Changes in subcutaneous blood flow during locally applied negative pressure to the skin.

The effect of locally applied subatmospheric pressure on subcutaneous blood flow was studied in 12 healthy subjects. Blood flow was measured on the forearm by the local 133Xe wash-out technique. Air suction between 10 mmHg and 250 mmHg was applied to the skin. Subatmospheric pressure of 20 mmHg caused only a minor increase of estimated vascular resistance of 9 per cent. Increasing the suction to 40 mmHg caused a pronounced vasoconstriction corresponding to an increase in vascular resistance of about 90%. Further increase in local suction beyond 40 mmHg caused no additional increase in vascular resistance. The vasoconstriction induced by local suction was abolished by local nervous blockade induced by lidocaine in low doses which do not affect myogenic activity of the vascular smooth muscle cells. This finding confirms previous studies that the vasoconstriction mainly is due to a local sympathetic veno-arteriolar axon reflex mechanism. The results suggest that the dominant part of the vasoconstriction induced by the local axon reflex occurs when vascular transmural pressure increases from 20 mmHg to 40 mmHg.