Effect of Carotid Baroceptor Stimulation upon the Forelimb Vascular Bed of the Dog

The response of the musculocutaneous vascular bed of the dog's forelimb to carotid baroceptor stimulation was determined by measuring pressures at the level of the large artery, small artery, small vein, and large vein along with limb blood flow. In one series, limb blood flow was uncontrolled. In two other series, the limb was perfused at a constant flow rate and was also isolated from collateral flow in one of these. Elevation of carotid sinus pressure in the constant flow isolated (CFI) series produced an average fall in total limb, small vessel, and venous segment resistance of 27%, 36%, and 22% respectively but no significant change in arterial segment resistance. Since transmural pressure fell significantly in all three segments, active vasodilatation must also have occurred in all, including the arterial. This is reflected in the significant increase in compliance calculated for both the lumped arterial and lumped venous segments. In any given animal, there was a positive correlation between the percentage reduction in systemic pressure and total limb resistance, but this correlation was not evident between animals. In the series in which limb blood flow was uncontrolled, flow decreased consistently and significantly when carotid sinus pressure was elevated, the average decrease being 30%. Despite possible confusion introduced by the presence of an added fixed resistance in the limb circuit (rotameter), it is probable that this finding faithfully reflects the behavior of the intact limb.