Abstract
Purpose: :
The human choroid revealed autoregulatory behavior during aerobic and isometric exercise that acutely raised the ocular perfusion pressure (OPP). It was hypothesized that blood flow was kept close to resting value by sympathetic vasoconstriction. The objective of the present study was to determine the degree of autoregulation during passive stimulation of the sympathetic nervous system (SNS).
Methods: :
ChBF parameters were recorded throughout three, 5 min. intervals in 12 healthy young adult volunteers. In the first interval, the body temperature was stabilized with warm compresses (40°C) placed atop and under the forearm, and a warm blanket over the shoulders. Immediately after the warm test phase, cold compresses (0°C) replaced the warm ones, and these were replaced a second time by warm compresses and blanket. The blood pressure was measured every minute and the intraocular pressure at the end of testing to calculate the OPP. The data for each subject was normalized to pretest values and group-averaged data across test conditions were compared by ANOVAs (alpha <0.05).
Results: :
During the first warm phase, the OPP decreased ~8.9% below baseline (p= 0.0001) while the ChBF remained unchanged (p> 0.05). Cold rapidly increased the OPP over baseline by 11.2% (p= 0.0001) and the ChBF by 5.8% (p= 0.0001). While the OPP decreased by~ 8% during the cold phase, the ChBF did not change from its initial overshoot of ~6% (p> 0.05). The second warm phase again reduced the OPP by ~9.0% below baseline (p= 0.0001) but had no effect on the ChBF (p> 0.05). Blood flow regulation during the warm intervals was driven by increased blood volume. In contrast, the volume did not change during the cold phase, but velocity increased by ~ 6% (p= 0.0001).
Conclusions: :
The human choroid is well regulated when the OPP falls below baseline, but fails when it exceeds baseline through passive stimulation of the SNS.
Keywords: blood supply • choroid • macula/fovea