Download coronary circulation

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‫االسراء اية ‪58‬‬
‫‪Dra abdelaziz Hussein, Mansoura‬‬
‫‪Faculty of Medicine‬‬
By
Dr. Abdel Aziz M. Hussein
Lecturer of Medical Physiology
Member of American Society of Physiology
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
• The coronary circulation concerned with
the blood supplying the cardiac ms.
• About 1/3 of people die from diseases of
coronary arteries.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
a)Coronary arteries:
•2 coronary arteries arise from aorta
just above the aortic valve
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Lt coronary
artery
Rt coronary
artery
-Lt atrium
-Lt ventricle
-Anterior part of
interventricular
septum
-Rt atrium
-Rt ventricle
-Posterior part of
interventricular
septum
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
a)Coronary arteries:
• There
are
small
anastomotic
connections ( ) the 2
coronaries, but they
are not sufficient to
supply the cardiac
ms with blood, if one
of them is occluded→
functional
end
arteries
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
b) Coronary capillaries:
They run parallel to the cardiac ms fibers.
There is about one coronary capillary for each
ms fiber.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
• c) Coronary venous
drainage:
• There are 2 venous
systems;
• i) Superficial system:
• It includes coronary sinus
and the anterior cardiac
vein
• They drain mainly left
ventricle
• They open into Rt atrium
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
• c) Coronary venous drainage:
• i) Superficial system:
• The coronary sinus drains about 60% of
total coronary venous blood.
• ii) Deep system:
• It includes thebesian veins which drain
small amount of the coronary venous blood
directly into all chambers of the heart.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
◊Value:
- At rest → it is about 70% of O2 in the
coronary arterial blood.
- On other tissues → it is about 25% of
O2.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Arterial O2
content
Venous O2
content
O2
consumption
O2%
extraction
Venous O2
reserve
Coronary
vessels (ml %)
Other tissue
vessels (ml %)
19
19
5
14
14
5
70%
25%
Low
High
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
• The coronary venous blood has low venous
O2 reserve.
• -In severe exercise, the O2 consumption is
↑ed by;
• a) ↑ed coronary blood flow.
• b) Marked ↓ in venous O2 reserve.
• c) ↑ O2 delivered from myoglobin.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
◊ Value:
• -During rest:
• It is about 250 ml/minute (about 5% of the
COP).
• -In severe exercise: It ↑es to 3-4 fold.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Measurement:
The CBF is measured by Kety method → depends on the
application of direct Fick's principle.
The person breathes subanaesthetic dose of N2O
mixed with oxygen for 10 minutes.
N2O uptake by the heart/min.
Coronary blood flow = ———————————————
Arterio - Venous coronary N2O difference
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
1) During systole:
• The CBF in the Lt ventricle falls to a low value
→ due to strong compression of the left
ventricular ms around the intramuscular vessels
during systole.
• The lowest CBF occurs during the isometric
contraction phase
(the flow may stop
completely)
• Such ↓ in CBF during systole is compensated
for by O2 delivered from myoglobin.
• Myoglobin is loaded with O2 during diastole
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
• 2) During diastole:
• The cardiac ms relax completely and so, the
blood flows rapidly into the coronary arteries.
• The highest CBF occurs during isometric
relaxation phase
N.B.
•Phasic changes in the Rt ventricle is relatively
less than that of the Lt ventricle because the
force of contraction of the Rt ventricle is far less
than that of the Lt ventricle
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Intrinsic
mechanisms
(autoregulation)
Extrinsic
mechanisms
1. Nervous
regulation
O2 demand
or need
2. Chemical
regulation
3. Mechanical
regulation
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
• It is the main mechanism controlling CBF.
◊Mechanism:
•It is regulated almost entirely by local need of cardiac ms
for nutrition.
•O2 demand is the major factor in local blood flow
regulation.
•O2 lack (due to ↑ heart activity) is followed by coronary VD
due to:
1) ↓ed O2 tension → in the coronary blood has a direct
relaxing effect on the smooth ms in the wall of the coronary
arteries.
2) O2 lack → release of VD substances by the tissues, such
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine and prostaglandin.
as adenosine K, H, CO2, bradykinin
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
1. Active hyperaemia occurs in the heart during
exercise.
2. Reactive hyperaemia occurs if the
coronaries are temporarily occluded
leading to increase of the CBF about 3-4
folds
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
a) Sympathetic ++:
•Direct action → VC due to ++ of α1 receptors and
mild VD due to ++ of β2 receptors.
•Indirect action → it ↑es the metabolic activity of the
heart → strong VD.
•The net effect of sympathetic ++ is an ↑ in the
coronary blood flow.
b. Parasympathetic++ → has an opposite effect
to sympathetic ++ on the coronary arteries.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
c. Anrep's reflex:
•↑ VR and venous pressure in the Rt atrium →
reflex coronary VD and ↑es the coronary B.F.
•Significance:
It is important in exercise to supply the cardiac
ms with more O2.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
d. Gastrocoronary reflex:
•Distension of the stomach with heavy meal
produces reflex coronary VC and ↓CBF →
anginal pain may be felt in certain persons after
heavy meals.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
a) Phases of cardiac cycle:
b) Heart rate:
• ↑HR → ↓es the coronary blood flow by
shortening of the diastolic period.
• ↓ HR → ↑es the coronary blood flow by
prolonging the diastole.
c) Mechanical occlusion of coronary artery:
• Reactive hyperaemia occurs
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
d) ABP:
•↑ed ABP→ ↑es coronary flow
•This is antagonized by ↑ed vagal tone
•↑ed vagal tone produces coronary VC and ↓CBF
→ so the net ↑ in coronary flow is slight.
• Conversely, diastolic BP e.g aortic regurge
  CBF.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
e) Cardiac output:
• Increase COP  increase coronary BF.
• Helped by:
•Increase COP  decrease vagal tone  VD of
coronary arteries  increase coronary BF.
•Net effect: great increase in coronary BF
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
1. Nitroglycerin sublingually has a fast coronary dilating
effect, within 2-3 minutes.
2. Long acting nitrates as iso-sorbide dinitrate given
orally also produce coronary dilatation.
3. Beta-blockers, e.g. propranolol and atenolol act by
reducing myocardial O2 requirements during exertion
and stress.
4. Calcium entry blocking agents, e.g. nifedipine and
verapamil also reduce myocardial O2 requirements and
induce coronary VD.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
• All these chemicals are important in
treatment of coronary artery diseases.
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
1. It is very short and rapid circulation.
2. The arterio-venous O2 difference is high, due to
high O2 extraction by the cardiac ms.
3. Very low venous O2 reserve.
4. It is the only circulation where blood flow occurs
mainly during diastole.
5. The coronary arteries are terminal arteries having
little anastomosis.
6. The coronary arteries are common sites for
atherosclerosis causing their narrowing or occlusion.
7. The metabolic factors especially myocardial O2 need
are the major controllers
of Hussein,
myocardial
blood flow.
Dra abdelaziz
Mansoura
Faculty of Medicine
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine
THANKS
Dra abdelaziz Hussein, Mansoura
Faculty of Medicine