Rheologic dissimilarities in female and male blood: potential link to development of cardiovascular diseases.

Oxygen Delivery Index (ODI) was introduced as the ratio of red blood cell concentration (hematocrit) to blood viscosity. The ODI can be considered an indirect characterization of oxygen transport to organs and tissues. ODI was obtained for 98 healthy donors (47 pre-menopausal women and 51 age-matched men). In this population ODI levels were found to be significantly lower (p < 0.001) in male blood (7.7 +/- 0.3 vs. 8.4 +/- 0.5 in female blood). Average ODI obtained for 15 cardiac patients (all males) was found to be significantly lower than that for healthy men. In red blood cell suspensions with the same hematocrit, ODI was found to decrease when plasma viscosity was increased via an increase in protein concentration. Additionally, it was found that ODI measured for samples of blood over a wide hematocrit range, obtained by dilution with autologous plasma, possessed the highest values at the hematocrit levels 30 to 40%. The decreased oxygen transport might contribute to the significantly higher morbidity and mortality from cardiovascular diseases for men compared to pre-menopausal women. ODI may be a useful parameter for evaluation of risk of development of cardiovascular disorders.