coronary circulation

DR NILESH KATE

MBBS,MD ASSOCIATE PROF

DEPT. OF PHYSIOLOGY

CORONARY CIRCULATION

OBJECTIVES. Coronary blood vessels Coronary blood flow: characteristic

features. Measurement of coronary blood flow. Regulation of coronary blood flow Factors affecting coronary blood flow. Coronary artery disease.

Wednesday, May 3, 2023

CORONARY BLOOD VESSELS Coronary arteries –

arise from Root of the Aorta

Right coronary artery – Supplies Rt ventricle, Rt atrium, the Posterior part of left ventricle, posterior part of Interventricular septum & SA node


CORONARY BLOOD VESSELS Left coronary artery –

supplies left ventricle, left atrium, Ant part of Interventricular septum & left branch of bundle of His.

Predominant supply. – 50% by Right coronary artery, 20% Left coronary artery, 30% Both.


CORONARY BLOOD VESSELS Major coronary arteries. –

Rt coronary artery travel in the Epicardium of heart ( superficial vessels) & subdivides into Penetrating branches.

End arteries- appears to be End arteries but shows some Anastomosis.


ANASTOMOSIS Types.

Cardiac – Between branches of two coronary artery & between branches of 2 coronary arteries & Deep Venous System.

Extra cardiac –Between coronary arteries & Vasa vasora of aorta, Vasa vasora of pulmonary arteries, intra thoracic arteries , bronchial arteries & Phrenic arteries.


CORONARY VEINS Coronary sinus -- Wide

vein which drain blood from Myocardium to Right atrium.

Tributaries are – Great cardiac veins, Small cardiac vein, Posterior vein of left ventricle & Oblique vein of left ventricle.


CORONARY VEINS Anterior cardiac vein

– Drains from right ventricle to right atrium.

Thebesian vein – coronary luminal vessels forms Deep Venous System.


CORONARY BLOOD FLOW: CHARACTERISTIC FEATURES

Normal coronary blood flow & oxygen demand. A continuous flow of

blood for supply of oxygen & nutrients



Normal coronary blood flow – at rest 250 ml (70ml/100 gm/min) 5% of cardiac output. During exercise

increases to 3-6 fold. Blood flow to left is

twice Rt ventricle.



Oxygen consumption by the myocardium.

Very high – 8ml/min/100 gm tissue

70-80% of oxygen extracted from each unit as compared to 25% in other tissue.


PHASIC CHANGES IN CORONARY BLOOD FLOW

Blood flow is determined by Balance between Pressure head Aortic pressure & Resistance by myocardium.



Blood flow to left ventricles During systole – During

contraction myocardium produces Throttling effect on coronary arteries , during Isometric contraction phase blood flow to heart practically Ceases.



During Diastole – Myocardium relax &

blood flow increases. Flow Increases

maximally in Isovolumic relaxation phase


EFFECT OF HEART RATE ON CORONARY BLOOD SUPPLY.

During Tachycardia Duration of diastole decreases so coronary blood flow reduces but due to Local Metabolite Regulation of blood flow is not seriously affected.


BLOOD FLOW TO RIGHT VENTRICLE & ATRIA.

Through coronary capillaries of right ventricle shows similar changes but to Less extent.

Blood flow occurs during Both systole & diastole.


BLOOD FLOW THROUGH CORONARY SINUS.

Inflow Rises from Iso volumic contraction phase reaches peak during Protodiastole phase & then gradually Falls.


CLINICAL IMPORTANCE OF PHASIC CORONARY BLOOD FLOW. Sub endocardial

region of left ventricle

In Aortic stenosis In Congestive Heart

failure.


SUBENDOCARDIAL REGION OF LEFT VENTRICLE

Most Vulnerable to Ischemia so most common site of Myocardial Infarction.

As this part receives almost No blood supply during systole.


COMPENSATORY MECHANISM

Capillary Density – Much Higher (1100 capillaries

/mm2) than Epicardial region (750 capillaries/mm2)

Minimum diffusion distance – 20% Shorter (16.5 µm)

as compared to Epicardial (20.5 µm)

Myoglobin content – Higher than Epicardial region.


IN AORTIC STENOSIS Pressure in Left

ventricle increases --so severe compression of coronary vessels during systole & Increase Chance Of MI.


IN CONGESTIVE HEART FAILURE.

Increase in Venous Pressure -- Decreases aortic diastolic pressure -- so effective coronary perfusion falls & Coronary Blood Flow Decreases.


.MEASUREMENT OF CORONARY

BLOOD FLOW.

Nitrous oxide method (Kety Method)

Radionuclides utilization techniques.

Coronary angiographic technique.

Electromagnetic flow meter technique.


NITROUS OXIDE METHOD (KETY METHOD)

Principle – based on Fick’s Principle.

Procedure – Inhale mixture of NO & air for 10 min.

During inhalation serial sample of arterial & coronary sinus venous blood taken at fixed intervals

Coronary blood flow

= N2O taken up/min

-------------------------------

(A-V)


RADIONUCLIDES UTILIZATION TECHNIQUES.

Radioactive Tracers pumped into cardiac muscle cells by Na-K ATPase enz & equilibrate with intracellular K pool.

Distribution of radioactive tracers is Directly proportional to Myocardial blood flow.


PROCEDURE Radionuclide Thallium -

201 injected IV. After 10 min amount of

Thallium taken by myocardial cells measured by Gamma-Scintillation camera

Areas of ischemia detected by low uptake.


CORONARY ANGIOGRAPHIC TECHNIQUE.

Combined with 133 Xe washout using crystal syntillation camera tells about coronary blood flow.


ELECTROMAGNETIC FLOW METER TECHNIQUE.

It tells about Phasic flow & flow per min.

Blood flow through left ventricle determined with the help of Electromagnetic Flow Meter implanted around main left coronary artery.


REGULATION OF CORONARY BLOOD FLOW

LOCAL CONTROL MECHANISM Auto regulation Role of local metabolite Role of endothelial cells.

NERVOUS CONTROL MECHANISM Direct nervous control Indirect nervous control Neurohumoral control factors.


LOCAL CONTROL MECHANISM AUTO REGULATION Ability of organ or tissue to

adjust its vascular resistance & maintain relatively constant blood flow over a wide range of blood pressure.

But Fails below 70 mm Hg blood pressure.


ROLE OF LOCAL METABOLITE At rest 50-70% oxygen

released to myocardium from Haemoglobin.

Almost direct & linear relationship observed between coronary blood flow & O2 consumption.


ROLE OF LOCAL METABOLITE Role of Adenosine

(Berne Hypothesis) – increased myocardial metabolism leads to degradation of Adenine nucleotide to adenosine.


ROLE OF LOCAL METABOLITE This crosses Myocardial cell

membrane , ECF, reaches Precapillary Sphincters of coronary system producing strong Vasodilator response.

Role of other metabolite – hydrogen ions, Bradykinins, CO2, PG are other vasodilator substances.


ROLE OF ENDOTHELIAL CELLS. Endothelium releases

vasodilator Autacoids – EDRF, Prostacyclin, Endothelium Derived Hyperpolarizing Factors (EDHF)

Also releases Vasoconstrictors Autacoids – Endothelin-1 , Angiotensin II, Endothelium Derived Contracting Factors (EDCF)


NERVOUS CONTROL MECHANISM

Direct nervous control

Indirect nervous control

Neurohumoral control factors.


DIRECT NERVOUS CONTROL Through Sympathetic & Parasympathetic nerve

supply. Sympathetic – Innervate Coronary vessels

Transmitters – E & NE NE – act on α receptors - Vasoconstriction E – act on β receptors – Vasodilation.

Net result is – Vasoconstriction. Parasympathetic – Through Vagus very little effect –

Vasodilation.


INDIRECT NERVOUS CONTROLTHROUGH ACTION ON HEART.

Sympathetic stimulation – Increases heart rate &

increase force of contraction of heart – increases

conversion of ATP to ADP – Coronary Vasodilation

– Overrides direct effect of sympathetic


INDIRECT NERVOUS CONTROLTHROUGH ACTION ON HEART.

Parasympathetic stimulation. Decreases

coronary blood flow.


NEUROHUMORAL CONTROL FACTORS.

ATP (Purine) – Released with NE causes

Vasoconstriction through P1 & Vasodilatation

through P2 receptors.

NEUROPEPTIDE Y (NPY) – Released with NE

during sympathetic stimulation causes severe

Vasoconstriction.


NEUROHUMORAL CONTROL FACTORS.

CALCITONIN GENE RELATED PEPTIDE (CGRP) –

with substance P releases EDRF & Produces

maximal Dilation of Epicardial coronary arteries.


FACTORS AFFECTING CORONARY BLOOD FLOW.

Mean aortic pressure. Muscular exercise. Emotional excitement. Hypotension. Hormones. Heart rate Effect of ions Metabolic factors. Temperature.


MEAN AORTIC PRESSURE. Force for driving

blood into coronary arteries.

Directly proportional.


MUSCULAR EXERCISE. At rest – 70ml/100

gm/min During exercise –

increases 4 times due to sympathetic stimulation by Increased heart activity Increase cardiac output Increase MAP


EMOTIONAL EXCITEMENT. Increase coronary

blood flow due to increase Sympathetic discharge


HYPOTENSION.

Hypotension – reflex increase in NE discharge –

coronary vasodilation – Increase CBF


HORMONES.

Thyroid Hormone – by increasing metabolism

Adrenaline & Non adrenaline – by acting on B receptors

Acetylcholine – Increases same as parasympathetic

stimulation

Pitressin – Decrease by decreasing coronary resistance

Nicotine – Increases by liberating NE.


HEART RATE As heart rate increases

– stroke volume decreases- phasic CBF & O2 consumption decreases

Inverse relationship.


EFFECT OF IONS

K ion in low conc – dilate coronary vessels –

Increases CBF

In Higher conc- constrict coronary vessels-

Decreases -CBF


METABOLIC FACTORS.


TEMPERATURE.

Hyperthermia – increase metabolism – increase

adenosine – Increase CBF

Direct relationship


CORONARY ARTERY DISEASE. Also called Ischemic Heart

disease – Causes –

Atherosclerosis of coronary arteries.

Thrombus formation. Embolus Spasm of coronary vessels Atheromatous coronary vessels

stenosis.


Thank You

coronary circulation

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