BLOOD-FLOW CESSATION AT EXTERNAL-PRESSURE IN RAT SKINFLAPS ISOTOPE WASHOUT COMPARED TO VITAL CAPILLARY MICROSCOPY

The question of blood flow cessation in a tissue caused by external compression and determined by isotope washout was elucidated. A depot of a 133Xe-histamine-solution was injected intradermally into skinflaps in rats and the washout was recorded. The microcirculation in the labeled skin area was studied simultaneously by vital microscopy. External compression was applied and the blood flow cessation external pressure (FCEP) was determined as the minimum external pressure sufficient to arrest the washout of 133Xe or to stop the movements of red blood cells in the microcirculation visualized. In 12 experiments, the FCEP was on average 46.3 mm Hg as determined by isotope washout and 45.1 mm Hg as determined by vital microscopy. The SD of the difference was 2.7 mm Hg and the range of pressures studied was 18 to 68 mm Hg. The cessation of 133Xe washout was an adequate measure of cessation of blood flow in the microcirculation.