Intraoperative evaluation of revascularization effect on ischemic muscle hemodynamics using near-infrared diffuse optical spectroscopies

Arterial revascularization in patients with peripheral arterial disease (PAD) reestablishes large arterial blood supply to the ischemic muscles in lower extremities via bypass grafts or percutaneous transluminal angioplasty (PTA). Currently no gold standard is available for assessment of revascularization effects in lower extremity muscles. This study tests a novel near-infrared diffuse correlation spectroscopy flow-oximeter for monitoring of blood flow and oxygenation changes in medial gastrocnemius (calf) muscles during arterial revascularization. Twelve limbs with PAD undergoing revascularization were measured using a sterilized fiber-optic probe taped on top of the calf muscle. The optical measurement demonstrated sensitivity to dynamic physiological events, such as arterial clamping/releasing during bypass graft and balloon inflation/deflation during PTA. Significant elevations in calf muscle blood flow were observed after revascularization in patients with bypass graft (+48.1 ± 17.5%) and patients with PTA (+43.2 ± 11.0%), whereas acute post-revascularization effects in muscle oxygenation were not evident. The decoupling of flow and oxygenation after revascularization emphasizes the need for simultaneous measurement of both parameters. The acute elevations/improvements in calf muscle blood flow were associated with significant improvements in symptoms and functions. In total, the investigation corroborates potential of the optical methods for objectively assessing the success of arterial revascularization.

Multifractal and lacunarity analysis of microvascular morphology and remodeling

OBJECTIVE

Classical measures of vessel morphology, including diameter and density, are employed to study microvasculature in endothelial membrane labeled mice. These measurements prove sufficient for some studies; however, they are less well suited for quantifying changes in microcirculatory networks lacking hierarchical structure. We demonstrate that automated multifractal analysis and lacunarity may be used with classical methods to quantify microvascular morphology.

METHODS

Using multifractal analysis and lacunarity, we present an automated extraction tool with a processing pipeline to characterize 2D representations of 3D microvasculature. We apply our analysis on four tissues and the hyaloid vasculature during remodeling.

RESULTS

We found that the vessel networks analyzed have multifractal geometries and that kidney microvasculature has the largest fractal dimension and the lowest lacunarity compared to microvasculature networks in the cortex, skin, and thigh muscle. Also, we found that, during hyaloid remodeling, there were differences in multifractal spectra reflecting the functional transition from a space filling vasculature which nurtures the lens to a less dense vasculature as it regresses, permitting unobstructed vision.

CONCLUSION

Multifractal analysis and lacunarity are valuable additions to classical measures of vascular morphology and will have utility in future studies of normal, developing, and pathological tissues.

Nitric oxide and the cardiovascular system: cell activation, vascular reactivity and genetic variant

Nitric oxide (NO), primarily identified as an endothelium-derived relaxing factor, is a free radical that signals different biological processes. The identification of NO synthase (NOS) isoforms and the subsequent characterization of the mechanisms of cell activation of the enzymes permitted the partial understanding of both the physiological interactions and of the mechanisms of the diseases in which NO is involved. Mainly expressed in the vascular endothelium, the endothelial NOS isoform (eNOS) plays an important role in the regulation of vascular reactivity and in the development and progression of atherosclerosis. The purpose of this review is to contextualize the reader about the eNOS structure and its mechanisms of cell activation. In view of the advances in molecular biology, we will also address the known mechanisms of gene expression regulation and the role of variants on the genetic code of eNOS associated with cardiovascular phenotypes. Although the importance of NO as an atheroprotective molecule is recognized, our focus will be the review of the literature on NO and its participation in the modulation of the muscle vasodilatation phenotype.

Influence of Early Antihypertensive Treatment on Vascular and Cardiac Design in SHR with and without Renal Hypertension

The present study was designed to explore to what extent pressure reduction by antihypertensive therapy and pressure elevation by renal hypertension are able to affect structural vascular and cardiac changes in young spontaneously hypertensive rats (SHR). Pressure elevation in SHR was induced by means of superimposing 2 kidney, 1 clip renal hypertension (2K1C). Pressure reduction was achieved by means of the vasoselective calcium antagonist felodipine from 6 to 13 weeks of age in both clipped and unclipped SHR. Vascular structure of the skeletal muscle was assessed hemodynamically by perfusing a hindlimb preparation and left ventricular dimensions were calculated from pressure-volume relationships of isolated hearts arrested in diastole. Induction of renal hypertension in SHR resulted, besides augmentation of arterial pressure in a marked concentric left ventricular hypertrophy, i.e. elevations of wall thickness to internal radius ratio. Likewise, in renal hypertensive SHR, a structural adaptation of the skeletal muscle vascular bed occurred, reflected as elevations of minimal vascular resistance and maximal generated perfusion pressure. Antihypertensive treatment for 8 weeks with felodipine reduced and also prevented mean arterial pressure from increasing further in SHR, and in SHR with superimposed renal hypertension by approximately 15% (p < 0.001 for both). In renal hypertensive SHR, felodipine partly prevented the development of exaggerated structural changes, both in the heart and in the skeletal muscle vascular bed, as reflected by reduced wall thickness to internal radius ratio and reduced minimal vascular resistance by 22% and maximal pressure response by 10% respectively (p < 0.01 for both parameters).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of daidzein, 4-methylbenzylidene camphor or estrogen on gastrocnemius muscle of osteoporotic rats undergoing tibia healing period

The effect of daidzein (D), 4-methylbenzylidene camphor (4-MBC) or estradiol-17beta-benzoate (E(2)) on muscle of osteoporotic rats during fracture healing was studied. After performing a metaphyseal tibia osteotomy in 96 osteoporotic 5-month-old female Sprague-Dawley rats, they received daily 50 mg D, 200 mg 4-MBC or 0.4 mg E(2) per kg body weight, or soy free (SF) diet up to 36 and 72 days. Mitochondrial activity, fiber area, and capillary density were analyzed in M. gastrocnemius. Osseous callus bridging of fracture was observed in half of the rats after 36 days. By day 72, fracture was healed in most of the animals. State 3 mitochondrial respiration significantly enhanced in E(2), 4-MBC and D groups versus SF after 36 days (30, 32 and 32 vs 23 pmol O(2)/s per mg). It declined after 72 days, however, in E(2) group it was still at a higher level versus SF (25, 23 and 21 vs 20 pmol O(2)/s per mg). Size of fast oxidative glycolytic (FOG) and fast glycolytic (FG) fibers, capillary density did not differ significantly between the groups, however, at day 36 an increase in D and 4-MBC groups was detectable. FOG diameter was 64, 66, 68, and 58 microm and FG diameter was 88, 98, 95, and 89 microm in SF, D, 4-MBC, and E(2) groups. The ratio of capillaries to muscle fiber was 1.1, 1.4, 1.3, and 1.1 in SF, D, 4-MBC and E(2) groups by day 36. D and 4-MBC react similar to estrogen thereby improving oxidative cell metabolism in severe osteoporotic rats. The level of mitochondrial activity was higher, though no significant morphological differences could be shown.

Effects of chronic iron deficiency anaemia on myoglobin content, enzyme activity, and capillary density in the human skeletal muscle

The influence of chronic iron deficiency anaemia on myoglobin content, maximal enzyme activities and capillarization in the human skeletal muscle was investigated. Muscle samples from musculus vastus lateralis were screened in an Indonesian population. The causes of iron deficiency were chronic intestinal bleeding or repeated pregnancy combined with low iron intake. The maximal activities of iron-dependent and non-iron-dependent glycolytic and oxidative enzymes as well as myoglobin showed similar values in the iron-deficient group and the matched control group. The activities of the oxidative enzymes in both the iron-deficient group and the controls were lower, however, compared even to untrained Swedish subjects. The capillary density was essentially within a normal range in both groups. It is concluded that chronic iron deficiency anaemia of a moderate or severe degree, with Hb concentrations of about 80-100 g.1(-1), does not cause an impaired biochemical function of the human skeletal muscle.

Laser-Doppler flowmetry--a non-invasive and continuous method for blood flow evaluation in microvascular studies

Skin viability has during the last decades been studied by a number of different techniques. Some of these are briefly presented in this paper. One method, based on the laser-Doppler principle, makes possible continuous and noninvasive measurement of blood flow in the outermost layer (1 mm) of the skin. The basic physical principles and the properties of this flowmeter are presented. Some clinical and research applications of laser-Doppler flowmetry in a number of medical disciplines are discussed.

Capillary permeability in skeletal muscle of normal subjects

Capillary diffusion capacity (CDC) and muscle blood flow (MBF) were determined from the anterior tibial muscle in 25 normal subjects by measuring the simultaneous clearance of 133xenon and sodium131iodide. The subjects were divided into two groups: one with a mean age of 31 years and the other with a mean age of 51. The older group had a significantly lower MBF (54.6 +/- 9.0 vs. 64.2 +/- 9.5 ml/100 g/min; p less than 0.05) and a significantly greater CDC (7.6 +/- 1.2 vs. 6.1 +/- 1.3 mol/min; p less than 0.01) than the younger group. There was a significant correlation between the CDC increase and the age of the subjects (r = 0.61; p less than 0.01). Furthermore, MBF decreased with increasing age (r = 0.48; p less than 0.05). No differences were found in MBF or CDC between female and male subjects. The mechanisms of increased capillary permeability are discussed.

Leg muscle circulation by 133Xenon clearance as a predictor of cardiovascular disease in an aged population

In a 10-year cardiovascular survey of an unselected population aged 70 at entry. 133Xenon clearance was carried out in the anterior tibial muscle in both legs after maximal exercise during ischaemia in 211 men and 166 women. The maximal blood flow and the delay time (Ti) until this was achieved were measured. Using multivariate Cox's regression analyses with mortality from cardiovascular diseases (CVD) and CVD events in the eighth decade as end-points, and maximal blood flow, Ti, distal pulse abnormality and intermittent claudication as possible predictors, high Ti was found to be an independent predictor of both end-points in both sexes. In further multivariate Cox's regression analyses including other possible CVD risk markers, high Ti was of individual predictive value for excess total mortality, excess CVD mortality and excess CVD events in both sexes. It is concluded that high Ti by 133Xenon clearance at the age of 70 is a powerful predictor of future CVD events.

Dynamic changes in the microcirculation of diabetics as related to diabetic microangiopathy

Reversible abnormalities of many vascular beds have been observed in early diabetes, before irreversible structural changes of diabetic microangiopathy became apparent. In the bulbar conjenctiva and in the kidney the changes are associated with vascular dysfunction and may be due to autonomic neuropathy. The role of autoregulation in these vascular beds is not clear. In the limb muscles and in the retina the functional abnormality in early diabetes and in those with only mild retinopathy is increased blood flow. This increase in blood flow is probably the result of autoregulatory adaptation to hypoxia induced by 2,3 diphosphoglycerate deficiency. Lactic acid accumulation may also contribute. Breakdown of the autoregulation in the retina results in the development of diabetic retinopathy. The late stages of retinopathy, new vessel formation, are an attempt at revascularisation of areas of capillary non-perfusion.

Metabolic effects of beta-adrenoceptor blockade on skeletal muscle at rest and during exercise

beta-Adrenoceptor antagonists influence the metabolic responses in man at rest and during exercise. Impaired working capacity and muscular fatigue have been reported in patients on beta-blockers and this could be due to an altered substrate supply to the muscles. The results from several studies show that the main effect of beta-blockade on metabolism is decreased lipolysis, with less fat available to the muscles. This results in an increased carbohydrate demand to maintain an unchanged aerobic metabolism, and liver and muscle glycogen stores are more rapidly depleted. beta-blockade also results in decreased lactate release from the muscles, probably due to a membrane effect and/or changed perfusion. It is concluded that beta-blockade a) decreases fat metabolism in the muscle, which secondarily increases the use of carbohydrates during exercise, resulting in earlier hypoglycaemia and/or depletion of muscle glycogen with reduction of the working capacity, b) impairs lactate transport from the muscle but does not cause lactate accumulation within the muscle which could be responsible for muscular fatigue.

beta-Adrenoceptor blockade and exercise: effects on endurance and physical training

beta-adrenoceptor antagonists influence almost all haemodynamic and metabolic actions in the body. High levels of sympathetic stimulation accompany aerobic exercise and it is known that beta-blockade results in a decreased working capacity. Furthermore it has also been questioned whether beta-blockade inhibits the normal response to physical training. Although adrenergic mechanisms are involved in muscle and liver glycogen breakdown, beta-blockade does not seem to reduce glycogen utilisation during exercise. Both selective and non-selective beta-blockade inhibit lipolysis and result in less free fatty acids being available for muscle utilisation. Surgical and chemical sympathectomy in animals has been shown to inhibit the responses to physical training but results are now available showing that beta-adrenergic blockade does not prevent the effect of physical conditioning in patients treated with propranolol. It is concluded that beta-blockade during prolonged exercise a) does not reduce oxygen uptake by the working muscles b) decreases fat metabolism, which secondarily increases the use of carbohydrates, resulting in earlier hypoglycaemia and/or depletion of muscle glycogen with reduction in working capacity c) does not inhibit central and peripheral adaptation to physical conditioning.

Metabolism in ischemic muscles before and after treatment with glucose-insulin-potassium infusion

Arteriosclerosis, arterial thrombosis and emboli in the lower extremities of man result in metabolic disorders in the muscles due to a deficit between oxygen required and oxygen made available. Furthermore, diminished perfusion pressure results in diminished exchange of substrates and electrolytes across the capillary walls. In the muscle cells there is a depression of glycolytic enzyme function and a stimulation of lipid activity, resulting in accumulation of free fatty acids and acidosis within the cells. In order to increase R.Q. in the muscles in question, infusion of glucose-insulin-potassium were installed via a catheter introduced into the superior vena cava for 3 days. Following this, muscle samples showed significant increase of carbohydrate metabolism as compared to lipid metabolism and nearly normalization of intracellular content of free fatty acids. This was accompanied by improvement of the clinical condition of the patients and loss of pain in the extremities affected.

Coupling between dietary changes, reduced body weight, muscle fibre size and improved glucose tolerance in middle-aged men with impaired glucose tolerance

Fourteen middle-aged med with impaired glucose tolerance were studied prior to and 6 months after exchange of simple carbohydrates for complex carbohydrates rich in fibers and saturated for polyunsaturated fats in their diet when exchangeable. Body weight was reduced by 6.4 kg (p less than 0.001). Physical work capacity was unchanged. Fasting blood glucose and insulin were lowered (p less than 0.001) at 6 months and so were the values during an OGTT at 120 min. Both serum triglyceride and cholesterol concentrations were reduced (p less than 0.01) by the changes diet, the most marked reduction being found in the VLDL fraction. HDL levels increased by 21% (p less than 0.01). Enzyme activities in gastrocnemius muscle specimens were subnormal and uninfluenced by changed dietary habits. The number of capillaries per fiber was normal throughout, but as muscle fiber size was reduced in relation to the decreased body weight, the number of capillaries/mm2 increased during the dieting period. It is suggested that the observed improvement in insulin sensitivity and glucose tolerance after a dietary period with weight reduction is related to and partly explained by shorter diffusing distances in weight-bearing muscles.

Ultrastructure of the microvessels in skeletal muscle in a case of systemic capillary leak syndrome

The microvessels of skeletal muscle were examined electron microscopically in a case of systemic capillary leak syndrome (SCLS). One biopsy was taken in a free interval of the disease and one about 6 hours after the onset of an attack with hypovolemia. The microvascular endothelium exhibited a large number of multivesicular bodies, especially in the specimen obtained during an attack. Possibly this indicates a high heterophagic activity of the endothelium. A blebbing of the luminal surface of arteriolar endothelium was observed in the attack specimen. Since a complement activation seemed to occur during attacks, the blebbing is tentatively interpreted as a sign of a complement-mediated injury to the endothelium, leading to a breakdown of the endothelial barrier. This mechanism might explain the dramatic increase of microvascular permeability to plasma proteins during an attack of SCLS. The findings did not indicate that the increase might depend on some disturbance of the transendothelial vesicular transport function, nor could any openings of endothelial junctions, as in inflammation, be demonstrated. Regionally the periendothelial basal lamina appeared thickened, a finding which seems common in angiopathies of different kinds.

[Dynamics organ blood flow in rats in postnatal ontogenesis]

In the 4-, 13-, 30-, and 65- 90-day-old Wistar rats the voluminous blood flow rate was measured in liver, kidney, small intestine wall, and in the predominantly white gracilis muscle of femur. A LAKK-01 laser-Doppler flowmeter and its cutaneous (for kidney) and needle (for other organs) probes were used; they provided estimation of blood flow (per organ mass unit) to the tissue depth of about 1 mm. It has been found that the blood flow rates (per organ mass unit fall in liver, intestine, and even more in muscle, whereas increase in kidney, particularly for the first month of life. Calculations show that in adult rats as compared with the 4-day-old pups (with their mass exceeding 22 times) the blood flow to muscle, liver, intestine, and kidney should rise 14, 17, 18 and 43 times, respectively.

The respiratory responses to the combined activation of the muscle metaboreflex and the ventilatory chemoreflex

The excessive hyperventilation seen during exercise in chronic heart failure (CHF) contributes to the limited exercise capacity in this condition. The hyperactivation of reflexes originating, independently, from muscle (ergoreflex) and from chemoreceptors (chemoreflex) has been suggested to play an important part in the mediation of the CHF ventilatory abnormalities. In this study we aimed to assess the ventilatory responses to the combined activation of the muscle ergoreflex and the ventilatory chemoreflex, achieved by post-exercise circulatory occlusion (PECO) and euoxic hypercapnia (end-tidal PCO(2) = 7 mmHg above normal), respectively.Three healthy women and three healthy men (29.33 +/- 1.28 yrs; mean +/- SD) undertook four trials, in random order, separated from each other by 30 min of rest: 2 min of isometric handgrip exercise followed by 2 min of PECO with hypercapnia, 2 min of isometric handgrip exercise followed by 2 min of PECO while breathing room air, 4 min of rest with hypercapnia and 4 min of rest while breathing room air.Ventilation (V(E)) was significantly elevated by the ventilatory chemoreflex and it was further elevated by 5.13+/-0.83 L/min (P<0.05) when the muscle ergoreflex was superimposed upon it. The response to the combination of these stimuli was significantly greater than the sum of the responses to the two stimuli when given independently (P<0.05).The results indicate that the interaction between the two reflexes has an additional stimulatory effect on ventilation and consequently could be involved in the limited exercise capacity in CHF.

Interferon-gamma limits Th1 lymphocyte adhesion to inflamed endothelium: a nitric oxide regulatory feedback mechanism

CD4(+) T helper (Th1 and Th2) cell localization to a site of inflammation is important for the development, maintenance and regulation of an immune response. The factors that regulate Th1 and Th2 cell recruitment into tissue are not fully understood. The aim of the present study was to examine the effect of different cytokine microenvironments on the recruitment of Th1 and Th2 lymphocytes into tissue. Fluorescently labelled Th1 or Th2 lymphocyte-endothelial interactions were observed via intravital microscopy of the cytokine-treated cremaster muscle. Our results show that TNF-alpha alone is sufficient to maximally recruit Th1 cells. Surprisingly, treatment with TNF-alpha + IFN-gamma significantly decreased Th1 adhesion and emigration in comparison to TNF-alpha treatment alone. The decreased adhesion of Th1 cells in response to TNF-alpha + IFN-gamma reflected a decreased ability to bind to ICAM-1 and was iNOS-dependent. This phenomenon was not observed with Th2 cells. These results suggest that IFN-gamma may play a key immunomodulatory role in the recruitment of different T lymphocyte subsets. Indeed, blockade of IFN-gamma or iNOS function during the Th1-mediated contact hypersensitivity response resulted in an acceleration and exacerbation of the late-phase inflammatory response.