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.
Friday, November 25, 2016

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

 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.

 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.

PHASIC CHANGES IN
CORONARY BLOOD FLOW
 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.

PHASIC CHANGES IN
CORONARY BLOOD FLOW
 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.Friday, November 25, 2016

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

 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 CONTROL
THROUGH 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 CONTROL
THROUGH 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.

CORONARY CIRCULATION

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