Comparison of the autoregulatory mechanisms between central retinal artery and posterior ciliary arteries after thigh cuff deflation in healthy subjects

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: Ten healthy male young subjects were studied. Flow velocities in retrobulbar vessels and systemic blood pressure 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 color Doppler imaging. 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 between - 9% and - 12% (p< 0.001 each) immediately after thigh cuff release and returned to baseline 6 to 7 pulse cycles later. Peak systolic flow velocity in the CRA decreased by - 10 ± 7% (p= 0.043) and returned to baseline earlier than systemic blood pressure, showing a delay of 3 pulse cycles after the blood pressure decrease. Peak systolic and end diastolic flow velocities in the PCAs decreased by - 13 ± 3% (p= 0.004) and by - 10 ± 1% (p= 0.0009), respectively and returned to baseline with a comparable time course to systemic blood pressure, reflecting no change in peripheral vascular resistance. There was a statistically significant difference in the time course of the velocity changes in the two selected arteries after thigh cuff release (p= 0.008). Conclusions: The results of the present study indicate differences in the autoregulatory behavior of the vascular beds peripheral to the CRA and the PCAs. Our data indicate that the vascular bed distal to the CRA shows better autoregulatory properties as compared to the PCAs. Whether this is related to a myogenic mechanism remains to be investigated. The thigh cuff technique represents an interesting approach to study dynamic autoregulation in the human eye.