1. ﴿و ما أوتيتم من العلم إلا قليلا﴾
بسم الله الرحمن الرحيم
﴿و ما أوتيتم من العلم إلا قليلا﴾
صدق الله العظيم الاسراء اية 58
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

2. Lecturer of Medical Physiology
Coronary Circulation By
Dr. Abdel Aziz M. Hussein
Lecturer of Medical Physiology
Member of American Society of Physiology
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

3. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Circulation
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

4. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Circulation
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

5. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Vessels
a)Coronary arteries:
2 coronary arteries arise from aorta just above the aortic valve
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

6. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Vessels
Lt coronary artery
-Lt atrium
-Lt ventricle
-Anterior part of interventricular septum
Rt coronary artery
-Rt atrium
-Rt ventricle
-Posterior part of interventricular septum
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

7. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

8. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Vessels
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

9. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Vessels
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

10. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Vessels
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

11. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Vessels
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

12. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
O2 consumption of heart
◊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

13. Characters of O2 consumption in coronaries and other systemic tissues
Coronary vessels (ml %)
Other tissue vessels (ml %)
Arterial O2 content 19
Venous O2 content 5 14
O2 consumption
O2% extraction
70%
25%
Venous O2 reserve
Low
High
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

14. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
O2 consumption of heart
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

15. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Blood Flow
◊ 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

16. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Coronary Blood Flow
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

17. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Phasic Changes in CBF
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

18. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

19. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Phasic Changes in CBF
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

20. Intrinsic mechanisms (autoregulation) 3. Mechanical regulation
Regulation of CBF
Intrinsic mechanisms (autoregulation)
O2 demand or need
Extrinsic mechanisms
1. Nervous regulation
2. Chemical regulation
3. Mechanical regulation
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

21. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Autoregulation of CBF
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 as adenosine K, H, CO2, bradykinin and prostaglandin.
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

22. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Autoregulation of CBF
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

23. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Autoregulation of CBF
Active hyperaemia occurs in the heart during exercise.
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

24. Active and reactive Hyperemia
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

25. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Nervous Factors
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

26. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Nervous Factors
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

27. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Nervous Factors
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

28. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Mechanical Factors
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

29. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Mechanical Factors
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

30. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Mechanical Factors
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

31. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
Chemical Factors
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

32. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

33. 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

34. Summary of Characteristics of coronary circulation
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 myocardial blood flow.
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

35. Angina pectoris and Myocardial Infarction
Dra abdelaziz Hussein, Mansoura Faculty of Medicine

36. Dra abdelaziz Hussein, Mansoura Faculty of Medicine
THANKS
Dra abdelaziz Hussein, Mansoura Faculty of Medicine