August 6, 2020
August 6, 2020

The Discussion Section question is:  

Add a comment pertaining to the effect of workload on coronary blood flow. Please detail our potential to image the ratio of decrease blood flow for  diagnostic value. Add to to the DICUSSION PANNEL for this unit.

Here some example for you :

1- The effect of workload on coronary blood flow and our potential to image the ratio of decrease blood flow for diagnostic value:

According to The Journal of the American Association, coronary blood flow is determined by the rate at which blood flows out of the coronary arteries to other parts of the body. For example, during rest, the amount of blood flows through the coronary arteries is 225 ml per minute which is 4-5% of total cardiac output. During stress, the blood flow is faster and the heart muscle contracts during systole. As a result, during diastole, the cardiac muscle relaxes to allow the flow of blood through the body without any resistance. One significant effect on coronary blood flow is the workload the heart is subjected to during stress. With an increase in stress rate, the heart reacts to pump blood in a faster rate to ensure oxygen is supplied to the rest of the body. When imaging, the vasodilator stress agents are helpful in decreasing the blood flow and relaxing the heart muscle. These pharmacological agents help when measuring the supply to the heart and viewing the heart’s workload.

2- The following is regarding the effect of workload on coronary blood flow and our potential to image the ratio of decrease blood flow for diagnostic value:

The heart is a very smart organ with very smart systems. An auto-regulatory mechanism known as coronary autoregulation is constantly maintaining the interaction of pressure and resistance of coronary blood flow. Decreases in pressure are compensated for by decreases in resistance and conversely, increases in pressure by increases in resistance so that flow remains constant for a give cardiac workload. This regulatory mechanism operates within the range of physiologic arterial pressures but fails during hypotension when flows become strongly dependent on the driving pressure.

For imaging purposes, pharmacological vasodilator stress agents seek to maximally lower the vascular resistance through relaxation of the vascular smooth muscle cell at the level of the microcirculation, thereby uncoupling coronary flow (supply) and myocardial work (demand). With the help of such pharmacological agents, imaging can take place in order for diagnostic purposes.


Schelbert H. R. (2010). Anatomy and physiology of coronary blood flow. Journal of nuclear cardiology : official publication of the American Society of Nuclear Cardiology, 17(4), 545–554. doi:10.1007/s12350-010-9255-x

3- The effect of workload on coronary blood flow and our potential to image the ratio of decrease blood flow for diagnostic value:

Blood flow to the heart mainly occurs during diastole, the great majority of blood flow to the left ventricle occurs during diastole. The diastolic pressure from the aorta propels blood through the coronary circulation. The more coronary blood flow to the left ventricle means the longer time that diastole will last. The right ventricle receives blood equally during both systole and diastole. Diastole lasts for about two thirds of the cardiac cycle. The coronary arties through the myocardium are compressed during ventricular contraction when fibers are thickening and are unable to fill.  The pressure within the left ventricle offers resistance to this flow. Blockage of coronary arteries can reduce coronary blood flow at rest, resulting in a buildup of a clot, and also anything that causes arteries to constrict and not allow the vasodilatation to even improve coronary blood flow.

For imaging potential of decreased blood flow, pharmacological vasodilator stress agents can be utilized to cause a lower vascular resistance through relaxation of the smooth muscles of the heart during a nuclear stress test. This can lead to measuring the supply and demand of the heart, it is which these pharmacological stress agents that when can possibly use to help increase the potential to image the ratio of decreased blood flow for diagnostic reasons and value.

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