Variation in red blood cell deformability and possible consequences for oxygen transport to tissue

Red blood cell (RBC)-plasma suspensions with a hematocrit of 10-12% were forced to flow through microchannels (equivalent diameter 6 microns, equivalent length 20 microns, 2600 in parallel) by applying a pressure difference of 20 cm H2O. Transit times for 100 microliters of fresh suspensions from 33 healthy male subjects aged between 24 and 63 ranged from 43.0 to 65.2 sec (mean +/- SD: 49.4 +/- 4.3 sec). Four measurements taken from two subjects at intervals over several weeks gave fluctuations of 45.1, 43.6, 47.6, and 45.9 sec and 52.3, 49.8, 60.1, and 50.0 sec, respectively. RBC deformability thus appeared to vary considerably between different subjects and also showed fluctuations between different days in any given subject. No correlation was obtained between the transit time and subject's age. However, higher whole blood hematocrit values were apparent in those suspensions that had longer transit times. A lower RBC deformability might be caused by dietary factors with resultant increased frequency of occasional stagnation of capillary blood flow, i.e., occasional tissue hypoxia. This would further result in an increased hematocrit.