Low Flow States in the Microvessels of Skeletal Muscle in Cat

With the tenuissimus muscle exposed for vital microscopy, the effects on macro‐ and micro‐circulation of aortic compression and of arterial bleeding were studied in cats anesthetized with chloralose. In the first case, arterial pressure in the hindlimbs was kept at 50 mm Hg for 2 ½ h and in the latter, the animal was rapidly bled with 40% of its total volume, and then observed for up to 4 h. — During aortic compression arterioles of 25 μm internal diameter increased their dimensions with about 40% and arteries of 70 μm with about 15%. The diameters of the venules showed a slight decrease. Linear flow rates in the capillaries decreased but there was an even distribution of the blood flow. No formation of thrombi was seen. — At arterial bleeding all the vessels first reduced their diameters during 10—20 min. Then arterioles of 25 μm diameter dilated, while the diameters of the other vessels remained reduced. In average the cats survived for 2 ½ h. Within a few minutes after the bleeding there was an adhesion of white cells to the venular walls and in later stages aggregates of red cells, platelets and white cells started to occlude most venules and capillaries leading to extensive “functional shunting” at the capillary level.