higher levels of active tension that WKY arterioles, indicating an altered length-tension curve in chronic arterial hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Noninvasive quantitative evaluation of atherosclerosis using MRI and image analysis.

A new medical image analysis system to quantify atherosclerosis in the lower abdominal aorta using magnetic resonance imaging is described. This medical image analysis and display system permits the quantification of the three-dimensional (3D) properties of the vessel wall and lumen cross-sectional area and volumes. Preliminary results of employing this medical image analysis capability on magnetic resonance images demonstrated a twofold increase in wall volume per unit vessel length, corresponding to intimal thickening, before luminal narrowing was detected. This work demonstrated the feasibility and usefulness of quantitatively evaluating the 3D properties of the vessel lumen and wall by using a combination of magnetic resonance imaging and image analysis. The demonstration that intimal wall thickening is observed in images before observable occlusion of the lumen can be expected to provide an important early indicator of the future development of atherosclerosis. Such capability will permit detailed and quantitative studies to assess the effectiveness of therapies, such as drug, exercise, and dietary regimens.

Mechanics and composition of cerebral arterioles in renal and spontaneously hypertensive rats.

The purpose of this study was to examine effects of hypertension on mechanics of cerebral arterioles in nongenetic and genetic models of chronic hypertension. Pressure (servo null) and diameter were measured in pial arterioles of anesthetized renal hypertensive rats (one-kidney, one clip), uninephrectomized normotensive rats, spontaneously hypertensive rats, and normotensive Wistar-Kyoto rats. During maximal dilatation with EDTA, external diameter of pial arterioles at 70 mm Hg pial arteriolar pressure was not significantly different in renal hypertensive and normotensive rats (86 +/- 5 [mean +/- SEM] versus 84 +/- 4 microns) but was less in spontaneously hypertensive rats than in Wistar-Kyoto rats (81 +/- 3 versus 92 +/- 3 microns; p < 0.05). Cross-sectional area of the arteriolar wall (histological) was greater in renal hypertensive than in normotensive rats (1,360 +/- 131 versus 952 +/- 89 microns 2; p < 0.05) and in spontaneously hypertensive rats than in Wistar-Kyoto rats (1,294 +/- 97 versus 817 +/- 86 microns 2; p < 0.05). The stress-strain relation obtained from pressure-diameter data during maximal dilatation with EDTA indicated that distensibility of pial arterioles, when fully relaxed, was greater in renal hypertensive and spontaneously hypertensive rats than in normotensive and Wistar-Kyoto rats. We used point-counting stereology to quantitate composition of pial arterioles in renal hypertensive rats. Cross-sectional area of smooth muscle and elastin was significantly greater in renal hypertensive than in normotensive rats (smooth muscle, 947 +/- 108 versus 620 +/- 62 microns 2; elastin, 101 +/- 11 versus 55 +/- 6 microns 2; p < 0.05), whereas cross-sectional area of collagen and basement membrane was not significantly different in the two groups (collagen, 6 +/- 1 versus 5 +/- 1 microns 2; basement membrane, 120 +/- 12 versus 104 +/- 8 microns 2). Thus, we conclude that 1) cerebral arterioles undergo hypertrophy in both renal hypertensive and spontaneously hypertensive rats; 2) cerebral arterioles in renal hypertensive rats do not undergo "remodeling" with a reduction in external diameter, whereas external diameter is smaller in spontaneously hypertensive than in Wistar-Kyoto rats; 3) distensibility of cerebral arterioles, when fully relaxed, is increased in renal hypertensive rats and is greater in spontaneously hypertensive than in Wistar-Kyoto rats; and 4) the distensible components of the arteriolar wall are increased disproportionately in cerebral arterioles of renal hypertensive rats, which may contribute to increases in arteriolar distensibility.

Reactivity and Sensitivity of the Mesenteric Artery in Adult Spontaneously Hypertensive Rats After Chronic Treatment with Indapamide

The effects of chronic treatment with indapamide (3 mg/kg/day) on the structure and function of the mesenteric artery were studied in two groups of spontaneously hypertensive rats (SHRs) using an experimental model of in situ localized mesenteric artery. Indapamide (n = 12) or placebo (n = 12) were given to 8-week-old rats for 4 weeks. After anesthesia and laparotomy, a segment of mesenteric artery (external diameter, 300-400 microns) was exposed for video-microscopic measurements. The diameter-pressure relationships were established under active conditions (phenylephrine, 10(-6) M) and passive conditions (potassium cyanide, KCN) for transmural pressure ranging from atmospheric pressure to 200 mm Hg. These studied arterial segments were then fixed and their wall cross-sectional areas (CSA) measured in transverse sections. Active wall stress and tension were defined as the differences in wall stresses and wall tensions calculated for active and passive conditions. Systolic arterial pressure and mesenteric CSA were decreased in treated rats (197 +/- 15 mm Hg vs. 211 +/- 12 mm Hg, p < 0.05; 16,230 +/- 1048 microns2 vs. 19,033 +/- 1082 microns2, p < 0.05). In both groups, mesenteric diameters were smaller under active than under passive conditions without significant differences in treated vs. untreated group under active conditions. The active wall tension was lower in treated (0.4 +/- 0.19 N/m) than in untreated rats (1.19 +/- 0.62 N/m, p < 0.05). However, there were no differences in active wall stress in both groups (103 +/- 47 kPa and 134 +/- 30 kPa).(ABSTRACT TRUNCATED AT 250 WORDS)