Opposite effects of hypertension and smoking on large artery wall shear conditions.

Wall shear phenomena were studied in the brachial artery in non-smoking and smoking normotensive and hypertensive subjects of similar age. Pulsed Doppler investigation revealed brachial artery diameter, and mean and systolic blood velocities (at the centerline of the vessel). A Poiseuillean blood velocity distribution was used to determine the wall shear rate and stress from velocity, diameter and viscosity. This was expressed in terms of mean and systolic values. Although hypertension and smoking both increased blood viscosity, hypertension reduced mean and systolic shear rates and stresses in non-smokers but not in smokers, and smoking increased mean and systolic shear rates and stresses in hypertensives but not in normotensives. Thus, the decreasing shear effect of hypertension was blunted by smoking, while the increasing shear effect of smoking was elicited by hypertension, suggesting an interaction of these factors on wall shear conditions.