Determinants of Vascular Resistance
The major determinant of vascular resistance is small arteriolar (known as resistance arterioles) tone. These vessels are from 450 µm down to 100 µm in diameter. (As a comparison, the diameter of a capillary is about 3 to 4 µm.)
Another determinant of vascular resistance is the pre-capillary arterioles. These arterioles are less than 100 µm in diameter. They are sometimes known as autoregulatory vessels since they can dynamically change in diameter to increase or reduce blood flow.
Any change in the viscosity of blood (such as due to a change in hematocrit) would also affect the measured vascular resistance.
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