Mary P. Wiedeman

Dimensions of Blood Vessels from Distributing Artery to Collecting Vein

Measurements of lengths, diameters, and numbers of post-capillary vessels were made in the bats wing. The cross-sectional area and capacity in the various portions of the vascular bed were calculated. The greatest total cross-sectional area in the entire vascular bed was found in the venules, a result not in agreement with similar reports made by others using measurements from vessels in fixed preparations. This discrepancy probably results from disagreement regarding the diameter of capillary vessels. Calculations to determine the per cent of total volume in each portion of the vascular bed showed that the venous system accounts for as much as 80% of the total vascular volume.

Blood Flow through Terminal Arterial Vessels after Denervation of the Bat Wing

Previous studies of microcirculation in the denervated wing of the unanesthetized bat showed that major arterial vessels increased markedly in diameter and lost their ability to contract spontaneously. Arteriolar vessels did not show such an increase in diameter, and furthermore their spontaneous contractile activity increased. These observations led to the idea that regulation of blood flow and blood pressure might be continued to some degree in the absence of central nervous control through enhanced activity of arteriolar vessels which just precede the capillary nets. Therefore a thorough study by direct microscopic observation of the behavior of arterial vessels in the following surgical and pharmacological denervation was made. The data support the hypothesis that loss of tone and loss of contractile activity in the large arterial vessels following denervation produce an increase of tone and activity in the smaller, more distally located vessels, thereby causing a redistribution of the site of regulation of flow through capillary nets. The largest arterial vessels showed and increase in average diameter of 38% after surgical denervation, while the terminal arterioles showed a decrease in average diameter of 24%. Neither phenoxybenzamine (Dibenzyline) norpentolinium (Ansolysen) were as effective as surgical denervation in producing relaxation of the large arterial vessels. Neither drug inhibited spontaneous contractile activity of the terminal vessels.

Defining the precapillary sphincter

Abstract Past and present use and abuse of the term precapillary sphincter is reviewed. The advantages of a uniform and functional definition are described, and a definition that is consistent with current information is proposed.

Leukocyte adherence in arterioles following extravascular tissue trauma

Abstract To study the effect of tissue injury on leukocyte adherence in arterial microvessels, small regions of tissue adjacent to vessels in the wing of the bat were exposed to single doses of laser irradiation. The experimental design provided data on the effect of (1) tissue injury of variable extent but a fixed distance from the arterial vessel and (2) tissue injury of a constant extent but at varying distances from the arterial microvessels. Preirradiation controls showed that normally no leukocytes could be observed either adherent to, or rolling along, the vessel wall. Following injury and after a quite variable latency time there was a time-dependent increase in the number of observed leukocytes. Using the latency time as an index, an analysis was applied to test the hypothesis that the laser irradiation released some substance which subsequently diffused to the vessel wall. The results of this analysis have shown that all the experimental latency time data can be explained on the basis of a model in which a diffusable “leukotactic” substance is released from the laser site in an amount that is proportional to the surface area of induced injury. Though the precise nature of the released substance is speculative, analysis shows that the process is characterized by an effective diffusion coefficient of approximately 7.0 × 10 −7 which is suggestive of highmolecular-weight substance.

Effect of Venous Flow on Frequency of Venous Vasomotion in the Bat Wing

Investigations indicated that an elevation in venous flow caused an increase in the frequency of rhythmic contractions of the small veins in the bat wing.

Lengths and Diameters of Peripheral Arterial Vessels in the Living Animal

Measurements of the length, diameter, and number of branches of arterial vessels were made from a distributing artery to the capillaries in a living bat. From the values so obtained, cross-sectional areas in various portions of the arterial bed were calculated. An almost linear decrease in the diameters of successively smaller vessels was found. There was also a linear relationship in the calculated total cross-sectional areas formed by the various vessels. The results are not in agreement with similar reports made by others using measurements from vessels in a fixed preparation.

The effects of cooling on the microvasculature after thermal injury

Abstract The application of cold water to allay pain and reduce edema in burned skin is known to be effective. Evidence suggests that the immediate application of cold water to a burned area reduces spreading of injury and subsequent necrosis. Several mechanisms have been suggested as the primary reason for the inflammatory response that appears after thermal injury, one of these being a damaged circulation. The purpose of this study was to see if cold water protected the circulation and if it contributed in this way to reducing the effects of the burn. Microscopic observations of blood vessels in the bats wing were made following thermal injury produced by heating a 3-cm diameter for 30 sec at 55°. Comparisons were made of the vessels of animals subjected for 4 hr to cold water (18–20°) flowing over the burned area and untreated animals. Significant differences were found in edema formation and subsequent renewal of normal flow.

Vascular reactions to laser in vivo

Abstract Platelet aggregates form in arterial vessels following exposure of the vessels to a single pulse ruby-red laser beam. Usually, a small cluster of red blood cells occupies the center of the aggregate. It appears that endothelial damage is not required for the platelet aggregation, but that platelet activity is initiated by rupture of red blood cells, possibly through the release of ADP from the injured red cells. Also, no shape change is noted in platelets that adhere to the vessel wall or to each other.

Contractile Activity of Arterioles in the Bat Wing during Intraluminal Pressure Changes

Spontaneous contractile activity in the smooth muscle cells that invest arteriolar vessels is widely variable. Arteriolar branches originating from the same parent vessel contract independently of one another with no similarity in frequency or duration of individual contractions. Direct microscopic observations were made of these vessels in the wing of unanesthetized bats before and after surgical denervation or nerve block by procaine. A major artery of the wing was cannulated and buffered saline was perfused in retrograde fashion to produce periods of increased intra-arterial pressure. Elevation of intraluminal pressure led to enhanced contractile activity both before and after denervation of the vessels. It is concluded that these vessels respond by contraction to increased pressure and that the response is not dependent on nervous activity.

Microvascular hemodynamic variations accompanying microvessel dimensional changes.

Abstract The bat wing is used as an experimental preparation and as a self-contained vascular bed. The number, dimensions, and distribution of the vessels of the real vascular bed are included into an analyzable, representative geometric configuration. Based on theoretical analysis and experimental data, equations are developed and utilized to characterize the pressure-flow relationships for each branching order of the vascular field. The geometric configuration and associated describing equations are used to determine the effects of microvessel diameter change on the distribution of resistance, pressure, and velocity throughout the microvasculature. Predicted hemodynamic changes are compared with available experimental data and evaluated in the light of current concepts concerning the significance of microvessel dimensional changes.