title: Ocular blood flow decreases during passive heat stress in resting humans.
abstract: BACKGROUND
  Heat stress induces various physiological changes and so could influence ocular circulation. This study examined the effect of heat stress on ocular blood flow.
  
  
  RESULTS
  Ocular blood flow, end-tidal carbon dioxide (P(ET)CO2) 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.
  
  
  CONCLUSIONS
  The findings of this study suggest that passive heat stress decreases ocular blood flow irrespective of the blood pressure or arterial partial pressure of CO2.
authors: Tsukasa
authors: T
authors: Ikemura
authors: Akane
authors: A
authors: Miyaji
authors: Hideaki
authors: H
authors: Kashima
authors: Yuji
authors: Y
authors: Yamaguchi
authors: Graduate School of Decision Science and Technology, Tokyo Institute of Technology, Ookayama 2-12-1-W9-1, Meguro, Tokyo 152-8552, Japan. naohayashi@hum.titech.ac.jp.
authors: Naoyuki
authors: N
authors: Hayashi
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002829:Choroid; D005123:Eye / Q000098:blood supply*; D018869:Heat-Shock Response / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D012039:Regional Blood Flow / Q000502:physiology*; D012171:Retinal Vessels; D012212:Rheology / Q000295:instrumentation / Q000379:methods; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide