If oxygen partial pressure decreases or the CO2 partial pressure increases, or the pH decreases (acidosis), erythrocyte deformability decreases (Figure 6.06). This results in impaired entry into capillaries by the erythrocytes, an increase in apparent blood viscosity, an increase in local resistance, and a decrease in flow, which in turn results in a decrease in PO2. The latter, in turn, worsens the condition, producing a positive, or destructive, feedback loop. Therefore, erythrocyte deformability is important and changes under various conditions.
In blood of normal hematocrit the erythrocytes are always deformed to some degree. Even with an ideal hexagonal arrangement - side by side and end to end, which never occurs in blood, the maximal hematocrit that can be achieved is 63% without some erythrocyte deformation.
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