physiology of the heart 3

Question 1

What are the first arteries that stem from the aorta and what is their role

Answer 1

The coronary arteries - These feed the heart muscles.

Question 2

What is a coronary angiogram?

Answer 2

A small dye is injected into the coronary artery to assess if an individual has coronary heart disease.

Question 3

What is coronary blood flow

Answer 3

Perfusion pressure / resistance

Question 4

When does coronary blood flow occur and why?

Answer 4

In diastole - because when the heart contracts it squashes its own blood supply due to the pressure in the heart being so high in systole.

Question 5

What is the basic metabolism of an arrested heart

Answer 5

2ml/min/100g

Question 6

What is the metabolism of a resting heart

Answer 6

8ml/min/100g

Question 7

What is the metabolism of a heart during heavy exercise

Answer 7

70ml/min/100g

Question 8

How does the metabolism of cardiac myocytes compare to that of skeletal muscle

Answer 8

It is much greater than skeletal

Question 9

Give the equation for oxygen delivery

Answer 9

Arterial O2 conc x coronary blood flow

Question 10

What is the result of a patient with coronary heart disease also having anaemia

Answer 10

Anaemia causes reduced O2 delivery - if the patient already suffers from CHD then tissues of the heart may become ischaemic

Question 11

What is the main target for increasing oxygen making it to the heart muscle?

Answer 11

Coronary blood flow. Not O2 conc as this sees very little change.

Question 12

Describe the aortic pressure trace

Answer 12

When the heart stops contracting, blood in the aorta attempts to rush back into the left ventricle but is prevented from doing so due to the aortic valve snapping shut. The peak pressure is the systolic pressure and the trough is the diastolic. Coronary blood flow only occurs in diastole so diastolic pressure must have something to do with coronary blood flow.

Question 13

Describe the left ventricle pressure trace.

Answer 13

To measure a catheter is placed in the left ventricle - The QRS complex is associated with ventricular systole.
Immediately after the heart is activated there is a huge increase in ventricular pressure up to 120mmHg.
When the ventricle relaxes pressure drops to almost zero.

Systolic pressure equates to the peak of the left ventricular pressure
Diastolic pressure equates to LVEDP. The LEVDP is the pressure that stretches the fibres and is important for contraction.

Question 14

What is the method of performing a left ventricle to aorta pressure trace.

Answer 14

The catheter is put in the left ventricle and then pulled into the aorta - this is a pull-back trace. The systolic BPs are the same, but diastolic pressures are different. The difference between the two is the perfusion pressure

Question 15

What are the pysical factors effecting diastolic coronary flow

Answer 15

The time interval of diastole and the difference in diastolic pressures of the aorta and LV.

Question 16

Describe three ways in which the perfusion pressure is decreased.

Answer 16

Reduced aortic diastolic pressure - Reduces the difference between aortic and LVEDP

Raised LVEDP - again reduces the difference

Tachycardia - Disproportionately reduces diastole compared to systole.

Question 17

Does tachycardia favour changes in systole or diastole

Answer 17

Systole stays te same

The heart rate increases due to a shortening of diastole. It relaxes quicker in order to again fill with blood and perform the next contraction. Some patients become ischaemic because of tachycardia.

Question 18

What is autoregulation of coronary blood flow

Answer 18

The ability of the heart to maintain a constant blood flow despite changes in perfusion pressure.

Question 19

How is autoregulation of coronary blood flow performed

Answer 19

The resistance of the vasculature bed is lowered when pressure drops. As a result flow is increased back toward the same level as when pressure initially dropped.

Question 20

What effect does hypoxia have on coronary arteries

Answer 20

Marked coronary vasodilation in situ but not in isolated coronary arteries.

Question 21

What is the local metabolite that causes coronary vasodilation during hypoxia, which can be used as a treatment as a result.

Answer 21

Adenosine

Question 22

What other local metabolites/ mediators cause coronary vasodilation

Answer 22

Increase potassium

Increased carbon dioxide

Increased lactate

Increased hydrogen ions.

Question 23

What other systems are responsible for autoregulation (not metabolites and mediators)

Answer 23

The autonomic NS and circulating hormones can often effect the coronaries but are much less important.

Question 24

What hormones are released from the heart and why

Answer 24

Released by stretching of atrial and ventricular muscle cells, raised atrial and ventricular pressures and volume overload

ANP from the atria - Atrial natriuretic peptide

BNP from the ventricles - Brain natriuretic peptide

Question 25

What is the effect of BNP and ANP

Answer 25

Increase renal sodium excretion (and water), increase vascular permeability, inhibit the release of aldosterone, angiotensin II, endothelin and anti-diuretic hormone.

They act as a counter-regulatory system to the renin-angiotensin system - to reduce BP

Question 26

What is the natural metaboliser of ANP/BNP and what drugs are used to inhibit its function

Answer 26

Neutral endopeptidiase (NEP)
NEP inhibition increases levels of natriuretic peptides in circulation - Sacubitril
Valsartan is an angiotensin II blocker