Blood viscosity is composited of deformability of red blood cells, aggregation of red blood cells and blood composition. Actually blood viscosity has been identified as a major contributor to primary hypertension, but it was not emphasized in the main stream of primary hypertension therapy.
Deformability of red blood cells
Sizes of red blood cells range 7-8.5 mm in diameter and diameters of capillaries range 6-8 mm. Most of red blood cells need to change form a bit to pass through capillaries smoothly (Fig.1). Ability for red blood cells to change form is termed deformability of red blood cells. It is related to cell membrane flexibility and volume of red blood cells. When the deformability of red blood cells decreases, blood flow resistance will increase and raise blood pressure, especially diastolic pressure. Red blood cells have a life span of 120 days. They undergo ageing once they are produced. There are new and aged red blood cells at different stages at any given time in our blood in all ages. Aged cells at late stage tend to swollen and membranes of aged red blood cells are less flexible due to accumulation of lipid oxidative damage and reduction of ATP production, which affect red blood cells to change form to pass through capillaries smoothly and hence, can significantly increase blood flow resistance. The percentage of low deformability of red blood cells tends to increase in aged people.
Fig. 1. Red blood cell deformity to pass through capillaries.
Aggregation of red blood cells
Red blood cells at low-shear flow rate or static conditions tend to aggregate to form clusters (Fig.2) or rouleaux-like aggregates. When blood flow is at high-shear flow rate condition, the aggregates can be reversibly dispersed into free individual cells. High blood pressure can drive blood flowing faster and put more force on clusters and hence, is helpful to disperse red blood cell aggregates. Therefore, hypertension itself is a result of circulation regulation to improve tissue blood perfusion. However, aged people can form more, firmer aggregates, which can significantly increase blood flow resistance and raise blood pressure. That is one of reasons why primary hypertension incidence increasing with age advancing.
Fig. 2. Illustration of aggregation of red blood cells.
Blood composition is associateed with haematocrit and plasma composition. They also contribute to blood viscosity. Haematocrit refers to the volume ratio of cell/plasma (their normal ratio is 0.45/0.55). Normal plasma contains 90% of water and 10% of proteins and other components. Haematocrit and plasma composition are relatively stable and are unlikely to contribute to primary hypertension.
Studies revealed that deformability and aggregation of red blood cells are two important factors in causing blood viscosity (or blood flow resistance) and raising blood pressures. Nine in ten hypertensive patients belong to primary hypertension. Blood viscosity is virtually behind all primary hypertensions. Current antihypertensive medication can only manipulate heartbeat, tone of arterial walls and blood volume to suppress blood pressures but cannot cure hypertension simply because it cannot treat the cause of hypertension. That is why patients have to take antihypertensive tablets daily once they start antihypertensive medication. Unfortunately, there is, so far, no appropriate drug available to treat the decrease of deformability and increase of aggregation of red blood cells. However, laser blood therapy is shining the new hope and opens a new way to treat primary hypertension. Please read "How can red laser lower blood pressure?" to understand why and how red laser can cure primary hypertension.
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