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K.I. Suh, R.R. Ansari, J.F. King, F.K. Manuel; Choroidal Hemodynamics in Zero Gravity Environment . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2624.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We investigate the effects of reduced ("zero") gravity environment on the choroidal blood flow and arterial blood pressure. Methods: The choroidal blood flow measurements were made using a head–mounted miniature Laser–Doppler flowmeter (Oculix) operating at a wavelength of 780 nm at a power of 100 µW. The velocity, volume and flow parameters were calculated from the Doppler shift resulted from red blood cells flowing through the choroid. Measurements on 25 human volunteers were completed in accordance with the approved NASA IRB protocol for human testing. The experiments were conducted on–board a wide body aircraft (KC–135) during parabolic flight trajectories (0g to 2g environment). Arterial blood pressure (BP) was measured continuously (beat–to–beat) using a BP instrument (Colin Medical). Results: Arterial BP Measurement: Compared to 1g baseline measurements, both systolic and diastolic arterial BP show significant increase in 2g environment (13.9 ± 2.8)% for systolic and (18.5 ± 5.3)% for diastolic and significant decrease in 0g environment (14.4 ± 5.0)% and (24.4 ± 10.1)% respectively. The pulse measurements showed virtually no change in 2g (–0.24 ± 2.9)% and a minor decrease in 0g (10.3 ± 4.5)%. Choroidal Blood Flow Measurements: Comparisons are only made for 1g baseline and 0g data, due to the presence of excessive vibration–induced noise in 2g environment. Beacause of this vibration, patients were not able to easily fixate to the incoming laser light. The result shows a significant increase in choroidal blood velocity (20.3 ± 15.4)%, in agreement with our previous ARVO 2003 report. The choroidal volume shows a smaller increase (4.7 ± 12.4)% in zero gravity environment. Conclusions: Choroidal blood flow increases in zero gravity, because of the significant increase in blood velocity and by a relatively small increase in volume. This could be due to the sudden rush of the blood to the upper extremities of the body in reduced gravity. On the other hand, the relatively small increase in choroidal blood volume seems to suggest a self–regulating mechanism in which the choroid tries to maintain constant blood flow. In order to better understand this mechanism, longer–duration experiments on the International Space Station (ISS) are needed. Acknowledgements: RRA would like to acknowledge the support from NASA–NEI/NIH Interagency Agreement, the John Glenn Biomedical Engineering Consortium, and the Collaborative Research Agreement between the NCMR in NASA GRC and the Institut de Recherche en Ophthalmologie (IRO) in Switzerland.
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