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Keiko Yamada, Rachelle Koch, Purva Atreay, Sinjin Swartz, Takatoshi Maeno, Chie Sotozono, Brendan Seto, Jorge G Arroyo; Human laser speckle retinal blood flow changes associate with exposure to varying concentrations of O2 and CO2. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1749.
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© ARVO (1962-2015); The Authors (2016-present)
Investigate the total and single vessel retinal vascular blood flow of healthy subjects after exposure to varying flow rates of 100% O2 and 5%CO2/95% O2.
Nine participants underwent imaging via the Laser Speckle Flowgraphy (Softcare Co, Fukuoka Japan) in order to measure the total vascular blood flow (BF) around their optic nerve head in units of mean blur rate (MBR) and the BF in a single retinal vessel in units of relative flow volume (RFV). Each measurement consisted of a series of images automatically taken then manually averaged over the course of an individual’s heartbeat.This experiment consisted of 4 measurements taken in triplicate: 1) baseline with no gas, 2) 6 liters per minute (LPM) of either oxygen or carbogen gas, 3) 12 LPM of gas, and 4) a post-gas measurement. A washout period of 2 minutes separated each stage and each gas session involved inhaling the appropriate gas for 2 minutes before images were taken. All participants underwent both pure O2 and carbogen tests, with no more than one gaseous mixture on a given day. Measurements were standardized to the average of the participant’s pre-gas measure on the specific testing day and presented as an average percentage of their “normal” retinal vascular blood flow ± this measure’s standard deviation.
Oxygen inhalation reduced overall RFV in a manner proportional to the gas flow rate (6 LPM: 0.94±.07, P=.04; 12 LPM: 0.82±.04, P<.001), while carbogen reduced RFV at 12 LPM (0.88±.05, P=.01) but not 6 LPM (1.0±.12, P=0.62). Thus, the additional of 5% CO2 to the pure oxygen mixture mitigated the reduction in BF in a single vessel. There was not, however, a difference in MBR between gases at any flow rate (6 LPM: P=.12; 12 LPM: P = .70; Post: P = .07). While higher levels of gaseous flow rate did correlation with a reduction in retinal perfusion (6 LPM: 91±9%, P<.001; 12 LPM: 85±9%, P<.001), these levels returned to pre-exposure rates after a two-minute washout period (Post: 99±9%, P=.91).
Hyperoxia reduces retinal vascular blood flow in a manner proportional to increasing concentration of inspired oxygen. While single vessel measurements appear to be sensitive to the addition of 5% CO2, the total retinal blood flow may not be. Future research may expand these findings to a larger, more diverse set of subjects and investigate if oxygen delivery to the retina is affected by demographic factors.
This is a 2020 ARVO Annual Meeting abstract.
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