Abstract
Invasive blood pressure measurements were performed in the common femoral- and popliteal artery of six limbs with occlusion of the superficial femoral artery during upright exercise (heel raising) and intraarterial alpha-receptor blockade. Femoral blood flow was obtained by an indicator dilution method injecting 131 RISA into the femoral artery and sampling from the popliteal artery. Exercise increased femoral blood flow from an average of 184 (SE +/- 27) cm3 . min-1 at rest to 531 (SE +/- 61) cm3 . min-1 during a 40 degrees head up tilt. Intraarterially induced alpha-receptor blockade caused a further increase in blood flow to 685 (SE +/- 86) cm3 . min-1 during exercise. Changes in collateral arterial resistance was calculated relative to the supine resting value. During exercise a decrease of 24% (SE +/- 13) was observed. After alpha-receptor blockade and exercise collateral resistance decreased by 46% (SE +/- 12). The results indicate that the passive head-up tilt induced a constriction of the collateral arteries which is abolished by heel raising exercise (ie standing on tip toe). It seems, however, that during these circumstances there still remains some alpha-receptor mediated constriction of the collateral arteries which is blocked by intraarterially injected alpha-receptor blocking agents.
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