Comparison of the Autoregulatory Mechanisms Between Central Retinal Artery and Posterior Ciliary Arteries After Thigh Cuff Deflation in Healthy Subjects

Abstract

Purpose: : To compare dynamic autoregulation in the Central Retinal Artery (CRA) and the Posterior Ciliary Arteries (PCAs) after a step decrease in systemic blood pressure.

Methods: : Eighteen healthy male young subjects were studied. Ultrasound parameters and systemic blood pressures were recorded in each subject before, during, and after a step decrease in blood pressure. Continuous blood pressure recordings were made with a finger plethysmograph system, and flow velocities in the CRA and the PCAs were continuously measured with Doppler ultrasound. Large bilateral thigh cuffs were inflated and a pressure approximately 20 mm Hg above peak systolic blood pressure was maintained for 3 minutes. A decrease in blood pressure was induced by rapid deflation of bilateral thigh cuffs. Experiments were performed separately for the CRA and the PCAs.

Results: : Systemic blood pressure showed a step decrease immediately after thigh cuff release (10%-15%) and returned to baseline 6 to 10 pulse cycles later. Flow velocities in the CRA returned to baseline earlier than systemic blood pressure, indicating peripheral vasodilatation, with a maximum of five to six pulse cycles after the blood pressure decrease. By contrast, flow velocities in the PCAs returned to baseline with a comparable time course than systemic blood pressure, reflecting no change in peripheral vascular resistance. There was a statistically significant difference in the time course of the resistance changes in the two selected arteries after thigh cuff release (P < 0.01).

Conclusions: : The results of the present study indicate differences in the autoregulatory behavior of the vascular beds peripheral to the CRA and the PCAs. Results in the CRA are compatible with either metabolic or myogenic vasodilatation. Results in the PCAs could indicate that there is no autoregulatory response in the distal vascular beds. The thigh cuff technique may represent an interesting approach to the study of dynamic autoregulation in the human eye.

Keywords: retina