Direct measurement of arteriovenous anastomotic blood flow after lumbar sympathectomy.

Absolute blood flows through hind limb capillaries and arteriovenous anastomoses (AVA) were determined by the radioactive microsphere technique of relative shunt measurement combined with direct (electromagnetic) measurement of femoral artery flow. Hemodynamic parameters were measured before and after laparotomy, after unilateral lumbar sympathectomy, during reactive hyperemia, and during alpha adrenergic blockade in normal and sympathectomized hindlimbs of six anesthetized dogs. After sympathectomy arteriovenous (A-V) shunting increased from 3.8 to 32.1% (p less than 0.05). AVA flow increased from 4 to 54 ml/minute (p less than 0.01), while capillary flow was unchanged. Nonsympathectomized limbs did not demonstrate these changes. During reactive hyperemia, capillary flow increased more than 100% (p less than 0.03) in both normal and sympathectomized limbs, while AVA flow was unchanged. After phentolamine (5 mg, intravenously), AVA flow increased from 2 to 19 ml/minute (p less than 0.01) only in nonsympathectomized limbs. Phentolamine mimicked surgical sympathectomy effects in nonsympathectomized limbs, with paw temperature, femoral flow, A-V O2 difference, A-V shunting, AVA flow, and capillary flow equal to sympathectomized limbs after phentolamine administration. In the acute canine model, increased blood flow after sympathectomy is due to increased nonnutritive AVA flow, with no change in total hindlimb capillary flow, both at rest and during reactive hyperemia.