Total, hind-limb blood flow was measured simultaneously in dogs by ⁴²K and ⁸⁶Rb clererance and by venous outflow collection. Surgical or tourniquet isolation of the hind limb allowed for the quantitative collection of venous outflow. The values obtained were in agreement demonstrating that ⁴²K and ⁸⁶Rb clearances are accurate measures of total hind-limb blood flow.

The distribution of blood flow to bone, muscle, and skin was determined by the clearance technique, and analysis of the extraction ratios of the tissues demonstrated that the distributions measured in this way could not he greatly in error. The distribution of blood flow was also simultaneously determined by a radioactive glass microsphere method. Good agreement was obtained and since the critical assumptions of the two approaches are different, it was concluded that both are valid for determining distribution to the bone, muscle, and skin of the hind limb in dogs.

For isolated limbs, the mean control perfusion value in milliliters per minute per 100 grams of tissue for bone was about 10, for muscle 5, and for skin, 8. For hind limbs of intact dogs, perfusion in milliliters per minute per 100 grams of the three tissues was 12 to 18 for bone, 5 for muscle and 8 for skin. Immediately following exercise, bone perfusion fell to about 5, muscle perfusion rose to 14 to 19, and skin declined to about one half of the control values.