Regulation of Coronary Blood Flow

OUTLINE

• CORONARY VESSELS

• CORONARY BLOOD FLOW

• AUTONOMIC INNERVATION OF HEART AND VASCULATURE

• FACTORS AFFECTING CORONARY BLOOD FLOW

• CORONARY AUTOREGULATION

• APPLIED ASPECTS

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ZULFANI ARIANTI ZAKARIA

CORONARY BLOOD SUPPLY

• CONSIST OF1) Arterial supply

2) Venous drainage

1.ARTERIAL SUPPLY

• The cardiac muscle is supplied by two coronary arteries

(a) the right and

(b) left coronary arteries.

• Both arteries arises from the sinuses behind the cusps of the aortic valves at the root of the aorta.

RT. CORONARY ARTERY

• Smaller than left coronary artery.

• Arises from anterior aortic sinus of ascending aorta.

COURSE:

• Emerges from the surface of heart between pulmonary trunk and right auricle.

• Winds round the inferior border to reach the diaphragmatic surface to reach the posterior inter-ventricular sulcus(groove).

• Terminates by anastomising with left

coronary artery

BRANCHES OF RCA

– Conus arteriosus br.

– SA Nodal

– Marginal br.

– Posterior interventricular artery

– Right atrial br.

– Anterior ventricular br.

– Posterior ventricular br.

LEFT CORONARY ARTERY

• Larger than the right coronary artery.

• Arises from left posterior aortic sinus.

COURSE• Runs forward and to the left and emerges

between the pulmonary trunk and the left auricle.

• Here the anterior inter-ventricular branch is given .

• The further continuation of the left coronary artery is sometimes called the circumflex artery.

• After giving off the anterior interventricular branch it runs to the left in the left anterior coronary sulcus.

• It winds around the left border and near posterior interventriular groove it terminates by anastomosing with the right coronary artery.

BRANCHES:

Anterior interventricular artery Left diagonal artery

Circumflex artery Left marginal artery

Anterior ventricular branch

Posterior ventricular branch

Atrial branch

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NURSYAFIKAH MUHAMAD NASIR

RIGHT DOMINANT

LEFT DOMINANT

CARDIAC DOMINANCE

VENOUS DRAINAGE OF THE HEART

• The venous drainage of the heart is by three means:

– Coronary sinus.

– Anterior cardiac veins

– Venae Cordis minimae.

Coronary sinus:

• Largest vein of the

heart

• Length: 3 cm long

• Situation: Coronary

sulcus.

Tributaries of CS:

-Great cardiac vein

-Middle cardiac vein

-Small cardiac vein

-Oblique vein of left atrium

-Right marginal vein

-Posterior vein of left

ventricle.

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WAN NUR AINI BINTI MOHAMAD ZAIN

CORONARY BLOODFLOW

• The cardiovascular system is composed of two circulatory paths ;

– Pulmonary circulation

The part of blood circulation which carries oxygen-depleted blood away from the heart, to the lungs, and returns oxygenated blood back to the heart.

– Systemic circulation

The part of blood circulation that carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart.

Pulmonary circulation

• Oxygen-depleted blood from the body enters the RA through the superior and inferior venae cavae.

• The blood is then pumped through the tricuspid valve into the RV.

• From the RV, blood is pumped through the pulmonary valve and into the pulmonary artery.

• The pulmonary artery splits into the right and left pulmonary arteries and travel to each lung.

• At the lungs, the blood travels through capillary beds on the alveoli where respiration occurs

removing CO2 and adding O2 to the blood.

• The oxygenated blood then leaves the lungs through pulmonary veins, which returns it to the LA, completing the pulmonary circuit.

Systemic Circulation

• Oxygen-rich blood from the lungs enters the LA through the pulmonary veins.

• The blood is then pumped through the mitral valve into the LV.

• From the LV, blood is pumped through the aortic valve and into the aorta, the body's largest artery.

• The aorta arches and branches into major arteries to the upper body before passing through the diaphragm, where it branches further into arteries which supply the lower parts of the body.

• Waste and CO2 diffuse out of the cell into the blood, while O2 in the blood diffuses out of the blood and into the cell.

• The deoxygenated blood continues through the capillaries which merge into venules, then veins, and finally the venae cavae, which drain into the RA of the heart.

• From the RA, the blood will travel through the pulmonary circulation to be oxygenated before returning again to the system circulation.

• Coronary circulation, blood supply to the heart muscle itself, is also part of the systemic circulation.

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Overview

• The right side receives oxygen-poor blood from the body and tissues and then pumps it to the lungs to pick up oxygen and dispel carbon dioxide

• Its left side receives oxygenated blood returning from the lungs and pumps this blood throughout the body to supply oxygen and nutrients to the body tissues

The heart=a muscular double pump with 2 functions

Characteristicsof coronary circulation

NORMAL CORONARY BLOOD FLOW

- Under resting conditions coronary blood flow (CBF) in the human heart averages 70ml/min/100g heart weight or about 225ml/min which is about 4-5% of the total cardiac output.

- In severe muscular exercise, the work of the heart increased and the CBF may be increased up to 2 liters/ minute.

– Coronary Inflow (arterial) occurs mainly during diastole, because during systole the coronary arteries are mechanically compressed by the contracting myocardium, i.e.

Systole of the heart coronary inflow

Diastole of the heart coronary inflow

- Coronary Outflow (venous) occurs mainly during systolic due to compression of the coronary veins by the contracting myocardium. During diastole coronary outflow and veins are filled.

Blood flow to Heart during Systole & Diastole

• Phasic nature

During systole when heart muscle contracts it compresses the coronary arteries therefore blood flow is less to the left ventricle during systole and more during diastole

• Coronary blood flow to the right side is not much affected during systole.

Reason---Pressure difference between aorta and right ventricle is greater during systole than during diastole, therefore more blood flow to right ventricle occurs during systole.

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NURUL EDDIYA KIEW

Autonomic Innervation of Heart and Vasculature

FACTORS REGULATING CORONARY BL.FLOW

• Physical

• Chemical

• Neural

• Hormonal

• Reflex

Physical Factors :1. Aortic Blood Pressure

CBF is directly proportional to aortic blood pressure (diastolic)

Diastolic pressure decreases or MAP decreases

CBF will decreases.

2. Heart Rate

Excessive in the heart rate

diastolic period

coronary filling

CBF

3. Cardiac Output

CBF is directly proportional to COP

Increased cardiac output

BP in aorta + reflex inhibition of the vagal vasoconstrictor tone

coronary vasodilatation

CBF

• C.B.F. occurs mainly during diastole due to

- compression of coronary blood vessels during systole by the contracted muscle fibers.

During diastolic phases :- C.B.F. is more than that during

systole.- Maximal blood flow during

iso volumetric relaxation phase

During systolic phase :- CBF is less than that

during diastole.- Minimal blood flow

during iso volumetric contraction phase.

Chemical Factors :1. Metabolic factors

cardiac metabolism

O2tension (local hypoxia)

CO2

K+, lactic acid & adenosine in the cardiac muscle

coronary vasodilatation -> CBF.

2. Drugs

Nitrites, angised, aminophylline, caffeine & Khellin (coronary vasodilator)

coronary vasodilatation

CBF

NERVOUS FACTORS

Direct effect:

• Parasympathetic:

vagus has very slight distribution to coronary, so its stimulation has slight dilator effect.

• Sympathetic:

Both alpha and Beta receptors exist in the coronary vessels. Sympathetic stimulation causes slight direct coronary constriction.

Indirect effect:

• Plays a far more important role in normal control of coronary blood flow than the direct.

• Sympathetic stimulation increase both heart rate and myocardial contractility, as well as its rate of metabolism leading to dilatation of coronary blood vessels.

• The blood flow increase proportional to the metabolic need of heart muscle

HORMONAL FACTOR

• Thyroxin cardiac metabolism coronary vasodilator CBF.

• Vasopressin (antidiuretic hormone) coronary vasoconst CBF.

REFLEX CONTROL

• Anrep’s reflex:

• Increased venous return causes increased pressure in right atrium, leading to reflex increase in CBF e.g. during muscular exercise.

• Gastro-coronary reflex:

• Distention of the stomach with heavy meal causes reflex vasoconstriction of coronary blood vessels decreasing CBF.

Coronary Autoregulation

• If there is sudden change in aortic pressure, coronary vascular resistance will adjust itself proportionally within few seconds; so that a constant blood flow is maintained.

• Range of autoregulation: 60 – 140 mmHg.

Mechanism:

• Myogenic response:

• an increase in passive stretch, caused by increased perfusion pressure, causes active smooth muscle contraction.

• Chemical theory:

• Decrease perfusion pressure leads to Increase adenosine & Decreased oxygen which causes Vasodilatation and increase CBF

• Endothelium derived relaxation factor (EDRF):

• Hypoxia, ADP, muscular exercise (increase distention force), stimulate vascular endothelium to secrete EDRF, which is a potent vasodilator, that causes coronary dilatation and increase CBF.

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NURRAH NADZIRAH BINTI MOHD RAUZIA

Applied aspects

2nd Year Pathology 2010

Thrombosis

• Inappropriate activation of haemostatic mechanisms– E.g. uninjured vessel or very minor injury

• Definition: – formation of solid mass of blood constituents within

vascular system in life

• Virchow’s triad:1. changes in the vessel wall

2. changes in blood flow

3. Hypercoagulable state

2nd Year Pathology 2010

Arterial Thrombi

Occlusive thrombus in wall of atherosclerotic coronary artery

Consequences of Thrombosis

• Arterial Thrombosis– Obstruction:

• Myocardial infarction due to coronary artery thrombosis

• Cerebral infarction (Stroke) due to carotid artery thrombosis

• Acute lower limb ischaemia & infarction due to femoral/popliteal artery thrombosis

• Venous Thrombosis e.g. deep leg veins– Obstruction:

• Local congestion, swelling, pain, tenderness

• Oedema and impaired venous drainage– Infection & varicose ulcers

2nd Year Pathology 2010

Fate of Thrombi

1. Dissolution– by fibrinolysis

2. Propagation – along length of vessel complete vessel occlusion

3. Embolization4. Recanalization

– capillaries invade thrombus to re-establish blood flow5. Organization

– Inflammation and fibrosis replacement by scar, may obliterate vessel lumen

Recent thrombi may be completely dissolvedOlder thrombi more resistent to fibrinolysis

(extensive fibrin polymerization)

2nd Year Pathology 2010

Embolism

• Any intravascular mass (solid, liquid or gas) carried by blood to site distant from point of origin

• Most derived from thrombi (thromboembolism)

• Lodge in vessels too small to permit further passage

– partial / complete vascular occlusion

– distal tissue ischaemia & infarction

• Arterial Thrombosis• Cardiac/aortic mural thrombi emboli to brain, kidneys, spleen

Atherosclerosis

• Plaques from atherosclerosis can behave in different ways.• They can stay within the artery wall. There, the plaque

grows to a certain size and stops. Since this plaque doesn't block blood flow, it may never cause symptoms.

• Plaque can grow in a slow, controlled way into the path of blood flow. Eventually, it causes significant blockages. Pain on exertion (in the chest or legs) is the usual symptom.

• The worst-case scenario consists of plaques that suddenly rupture, allowing blood to clot inside an artery. In the brain, this causes a stroke; in the heart, a myocardial infarction