Purpose: The purpose of this study was to investigate the response of the retinal arteriole to an acute increase in systemic blood pressure (BP).
Methods: Sixteen healthy volunteers underwent a 5-minute cold pressor test (CPT) on the left hand. Retinal blood flow (RBF) was determined using a laser Doppler velocimetry system that enables simultaneous measurements of blood velocity and vessel diameter in a retinal artery every 30 seconds for the duration of the CPT. The mean arterial BP (MABP) was measured every 30 seconds during the test.
Results: The MABP immediately increased and reached the maximum level (from 85.1 +/- 2.7 to 103.7 +/- 5.0 mm Hg; P < 0.01) 1.5 +/- 0.2 minutes after the CPT began. The peak increase in velocity (from 30.6 +/- 1.3 to 46.1 +/- 2.1 mm/sec; P < 0.01) occurred at 1.6 +/- 0.2 minutes, resulting in an increase in RBF (from 10.1 +/- 1.0 to 14.3 +/- 1.4 microL/min; P < 0.01). The peak decrease in diameter (115.8 +/- 5.0 to 105.1 +/- 5.0 microm; P < 0.01) occurred at 2.9 +/- 0.3 minutes and the RBF returned to the baseline value. The increases in MABP significantly correlated with the decreases in diameter (r = -0.674, P = 0.0059).
Conclusions: The CPT caused an acute increase in MABP that was associated with a transient increase in RBF and blood velocity, followed by constriction of the retinal arterioles and return of RBF to baseline. The results suggest that constriction of the retinal arterioles plays an important role in the maintenance of RBF in response to an acute increase in systemic BP.