Comparison of optic nerve head and choroidal blood flow regulation during isometric exercise

Abstract

AbstractPurpose In the recent years the response of choroidal blood flow (ChBF) to isometric exercise has been characterized in some details. Generally, the degree of blood flow increase is lower than the degree of ocular perfusion pressure (OPP) increase indicating for some regulatory capacity of the choroid during these conditions. In the present study we compared the response of optic nerve head (ONH) blood flow and ChBF in response to isometric exercise.Methods Two study days were performed in 48 healthy young subjects. 24 subjects participated in the choroidal studies and 24 subjects in the ONH studies. The effect of a 6 minutes squatting period on ChBF and ONH blood flow was studied. ChBF and ONH blood flow were measured using laser Doppler flowmetry. OPP was calculated as 2/3*mean arterial pressure‐intraocular pressure.Results ChBF and ONH blood flow increased during isometric exercise (p < 0.001 each). The increase was, however, in both vascular beds less pronounced than the increase in OPP indicating for some degree of blood flow regulation. The pressure/flow curves revealed that ChBF was constant until OPP of about 60% above baseline, whereas ONH blood flow was constant until OPP of about 40% above baseline.Conclusion During isometric exercise ChBF regulates better than ONH blood flow. In some subjects an interesting phenomenon was found in the ONH blood flow experiments. During isometric exercise blood pressure temporarily decreased slightly, when subjects were exhausted from squatting. These periods were sometimes associated with a pronounced decrease in ONH blood flow (up to 30% below baseline values) although the OPP was still much higher than at baseline. The significance of this observation is unknown.