Effect of exercise on arteriolar blood rheology in health and cardiovascular disease
Description
The effect of regular exercise on blood rheology, in both healthy and unhealthy subjects, was examined. To facilitate viscosimetry, a new hematocrit-independent viscosity parameter, named viscous resistance (VR) was defined and methodology developed that abrogates the necessity for hematocrit normalization or manipulation. In addition, in order to evaluate possible mechanisms whereby exercise may influence effective blood ($\rm\mu\sb{eff}$) viscosity, the effects of plasma viscosity (PV), cell free margin (CFM), fibrinogen and RBC aggregation on blood viscosity were examined PV correlates positively with high flow $\rm\mu\sb{eff}$ and VR (20 nl/sec), but not low flow $\rm\mu\sb{eff}$ or VR (0.5 nl/sec). Fibrinogen is an important determinant of PV. CFM positively correlates with $\rm\mu\sb{eff}$ and VR, at both low and high flow rates. RBC aggregation and fibrinogen concentration are important contributors to CFM at low flow rates, but not high flow rates A cross sectional study found regular runners to have lower $\rm\mu\sb{eff}$ and VR, and elevated RBC conductance (C$\sb{\rm rbc}$) compared to non-exercisers. In addition, a prospective rheology study found marathon training to reduce $\rm\mu\sb{eff}$, VR, and PV, and to increase C$\rm\sb{rbc}$. The benefits of running to blood rheology are further supported by the finding that an individual's change in VR and C$\sb{\rm rbc}$, is inversely related to the initial degree of fitness. The change in VR and C$\rm\sb{rbc}$ positively correlates with changes in human performance testing (VO$\sb{\rm 2max}$), which demonstrates the importance of blood viscosity in oxygen delivery and aerobic performance Subjects with coronary heart disease (CHD) were found to have significantly increased $\mu\sb{\rm eff}$ and VR, and decreased C$\sb{\rm rbc}$, compared to age matched healthy controls. A supervised, twelve week, cardiac rehabilitation program reduced the CHD groups' VR, PV, and RBC aggregation index, and increased C$\sb{\rm rbc}$. The rheological improvements are inversely related to the subjects' initial values. The worse a subject's initial rheological profile, the greater the potential benefit from cardiac rehabilitation Elevations in blood viscosity, RBC aggregation, and most importantly, plasma viscosity have all been identified as major risk factors for CHD. The decrease in all three of these parameters with cardiac rehabilitation may at least partially explain the reduction in mortality and morbidity associated with cardiac rehabilitation