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E.A. Polska, K. Karl, B. Pemp, L. Schmetterer; Effect of Calcium Channel Blocker Nifedipine on Regulation of Choroidal Blood Flow During Isometric Exercise . Invest. Ophthalmol. Vis. Sci. 2006;47(13):480.
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There is evidence that the choroid regulates its blood flow during isometric exercise induced changes in ocular perfusion pressure. In the present study we tested the hypothesis that the calcium channel blocker nifedipine modifies this regulation.
12 healthy male volunteers participated in a randomized, placebo–controlled, double masked, two way cross over study. The subjects received either nifedipine or placebo on different study days. Choroidal blood flow (ChBF), mean arterial blood pressure (MAP), intraocular pressure (IOP), and pulse rate were assessed at baseline and during squatting for 6 minutes. Measurements of ChBF were performed with a compact laser Doppler flowmeter. The IOP was measured with an applanation tonometer. Ocular perfusion pressure was calculated as OPP=2/3*MAP–IOP. For ChBF and OPP percent changes from baseline were calculated and the pressure–flow curves of the choroid were computed.
Ocular perfusion pressure increased until about 70% during all squatting periods. Under physiological conditions and during placebo infusion isometric exercises caused only small changes in choroidal blood flow. In contrast, nifedipine induced a significant alteration of the autoregulation when OPP was about 60% increased (p=0.007 vs. placebo).
The present study confirms a regulatory capacity in the choroid during isometric exercise. Our data indicate that calcium channel blocker nifedipine alters the choroidal pressure–flow relationship.
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