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Biomedical subjects

B W Zweifach

Publications and source records attributed to B W Zweifach.

At least 55 records · Page 3Linked to original sources
PubMed1984

New morphological evidence for a mechanism of lymph formation in skeletal muscle.

A new mechanism of lymph formation associated with pulsation and vasomotion of arterioles is proposed in skeletal muscle. To provide evidence for this proposal, an investigation of the lymphatic vessels in the spinotrapezius muscle of the rat was undertaken. The lymphatics were visualized by microinjection of a contrast medium (Evans blue albumin), and histological sections of the muscle were prepared and examined with the light and the electron microscope. The studies indicated that lymphatics ranging in size from 20 to 200 micron in this skeletal muscle have no smooth muscle but only a thin lining of endothelium. All lymphatics lie in immediate proximity to the arcading and transverse arterioles and occasional muscular venules, and appeared to be wrapped around them. It was further observed that when the arterioles were dilated, the contiguous lymphatics were partially or completely collapsed, whereas lymphatics around contracted arterioles were wide open. No significant deformation of the adjacent skeletal muscle cells was observed. These results suggest that the contraction of vascular smooth muscle, as well as pulsatile elastic distension of arterioles, may cause periodic changes in lymphatic volume and thereby serve as peristaltic mechanisms for lymph transport. Vascular smooth muscle may thus influence not only blood flow in the microcirculation, but also water transport in the interstitium and into the lymphatics.

Animals↗
PubMed1983

The application of an improved dual-slit photometric analyzer for volumetric flow rate measurements in microvessels.

The dual-window photometric analyzer is currently a widely used instrument to estimate volumetric flow rates in microvessels. This instrument provides an analog voltage that is proportional to cell velocity, but the question arises how this voltage is related to the mean velocity in the blood vessel. It requires a separate investigation and in this report a calibration of an improved version of a dual-window photometric analyzer for volumetric flow rate measurements in microvessels as large as 470 microns in diameter is presented. The relationship between correlator velocity and blood mean velocity is presented in a closed empirical form. Within a 5% error of the mean it is found to be dependent on tube diameter but independent of hematocrit (between 3 and 40%). A rotating transparent disc plated with dried red blood cells was used to test the dynamic response of the instrument for frequencies up to 10 Hz. The amplitude reduction was less than 10% up to 3 Hz. Thereafter it fell off at 6 db/octave.

Animals↗
PubMed1981

Anesthesia and microvascular dynamics in spontaneously hypertensive rats.

Studies on pressure dynamics in rats under local anesthesia were carried out to provide background information for subsequent intravital analysis of microvascular behavior in a skeletal muscle. An alpha-chloralose-urethan mixture (1:13.3%) was selected as the general anesthesia having the least effect on systemic pressures in spontaneous hypertensive (SHR) as well as normotensive (WKY), Sprague-Dawley and Wistar-Kyoto rats. Anesthetic agents, in general, lower systemic blood pressure in SHR by 30--50 mmHg and thereby distort microcirculatory flow and blood vessel-diameter relationships. Insertion of a plastic catheter into the trachea of the anesthetized rat, to maintain an open airway, had a complex effect on heart rate and systemic blood pressure and left the pressure in an unstable state. Severity of the change depended on the age of the rat and the anesthetic agent; hypertensive animals were especially vulnerable.

Age Factors↗
PubMed1978

Endoneurial pressure in hexachlorophene neuropathy.

Increased endoneurial pressure of up to 17.0 cm H2O was recorded in the peripheral nerves of rats fed hexachlorophene in their laboratory diet. The pressure was measured using a micropressure transducer developed for recording pressure in the microcirculation. The results were correlated with morphologic findings. Teased nerve fibers and araldite-embedded specimens of hexachlorophene damaged sciatic nerve revealed the characteristic severe intramyelinic edema due to splits in the minor dense lines of compact myelin giving rise to wide interlamellar spaces as shown in previous studies. The endoneurial pressure of rats exposed to hexachlorophene for 11 days and subsequently fed a normal diet returned to normal (0.2-3.0 cm H2O) after 12 days, and morphologic examination showed few residual abnormalities. Prolonged exposure to hexachlorophene for up to 4 weeks caused widespread axonal degeneration in addition to intramyelinic edema. Animals treated with hexachlorophene for 21 days followed by a normal diet for 14 days showed degenerated axons, phagocytosis of myelin as well as interstitial edema and elevated endoneurial pressure. It is suggested that axonal degeneration in hexachlorophene neuropathy is caused by increased endoneurial pressure.

Animals↗
PubMed1978

The distribution of blood rheological parameters in the microvasculature of cat mesentery.

In vivo studies of the rheological behavior of blood in the microcirculation were conducted by direct in situ measurements in cat mesentery. Upstream to downstream pressure drops were measured in unbranched arterioles, capillaries, and venules, with diameters from 7 to 58 micrometer. Simultaneous measurements of red cell velocity and vessel geometry facilitated computation of bulk velocity, pressure gradient, apparent viscosity, wall shear stress, and resistance. Arteriovenous distributions of these parameters revealed the following. Maximum pressure gradient (0.015 cm H20/micrometer) occurs in the true capillaries (7 micrometer in diameter); intravascular wall shear stress averaged 47.1 dynes/cm2 in arterioles and 29.0 dynes/cm2 in venules. Extreme values as great as 200 dynes/cm2 were observed in a few shunting arterioles. Apparent viscosity averaged 3.59 cP in arterioles, 5.15 cP in venules, and 4.22 cP overall. Intravascular resistance per unit length of microvessel varied with luminal diameter as a power law function with exponents of -4.04 for arterioles, -3.94 for venules, and -3.99 for all vessels combined. This apparent maintenance of Poiseuille's law is attributed to the opposing processes of hematocrit reduction and decreasing shear rate as blood is dispersed in successive arteriolar segments, and the converse action of these processes in the venous confluences which lessen the extent of network variations in apparent viscosity. Reductions in bulk velocity from the normal flow state to below 0.5 mm/sec resulted in increases in apparent viscosity by a factor of 2 to 10, which are attributed primarily to obstruction of the lumen by leukocyte-endothelium adhesion.

Animals↗
PubMed1977

Contractile stimuli in collecting lymph vessels.

Contractility was investigated in collecting lymph vessels of rat and guinea pig mesentery. Lymphatic diameter and micropressure were simultaneously recorded under normal conditions and during micromanipulation of intralymphatic pressure. Spontaneous activity involved characteristic changes in intralymphatic pressure coincident with opening and closure of upstream and downstream valves. Contractions were irregular but still predictable by noting the trend of intraluminal pressure as it approached a threshold level. Mechanical obstruction upstream of lymph vessels reduced lymph pressure and contraction frequency. Microinjection or withdrawal of fluid caused contraction frequency. Microinjection or withdrawal of fluid caused contraction frequency to rise and fall, respectively. Contraction rate was not affected by the level of general anesthesia. Lymphatic wall tension, as calculated from pressure-radius variables, correlated well with contraction frequency, suggesting a myogenic origin for the contractile mechanism. However, lymphatic smooth muscle may be inherently unstable since some contractility persists despite an absence of pressure stimuli.

Animals↗
PubMed1977

A method for determining segmental resistances in the microcirculation from pressure-flow measurements.

On the basis of an electrical analog, open circuit impedance functions were used to analyze the microcirculation. No specific structure need be assumed except a two-port, two-terminal network in which the major artery and vein supplying the tissue represent the input port and the two ends of the microvessel under study are the output port. The open circuit measurements were made by occluding microvessels in the exteriorized omentum of anesthetized rabbits. The pressure upstream and downstream to the occlusion defines the source pressure of a Thévenin's equivalent circuit. The equivalent resistance value was calculated by plotting the flow through a given microvessel against the pressure developed during a gradual occlusion. The changes in pressure vs. the changes in flow during a progressive occlusion were found to be linearly related. The Thévenin's equivalent resistance was maximum downstream to an occluded artery and upstream to the occluded vein. Within the capillary network, source pressures consistently were within a narrow range. Topically applied norepinephrine resulted in marked changes in source resistance and no changes in source pressures. Threshold doses of norepinephrine given intravenously resulted in changes in source pressures, but minimal changes in source resistance, even though a substantial change in vascular resistance was indicated when calculated on the basis of arterial pressure minus micropressure divided by microvessel flow. The present method defines the functional characteristics of the distributing vessels in terms of two pressures and two equivalent resistances and is relatively easy to perform. The technique can be used to determine the vascular components involved in the response to particular stimuli.

Administration, Topical↗
PubMed1977

Quantitative studies of microcirculatory structure and function. III. Microvascular hemodynamics of cat mesentery and rabbit omentum.

We made simultaneous measurements of intravascular pressure and red blood cell velocity for vessels which make up the modular configuration of microvascular networks in mesentery and omentum. An analysis of these variables and the computed volumetric flow rates is presented for arterioles which had a maximum diameter of 56 micrometer through the "true capillaries" (typically 7 micrometer for mesentery and 8 micrometer for omentum) to 56-micrometer venules. The spatial variance of pressure and flow is related to topographical features of each network. Vascularization statistics for each network are presented and demonstrate a unique ratio of potential microvascular exchange area to module planar area, with values of 0.71 +/- 0.22 (SD) for omentum and 0.19 "/- 0.03 (SD) for mesentery. Analysis of the volumetric flow rate for each module demonstrates a linear relationship to the planar area of tissue serviced by each modular network. In situ perfusion rates of 1180 ml/min per 100 g and 105 ml/min per 100 g were determined for omentum and mesentery, respectively. The hemodynamic resistance of the omental and mesenteric circuitry was evaluated, and in the case of the omentum, found to be inversely proportional to the planar area of the module. The arterial to venous distribution of pressure and flow for the mosaic of contiguous modules in omentum and mesentery is described and related to the deployment of parallel and serial microvessels of each network.

Animals↗