Cardiac Output

This presentation is apt for Physiotherapy students or students of basic medical school.

1. CARDIAC OUTPUT Dr. Blessy Joel (PT) MPT (Cardio Respiratory diseases)

2. DEFINITION NORMAL VALUE DETERMINANTS STROKE VOLUME AND ITS REGULATION HEART RATE AND ITS REGULATIONS ITS VARIATIONS

3. Cardiac output (CO)  is a measurement of the amount of blood pumped by each ventricle in one minute. To calculate this value, multiply stroke volume (SV), the amount of blood pumped by each ventricle, by heart rate (HR), in contractions per minute (or beats per minute, bpm ). It can be represented mathematically by the following equation: CO = HR × SV

4. Stroke volume is expressed in mL /beat and heart rate in beats/minute. Therefore, cardiac output is in mL /minute. Cardiac output may also be expressed in liters/minute. Stroke volume depends on–  End diastolic volume  Contractility

5. Cardiac Output is an excellent example to exhibit the efficiency of the  human heart.  It is related to the amount of blood pumped by the heart per minute. A normal cardiac output would be about five litres (5 litres ) of blood per minute in a healthy individual.

6. FACTORS AFFECTING CO Cardiac output is maintained by four factors:  Venous return  Force of contraction  Heart rate  Peripheral resistance

7. 1.Venous Return This is the amount of blood that enters the Right Atrium through the veins per minute. After a certain time interval, the venous return becomes equal to the cardiac output. Venous return in turn, depends on following factors: Respiratory pump Muscle pump Gravity Venous pressure

8. 2.Force of Contraction The stroke volume and the cardiac output increases with the increase in the force of contraction. Frank -Starling law of the heart states that when increased volume of blood flows into the heart, the cardiac muscle contracts with increased force and this empties the extra blood that has entered from the systemic circulation leading to --- increased cardiac output.

9. PRELOAD •It is stretching of cardiac muscle fibre at the end of diastole, just before contraction •Cardiac output is directly proportional to pre-load. AFTERLOAD •It is the force against which ventricles must contract and eject the blood. •Force of contraction and cardiac output is inversely proportional to after-load.

10. 3.Heart Rate The cardiac output increases with the increase in heart rate. Any factor which changes heart rate will also change Cardiac output. Cardiac Output Formula The equation for cardiac output is: Cardiac Output (CO) = HR x SV

11. 4. Peripheral Resistance •Peripheral resistance is the resistance offered to blood flow at the peripheral bloodvessels . •Peripheral resistance is the resistance or load against which the heart has to pump theblood . •Cardiac output is inversely proportional to peripheral resistance.

12. Cardiac Output Calculation For example: If the heart rate is 70 bpm and stroke volume is 70 ml. Using the formula:  HR X SV = 70 X 70 = 4900 ml/min or 4.9 liters per minute.

13. Some of the methods to measure cardiac output are listed below: Doppler ultrasound Echocardiography Transcutaneous Transoesophageal Low output results in heart failure, a severe infection or  heart diseases . The high output may be an indicator of blood infections.

14. Cardiac Index “Cardiac index is defined as the cardiac output divided by the body surface area.” It is a hemodynamic parameter that relates the cardiac output from the left ventricle in one minute to the body surface area. Cardiac Index = Cardiac Output/Body Surface Area Stroke volume index is the stroke volume divided by the body surface area.

15. The average human being who weighs 70 kg has a body surface area of about 1.7 sq meters, which means that the normal average cardiac index for adults is about 3 L/min/m2 of body surface area.

16. Major Factors Influencing Cardiac Output:   Cardiac output is influenced by heart rate and stroke volume, both of which are also variable.

17. SVs are also used to calculate  ejection fraction , which is the portion of the blood that is pumped or ejected from the heart with each contraction. To calculate ejection fraction, SV is divided by EDV. the ejection fraction is normally expressed as a percentage. Ejection fractions range from approximately 55–70 percent, with a mean of 58 percent.

18. EJECTION FRACTION Ejection fraction (EF) is a measurement, expressed as a percentage, of how much blood the left ventricle pumps out with each contraction.  Ejection fraction refers to the fraction (or portion) of enddiastolic volume (see below) that is ejected out by each ventricle per beat . From 130 to 150 mL of end­diastolic volume, 70 mL is ejected out by each ventricle (stroke volume). Normal ejection fraction is 60% to 65%.

19. Exercise and Maximum Cardiac Output In healthy young individuals, HR may increase to 150 bpm or higher during exercise. SV can also increase from 70 to approximately 130 mL due to increased strength of contraction.

20. This would increase CO to approximately 19.5 L/min, 4–5 times the resting rate. Top cardiovascular athletes can achieve even higher levels. At their peak performance, they may increase resting CO by 7–8 times. Since the heart is a muscle, exercising it increases its efficiency. The difference between maximum and resting CO is known as the  cardiac reserve . It measures the residual capacity of the heart to pump blood.

21. What controls heart rate? Heart rate controlled by the two branches of the autonomic (involuntary) nervous system. The sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The sympathetic nervous system (SNS) releases the hormones ( catecholamines - epinephrine and norepinephrine ) to accelerate the heart rate. The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate. Such factors as stress, caffeine, and excitement may temporarily accelerate your heart rate, while meditating or taking slow, deep breaths may help to slow your heart rate.   Exercising for any duration will increase your heart rate and will remain elevated for as long as the exercise is continued.

22. VARIATIONS IN CARDIAC OUTPUT PHYSIOLOGICAL CAUSES •Age-↑ ses with age •Sex-less in females more in males •Body build-↑ ses with body build •Exercise-↑ ses with exercise •High altitude-↑ ses •Pregnancy-↑ ses •Sleep-↓ ses

23. PATHOLOGICAL CAUSES •Increase in- 1.Fever 2.Anemia 3.Hyperthyroidism •Decrease in- 1.Shock 2.Hypovolumia 3.Hemorrhage 4.Congestive cardiac failure 5. Hypothyroidism