The Nature and Reversibility of Hypothermia-Induced Alterations of Blood Viscosity

This study evaluates the nature and reversibility of the increase in whole blood viscosity known to be induced by hypothermia. Anticoagulated samples were obtained from normal volunteers and were assayed for cellular deformability by 4.7 μm membrane filtration of whole blood (n = 12) and washed RBCs (n = 10). Results were expressed as filtration rate. Specimens were evaluated for plasma (n = 10) and whole blood (n = 12) viscosity by cone plate viscometer. All assays were sequentially performed at 30°, 34°, and 37°C and differences analyzed by paired t test. Hypothermia resulted in significant impairment of cellular deformability, which was reversed by rewarming:30°C 34°C 37°CWhole blood (cells/sec/cm) 64.852 71.674 79.219 p < 0.001Washed RBCs (cells/sec/cm) 90.731 97.589 120.435 p < 0.002Hypothermia also resulted in a significant increase in plasma viscosity (mean difference = 0.5426 centipoise, p < 0.02), which was likewise reduced on rewarming. The increase in whole blood viscosity associated with hypothermia is secondary to both diminished cellular deformability and increased plasma viscosity. Both of these alterations are reversible with appropriate rewarming.