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Biomedical subjects

R S Reneman

Publications and source records attributed to R S Reneman.

At least 235 records · Page 13Linked to original sources
PubMed1988

Effective diameter as a determinant of local vascular resistance in presence of vasomotion.

The mean resistance of arterioles exhibiting rhythmic changes in diameter (vasomotion) depends on the mean vascular diameter and the amplitude and shape of the vasomotion pattern. The effective diameter, defined as the diameter of a tube with constant diameter and the same vascular resistance as the vessel showing vasomotion, was calculated using Poiseuille's law. The effective diameter was used to compare the results of model calculations of square wave, sinusoidal, and triangular vasomotion patterns with those obtained from rabbit tenuissimus muscle arterioles. Due to the variability of the actual vasomotion waveforms, approximation of the effective diameter using the mean diameter, the relative vasomotion amplitude, and an assumed waveform led to erroneous results. Therefore, effective diameter should be calculated directly from the actual arteriolar diameter tracings to take into account all irregularities in the vasomotion pattern.

Animals↗
PubMed1988

The alpha-adrenergic receptor blocking effect of ketanserin and the interaction between alpha-adrenergic and S2-serotonergic receptor blockade.

The alpha 1-adrenergic receptor blocking effect of ketanserin, the blocking properties of this compound for nonspecific stimulation with angiotensin II, and the alpha-adrenergic receptor blocking properties and the blood pressure lowering effect of phentolamine, ritanserin, and the combination of both compounds were studied in patients on cardiopulmonary bypass (constant flow rate, mild hypothermia) undergoing coronary artery bypass grafting. Phenylephrine was used as alpha 1-adrenergic agonist. Ketanserin reduces the alpha 1-agonistic effect of phenylephrine on blood pressure in a dose-dependent manner up to a dose of 10 mg. Ketanserin did not block the nonspecific vasoconstriction, as induced by angiotensin II. The moderate blood pressure lowering effect of phentolamine was substantially potentiated by ritanserin, which in itself did not affect blood pressure. The findings in this study indicate that the blood pressure lowering activity of ketanserin results from a combined blockade of alpha 1-adrenergic and S2-serotonergic receptors.

Adrenergic alpha-Antagonists↗
PubMed1987

Accumulation of lipids and lipid-intermediates in the heart during ischaemia.

The content of non-esterified fatty acids (NEFA) and their CoA and carnitine esters is low in normoxic cardiac tissue. The majority of fatty acids is esterified in the triacylglycerol and phosphoglyceride pool. During myocardial ischaemia beta-oxidation of fatty acids is inhibited. In addition, turnover of the esterified fatty acid pools is most likely disturbed. Accumulation of hydroxy fatty acids, acylCoA and acylcarnitine rapidly occurs after the onset of ischaemia. The accumulation of NEFA is a slower process. In addition to extracellular sources, NEFA originate also from intracellular lipid pools, most likely from phosphoglycerides. Although it has been suggested that activation of phospholipase A2 occurs in ischaemic tissue, the mechanism underlying the enhanced degradation of phosphoglycerides ist still incompletely understood.

Acyl Coenzyme A↗
PubMed1987

Influence of intracellular Ca2+-overload in eicosanoid synthesis of the myocardium.

Intracellular Ca2+-overload in the myocardium can be induced not only after readmission of Ca2+-containing fluid to rat hearts previously perfused with a Ca2+-free buffer, a phenomenon called "the calcium paradox", but also during administration of a Ca2+-ionophore to cardiac tissue. In rat hearts, the myocardial damage induced by the Ca2+ paradox was more pronounced than that after administration of the Ca2+-ionophore A23187, as indicated by the amount of lactate dehydrogenase released. The accumulation of NEFA, and especially arachidonic acid, was greater during the Ca2+ paradox than after the administration of the Ca2+-ionophore. Administration of the Ca2+-ionophore resulted in a considerable release of 6-keto-F1 alpha (the stable breakdown product of prostacylclin), and LTD4 and LTE4 (breakdown products of LTC4). In contrast, the formation of eicosanoids was absent during the Ca2+ paradox. It is concluded that the relation between Ca2+-overload and accumulation of arachidonic acid is ambiguous and that there is no close relation between the amount of arachidonic acid accumulated and the formation of eicosanoids in Ca2+-overloaded tissue. The absence of eicosanoid formation during the Ca2+ paradox might be explained by compartmentation of the arachidonic acid accumulation and its converting enzymes or impairment of the enzymatic machinery required for eicosanoid synthesis.

Animals↗
PubMed1987

A numerical and experimental analysis of the flow field in a two-dimensional model of the human carotid artery bifurcation.

Axial velocities were measured in an enlarged, two-dimensional, rigid model of the carotid artery bifurcation by means of a laser-Doppler anemometer, under both steady and unsteady flow conditions. Also a numerical model was developed, based on the finite element approximation of the Navier-Stokes and continuity equations. From this study it appeared that the numerically predicted velocities agree well with the experimentally obtained values. Besides, the bifurcation hardly influenced the upstream flow in the main branch (common carotid artery), high velocity gradients were observed at the divider walls of the daughter branches (internal and external carotid arteries) and large zones with reversed flow were present near the nondivider walls of these branches. For steady flow the maximal diameter of this zone at the entrance of the internal carotid artery (carotid sinus) was about 25% of the local diameter of this branch. For unsteady flow this zone was absent during the initial phase of flow acceleration and maximal at the end of flow deceleration with a maximal diameter of about 50% of the local diameter of the carotid sinus.

Carotid Arteries↗
PubMed1987

Arteriolar vasomotion and arterial pressure reduction in rabbit tenuissimus muscle.

Spontaneous arteriolar vasomotion and its relation to arterial pressure reduction was studied in the rabbit tenuissimus muscle using intravital microscopy. Vasomotion was observed in all transverse arterioles and their first-order side branches. Vasomotion frequency ranged from 5 to 32 cycles per minute (median: 25 cpm). The relative vasomotion amplitude in transverse arterioles varied from 0.06 to 0.44 (median: 0.22). Vasomotion was generally of the on-off type in first-order side branches. A gradual reduction in arterial pressure as achieved by aortic occlusion resulted in an abrupt disappearance of vasomotion. Vasomotion disappeared between 19 and 59 mm Hg (median: 30.4 mm Hg). No differences were found between the pressures at which vasomotion ceased in transverse arterioles and first-order side branches. With a further reduction of arterial pressure transverse arterioles attained a maximal diameter of 98-265% (median: 119%) of the maximal diameter during vasomotion. After release of occlusion vasomotion reappeared much earlier in the first-order side branches than in their feeding transverse arterioles. It is concluded that although vasomotion influences capillary perfusion, it does not play a major role in the adaptation of vascular resistance following a reduction in arterial pressure.

Animals↗
PubMed1987

Pressure regulation in muscle of unanesthetized bats.

In unanesthetized bats direct microvascular pressure measurements were made in the tensor plagiopatagii muscle without surgical intervention. Pressure recordings showed great variability due to vasomotion and other physiological stimuli, but were in the same order of magnitude as described in muscle of other species in the anesthetized state. A substantial part of the pressure gradient is dissipated at the level of the small arterioles. Arterial pressure was changed by depressurizing a box containing the body of the bat, while the muscle was under atmospheric condition. In all larger arterioles and in 12 of 19 smaller arterioles a linear relation existed between microvascular pressure and box pressure. Of 19 small arterioles, 7 exhibited a clear biphasic regulatory response to a decrease in arterial pressure. The data are discussed in relation to different models of regulation.

Anesthesia↗
PubMed1987

Does capillary recruitment exist in young rabbit skeletal muscle?

Recruitment of terminal arterioles and capillaries was studied in the tenuissimus muscle of 16 young urethane anesthetized rabbits. In one set of experiments (8 animals) intravital fluorescence microscopy was used to visualize transverse arterioles and to assess the number of their first order side branches (functionally the terminal arterioles) perfused with red blood cells before and after vasodilation (10(-4)M adenosine, applied topically). In another set of experiments (8 animals) the number of muscle capillaries perfused with red blood cells from the same parent arteriole was determined at rest and during vasodilation (reactive hyperemia), using bright field microscopy. All capillaries and first order side branches that were perfused during vasodilation were also perfused at rest. These findings indicate that in this skeletal muscle preparation no recruitment of arterioles or capillaries occurs in an anatomical sense of the word.

Animals↗
PubMed1987

A versatile incident illuminator for intravital microscopy.

A simple incident illuminator (epiilluminator) for intravital microscopy using a mirror with 50% reflectance and 50% transmittance, placed at 45 degrees to the optical axis of the microscope, in combination with a polarizer and analyzer is described. Such a system can easily be mounted in a Ploemopak incident illuminator as used for fluorescence microscopy. Images of the red blood cells contained in the microvessels appear as dark on a light background. With the use of the system, microscopic images of good quality could be obtained from human skin capillaries, and skin, pial and intestinal microvessels in rats. In muscle, however, only the superficial capillaries could be adequately visualized.

Capillaries↗
PubMed1987

A model for chronic study of vascular morphology and reactivity of physically intact rat skin microcirculation.

A non-invasive, non-traumatic model has been developed for long term study of the vascular anatomy, blood cell velocity and vascular reactivity of the cutaneous microcirculation of the rat. In the anesthetized rat, the hairless area of a toe close to the nail could be visualized by intravital video microscopy without manipulation of the skin. Good image quality of the vascular bed was obtained with the use of an incident illuminator equipped with a 50% mirror at 45 degrees to the optical axis and a polarizer-analyzer system in combination with a mercury lamp. This microscope system allows for visualization of the superficial vasculature of the skin, while microvessels can be repeatedly identified for several weeks. To test for vascular reactivity off-line analysis of blood cell velocity was performed in the control situation and during reactive hyperemia, using a video dual-window system and a cross-correlator. The mean control velocity in venules selected for testing of vascular reactivity was 70 micron/s. In these vessels a reproducible pattern of reactive hyperemia was seen with a mean peak velocity of 655 micron/s following arterial occlusion of 180 s. Possible applications of the model are discussed.

Animals↗
PubMed1987

Peripheral vascular effects of ketanserin and nifedipine during cardiopulmonary bypass.

Ketanserin, a selective S2-serotonergic receptor antagonist with alpha 1-adrenergic receptor-blocking properties, as well as nifedipine, a classic calcium channel blocker, is used as an antihypertensive agent during and following cardiac surgery. In a double-blind prospective study, using hypothermic cardiopulmonary bypass as a study model, ketanserin (10 mg i.v.) and nifedipine (2 mg i.v.) were evaluated with respect to their effects on the peripheral circulation. The results showed that ketanserin and nifedipine dilate the arterial side of the vasculature, but that ketanserin, unlike nifedipine, also dilates the venous capacitance vessels; nifedipine even caused a short-lasting venous vasoconstriction. Since venous tone is increased during and following cardiopulmonary bypass, antihypertensive treatment with ketanserin might be advantageous under these circumstances.

Aged↗
PubMed1987

Cessation and onset of muscle capillary flow at simultaneously reduced perfusion and transmural pressure.

The effect of simultaneously reduced perfusion and transmural pressure on muscle capillary flow was investigated in the tensor plagiopatagii muscle of unanesthetized bats. Perfusion and transmural pressure were simultaneously changed by suction applied to a sealed box containing the body of the bat, while the wing with the muscle under observation outside the box was exposed to atmospheric pressure. Flow ceased in almost all of the muscle capillaries at box pressures ranging from -46 to -96 mmHg (n = 40; median value: -66 mmHg). When flow in the muscle had ceased, flow was still present at a reduced level in capillaries on top of the muscle and in the web. No signs of obstruction to flow in the feeding or collecting vessels were found. The results are not in accordance with the phenomena causing cessation of flow as predicted by the theories of critical closure or interfacial tension. To restore flow in the muscle capillaries suction to the box had to be reduced by 14 mmHg (medium value; range 4 to 35 mmHg). The latter data conforms to the possible existence of yield stress in small vessels.

Animals↗
PubMed1987

Nomenclature of Raynaud's phenomenon: a capillary microscopic and hemorheologic study.

Hemorheologic parameters and nailfold capillaries were investigated in 72 patients with ischemic hand phenomena and 25 normal subjects. Red blood cell (RBC) aggregation and plasma viscosity were normal in all groups except in patients with secondary Raynaud's phenomenon; in this group, these parameters were significantly increased (p less than 0.001). The capillary density in the nailfold was significantly lower in patients with secondary Raynaud's phenomenon or acrocyanosis (p less than 0.001). The capillary diameters were slightly increased in patients with primary Raynaud's phenomenon, moderately increased in patients with acrocyanosis (more than twofold), and markedly increased in patients with secondary Raynaud's phenomenon (fourfold to fivefold). Nailfold velocity, before and after cold provocation, was decreased in all patients (p less than 0.001). The findings in this study support the conclusion that patients with primary and secondary Raynaud's phenomenon, acrocyanosis, or asphyxia digitorum can be distinguished by combining hemorheologic observations with morphologic and functional microscopic investigations of the nailfold capillaries. The nomenclature currently employed in our clinic can be used to define these different phenomena.

Adult↗
PubMed1986

The effect of diltiazem on myocardial recovery after regional ischemia in dogs.

The effect of diltiazem on post-ischemic metabolic and functional recovery was investigated in regionally ischemic dog hearts. The duration of ischemia was 60 min, followed by 60 min of reperfusion. Diltiazem (bolus injection of 0.1 mg X kg-1 body weight prior to ischemia, followed by a continuous infusion of 0.1 mg X kg-1 X h-1) had no effect on residual coronary flow in the centre of the ischemic area, but blunted the reactive hyperemia response after restoration of flow. The drug partially prevented the depletion of ATP and glycogen in the severely underperfused subendocardial layers, i.e. when residual flow was below 0.1 ml X min-1 X g-1. Reduction of the content of these substances in the subepicardial layers was moderate and not influenced by diltiazem. Segment shortening in the subepicardial layers disappeared whereas segment lengthening was observed in the subendocardial layers during the ischemic period. Diltiazem did not prevent the loss of contractile function. Despite an initial restoration of contractile function within 10 min after reperfusion, no significant beneficial effect of diltiazem treatment on mechanical function of the reperfused area was present thereafter.

Adenosine Triphosphate↗
PubMed1986

Methods to measure blood flow velocity of red blood cells in vivo at the microscopic level.

Several methods to measure red blood cell velocity in microvessels by electronic means are discussed. Signals are generated by the red blood cells present in the microscopic image of the microvessels. These signals can be converted to obtain an output signal proportional to the actual red blood cell velocity. The method of spatial filtering by interlacing gratings is discussed in terms of a filter with an input signal. Adaptation of optical factors that might improve the velocity measurement is obtained by a mathematical analysis. Different methods of correlation are presented. The temporal correlation (dual slit and video window) and spatial correlation methods are discussed in relation to factors influencing the quality of the correlogram, the peak of which is proportional to red blood cell velocity. The conversion of red blood cell velocity to volume flow is put in perspective.

Animals↗
PubMed1986

A microcomputer system for haemodynamic measurements in isolated, working rat hearts.

This study describes the application of an Apple IIe microcomputer in combination with a pre-processor in the on-line calculation of haemodynamic variables of the isolated working rat heart and of relative rapid changes in these variables, induced by variations in left atrial filling pressure (preload) and end-diastolic aortic pressure (afterload). Variables such as heart rate, systolic and diastolic left ventricular pressure, the maximal positive and negative first derivative of the left ventricular pressure, systolic and diastolic aortic pressure and aortic flow were continuously calculated and printed at minimal intervals of 6 s. A newly designed procedure to detect the activation of the electrogram, which was necessary to start the detection of a new cardiac cycle, is described.

Animals↗
PubMed1986

Mapping of epicardial deformation using a video processing technique.

A method has been developed to measure deformation of the canine epicardium during the cardiac cycle simultaneously in a number (eight) of small regions (1 X 1 cm2). Approximately 50 white markers (diameter 1.5 mm) are attached to the epicardium and their motion is recorded on tape by a video camera. Marker positions are detected by computer processing of the digitized images. In each region the three deformation parameters are calculated from the displacements of all markers in that region by means of a least-squares criterium. In the experimental situation in the center of the area of the epicardium analyzed the accuracy of measuring circumferential strain, base-to-apex strain and shear is +/- 0.005, +/- 0.005 and +/- 0.002 rad, respectively. The method has been applied in an experiment in which local ischemia of the left ventricular wall was induced by occluding the anterior descending branch of the left coronary artery. Healthy and ischemic regions could clearly be distinguished by the differences in deformation.

Animals↗