6) The body quite readily accommodates to the reduction in coronary artery radiu

Question

6) The body quite readily accommodates to the reduction in coronary artery radius by increasing the radius of blood vessels downstream (via auto-regulation), which reduces the overall resistance of the circulatory system and raises the local flow rate in the coronary artery to an acceptable value. However, as the numbers in the previous parts suggest, an 80% reduction severely reduces the flow rate (over 99%). What if the body could maintain a flow rate of 1 mL/s in the 80% occluded vessel by raising the pressure? What pressure drop occurs across an 80% occluded artery at a flow rate of Qml mL/s? mmHg Submit

Explanation / Answer

1.The higher the pressure exerted by the heart, the faster blood will flow. It is an example of a direct relationship between two quantities (blood flow rate and pressure difference). Another factor which controls the blood flow rate, and it is resistance of the blood vessels to blood flow. This resistance is simply due to the width of the vessels - it's hard to push a lot of blood through a thin tube. Thus, we have an inverse relationship between blood vessel resistance and the blood flow rate - the higher the resistance, the slower the flow rate.

The relationship is expressed as follows:

Blood flow rate= pressure difference ÷ resistance

If the body maintains a flow rate of 1ml/ s in the 80% occluded vessels by the raising pressure it will creates a difference across the membrane of a blood cell causes a shift of water and a change of cell volume. The changes in shape and flexibility affect the mechanical properties of whole blood. A change in plasma osmotic pressure alters the hematocrit, that is, the volume concentration of red cells in the whole blood by redistributing water between the intravascular and extravascular spaces. This in turn affects the mechanics of the whole blood.

2. Mean arterial pressure formula:

MAP = 1/3 * SBP + 2/3 * DBP

DBP is the diastolic blood pressure.

This relation can be different in patients with bradycardia or tachycardia. Such patients' cardiac cycle is slightly different (the shape of the arterial pressure pulse becomes "narrower"), and the MAP is closer to an arithmetic mean of SBP and DBP. Typically, electronic circuitry or digital techniques are required to find the MAP in these cases.

You can also use the mean arterial pressure calculator to find the pulse pressure PP. Simply subtract the diastolic pressure from the systolic one:

PP = SBP - DBP

So, if the flow rate {Q ml} ml/s of blood in occluded artery the pressure can be calculated as by the formula given in mm Hg.

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