Which factor has the greatest effect on peripheral resistance?

Which factor has the greatest effect on peripheral resistance?

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

Answer: (D)

Vessel diameter sets the level of peripheral resistance. Resistance to flow through a tube increases dramatically as the radius decreases, described by Poiseuille’s law where resistance is proportional to 1 over the radius to the fourth power. Because small changes in arteriole radius drastically alter flow, diameter is the strongest determinant of systemic vascular resistance and thus of the pressure the heart must generate to push blood through the circulation. Blood viscosity does affect resistance, but its effect is smaller than that produced by radius changes. Heart rate modulates flow by changing cardiac output rather than the inherent resistance of the vessels. Blood oxygen content can influence vessel tone indirectly, but the primary driver of resistance remains the current diameter of the vessels.

Vessel diameter sets the level of peripheral resistance. Resistance to flow through a tube increases dramatically as the radius decreases, described by Poiseuille’s law where resistance is proportional to 1 over the radius to the fourth power. Because small changes in arteriole radius drastically alter flow, diameter is the strongest determinant of systemic vascular resistance and thus of the pressure the heart must generate to push blood through the circulation.

Blood viscosity does affect resistance, but its effect is smaller than that produced by radius changes. Heart rate modulates flow by changing cardiac output rather than the inherent resistance of the vessels. Blood oxygen content can influence vessel tone indirectly, but the primary driver of resistance remains the current diameter of the vessels.