Which factor has the greatest effect on peripheral resistance?

Which factor has the greatest effect on peripheral resistance?

• A. Blood Viscosity
• B. Blood Vessel Diameter
• C. Heart Rate
• D. Blood Oxygen Content

Answer: (B)

Peripheral resistance is determined mainly by the radius (diameter) of the blood vessels. This comes from Poiseuille's law, which shows that resistance to flow is inversely proportional to the fourth power of the radius (R ∝ 1/r^4). Because of this fourth-power relationship, even small changes in vessel diameter produce large changes in resistance. For example, halving the radius increases resistance about 16-fold, while doubling the radius decreases resistance about 16-fold. Viscosity does affect resistance, but its impact is much smaller within normal physiological ranges compared to changes in radius. Heart rate influences cardiac output and blood flow demand rather than directly altering the baseline resistance of the vessels. Blood oxygen content can affect local vessel tone via autoregulation in some tissues, but it does not set peripheral resistance as a primary, global parameter.

Peripheral resistance is determined mainly by the radius (diameter) of the blood vessels. This comes from Poiseuille's law, which shows that resistance to flow is inversely proportional to the fourth power of the radius (R ∝ 1/r^4). Because of this fourth-power relationship, even small changes in vessel diameter produce large changes in resistance. For example, halving the radius increases resistance about 16-fold, while doubling the radius decreases resistance about 16-fold.

Viscosity does affect resistance, but its impact is much smaller within normal physiological ranges compared to changes in radius. Heart rate influences cardiac output and blood flow demand rather than directly altering the baseline resistance of the vessels. Blood oxygen content can affect local vessel tone via autoregulation in some tissues, but it does not set peripheral resistance as a primary, global parameter.