Indirect measurement of instantaneous arterial blood pressure in the rat

We devised a hydraulic servo-control system for indirect blood pressure measurement in the rat's tail, by which beat-to-beat systolic and diastolic blood pressure can be obtained. In this method the principle of "unloading vascular wall" proposed by Shirer (1962) is employed. The proposed system is composed of a transmittance photoelectric plethysmograph with an occluding cuff, a small diaphragm actuator for compressing and decompressing the segment by the hydraulic pressure, and an electromagnetic shaker driven by a volume servo circuit in accordance with the signal from the photoelectric plethysmograph. The plethysmographic signal is clamped at a proper value corresponding to the unload vascular volume by the instantaneous hydraulic servo control. The cuff pressure thus automatically controlled follows the intra-arterial pressure in the tail segment. The accuracy of this method was evaluated in comparison with direct measurement of blood pressure recorded simultaneously from 16 unanesthetized spontaneously hypertensive and normotensive rats. Close agreement between the simultaneous data from these two methods were observed.