cardiac physiology

1. CARDIAC PHYSIOLOGY BY HeTa PaTeL Final Year B.P.T. KMPIP

2. OBJECTIVES Functions of heart Cardiac cycle Properties of heart Cardiac work Heart sound ECG Cardiac output Heart rate Blood pressure Regulation of cardiac function Cardiac reflexes

3. THE HEART

4. Functions of the Heart Generating blood pressure Routing blood: separates pulmonary and systemic circulations Ensuring one-way blood flow: valves Regulating blood supply Changes in contraction rate and force match blood delivery to changing metabolic needs

5. CHAMBERS OF HEART

6. CARDIAC CYCLE Sequence of electrical & mechanical events during the course of single heart beat . Phases Isovolumic contraction Phase Ejection Phase Isovolumic Relaxation Diatsolic Phase

7. Pressure - volume diagram

8. Excitation system

9. ACTION POTENTIAL

10. ACTION POTENTIAL Fast-response action potentials His-Purkinje system Atrial or ventricular cardiomyocytes Slow-response action potentials SA and AV nodes.

11. Cardiac work Stroke work output of the heart Amount of energy that the heart converts to work during each heartbeat while pumping blood into the arteries. Minute work output Total amount of energy converted to work in 1 minute stroke work output × heart rate.

12. Types of Cardiac Work Volume-pressure work or External work Used to move the blood from the low-pressure veins to the high-pressure arteries. Kinetic energy of blood flow or Internal work used to accelerate the blood to its velocity of ejection through the aortic and pulmonary valves.

13. Cardiac work

14. EFFICIENCY OF CARDIAC CONTRACTION The ratio of work output to total chemical energy expenditure . Maximum efficiency of the normal heart is between 20 and 25 % In heart failure, it can be 5 – 10%

15. CARDIAC OUTPUT ●Co is a quantity of blood pumped into the aorta each minute by the heart Normal value is 5-6 lit/min CO =HR*SV

16. FACTORS AFFECTING CO

17. CO IS DIRECTLY PROPOTIONAL TO VENOUS RETURNS. FACTORS AFFECTING VENOUS RETURN ●Respiratory pump ●Muscle pump ●Gravity ●Venous presser 1)VENOUS RETURN

18. 2)Force of contraction ●PERLOAD It is stretching of cardiac muscles fiber at the end of diastole just before contraction. it is depend upon venous return & ventricles filling. it is directly propotional to co. ●AFTERLOAD It is the force against which the ventricle must contract &eject the blood. it is invesely propotional to CO

19. 3) Heart rate 4)Peripheral resistance

20. Heart Rate Most variable determinant Controlled by multiple systems cardiac conduction system central nervous system autonomic nervous system pharmacologic controls

21. Effect of increasing HR on cardiac function Shortening of systole Shortening of diastole Decreased myocardial perfusion time Decreased ventricular filling Rate dependent change in SV Rate dependent change in cardiac output Rate dependent positive inotropic effect

22. Blood pressure Arterial blood pressure is defined as the lateral pressure exerted by the contained column of blood in the wall of arteries. REGULATION OF BP 1)NERVOUS MECHANISM by baroreceptor chemoreceptor 2)RENAL MECHANISM by renin angiotensin mechanism

23. 3)Hormonal mechanism ● HORMONS WILL INCREASING BP ADRENALINE NORADRENALINE THYROXINE ALDOSTERONE ANGIOTENSIN SEROTONIN ●HORMONS WILL DECREASING BP BRADYKININ HISTAMIN ACETYLCHOLINE PROSTAGLANDIN

24. REFLEXES 1) Baroreceptor Reflex (Carotid Sinus Reflex) 2) Chemoreceptor Reflex 3) Proprioceptive Reflex 4) Bainbridge reflex 5) Bezold-Jarisch reflex 6) Valsalva Maneuver 7) Cushing Reflex 8) Oculocardiac Reflex

25. 1) BARORECEPTOR REFLEX

26. Baroreceptor Reflex Responsible for the maintenance of blood pressure Important role during acute blood loss and shock Volatile anesthetics (particularly halothane) inhibit the heart rate component. Concomitant use of calcium channel blockers, ACE inhibitors, or PDE inhibitors will lessen the cardiovascular response. Patients with chronic hypertension often exhibit perioperative circulatory instability as a result of a decrease in their baroreceptor reflex response.

27. 3) Chemoreceptor Reflex

28. Chemoreceptor Reflex Mediated by Chemosensitive cells in the carotid bodies and the aortic body. Sinus nerve of Hering and vagus nerve Chemosensitive area of the medulla At PaO 2 <50 mm Hg or in acidosis respiratory centers stimulated and increasing ventilatory drive. Activation of the parasympathetic system reduction in heart rate and myocardial contractility.

29. 4)Bainbridge reflex Elicited by stretch receptors located in the right atrial wall and the cavoatrial junction vagal afferent signals Cardiovascular center in the medulla ↑ right-sided filling pressure inhibits parasympathetic activity →↓ heart rate. Direct effect on the SA node by stretching the atrium. Depends on the underlying heart rate before stimulation.

30. 5) Bezold-Jarisch reflex Elicited by chemoreceptors and mechanoreceptors within the LV wall Vagal afferents ↑ parasympathetic tone Noxious ventricular stimuli induces the triad of hypotension, bradycardia , and coronary artery dilatation. Implicated in cardiovascular conditions Myocardial ischemia or infarction Thrombolysis Revascularization Syncope Less pronounced in patients with Cardiac hypertrophy Atrial fibrillation

31. 6) Valsalva Maneuver Valsalva maneuver → ↓CO and BP. Sensed by baroreceptors → sympathetic stimulation ↑heart rate and myocardial contractility. When the glottis opens, venous return ↑ →↑BP. Sensed by baroreceptors → stimulate parasympathetic efferent pathways to the heart.

32. 7) Cushing Reflex Cerebral ischemia at the medullary vasomotor center ↓ Activation of the sympathetic nervous system ↓ ↑ HR, BP, and myocardial contractility ↓ Improve cerebral perfusion As a result of the high vascular tone, reflex bradycardia mediated by baroreceptors will ensue.

33. 8) Oculocardiac Reflex Stretch receptors ↓ Short and long ciliary nerves ↓ Ophthalmic division of the trigeminal nerve ↓ Gasserian ganglion ↓ Increased parasympathetic tone ↓ Bradycardia . Incidence during ophthalmic surgery- 30% to 90%.

34. references Essentials of medical physiology : K. Sembuligam 5 edi Textbook of medical physiology : Guyton & hall Textbook of physiology : A.K.Jain Review of medical physiology : William F. Ganong 22 edi Internet