Relationship between Blood Pressure and Diameter of Ascending Aorta in Normal and Hypertensive Rabbits

Abstract Earlier studies of strips from rabbit aorta suggest that hypertensive resetting of aortic baro‐receptor activity (Aars 1968a) might be due to hypertensive changes of the aortic wall in the receptor area (Aars 1968b). In order to obtain information under conditions equal to the demonstration of resetting, the relationship between blood pressure and diameter of ascending aorta has been examined in 11 normal rabbits and five rabbits with renal hypertension of about one week's duration. The transit time of ultrasonic pulses between two crystals glued to aorta was used to measure the aortic diameter. Below 70–100 mm Hg, aortic distensibility was equal in hypertensive and normal rabbits. The normal aorta became markedly stiffer at higher pressures, whereas in hypertensive rabbits the relationship between pressure and diameter remained linear to near hypertensive control pressures. This indicates that at pressures below approximately 130 mm Hg, stretching of aortic wall elements‐and presumably stimulus to baroreceptor activity‐was less in hypertensive than in normal animals. The curves for dynamic elastic modulus were also shifted to higher pressures, illustrating the ability of the aortic wall to maintain almost the same distensibility at control pressures in hypertensive and normotensive conditions. The rate of change of pulsatory diameter variations was closely related to their amplitude, and this relationship did not differ significantly in normal and hypertensive rabbits.