Rebreathing into a bag increases human retinal macular blood velocity.

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Abstract
AIMS--The effect of rebreathing into a bag (RB) on retinal macular blood velocity was evaluated in healthy volunteers. METHODS--Ten normal volunteers, whose ages ranged from 17 to 34 years, performed RB over 135 to 260 seconds (mean (SD) 193 (38) seconds) while retinal macular blood velocity was determined non-invasively using the blue field simulation technique. RESULTS--Leucocyte velocity significantly increased (p < 0.05) at 2 minutes and at the end of RB by 53% (42%) and 92% (65%), respectively (95% confidence interval of the mean (CIM)). All subjects observed an increase in the density of leucocytes. At the end of RB, mean systolic brachial arterial pressure and heart rate were significantly increased by 24% (11%) and 37% (15%) respectively (p < 0.01). At 2 minutes, end tidal oxygen concentration in the exhaled air was 47% (8%) (95% CIM) below and carbon dioxide was 41% (16%) above baseline (p < 0.001). The RB produces a large increase in macular leucocyte velocity, suggesting an increase in blood flow. CONCLUSION--Although RB has some systemic risk due to hypoxia and hypercapnia, RB for a short period of 1 or 2 minutes might be of help in the treatment of retinal arterial obstructive diseases in young patients without cardiovascular disorders if other treatments do not show any beneficial effects.