Ocular blood flow decreases during passive heat stress in resting humans |
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Authors: | Tsukasa Ikemura Akane Miyaji Hideaki Kashima Yuji Yamaguchi Naoyuki Hayashi |
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Institution: | 1.Graduate School of Human-Environment Studies, Kyushu University, Kasuga-koen 6-1, Kasuga, Fukuoka 816-8580, Japan;2.Graduate School of Decision Science and Technology, Tokyo Institute of Technology, Ookayama 2-12-1-W9-1, Meguro, Tokyo 152-8552, Japan |
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Abstract: | BackgroundHeat stress induces various physiological changes and so could influence ocular circulation. This study examined the effect of heat stress on ocular blood flow.FindingsOcular blood flow, end-tidal carbon dioxide (PETCO2) and blood pressure were measured for 12 healthy subjects wearing water-perfused tube-lined suits under two conditions of water circulation: (1) at 35°C (normothermia) for 30 min and (2) at 50°C for 90 min (passive heat stress). The blood-flow velocities in the superior temporal retinal arteriole (STRA), superior nasal retinal arteriole (SNRA), and the retinal and choroidal vessels (RCV) were measured using laser-speckle flowgraphy. Blood flow in the STRA and SNRA was calculated from the integral of a cross-sectional map of blood velocity. PETCO2 was clamped at the normothermia level by adding 5% CO2 to the inspired gas. Passive heat stress had no effect on the subjects’ blood pressures. The blood-flow velocity in the RCV was significantly lower after 30, 60 and 90 min of passive heat stress than the normothermic level, with a peak decrease of 18 ± 3% (mean ± SE) at 90 min. Blood flow in the STRA and SNRA decreased significantly after 90 min of passive heat stress conditions, with peak decreases of 14 ± 3% and 14 ± 4%, respectively.ConclusionThe findings of this study suggest that passive heat stress decreases ocular blood flow irrespective of the blood pressure or arterial partial pressure of CO2. |
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Keywords: | Retinal circulation Choroidal circulation Hyperthermia |
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