6.Cardiac Cycle 3.pptx physiology lecture.

Physiology of cardiac cycle.

1. CARDIAC CYCLE – 3 (SGD)

2. A 69-year-old woman with end-stage renal disease reported in emergency with sudden onset of abdominal pain and vomiting after a routine hemodialysis treatment. Her medical history included long-standing diabetes mellitus, hypertension, and end-stage renal disease that had necessitated dialysis for the past 4 years. On examination BP 141/87 mmHg, Pulse100beats/min, RR 32/min, ECG revealed a wide QRS complex rhythm. Serum potassium level was found to be at 10.0 mEq /L(normal 4.0 and 4.5 mEq/L) CASE SCENARIO

3. Define Frank starling law? What does frank starling law represent? Elucidate the mechanism of Frank starling law? How does cardiac contractility is affected by increase Potassium and Calcium ions? Why does heart become flaccid in electrolyte imbalance? Does increase or decrease in temperature has any affect on cardiac contractility? How

4. By the end of this session, all students should be able to: Correlate the regulation of heart pumping with the Frank Starling mechanism of heart contractility Discuss the role of following in Cardiac Performance: Potassium ions Calcium ions Temperature Learning Objectives

5. When a person is at rest ,the heart pumps only 4 to 6 liters of blood each minute. During strenuous exercise, the heart may be required to pump four to seven times this amount Regulation Of Heart Pumping

6. Volume pumped by the heart is regulated by: Intrinsic cardiac regulation of pumping in response to changes in volume of blood flowing into the heart Control of heart rate and strength of heart pumping by the autonomic nervous system

7. The amount of blood pumped by the heart each minute is normally determined almost entirely by the rate of blood flow into the heart from the veins, which is called venous return. The heart pumps incoming blood into the arteries so that it can flow around the circuit again Intrinsic Regulation Of Heart Pumping

8. This intrinsic ability of the heart to adapt to increasing volumes of inflowing blood is called the Frank-Starling mechanism of the heart , in honour of Otto Frank and Ernest starling.

9. Within physiological limits, the heart pumps all the blood that returns to it by way of the veins

10. Basically, the Frank-Starling mechanism means that the greater the heart muscle is stretched during filling, the greater is the force of contraction and the greater the quantity of blood pumped into the aorta

11. When an extra amount of blood flows into the ventricles, the cardiac muscle is stretched to a greater length Explanation Of The Frank –Starling Mechanism

12. This stretching in turn causes the muscle to contract with increased force because the actin and myosin filaments are brought to a more nearly optimal degree of overlap for force generation The ventricle, because of its increased pumping, automatically pumps the extra blood into the arteries

13. Stretch of the right atrial wall directly increases the heart rate by 10 to 20 percent , which also helps increase the amount of blood pumped each minute, although its contribution is much less than that of the frank starling mechanism

14. The relationship between ventricular stroke volume and end –diastolic volume is called the frank- starling curve Frank- Starling Curve

15. One of the best ways to express the functional ability of the ventricles to pump blood is by ventricular function curves. Ventricular function curves are another way of expressing the frank –starling mechanism of the heart. VENTRICULAR FUNCTION CURVES

16. That is, as the ventricles fill in response to higher atrial pressure, each ventricular volume and strength of cardiac muscle contraction increase, causing the heart to pump increased quantities of blood into the arteries.

17. As the atrial pressure for each side of the heart increases, the stroke work output for that side increases until it reaches the limit of the ventricle’s pumping ability. Stroke Work Output Curve

18. As the right and left atrial pressure increase, the respective ventricular volume outputs per minute also increases . Ventricular Volume Output Curve

19. Preload is the volume of blood in the ventricles at the end of diastole(end diastolic pressure) Increased in : Hypervolemia, Heart failure Preload And Afterload

20. Afterload is the resistance left ventricle must overcome to circulate blood. Increased in : Hypertension Vasoconstriction

21. The normal state of cardiac cell membrane polarization is dependent upon the maintenance of a normal ionic balance across the membrane Electrolytes And Heart

22. Effect Of Potassium, Calcium And Temperature On Cardiac Functions

23. The heart is made of cardiac muscle fibers, which contract without conscious effort because they are connected to nerves from the autonomic nervous system. The generation and spread of electrical signals via nerves is dependent on a variety of electrolytes such as sodium, potassium, calcium, magnesium and chloride.

24. Potassium is specifically needed for voltage-gated potassium channels to work in the outer membranes of cardiac muscle cells These channels open in response to a change in voltage and are responsible for terminating action potentials and contractions while initiating repolarization

25. Causes Of Hyperkalemia

26. Elevation of potassium concentration to only 8 to 12 mE /L —two to three times the normal value - can cause severe weakness of the heart, abnormal rhythm, and death Excess potassium in the extracellular fluids causes the heart to become dilated and flaccid and also slows the heart rate Effect Of Excess Potassium On Heart Function

27. Large quantities of potassium also can block conduction of the cardiac impulse from the atria to the ventricles through the A-V bundle

28. In the heart, hypokalaemia causes hyperpolarization in the myocytes' resting membrane potential The more negative membrane potentials in the atrium may cause arrhythmias because of more complete recovery from sodium-channel inactivation, making the triggering of an action potential less likely. Effect Of Low Potassium On Heart Function

29. Causes Of Hypokalemia

30. Potassium Rich Foods

31. Effect Of Calcium Ions On Heart Fuctions

32. Intracellular calcium release from the sarcoplasmic reticulum (SR) is required for cardiac muscle contraction

33. Excess calcium ions cause effects almost exactly opposite to those of potassium ions , causing the heart to move toward spastic contraction This effect is caused by a direct effect of calcium ions to initiate the cardiac contractile process Effect Of Excess Calcium Ions On Heart Function

34. Conversely , deficiency of calcium ions causes cardiac weakness , similar to the effect of high potassium Fortunately, calcium ion levels in the blood normally are regulated within a very narrow range Cardiac effects of abnormal calcium concentrations are seldom of clinical concern Effect Of Low Calcium Ions On Heart Function

35. Increased body temperature greatly increases the heart rate , sometimes to double the normal rate Decreased temperature greatly decreases heart rate , which may fall to as low as a few beats per minute when a person is near death from hypothermia in the body temperature range of 60° to 70°F EFFECT OF TEMPERATURE ON HEART

36. These effects presumably result from the fact that heat increases the permeability of the cardiac muscle membrane to ions that control heart rate, resulting in acceleration of the self-excitation process

37. Contractile strength of the heart often is enhanced temporarily by a moderate increase in temperature, such as that which occurs during body exercise, but prolonged elevation of temperature exhausts the metabolic systems of the heart and eventually causes weakness

38. Cardiac Output Cardiac output is the quantity of blood pumped into the aorta each minute by the heart. Cardiac Index Cardiac output per square meter of body surface area

39. Define Frank starling law What does frank starling law represent Elucidate the mechanism of Frank starling law How does cardiac contractility is affected by increase Potassium and Calcium ions Why does heart become flaccid in electrolyte imbalance Does increase or decrease in temperature has any affect on cardiac contractility? How RELEVANT QUESTION