Concentration Profiles for Gas Diffusion in Skeletal Muscle in vitro and in vivo

Heat-washout: a new method for measuring cutaneous blood flow rate in areas with and without arteriovenous anastomoses

A new method, the heat-washout method, for measuring total cutaneous blood flow rate is introduced. The measurements were performed with a transcutaneous (tc) PO2-electrode that is capable of heating and measuring local temperature, and it is constructed with a thermostatically controlled cap. The probe was heated electrically to a selected temperature 2-10 degrees above normal skin temperature. When the temperature was stable, the heating element was turned off, and the temperature was registered every 10 s until a stable baseline temperature, Tb, was obtained. Tb was subtracted from the registered temperatures giving deltaTs that were plotted in a semilogarithmic diagram. The heat-washout was monoexponential, and the slope was used for calculating blood flow rate in accordance with the principle of Kety, using a known partition coefficient. The method was applied to the forearm in two subjects, and the results were compared to blood flow rates obtained simultaneously by the 133Xe-washout method in the same area. The equation of the regression line was y = 2.5 + 0 x 968X and the correlation coefficient was 0 x 986 at temperature levels of 37-45 degrees C. In the pulp of the thumb, blood flow rates, in arteriovenous anastomoses, were estimated in two subjects by subtracting the capillary blood flow rate, measured by 133Xe-washout, from the total cutaneous blood flow rate, measured by heat-washout. Due to a relatively low diffusions coefficient for 133Xe compared to heat, 133Xe cannot be used for measurement of blood flow rate in arteriovenous anastomoses.

Mucosal/submucosal blood flow in the small intestine in pigs determined by local washout of 133Xe and microsphere techniques

In 11 anaesthetized pigs a laparotomy was performed and the mucosal and submucosal blood flow rate in the small intestine of the pig was determined by a local application of 133Xe and by 6.5-microns radioactive microspheres. The 133Xe washout plotted in a semilogarithmic diagram showed a multiexponential configuration. As localization studies of 133Xe in the intestinal mucosa showed a constant high concentration of 133Xe in the luminal part of the mucosa due to shunting by diffusion, the initial slope of the 133Xe washout was used for blood flow determination in the mucosa/submucosa. There was a good relationship between blood flow determined by the two techniques. The correlation coefficient, R, between the two techniques was 0.89.

Distribution of coronary blood flow across the canine left ventricular free wall during reactive hyperemia

In a group of open-chest anesthetized dogs, reactive hyperemia (RH) in epi- and endocardial layers of the myocardium was quantitated by measurements of cumulative excess blood flow (CEBF) In the hyperemic period following occlusions of the left anterior descending coronary artery (LAD) for 10 to 120 s. Blood flow measurements were obtained by means of the local X3-133 washout technique. When ischemia was extended from 10 to 45 s, CEBF increased significantly and uniformly in both layers; with further extension of the ischemia to 60, 90 and 120 s, the increment in CEBF was significantly greater in the endocardial than in the epicardial layer (29, 57 and 64% greater, respectively). In accordance with the concept that CEBF is mainly controlled by metabolic factors, this result supports the hypothesis that the capacity for formation of vasodilatory "metabolites" is greater in the subendocardial tissue. Left ventricular wall was homogeneously perfused in the pre-occlusive period and during maximal vasodilation of the coronary bed. In another group of dogs, maximal vasodilation and abolishment of local autoregulation was ascertained by 30 s of occlusion of LAD. When diastole in the post-occlusion period was shortened by 33%, i.e. from about 37.5 s. min-1 to about 25.5s.min-1 by artificial pacing at 250 min-1, endocardial maximum blood flow amounted to only 43% of that of the corresponding epicardial region, which apparently was not affected by the increased heart rate.

Diffusion bypass of xenon in brain circulation

The diffusion bypass of 133 Xe between arteries and veins was studied in the brains of anesthetized dogs. A mixture of 51 Cr-labeled red cells and 133 Xe was injected as a bolus into the internal carotid artery. Gas-tight venous samples were taken every 0.4-0.8 seconds from the superior sagittal sinus. An excess of 133 Xe in the early venous blood samples over that expected from blood-tissue equilibration considerations was demonstrated in all the experiments. The excess was most marked in the first samples, and it was enhanced by lowering cerebral blood flow by decreasing the cerebral perfusion pressure to 20-30 mm Hg. We concluded that diffusion bypass of the tissue by 133 Xe is the most likely explanation for these experimental findings. The fraction of the bolus which appeared to bypass the tissue amounted to about 2-3% at the normal perfusion pressure (i.e., normal blood flow) and about 10% at a reduced cerebral perfusion pressure of 20-30 mm Hg (i.e., about half of normal blood flow). We concluded that measurement of cerebral blood flow by a bolus injection of 133 Xe in the internal carotid artery and external detection of the washout is not influenced significantly by the diffusion bypass of 133 Xe in the normal flow range.