Peripheral resistance tends to increase when which factor rises?

Peripheral resistance tends to increase when which factor rises?

• A. Blood viscosity
• B. Vessel elasticity
• C. Vessel length
• D. Heart rate

Answer: (A)

Peripheral resistance rises when the thickness of the blood increases. This is because resistance is directly tied to blood viscosity: thicker blood has more friction as it slides along vessel walls, so more pressure is needed to maintain the same flow. In the resistance relationship, R is proportional to viscosity (along with length) and inversely proportional to the radius to the fourth power, so even modest increases in viscosity push resistance up significantly. Vessel length would also raise resistance, but its effect is smaller in this context, and heart rate doesn’t set the intrinsic friction within the vessels.

Peripheral resistance rises when the thickness of the blood increases. This is because resistance is directly tied to blood viscosity: thicker blood has more friction as it slides along vessel walls, so more pressure is needed to maintain the same flow. In the resistance relationship, R is proportional to viscosity (along with length) and inversely proportional to the radius to the fourth power, so even modest increases in viscosity push resistance up significantly. Vessel length would also raise resistance, but its effect is smaller in this context, and heart rate doesn’t set the intrinsic friction within the vessels.