Blood flow rate during orthostatic pressure changes in the pulp skin of the first toe

Determination of the local regulation of cutaneous blood flow through nutritive capillaries and through arteriovenous anastomoses of the pulp of the first toe in response to passively induced orthostatic blood pressure changes in normal subjects and in patients with occlusive atherosclerotic disease.

Six normal subjects, seven patients with unilateral, crural intermittent claudication and six patients with unilateral, chronic critical ischaemia.

Blood flow rates were measured in supine subjects by the heat washout method (the sum of blood flow rate in arteriovenous anastomoses and blood flow rate in nutritive capillaries) and by the 133Xenon washout method (blood flow rate in nutritive capillaries) after local, atraumatic labelling. Measurements were made with (a) the toe passively elevated to 50 cm above heart level, (b) at heart level and (c) passively lowered to 50 cm below heart level.

Autoregulation of nutritive blood flow was present in normal subjects and in claudicants, but the local sympathetic veno-arteriolar axon reflex was absent in both groups. In patients with critical ischaemia blood flow rate was the same in the supine position and during lowering in arteriovenous anastomoses and in nutritive capillaries. The arteriovenous anastomoses had distinct and characteristic reaction patterns in response to lowering in each of the three examined groups and to elevation in normal subjects and in patients with intermittent claudication (not measured in patients with critical ischaemia).

The microvascular responses to changes of orthostatic blood pressure differed among the three groups (normal subjects, patients with intermittent claudication, patients with critical chronic leg ischaemia). The heat washout method may be used to detect the functional significance of occlusive atherosclerotic disease.