Critical Closing Pressure of Vessels Supplying the Capillary Loops of the Nailfold

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Abstract
The critical closing pressure (CCP) of vessels supplying the capillary loops of the nailfold was estimated as the digital systolic pressure minus the air pressure required on the finger to just prevent flow of blood in the capillary loops. The digital blood pressure was estimated by an auscultatory method and the presence or absence of flow in the loops was detected by direct microscopic examination. It was shown that the method is valid and does not simply measure a local intravascular pressure or some rheological factor. The CCP was lower after body heating than after body cooling and was markedly reduced by anesthetization of the digital nerves. In hypertensive patients the CCP was higher than in normal subjects.