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 microns 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 degrees, 34 degrees, and 37 degrees C and difference analyzed by paired t test. Hypothermia resulted in significant impairment of cellular deformability, which was reversed by rewarming: [table: see text] Hypothermia also resulted in a significant increase in plasma viscosity (mean difference = 0.5426 centipoise, p less than 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.