Effect on red blood cells

Red blood cells (RBCs) are concave discs and deformed into any shape, when they pass through the capillary, as the diameter of the capillary is smaller than the RBC diameter. The degree of deformability is an important determinant of blood viscosity. In animal experiments, deformability increases at pressures below 202.6kPa (2ata) and decreases with higher pressures.

In a rat experiment42, for example, RBC deformabibility was assessed with two different techniques, with the ektacytometer and with micropore filters. Exposure to HBO at 283.6kPa (2.8ata) for 6 hours led to a significant decrease of RBC deformability (p<0.0001) with the micropore filter method. This effect was reversible as it was not observed in the group of animals investigated 24 hours after exposure.

An investigation in 70 patients43 showed an increased deformability after exposure to HBO at 202.6kPa (2.0ata) for 90 min (p<0.001) measured by the Stolz method. The decreased viscosity may support blood flow and gas exchange at the capillary level. Elevated ambient pressure per se enhances RBC aggregability which has been studied in eleven human volunteers44 during dives to 919kPa (9.19bar, 300fsw). The median RBC aggregate size was significantly increased at depth.

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