Indirect blood pressure measurements in the rabbit: correlations with direct aortic and ear pressures

Blood pressures in the central artery of the ear were determined in rabbits by the use of a modified Grant-Rothschild pressure capsule using two end-points defined as the complete cessation (occlusion) or restoration (opening) of the arterial blood flow. In normal rabbits, the opening values measured by the capsule were closely related to diastolic pressures measured directly in the aorta or in the central artery of the ear, whereas the values obtained during arterial occlusion were higher, by a reproducible amount, than the direct systolic recordings in both the ear and the aorta. In rabbits rendered chronically hypertensive, systolic and diastolic blood pressures measured directly in the aorta and the ear were less (in a predictable manner) than their correspondent occlusion and opening values recorded with the capsule. The amount of this difference increased proportionally as blood pressure increased. Differences between direct and capsular recordings were less consistent in rabbits made acutely hypertensive with infusions of angiotensin. Through regression analysis, systolic and diastolic pressures in the aorta and in the central artery of the ear can be reliably predicted from capsular reading.