Possible Role of Increased Blood Viscosity in the Hemodynamics of Systemic Hypertension

It has long been recognized that the viscosity of a fluid contributes importantly to the resistance to its flow. For .150 years, the Poiseuille equation has drawn attention to resistance to flow in a tube as directly related to the viscosity of the fluid as well as the tube’s geometry. 1 In contrast to the extensive studies of vascular geometry in hypertension, relatively little attention has been paid to the possible contribution of altered blood viscosity to elevated vascular resistance in systemic hypertension. A few studies have reported elevated levels of whole blood viscosity (WBV) in patients with essential hypertension.2‐5 However, as with all studies comparing clinical patients with recruited normal volunteers, it is uncertain whether subject selection may have influenced results. Specifically, it is unclear whether WBV is higher in unselected patients with essential hypertension than in apparently normal adults from the same population. Furthermore, it is also unknown whether the elevation in WBV is proportionate to the increase in peripheral resistance in such patients and thereby could play a role in the pathogenesis of essential hypertension.6