Question

Figure 11.7shows how a common measurement of arterial blood pressure is made. Is there any effect on the measured pressure if the manometer is lowered? What is the effect of raising the arm above the shoulder? What is the effect of placing the cuff on the upper leg with the person standing? Explain your answers in terms of pressure created by the weight of a fluid.

Short answer

The recorded pressure is unaffected by the manometer being lowered.

Step-by-step solution

Conceptual Introduction

Fluid statics, often known as hydrostatics, is a branch of fluid mechanics that investigates the state of balance of a floating and submerged body, as well as the pressure in a fluid, or imposed by a fluid, on an immersed body.

Define the mercury manometer

The use of mercury manometers to measure arterial blood pressure is common.

As illustrated in the illustration, an inflatable cuff is put on the upper arm (Figure 11.7).

The individual taking the measurement produces pressure by squeezing the bulb, which is transferred unchanged to both the major artery in the arm and the manometer.

Blood flow below the cuff is stopped off when the applied pressure exceeds the blood pressure.

After that, the individual taking the measurement gradually relaxes the applied pressure while listening for blood flow to resume.

The heart's pumping activity causes blood pressure to pulse, reaching a maximum, known as systolic pressure, and a low, known as diastolic pressure, with each beating.

What if manometer is lowered?

If the manometer is lowered, it has no influence on the recorded pressure, but if the manometer is not at eye level, the reading will be inaccurate.

The arm is not in level with his heart when it is above the shoulder because the pressure caused by blood weight is low, blood pressure will be lower than blood pressure recorded at the heart level.

Step 4: The effect of placing the cuff on the upper leg with the person standing

When the cuff is positioned on the upper leg, the pressure exerted by the weight of blood is greater, resulting in a higher blood pressure than the blood pressure at heart level.

The pressure exerted by the blood is more as the formula of the pressure as the height of the fluid column increases the pressure increases.

$\mathit{P}\mathbf{=}\mathit{h}\mathit{\rho }\mathit{g}$

Where h is the height of the fluid column, in this case the height of the blood column above the legs are more compare to that of arms.

Hence, we can conclude that the recorded pressure is unaffected by the manometer being lowered. The pressure imposed by the weight of blood is larger when the cuff is placed on the upper leg, resulting in a higher blood pressure than the blood pressure at heart level