Nutritive Capillaries Research Articles

Leukocyte-endothelium interaction in the microvasculature of postischemic striated muscle.

Microvascular manifestation of postischemic reperfusion injury is hallmarked by two distinct events, i.e. perfusion failure of nutritive capillaries (“no-reflow”) (Majno et al., 1967; Menger et al., 1992a), and the sequelae of “reflow-paradox”-associated mechanisms, which include accumulation of leukocytes, leukocyte-endothelium interaction and loss of endothelial integrity (Menger et al., 1992b). Both reperfusion-dependent events contribute to the aggravation of ischemia-induced parenchymal tissue injury, either through prolongation of focal ischemia (“no-reflow”),or the action of leukocyte-derived cytotoxic mediators (“reflowparadox”),such as reactive oxygen metabolites and proteolytic enzymes (Granger, 1988; Lehr et al., 1991; Menger et al., 1993a).KeywordsLeukocyte AdherenceFocal IschemiaWall Shear RateReactive Oxygen MetabolitePostcapillary VenuleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Warm retrograde cardioplegia

Hypothermia is believed to be the most important aspect of successful myocardial protection with retrograde coronary sinus cardioplegia. Because nutritive capillary flow to the right ventricle and septum is thought to be diminished with retrograde perfusion, these areas of the myocardium are considered at higher risk for intraoperative deterioration without the added protection of hypothermia. Recently we introduced warm aerobic arrest as an alternative to conventional methods of myocardial protection. We present our clinical results in 37 patients with mitral valve disease (+/- aortic valve, aortic root, or coronary artery disease) who underwent various cardiac procedures for which warm blood cardioplegic solution was delivered continuously via the coronary sinus after antegrade arrest. Thirty-five of the patients were in New York Heart Association class III or IV, and 19 patients had grade 3 or grade 4 left ventricular function. Sixteen patients had pulmonary hypertension, three with suprasystemic pressures, and marked right ventricular hypertrophy. Two patients had associated left ventricular hypertrophy. Nearly all patients returned to normal sinus rhythm shortly after removal of the aortic crossclamp, and they were easily discontinued from cardiopulmonary bypass even with crossclamp times of 3 hours. The 30-day hospital mortality rate was 2.7%. The perioperative myocardial infarction rate was 5.4%, and the prevalence of low-output syndrome was 10.8%. The results suggest that retrograde coronary sinus perfusion of blood cardioplegic solution at 37 degrees C is an effective method of myocardial protection even in patients with pulmonary hypertension at high risk for right ventricular failure. Its efficacy in this circumstance does not reside in its ability to deliver hypothermia.

Distribution pattern of capillary and venular red blood cell velocity following ischemia-reperfusion in striated muscle.

Ischemia-reperfusion induced changes in distribution pattern of RBC-velocity of nutritive capillaries and postcapillary venules was analyzed in striated muscle using intravital fluorescence microscopy in awake hamsters. Four hours of ischemia to striated muscle contained in the dorsal skinfold preparation (n = 10) revealed a significant (p < 0.01) decrease of capillary, but only a slight decrease of mean venular RBC-velocity during the entire reperfusion period. However, analysis of distribution pattern of single values revealed a shift of the histograms to the left, including pronounced skewness as mean values approached zero. This characteristic phenomenon may be due to an increase of microvascular hematocrit and/or decrease in deformability of red blood cells during ischemia-reperfusion. Beside other factors, the impairment of flow properties and flow conditions of the blood may contribute to the development of microvascular reperfusion injury.

The blood vascular architecture of the salamander external gill: a scanning electron microscopic study of corrosion casts.

The blood vascular architecture in three-paired external gills of salamander tadpoles, Hynobius dunni Tago, was demonstrated with special reference to metamorphosis by scanning electron microscopy of vascular corrosion casts. In the fully developed gill, each of the three-paired afferent branchial arteries gave off secondary afferent filament arterioles. The afferent filament arteriole drained toward the efferent filament arteriole, forming the loop at the posterior extremity of the gill filament. The branched capillaries from the afferent filament arteriole formed two plates of respiratory capillary networks with irregular honeycomb-shaped meshes. In addition, there were non-respiratory shunts as bypass of the blood circulation between the afferent and efferent branchial arteries without branching filament arterioles. Furthermore, the deep venous plexus and subepithelial capillary plexus were seen around each efferent branchial artery. The filament central venule in the central part of the filament merged into the venous plexus. Nutritive capillaries branched from efferent branchial arteries also drained toward the venous plexus. Such general vascular architecture is simpler than that of the fish. During metamorphosis, the pattern of the vascular distribution, especially filament net capillaries became irregular, and then markedly tortuous or convoluted blood vessels occurred in the absorbing gill. At the metamorphic climax, the capillary network practically disappeared in the remnant of the gill but the bypass shunt as a non-respiratory artery remained almost unchanged.

Laser Doppler flowmetry in evaluation of lower limb resting skin circulation. A study in healthy controls and atherosclerotic patients.

Laser Doppler flowmetry (LDF) was used to evaluate lower limb resting skin perfusion in sixty subjects divided into four groups: healthy young and elderly controls, and patients with intermittent claudication or critical ischaemia. Measurements were performed in pulp skin containing microvascular AV anastomoses and in the skin of leg and thigh where these shunts are absent. In toe pulp controls and claudicators had higher perfusion values than in leg and thigh skin (p less than 0.01), indicating that the LDF method evaluates flow both in nutritional capillaries, AV anastomoses and in dermal vascular plexa. Elderly controls had higher flux values in the pulp than claudicators (p less than 0.01), and claudicators had higher values than patients with critical ischaemia (p less than 0.01), showing that LDF could differentiate between the clinical groups. Study of reproducibility confirmed that values were reproducible on a given population. Day to day variation was considerable in individual subjects, probably because of changes in sympathetic vascular tone and because of different vascular architecture in the measuring volumes which are only some few mm3. The fact that LDF measures total skin blood flow explains why several papers have found a poor correlation between LDF and methods which mainly evaluate nutritional blood flow. The method is non-invasive, continuous and easy to perform. Laser Doppler flowmetry may have several clinical applications, like evaluating progress of atherosclerotic disease or therapeutic effects of drugs or operations. To increase the reproducibility of resting skin flux measurements local heating of the skin is recommended and the measurements should be performed with an integrating probe, which averages the readings obtained at several positions simultaneously.

Microcirculatory methods for evaluating the effect of vasoactive drugs in clinical practice.

Microcirculatory methods have to be used in order to be able to evaluate the effect of vasoactive drugs in ischemic skin areas. During the past two decades several new such techniques for studying the microcirculation in man have been developed. These techniques have shown to be of great value for evaluating drug effects in patients with disturbed peripheral circulation. One such method is the non-invasive Laser Doppler technique. It measures both the nutritional and the non-nutritional thermoregulatory vascular bed of the skin. The data achieved are only semiquantitative, but the method has been shown to be clinically very useful for studying the dynamics of total skin microcirculation in a specific area. In order to be able to study directly what happens in the nutritional capillaries microscopical methods have to be used. Two such techniques are available in clinical practice. By an ordinary light microscope the capillaries can be directly visualized. A specific classification system can be used to evaluate the degree of ischemic damage to an area. The effect of different kinds of therapeutic procedures for improving the microcirculation in an ischemic area can be easily evaluated. By the combination of a light microscope and a sensitive TV-camera the blood flow in single skin capillaries can be measured at a magnification of 250-1 000 times. This method is well suited for testing the immediate effects of vasoactive substances on the nutritional skin circulation both in healthy subjects and in patients with different kinds of cardiovascular diseases.

The relationship between macro- and microcirculation clinical aspects.

A large number of methods are today available for the clinical evaluation of the arterial blood supply to an extremity or part of an extremity. However, these methods are not sensitive enough for determining the nutritional status of a tissue in the extremity affected by vascular disorders. This is especially true for the skin where most of the blood is used for thermoregulation and only a small fraction goes through the nutritional capillaries. Blood may enter the subpapillary vascular network through AV-shunts and bypass the nutritional skin capillaries. Therefore microcirculatory methods has to be used in order to be able to evaluate the nutritional status of a certain skin area. One of the clinically most useful methods for this purpose is vital capillary microscopy. By classifying structural changes of the nutritional capillaries in an area susceptible to ischemia, the risk of necrosis can be evaluated. Marked discrepancies between the total circulation of the are and the nutritional status of the tissue can be seen especially in patients with peripheral vascular disorders and/or diabetes. The total circulation may be markedly reduced but necrosis does not occur until the nutritional circulation of the ischemic skin area is completely abolished for a certain period of time. On the other hand it is sometimes seen in clinical practise that ischemic skin necrosis may develop in a region with rather good macrocirculation. These findings are of utmost importance when the effect of a certain treatment should be evaluated. The effect has to be studied directly in the target organ, and that is the nutritional vascular bed of the ischemic area.

Dynamics of Skin Microcirculation in Humans

The human cutaneous microcirculation has so far been studied by rather crude methods, such as plethysmography and 133Xn clearance. New sophisticated and noninvasive techniques are now available, with which the microcirculation of the skin can be continuously studied and measured for hours. With two such methods, i.e., Laser-Doppler flowmetry and dynamic capillaroscopy, fast dynamic fluctuations of the microcirculation can be followed. Under resting conditions, the total skin flow of a small area (1-2 mm2) varies consistently with time. These variations are caused by the arterial pulse, but also by active vasomotion with a frequency of about 4-8 cycles/min. These fluctuations can also be seen in single skin capillaries, but with a somewhat faster frequency: 6-10 cycles/min. The reaction of the cutaneous microcirculation to provocation tests, such as postocclusive reactive hyperemia response and venous occlusion (50 mm Hg), can also be studied. The time to peak during postocclusive reactive hyperemia is very consistent. In response to venous congestion, capillary flow rate falls drastically, whereas Laser-Doppler flow is much less dramatically reduced. These discrepancies suggest that the Laser-Doppler flowmeter records blood flow in skin vessels in addition to the superficial, nutritional capillaries. The dynamic pattern of the skin microcirculation is altered in patients with hypertension, diabetes, and obstructive arterial disease.

Capillary blood flow: videodensitometry in the atherosclerotic patient.

Recently the noninvasive technique of videomicroscopy has demonstrated qualitative morphologic changes in the nutritional skin capillaries in atherosclerotic (ATS) patients. The purpose of this study is to quantitatively examine the ATS microcirculation and effects induced by reconstructive surgery. Capillary blood flow velocity (CBV) of single vessels within the nail fold of the large toe was measured by dual-sensor videodensitometry in 14 ATS patients (age 45 to 80 years) and 11 age-matched controls. In addition to CBV, capillary diameter (CD) and the number of flow-active capillaries (FC) were also measured at constant temperature. Of the 14 patients, eight had measurements repeated 1 week after reconstructive surgery. The measurements were obtained at rest and then periodically after a 45-second period of pedal inflow occlusion. Respective group averages at rest for CBV, CD, and FC for the 14 ATS patients were as follows: 0.16 mm/sec, 10.5 micron, and 6.8 capillaries per field. Corresponding values for the control subjects were 0.10 mm/sec, 8.7 micron, and 5.3 capillaries per field. Combining CBV, CD, and FC into a measurement of volume capillary flow yielded a value of 281 pl/sec/mm2 for the patients and only 85 pl/sec/mm2 for the controls (p less than 0.02). Peak postocclusion CBV significantly increased, whereas FC significantly decreased relative to rest in the control group; however, the only patient group that responded to occlusion-induced ischemia was the postoperative group. In these patients there was a decrease in CBV and an increase in FC relative to rest. These responses are exactly opposite to those in the age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Vital capillary microscopy for assessment of skin viability and microangiopathy in patients with diabetes mellitus.

Vital capillaroscopy is useful in clinical practice to study the nutritional skin capillaries and for evaluating the risk for skin necrosis in patients with peripheral ischemia. This method is especially valuable in the investigation of patients with diabetes mellitus (DM) in whom the arterial inflow to the foot can be almost normal despite the development of skin necrosis due to impaired nutritional circulation. When the capillary morphology in the feet of asymptomatic diabetic patients was investigated, significantly more areas with widely dilated capillaries were present both in insulin and tablet treated patients compared to controls. By using dynamic capillaroscopy the flow velocity in skin capillaries can be determined under physiological conditions. Fourteen diabetic patients were compared with matched non-diabetic controls. The capillary blood flow during resting conditions was equal in the two groups but a delay in the postocclusive reactive hyperemia response was seen in the diabetic patients. The reason for this may be a vasomotor dysfunction in the precapillary arterioles or an increased blood viscosity. Further studies using dynamic vital capillaroscopy may improve our knowledge of the complex mechanisms responsible for diabetic microangiopathy.

Distribution of flow and red cell flux in the microcirculation

The distribution of blood cells in the vascular system is not homogeneous, red cell concentration in the small vessel compartment being significantly lower than in the large vessel compartment. This is to some extent due to the difference in travelling speed between cells and plasma in the microcirculation (Fahraeus effect). However, even in the terminal vessel network haematocrit varies considerably as a result of plasma skimming phenomena. Thus, local (capillary) haematocrit is a function of flow rate distribution at bifurcations. Red cell concentration in the majority of capillaries is substantially lower than in any other vessel category, while a small number of capillaries carry an increased haematocrit, thereby satisfying mass balance. The haematocrit distribution as well as the average level of capillary haematocrit is a function of small vessel volume which in turn depends on pre-capillary resistance: vasodilation leads to increased capillary haematocrit and vice versa. Thus, one of the physiological functions of the resistance vessels is to determine the level of microvascular haematocrit. Alteration of red cell microrheology leads to a reduction of capillary O2-transport capacity mainly by reducing the haematocrit in nutritive capillaries.

Capillary Function in Connective Tissue

(1980). Capillary Function in Connective Tissue. Scandinavian Journal of Rheumatology: Vol. 9, No. 1, pp. 3-9.

Vascular organization of the catfish gill filament

Light and scanning electron microscopic observations were made on methyl-methacrylate corrosion casts of the blood vessels in the gills of channel catfish (Ictalurus punctatus). The vasculature of the gill filament can be divided into three distinct pathways: 1. the well-known respiratory circulation which includes the afferent filamental artery (AF), afferent lamellar arteriole (AL), lamella (L), efferent lamellar arteriole (EL) and efferent filamental artery (EF), 2. a nutritive pathway from the EF through small nutritive capillaries (NC) and into one of several filamental veins (FV), and 3. an interlamellar circulation in which small prelamellar arterio-venous anastomoses (PAVA) connect the AL into a series of organized vascular spaces (interlamellar vessels, ILV's) that underlie the interlamellar filamental epithelium. Several sinus like spaces associated with AF, EF and the filamental cartilagenous support were also observed. The physiological significance of these vascular pathways is discussed.

Capillary flow in hemorrhagic shock. 3. Metaraminol and capillary flow in the nonanesthetized and anesthetized pig.

Although vasopressors have been used extensively in the treatment of hypovolemic shock, convincing evidence of their clinical efficacy is lacking. Many contemporary investigators, recognizing that a deficiency in capillary blood flow is accepted as the basic pathophysiologic defect in shock,1-4have tried to determine the effect of vasopressors on small vessel flow. However, their efforts have been hindered by the lack of a method for measuring capillary flow. Unfortunately, most related work has dealt with an estimation of capillary flow based on the measurement of large vessel flow in anesthetized animals using operative methods. The hemodynamic variables introduced by anesthesia,5-9operative manipulation,7 -10and the frequently resultant hypothermia5,11and hypovolemia have been overlooked often. Furthermore, these methods fail to differentiate nutritive capillary flow from arteriovenous pathway flow. If we are to evaluate flow changes in the microcirculation, we must use direct methods which eliminate these variables.

Capillary function in connective tissue.

SummaryHigh-resolution vital microscopy of capillary function in perichondral connective tissue in rabbits call attention to a structural complex consisting of endothelial plasma layer, nuclear endothelial cell region and periendothelial granulated cell which probably serves as a local regulating mechanism for the nutritive capillary flow. The change in shape of the blood corpuscles when they pass the capillary is pointed out. The connective tissue capillaries constitute a dynamic, active component of the vascular pathway rather than rigid, passive tubes as previously believed.