Hydraulic Servo Control Research Articles

Indirect measurement of instantaneous arterial blood pressure in the human finger by the vascular unloading technique.

For the indirect measurement of beat-to-beat systolic and diastolic pressure in the human finger, a new hydraulic servocontrol system was designed to maintain the vascular volume in the unloaded state. The servocontrol system consists of a compression chamber equipped with an occluding cuff and a photoelectric plethysmograph, an electromagnetic shaker, and a volume servo circuit. The shaker connected to a diaphragm actuator is used for controlling the cuff pressure. The vascular volume change in the finger is detected by the photoelectric plethysmograph. The plethysmographic signal is fed into the servo circuit to control the cuff pressure, which is clamped at a proper value corresponding to the unloaded vascular volume. At this state the controlled cuff pressure follows the intraarterial pressure. The accuracy of this method was evaluated using an in vitro vascular model of the finger. Comparisons with direct measurement were carried out successfully in four normotensive and six hypertensive subjects.

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.