LEC.07. Coronary circulation.ppt LEC.07. Coronary circulation.ppt

LEC.07. Coronary circulation.ppt

1. Coronary circulationCoronary circulation
By Prof. By Prof.
Soheir HelmySoheir Helmy

2. Coronary circulationCoronary circulation

It is concerned with the blood supplying It is concerned with the blood supplying
the cardiac muscles.the cardiac muscles.

Coronary vessels:-Coronary vessels:-
The heart is supplied by 2 coronary The heart is supplied by 2 coronary
arteries arising from the aorta just arteries arising from the aorta just
above the aortic valve.above the aortic valve.
The The leftleft coronary artery supplies coronary artery suppliesthe the
LT. atrium, the LT ventricle & the LT. atrium, the LT ventricle & the
anterior part of inter ventricular septum anterior part of inter ventricular septum

3. Coronary circulationCoronary circulation

The The rightright coronary artery:- supplies the coronary artery:- supplies the
RT. Atrium ,RT ventricle ,and the post. RT. Atrium ,RT ventricle ,and the post.
Part of inter ventricular septum.Part of inter ventricular septum.
The coronary arteries are The coronary arteries are functional endfunctional end
arteries. arteries. There areThere are small anastomotic small anastomotic
connection between the 2 coronaries connection between the 2 coronaries
which are not sufficient to supply the which are not sufficient to supply the
cardiac muscle with blood if one of cardiac muscle with blood if one of
them is occluded.them is occluded.

6. Coronary circulationCoronary circulation
The heart comprise 0.5% of the total body weight...The heart comprise 0.5% of the total body weight...
..
 Under restingUnder resting condition the coronary blood flow is condition the coronary blood flow is
about 5% of the COP , it is about 250 ml/min.about 5% of the COP , it is about 250 ml/min.
 The coronary capillaries run parallel to the cardiac The coronary capillaries run parallel to the cardiac
muscle fiber ,and there is about one coronary muscle fiber ,and there is about one coronary
capillary for each muscle fiber capillary for each muscle fiber
 .All the capillaries are open all the time (there is no .All the capillaries are open all the time (there is no
vasomotion). vasomotion).
 Most of the O2 is extracted from the blood as it Most of the O2 is extracted from the blood as it
passes through myocardial capillaries.passes through myocardial capillaries.

7. O2 consumption of the heartO2 consumption of the heart

The heart has a very high basal O2The heart has a very high basal O2 consumption. consumption.
About 8-10 ml/100gm.About 8-10 ml/100gm.

O2 in coronary artery = 19ml%O2 in coronary artery = 19ml%

O2 in coronary vein = 5ml%O2 in coronary vein = 5ml%

The highest arterio venous oxygen difference of all The highest arterio venous oxygen difference of all
organs.organs.

Low venous O2 reserveLow venous O2 reserve

This is in contrast to other tissues.This is in contrast to other tissues.

8. Phasic changes in coronary bloodPhasic changes in coronary blood
flowflow

During systole:-During systole:-

The coronary blood flow falls to a lowThe coronary blood flow falls to a low value ,which is value ,which is
opposite to the flow in all other beds in the body. Due opposite to the flow in all other beds in the body. Due
to strong compression of the ventricular muscles to strong compression of the ventricular muscles
around the intramuscular vessels.around the intramuscular vessels.

This decrease in blood flow during systole is This decrease in blood flow during systole is
compensated by O2 delivered from myoglobin.compensated by O2 delivered from myoglobin.

During diastole:- During diastole:- the cardiac muscle relaxes and the cardiac muscle relaxes and
blood flows rapidly into the coronary arteries blood flows rapidly into the coronary arteries

9. 
Phasic changes in blood flow to the right ventricle Phasic changes in blood flow to the right ventricle
are less pronounced are less pronounced because of the lesser force of because of the lesser force of
contraction. contraction.

Perfusion timePerfusion time

Any increase in heart rate affect diastolic time more Any increase in heart rate affect diastolic time more
than systolic time and reduces the perfusion timethan systolic time and reduces the perfusion time..

10. Coronary blood flowCoronary blood flow

11. Regulation of coronary blood Regulation of coronary blood
flowflow

IntrinsicIntrinsic mechanism mechanism
(autore(autoregulation)gulation)

The coronaryThe coronary blood blood
flow is regulated by flow is regulated by
the metabolic need the metabolic need
of the heart.of the heart.

CBF is increased CBF is increased
when cardiac work when cardiac work
increased &vice versaincreased &vice versa

Extrinsic mechanismExtrinsic mechanism

Nervous factorsNervous factors

Chemical factorsChemical factors

Mechanical factorsMechanical factors

12. Coronary perfusion pressureCoronary perfusion pressure

During systole, intramuscular blood vessels are compressed and During systole, intramuscular blood vessels are compressed and
twisted by the contracting heart muscle and blood flow to the twisted by the contracting heart muscle and blood flow to the
left ventricle is at its lowest. left ventricle is at its lowest.

In systole, intramyocardial blood is propelled forwards towards In systole, intramyocardial blood is propelled forwards towards
the coronary sinus and retrogradely into the epicardial vessels, the coronary sinus and retrogradely into the epicardial vessels,
which act as capacitorswhich act as capacitors..

During diastole when the muscle relaxes, Flow resumes During diastole when the muscle relaxes, Flow resumes

The coronary perfusion pressure is the difference betweenThe coronary perfusion pressure is the difference between

the aortic diastolic pressure and left ventricular end-diastolic the aortic diastolic pressure and left ventricular end-diastolic
pressure (LVEDP )pressure (LVEDP )

60- 160 mm Hg is the normal range for coronary 60- 160 mm Hg is the normal range for coronary perfusion perfusion
pressurepressure

13. IntrinsicIntrinsic mechanism(autoregulation)mechanism(autoregulation)
OxygenOxygen demand is the major factor in local blood flow demand is the major factor in local blood flow
regulation.regulation.
Oxygen lack (hypoxia)Oxygen lack (hypoxia) causes causes v vasodilatationasodilatation HOW? HOW?
Decrease O2Decrease O2 tension in the coronary blood has a tension in the coronary blood has a
direct relaxing effect on the smooth muscles of the direct relaxing effect on the smooth muscles of the
wall of the coronary arteries.wall of the coronary arteries.
Decrease O2Decrease O2 tension tension  release of vasodilator release of vasodilator
substances by the tissues such as adenosine, K , CO2 substances by the tissues such as adenosine, K , CO2
and bradykinin.and bradykinin.

15. Extrinsic mechanismExtrinsic mechanism

1- nervous factors.1- nervous factors.

2- mechanical factors.2- mechanical factors.

3-chemical factors3-chemical factors

16. Nervous factorsNervous factors

Sympathetic stimulation:-Sympathetic stimulation:-
V.CV.C by a direct effect by a direct effect
V.DV.D byby indirect mechanism throughindirect mechanism through increase increase
metabolic activity of the heart ,metabolic activity of the heart ,butbut the net result is the net result is
an increase in coronary blood flow.an increase in coronary blood flow.
Parasympathetic stimulation:-Parasympathetic stimulation:-

Direct Direct V.DV.D effect. effect.
It decrease H.R &the metabolic activity of the heart is It decrease H.R &the metabolic activity of the heart is
decreased. This lead todecreased. This lead to V.C V.C and decrease coronary and decrease coronary
blood flow.blood flow.

17. Chemical factors:Chemical factors:
1.1.NiNitroglycerin.troglycerin.
2.2.LongLong acting nitrates. acting nitrates.
3.3.BetaBeta blockers e.g blockers e.g propranolol act by reducing propranolol act by reducing
myocardial O2 consumption ,H.R and cardiac muscle myocardial O2 consumption ,H.R and cardiac muscle
contractility.contractility.
4.4.CalciumCalcium channel blockers. channel blockers.
All theseAll these chemicals produce coronary dilatation and are chemicals produce coronary dilatation and are
important in the treatment of coronary artery important in the treatment of coronary artery
diseases.diseases.

18. Anti platelet drugs, anticoagulants and Anti platelet drugs, anticoagulants and
lipid lowering drugslipid lowering drugs

These agents act inside the lumen to prevent These agents act inside the lumen to prevent
further reduction in the vessel diameter. further reduction in the vessel diameter.

Statins inhibit, the enzyme involved in Statins inhibit, the enzyme involved in
cholesterol synthesis.cholesterol synthesis.

Antiplatelet drugs prevent platelet Antiplatelet drugs prevent platelet
aggregation, often the initial step in the aggregation, often the initial step in the
formation of an occlusive thrombus.formation of an occlusive thrombus.

Antithrombin agents act at various sites in the Antithrombin agents act at various sites in the
coagulation cascade to inhibit thrombin coagulation cascade to inhibit thrombin
formation. formation.

19. Drugs acting on angiotensinDrugs acting on angiotensin

Angiotensin-converting enzyme inhibitors reduce Angiotensin-converting enzyme inhibitors reduce
conversion of angiotensin I to angiotensin II.conversion of angiotensin I to angiotensin II.

These drugs reduce angiotensin-mediated These drugs reduce angiotensin-mediated
vasoconstriction and enhance myocardial perfusion vasoconstriction and enhance myocardial perfusion
by vasodilatation without reflex tachycardia.by vasodilatation without reflex tachycardia.

Over time, it also regulates fibrous tissue formation Over time, it also regulates fibrous tissue formation
after tissue injury.after tissue injury.

20. Mechanical factors:Mechanical factors:

The heart rate.The heart rate.


Phases of Cardiac cycle.Phases of Cardiac cycle.
Arterial blood pressure.Arterial blood pressure.

21. Heart rateHeart rate

Total coronary flow is greater in Total coronary flow is greater in diastolediastole
than in than in systole.systole.
Increased heart rateIncreased heart rate in normal subject in normal subject::
Increased cardiac work &decreased Increased cardiac work &decreased
diastolic perioddiastolic period >>restrict coronary >>restrict coronary
flowflow
But at the same time there is an But at the same time there is an
increase in metabolism>>dilatation of increase in metabolism>>dilatation of
coronary vessels.coronary vessels.

22. In heart with limited blood flowIn heart with limited blood flow

Such as in coronary insufficiencySuch as in coronary insufficiency

Increased heart rate may cause chest Increased heart rate may cause chest
pain (angina).pain (angina).

Because flow can not increase to meet Because flow can not increase to meet
the increased O2 demand.the increased O2 demand.

23. Heart rateHeart rate

Decrease in the heart rate:-Decrease in the heart rate:-

The metabolic activity of the heartThe metabolic activity of the heart decreased.decreased.

The amountThe amount ofof vasodilator metabolic vasodilator metabolic
substances will be decreased so the coronary substances will be decreased so the coronary
blood flow decreases to parallel the decrease blood flow decreases to parallel the decrease
in cardiac metabolism.in cardiac metabolism.

24. Phases of Cardiac cycle.Phases of Cardiac cycle.
The left ventricle:-The left ventricle:-

Gets its blood supply mainly duringGets its blood supply mainly during diastole. diastole.
during the contraction phase ,the left ventricular during the contraction phase ,the left ventricular
myocardial fibers squeeze the coronary vessels myocardial fibers squeeze the coronary vessels
between them and stop the blood flow in them.between them and stop the blood flow in them.

The rightThe right ventricle:-ventricle:-

The contraction ofThe contraction of myocardial fibers ismyocardial fibers is weaker it weaker it
does not stop the flow in RT coronary vessels. does not stop the flow in RT coronary vessels.
so the flow is continuous through out the so the flow is continuous through out the
cardiac cycle.cardiac cycle.

25. Coronary artery diseasesCoronary artery diseases

Angina pectoris:-Angina pectoris:-

Myocardial ischemiaMyocardial ischemia due to decreased due to decreased
coronary blood flow.coronary blood flow.

It is characterized by It is characterized by short attacksshort attacks of sever of sever
pericardial pain which is mostly substernal and pericardial pain which is mostly substernal and
usually radiate to the left shoulder and arm.usually radiate to the left shoulder and arm.

The attackThe attack is brought about by is brought about by
effort ,excitement ,and sudden exposure to effort ,excitement ,and sudden exposure to
cold.cold.

Causes:-Causes:- coronary spasm, atherosclerosis, coronary spasm, atherosclerosis,
aortic stenosis ,and aortic regurgitation.aortic stenosis ,and aortic regurgitation.

27. Coronary artery diseasesCoronary artery diseases

Myocardial infarction:-Myocardial infarction:-

It meansIt means necrosis of a part of the necrosis of a part of the
myocardium due to sever prolonged myocardium due to sever prolonged
ischemia or sudden occlusion of a major ischemia or sudden occlusion of a major
coronary artery.coronary artery.

It produce irreversible changes of the It produce irreversible changes of the
muscle cells.muscle cells.