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Skin perfusion pressure measured as the external pressure required to stop isotope washout. Methodological considerations and normal values on the legs.

The skin perfusion pressure was measured as the external pressure required to stop blood flow, as evidenced by cessation of the washout of an intracutaneous depot of [131I-]antipyrine mixed with histamine. The external pressure on the skin was measured by an 11 x 11 cm slack air-filled plastic cushion connected to a mercury manometer and interposed between the labelled area and a blood pressure cuff. The 'flow cessation external pressure' (FCEP) varied parallel to the intra-arterial femoral mean blood pressure, but was on the average 10.8 mmHg (SD 6.4) lower. FCEP was measured on twenty normal subjects at four different segments of the leg. The average differences between auscultatory brachial mean blood pressure and FCEP were: thigh 12.0 mmHg (SD 7.6); calf 10.4 mmHg (SD 7.4); ankle 12.9 mmHG (SD 10.1); foot 20.2 mmHg (SD 12.1). The SD of the difference between measurements on two different days, performed in forty-four patients with different degrees of occlusive arterial disease, varied between 5.6 and 8.3 mmHg at the different levels. The present data indicate that the skin perfusion pressure on the legs in normal subjects lies approximately 10 mmHg lower than the systemic mean arterial blood pressure.