Functional Capillary Rarefaction Research Articles

Impaired skeletal muscle performance as a consequence of random functional capillary rarefaction can be restored with overload-dependent angiogenesis.

Key points Loss of skeletal muscle capillaries is thought to contribute to a reduction in exercise tolerance, but the relative contribution of a compromised microcirculation with disease, in isolation of co‐morbidities, to impaired muscle function is unknown.We therefore developed a novel method to randomly occlude capillaries in the rat hindlimb to mimic the capillary rarefaction observed in many conditions.We demonstrate that muscle fatigue resistance is closely coupled with functional microvascular density, independent of arterial blood flow, while disturbance of the microcirculation leads to long‐term impairment of muscle function if left untreated.Mechanical stretch due to muscle overload causes a restoration of fatigue resistance via angiogenic remodelling.These observations highlight the importance of a healthy microcirculation and suggest that restoring impaired microvascular supply, regardless of disease co‐morbidities, will assist recovery of exercise tolerance in a variety of conditions that limit quality of life. To what extent microvascular rarefaction contributes to impaired skeletal muscle function remains unknown. Our understanding of whether pathological changes in the microcirculation can be reversed remains limited by a lack of basic physiological data in otherwise healthy tissue. The principal objectives here were to: (1) quantify the effect of random microvascular rarefaction on limb perfusion and muscle performance, and (2) determine if these changes could be reversed. We developed a novel protocol in rats whereby microspheres injected into the femoral artery allowed a unilateral reduction in functional capillary density in the extensor digitorum longus (EDL), and assessed acute and chronic effects on muscle function. Simultaneous bilateral EDL force and hindlimb blood flow measurements were made during electrical stimulation. Following functional capillary rarefaction there was an acute microsphere dose‐dependent reduction in muscle fatigue resistance (P < 0.001), despite preserved femoral artery perfusion. Histological analysis of EDL samples taken from injected animals confirmed a positive correlation between the proportion of functional capillaries and fatigue resistance (P = 0.002). Such impaired performance persisted for at least 2 weeks (P = 0.016). Concomitant mechanical overload improved both perfused capillary density and fatigue resistance (P<0.05), confirming that the capacity for muscle remodelling was retained following chronic distributed ischaemia, and that the impact of capillary rarefaction could be alleviated. These results demonstrate that loss of functional capillaries is detrimental to muscle function, even in otherwise healthy tissue, independent of arterial perfusion. Restoration of muscle performance following a mechanical overload stimulus indicates that angiogenic treatments to alleviate microvascular rarefaction may be key to restoring exercise tolerance.

Sublingual functional capillary rarefaction in chronic heart failure.

Microcirculatory changes contribute to clinical symptoms and disease progression in chronic heart failure (CHF). A depression of coronary flow reserve is associated with a lower myocardial capillary density in biopsies. We hypothesized that changes in cardiac microcirculation might also be reflected by a systemic reduction in capillaries and visualized by sublingual videomicroscopy. The aim was to study invivo capillary density and glycocalyx dimensions in patients with CHF vs healthy controls. Fifty patients with ischaemic and nonischaemic CHF and standard treatment were compared to 35 healthy age-matched subjects in a prospective cross-sectional study. Sublingual microcirculation was visualized using a sidestream darkfield videomicroscope. Functional and perfused total capillary densities were compared between patients and controls. A reduced glycocalyx thickness was measured by an increased perfused boundary region (PBR). Median functional and total perfused capillary densities were 30% and 45% lower in patients with CHF (both P<.001). Intake of oral vitamin K antagonists was associated with significantly lower capillary densities (P<.05), but not independent of NT-proBNP. Dimensions of the glycocalyx were marginally lower in CHF patients than in healthy controls (<7% difference). However, PBR correlated significantly with inflammation markers (fibrinogen: r=.58; C-reactive protein: r=.42), platelet counts (r=.36) and inversely with measures of liver/renal function such as bilirubin (r=-.38) or estimated glomerular filtration rate (r=-.34) in CHF patients. CHF patients have got a markedly lower functional and total perfused capillary density in sublingual microvasculature when compared to controls, indicating a systemic decrease in microcirculation.

Cerebral microvascular dysfunction in metabolic syndrome is exacerbated by ischemia\u2013reperfusion injury

BackgroundMetabolic syndrome (MetS) is associated with an increased risk of cerebrovascular diseases, including cerebral ischemia. Microvascular dysfunction is an important feature underlying the pathophysiology of cerebrovascular diseases. In this study, we aimed to investigate the impacts of ischemia and reperfusion (IR) injury on the cerebral microvascular function of rats with high-fat diet-induced MetS.ResultsWe examined Wistar rats fed a high-fat diet (HFD) or normal diet (CTL) for 20 weeks underwent 30 min of bilateral carotid artery occlusion followed by 1 h of reperfusion (IR) or sham surgery. Microvascular blood flow was evaluated on the parietal cortex surface through a cranial window by laser speckle contrast imaging, functional capillary density, endothelial function and endothelial–leukocyte interactions by intravital videomicroscopy. Lipid peroxidation was assessed by TBARs analysis, the expression of oxidative enzymes and inflammatory markers in the brain tissue was analyzed by real-time PCR. The cerebral IR in MetS animals induced a functional capillary rarefaction (HFD IR 117 ± 17 vs. CTL IR 224 ± 35 capillary/mm2; p < 0.05), blunted the endothelial response to acetylcholine (HFD IR −16.93% vs. CTL IR 16.19% from baseline inner diameter p < 0.05) and increased the endothelial–leukocyte interactions in the venules in the brain. The impact of ischemia on the cerebral microvascular blood flow was worsened in MetS animals, with a marked reduction of cerebral blood flow, exposing brain tissue to a higher state of hypoxia.ConclusionsOur results demonstrate that during ischemia and reperfusion, animals with MetS are more susceptible to alterations in the cerebral microcirculation involving endothelial dysfunction and oxidative stress events.

Acute Chagas disease induces cerebral microvasculopathy in mice.

Cardiomyopathy is the main clinical form of Chagas disease (CD); however, cerebral manifestations, such as meningoencephalitis, ischemic stroke and cognitive impairment, can also occur. The aim of the present study was to investigate functional microvascular alterations and oxidative stress in the brain of mice in acute CD. Acute CD was induced in Swiss Webster mice (SWM) with the Y strain of Trypanosoma cruzi (T. cruzi). Cerebral functional capillary density (the number of spontaneously perfused capillaries), leukocyte rolling and adhesion and the microvascular endothelial-dependent response were analyzed over a period of fifteen days using intravital video-microscopy. We also evaluated cerebral oxidative stress with the thiobarbituric acid reactive species TBARS method. Compared with the non-infected group, acute CD significantly induced cerebral functional microvascular alterations, including (i) functional capillary rarefaction, (ii) increased leukocyte rolling and adhesion, (iii) the formation of microvascular platelet-leukocyte aggregates, and (iv) alteration of the endothelial response to acetylcholine. Moreover, cerebral oxidative stress increased in infected animals. We concluded that acute CD in mice induced cerebral microvasculopathy, characterized by a reduced incidence of perfused capillaries, a high number of microvascular platelet-leukocyte aggregates, a marked increase in leukocyte-endothelium interactions and brain arteriolar endothelial dysfunction associated with oxidative stress. These results suggest the involvement of cerebral microcirculation alterations in the neurological manifestations of CD.

Blockade of the renin–angiotensin system improves cerebral microcirculatory perfusion in diabetic hypertensive rats

We examined the functional and structural microcirculatory alterations in the brain, skeletal muscle and myocardium of non-diabetic spontaneously hypertensive rats (SHR) and diabetic SHR (D-SHR), as well as the effects of long-term treatment with the angiotensin AT1-receptor antagonist olmesartan and the angiotensin-converting enzyme inhibitor enalapril. Diabetes was experimentally induced by a combination of a high-fat diet with a single low dose of streptozotocin (35mg/kg, intraperitoneal injection). D-SHR were orally administered with olmesartan (5mg/kg/day), enalapril (10mg/kg/day) or vehicle for 28days, and compared with vehicle-treated non-diabetic SHR or normotensive non-diabetic Wistar–Kyoto rats. The cerebral and skeletal muscle functional capillary density of pentobarbital-anesthetized rats was assessed using intravital fluorescence videomicroscopy. Chronic treatment with olmesartan or enalapril significantly lowered blood pressure and reversed brain functional capillary rarefaction. Brain oxidative stress was reduced to non-diabetic control levels in animals treated with olmesartan or enalapril. Histochemical analysis of the structural capillary density showed that both olmesartan and enalapril increased the capillary-to-fiber ratio in skeletal muscle and the capillary-to-fiber volume density in the left ventricle. Olmesartan and enalapril also prevented collagen deposition and the increase in cardiomyocyte diameter in the left ventricle. Our results suggest that the association between hypertension and diabetes results in microvascular alterations in the brain, skeletal muscle and myocardium that can be prevented by chronic blockade of the renin–angiotensin system.

Microvascular Effects of Centrally Acting Antihypertensive Drugs in Spontaneously Hypertensive Rats

We investigated the effects of oral long-term antihypertensive treatment using centrally acting sympathoinhibitory drugs on capillary density in the skin, skeletal muscle, and heart in the spontaneously hypertensive rat (SHR). Wistar Kyoto rats (WKY) were used as normotensive control groups. Functional capillary density was assessed using intravital fluorescence videomicroscopy and structural capillary density with histochemical analysis. Groups of 10 SHRs were orally treated over 28 days with clonidine (0.1 mg x kg x d), rilmenidine (1 mg x kg x d), or moxonidine (10 mg x kg x d). A group of WKY was also treated with clonidine (0.1 mg x kg x d). Treatment with all antihypertensive drugs induced a normalization of arterial pressure accompanied by a reversion of functional capillary rarefaction in the skeletal muscle and skin of SHR. Clonidine treatment also reduced arterial pressure and increased functional capillary density in the skin and skeletal muscle of WKY. Histochemical analysis showed that SHR had a lower capillary to fiber ratio in the skeletal muscle (P < 0.0001), which was normalized by all treatments. The capillary volume density to fiber volume density ratio in the left ventricle of SHR was also significantly reduced (P < 0.0001). However, myocardial capillary rarefaction was not altered by the different treatments. In conclusion, the results showed that long-term antihypertensive treatment with centrally acting drugs enhanced tissue perfusion and reversed capillary rarefaction in the skeletal muscle of SHRs.

Severe obstructive sleep apnoea exacerbates the microvascular impairment in very mild hypertensives

Different studies have shown that obstructive sleep apnoea syndrome (OSAS), frequently associated with hypertension, represents a harmful and independent risk for cardiovascular diseases. The aim of our study was to ascertain whether the occurrence of OSAS could worsen microcirculatory impairment in very mild hypertensives. One hundred untreated very mild hypertensives underwent polysomnography and subdivided into 32 non-OSAS, 33 mild OSAS and 35 severe OSAS patients on standardized criteria. They underwent routine blood chemistry, ambulatory blood pressure monitoring and anthropometric analysis. Skin capillary density (n mm(-2)) of forearm (FAC) and periungueal (PUC) fields was obtained through videocapillaroscopy. By a venous congestion manoeuvre, PUC was maximized (CVC) and secondary capillary recruitment (GAIN) was calculated. These measurements served as indices of structural and functional capillary rarefaction, respectively. Severe OSAS hypertensives showed reduced FAC (P < 0.001) and PUC (P < 0.001) as compared to those with mild OSAS and non-OSAS, but a greater CVC (P < 0.01) and GAIN (P < 0.001). Multiple regression analysis showed that PUC was inversely related to total sleep time with oxyhaemoglobin saturation at < 90% (TST90) (P < 0.001) and FAC to the apnoea-hypopnoea index (AHI) (P < 0.001) and to the sleep propensity (P < 0.01). CVC was positively associated to AHI (P < 0.001) and GAIN to TST90 (P < 0.05). The findings suggest that OSAS, by means of reduced basal and functional capillarity rarefaction, might pose an additional risk of impaired peripheral perfusion in very mild hypertensives. A microcirculation study therefore should be a part of the clinical approach in patients at high cerebro-cardiovascular risk such as hypertensives and patients with OSAS.

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.

Effects of Antihypertensive Drugs on Capillary Rarefaction in Spontaneously Hypertensive Rats: Intravital Microscopy and Histologic Analysis

We investigated the effects of chronic oral antihypertensive treatment on functional and structural capillary rarefaction in spontaneously hypertensive rats (SHR). Wistar Kyoto rats (WKY) were used as a normotensive control group. In untreated rats, intravital videomicroscopy showed that functional capillary density was lower in SHR skeletal muscle (WKY 395 +/- 17 and SHR 258 +/- 13 capillaries/mm, P < 0.01) and ear skin (WKY 391 +/- 18 and SHR 210 +/- 15 capillaries/mm, P < 0.01). A linear relationship was seen between skeletal muscle and skin capillary densities (r = 0.654, P < 0.0001). Histologic analysis showed that SHR had a lower capillary-to-fiber ratio in the skeletal muscle (WKY 1.74 +/- 0.08 and SHR 1.40 +/- 0.06, P < 0.01). Capillary volume density-to-fiber volume density ratio in the left ventricle of SHR was also reduced (WKY 0.55 +/- 0.09 and SHR 0.42 +/- 0.09, P < 0.01). The animals were treated with the angiotensin-converting enzyme (ACE) inhibitor enalapril, the angiotensin II type I receptor (AT1) receptor antagonist losartan, the beta-blocker atenolol, or the calcium channel blocker nifedipine, resulting in similar reductions in systolic blood pressure (19.8%, 19.1%, 17.4%, and 18.2%, respectively, P > 0.05). Atenolol did not induce any change in functional capillary density of SHR. Losartan and nifedipine completely reversed functional capillary rarefaction in both muscle and cutaneous tissues, whereas enalapril significantly increased functional capillary density only in the skin. The skeletal muscle capillary-to-fiber ratio was normalized by enalapril, losartan, and nifedipine. Treatments with enalapril or losartan normalized the cardiac structural capillary rarefaction of SHRs, whereas atenolol and nifedipine had no effect. Our results suggest that different pharmacologic classes of antihypertensive drugs with similar effect on blood pressure differ in terms of their effect on the microcirculation.

Original Research: Capillary rarefaction in treated and untreated hypertensive subjects

This study aimed to determine if capillary rarefaction is detectable and associated with endothelial dysfunction in persons with mild systolic blood pressure (SBP) elevation. Capillary density and endothelial function were quantified for 150 nondiabetic participants, grouped by blood pressure (BP) as normotensive, untreated high BP, and treated high BP. Structural capillary rarefaction measures were not different between the three groups. Functional capillary rarefaction measures were significantly lower in both high BP groups compared to normotensives, and correlated inversely with endothelial function. The study findings indicate that the hypertensive vascular pathologic process is already underway at modest levels of blood pressure elevation.

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.