Effects of externally applied compression on blood flow in subcutaneous and muscle tissue in the human supine leg.

The effect of positive tissue pressure on blood flow in subcutaneous adipose tissue and skeletal muscle tissue was studied in eight healthy humans resting in the supine position. Blood flow was measured by the local 133Xe clearance technique in the mid-calf region. Tissue pressure was increased by inflating a whole leg cuff to pressure levels between 10 and 60 mmHg. In subcutaneous tissue as well as in skeletal muscle tissue, blood flow and local vascular resistance was not significantly changed at compression with 10 mmHg (P greater than 0.1). The pressure-flow curve obtained from subcutaneous tissue was curvilinear with the convexity towards the pressure axis, as blood flow was significantly reduced, while local vascular resistance was significantly increased by further increase in cuff pressure. Compression with 60 mmHg reduced subcutaneous blood flow to 21% of the reference value (P less than 0.01), while local vascular resistance was increased 91% above the reference value (P less than 0.01). In skeletal muscle tissue the pressure-flow curve was curvilinear with the convexity towards the flow axis, as local vascular resistance was reduced to 93% of the reference value at compression with 20 mmHg (P less than 0.05). Compression with 60 mmHg reduced muscle blood flow to 41% of the reference value (P less than 0.01), while local vascular resistance was increased 32% above the reference value (P less than 0.05). Venous distension in compressed subcutaneous tissue increased blood flow with 46% (P less than 0.02), while regional vascular resistance was reduced with 53% (P less than 0.01). In skeletal muscle tissue the same procedure was not followed by significant changes in blood flow or vascular resistance (P less than 0.01). It is concluded that the observed difference between the two tissues could be caused by a difference in vessel collapsibility. Another mechanism responsible could be a difference in autoregulatory capacity.