Horrock’s apparatus estimates
**Question:** Horrock's apparatus estimates
A. resistance to blood flow
B. compliance of blood vessels
C. elasticity of blood vessels
D. viscosity of blood
**Core Concept:** Horrock's apparatus is a device used to measure the resistance to blood flow in a particular region of the body. It is named after William Horrock, a British physician who first described the technique in 1929.
**Why the Correct Answer is Right:** Horrock's apparatus involves passing a known volume of blood through a known length of blood vessel while measuring the pressure difference across the vessel. The resistance (R) can be calculated using the formula:
R = Pressure difference / Flow rate
Blood flow rate (Q) can be calculated using the formula:
Q = Flow rate / Cross-sectional area
Substituting R and Q in the formula for resistance, we get:
R = Pressure difference / (Flow rate / Cross-sectional area)
R = (Pressure difference / Flow rate) * Cross-sectional area
Hence, the correct answer is D - Horrock's apparatus estimates the viscosity of blood, as the formula shows that resistance is directly proportional to the viscosity of the fluid (in this case, blood) and inversely proportional to the cross-sectional area and blood flow rate.
**Why Each Wrong Option is Incorrect:**
A. Resistance is calculated, not viscosity. The apparatus measures resistance to blood flow, not blood viscosity.
B. Compliance of blood vessels is measured using a different technique, not Horrock's apparatus. Compliance refers to the ability of a blood vessel to expand or contract, while resistance is a property of the blood itself.
C. Elasticity of blood vessels is a different property from resistance. Elasticity refers to the ability of blood vessels to return to their normal shape after being deformed, while resistance is a property of the blood.
**Clinical Pearl:** Horrock's apparatus can give valuable information about the blood properties during diagnosing and treating cardiovascular diseases, as blood viscosity, resistance, and compliance all play crucial roles in understanding the hemodynamic status of a patient.