Effect of hip position on blood flow to the femur in puppies.

Utilizing radioactive microspheres, blood flow to the femoral head of immature dogs was measured. Blood flow was measured with the leg in the control position, maximal abduction, submaximal abduction, and the human position of hip immobilization. Maximal abduction (to 90 degrees) significantly decreased flow to the capital femoral epiphysis. Submaximal abduction and the human position did not reduce blood flow. Measurement of flow in the control position immediately after forced abduction demonstrated marked reactive hyperemia. These data indicate that ischemia occurs during 90 degrees forced abduction of the hip. This finding supports the use of lesser degrees of abduction for hip immobilization in the treatment of congenital dislocation of the hip. The vascular anatomy of the head of the femur in puppies and children suggests that these data can be extrapolated to man.

Regulation of blood flow to the aortic media in dogs.

Morphologic observations suggest that the inner layers of the thoracic aorta in man and dog are avascular and the outer layers have vasa vasorum. It appears that vasa vasorum are essential in the thoracic aorta because their interruption produces medial necrosis. These experiments provide the first measurements of blood flow through aortic vasa vasorum and examine physiologic regulation of that flow. During control conditions the outer two-thirds of the media of the thoracic aorta received 10 ml/min per 100 g blood flow through vasa vasorum. Flow to the inner third of the aorta was 1 ml/min per 100 g. Flow to both the inner and outer media of the abdominal aorta was less than 1 ml/min per 100 g. Adenosine increased blood flow to vasa vasorum in the outer media of the thoracic aorta from 7 to 18 ml/min per 100 g, but did not increase flow to the inner layers of the aorta. Hemorrhagic hypotension decreased flow in the outer media of the thoracic aorta from 14 to 2 ml/min per 100 g. Acute hypertension failed to increase blood flow through vasa vasorum, as conductance decreased significantly. These studies indicate that vasa vasorum provide a considerable amount of blood flow to the outer layers of the thoracic aorta. The vessels are responsive to physiologic stimuli because they dilate during infusion of adenosine and constrict during both hemorrhagic hypotension and acute hypertension. We speculate that the failure of blood flow to the aortic wall to increase during acute hypertension might, if it were sustained, contribute to aortic medial necrosis.