Ischaemic Heart Disease Flashcards
during what phase does the heart extract most of its oxygen from the coronary arteries?
during diastole (so dependent on diastolic pressure)
If there is a greater demand of oxygen from the heart what happens to the rate of blood flow and the amount of O2 extracted?
- increased blood flow
- no increase in amount of O2 extracted
what is the main cause of O2 demand?
-change in vascular resistance?
why does vascular resistance affect O2 demand?
- oxygen demand is affected by (blood flow X O2 conc gradient b/w artery and vein)
- but the conc gradient doesn’t change much, i.e. it’s always high
- and blood flow is affected by (aortic pressure / coronary resistance)
- if the aortic pressure remains unchanged, then the coronary resistance must reduce to increase blood flow hence increase O2 demand.
Explain how metabolic factors affect oxygen demand and blood flow?
- O2 acts as a vasoconstrictor
- Lack of O2 (hypoxia) = vasodilation
- This prevents regeneration of ATP from AMP
- Adenosine, a direct vasodilator that acts on A2 adenosine receptors on vascular muscle, levels rise in myocardium
- Lactate, H+ and prostacyclin (PGI2) accumulate and cause vasodilation
Explain how endothelium-mediated factors affect oxygen demand and blood flow?
- bradykinin, histamine and Ach release NO
- NO diffuses into vascular muscle
- cGMP levels rise activating protein kinase G
- causes vascular relaxation
- resulting in vasodilation, hence increased blood flow, therefore increased O2 demand.
Explain how neurohumoral factors affect oxygen demand and blood flow?
- adrenaline and noradrenaline bind to alpha1-adrenoreceptors in the epicardial vessels causing vasoconstriction
- adrenaline and noradrenaline bind to β-adrenoreceptors in the subendocardial vessels causing vasodilation
what is it called when the oxygen supply doesn’t meet the oxygen demand?
ischaemia
what is myocardial ischaemia?
when the oxygen supplied to the heart doesn’t meet the demand for oxygen
what is coronary reserve?
the capacity to increase perfusion more than the resting perfusion value
what is the effect of narrowing the large epicardial coronary artery?
- increases blood resistance to flow
- pressure falls below diastolic pressure
- use up coronary reserve
what effect does narrowing the small arterioles e.g. by an atheroma developing?
increased resistance to blood flow but not as much as in the large arteries as the small ones can dilate.
what is the effect of lack of blood/oxygen to the heart?
- myocardial ischaemia
- chest pain (angina)
- myocardial infarction (MI)
- hypotension
- Anaemia
what is wall tension?
the force generated per unit myocardial area
What is Laplaces’ law?
Cardiac Wall Tension = (transmural pressure X radius) / (2 X wall thickness)
If the stroke volume and cardiac output decreases but there’s no change in wall thickness, what would happen?
- ventricular pressure rises
- ventricular radius increases
- wall tension increases
- Myocardial O2 demand rises
- Sympathetic counteractive stimulation (HR increases and Vasoconstriction occurs)
- ventricular myocardium hypertrophy therefore occurs
Risk factors of coronary heart disease/myocardial ischaemia?
Modifiable Risk Factors: 1. Hypertension 2. Diabetes 3. Hypercholesterolaemia(Total : HDL-C, LDL-C) 4. Smoking 5. Diabetes mellitus 6. Sedentary life-style 7. Obesity Non-modifiable Factors: 8. Age 9. Male Gender 10. Family history
what causes Angina Pectoris?
- transient (shot-lasting) episodes of myocardial ischaemia
- which causes pain after the heart switches to anaerobic metabolism
what is stable angina?
- pain experienced on exertion of emotional stress
- indication of significant artery narrowing
- pain ends when rested
what is unstable angina?
- incomplete occlusion causing pain on minor exertion
- can also cause pain when at rest due to blockage
- blood flows through other vessels or small arteries dilate to allow more blood supply (aka collateral blood supply). This happens to meet O2 demand
what is variant angina?
- Focal Coronary Vasospasm (Localised spasm of the coronary artery causing vasoconstriction)
- pain experienced due to lack of O2 supplied at rest
During non-aerobic respiration what is produced and what does it dissociate into?
- Lactic acid is produced
- Dissociates into Lactate and H+
what is the consequence of low ATP and high H+ concentrations?
causes abnormal ventricular contraction
what can happen as a result of persistent ischaemia?
- acidosis (due to inhibited glycolysis)
- Myocardial Infarction
