1. Factors affecting cardiac output
DR S.PARTHASARATHY MD., DA., DNB., DIP. DIAB. PhD, FICA, IDRA, Diploma in software based statistics

2. Volume ejected by left ventricle to the aorta and thus to the rest of the body
Cardiac output is the amount of blood the heart pumps in 1 minute

3. Male 5 – 6 litres / minute
Females – 4 – 4.75 litres / minute may be less
Children 350 ml/ kg/ minute – birth
150 – 200 ml/ kg / minute after one week
Cardiac index – 3 – 3.2 litres/min/m2

4. Basically Cardiac output = heart rate * stroke volume
70/ minute * 70ml/ cycle
= 4900 ml = approx 5 litres / minute

5. Permissive role of the heart
The Frank-Starling relationship is an intrinsic property of myocardium by which stretching of the myocardial sarcomere results in enhanced myocardial performance for subsequent contractions
13 – 15 litres/ minute
Permissive role

6. Starling law or the catapult theory
Permissive role is increased in exercise & Athletes
Decreased in heart diseases
Starling law or the catapult theory

7. Catapult Stretch End diastolic fibre length – true preload
LV compliance , volume
Mitral valve
Atrial contractility
Pulmonary hypertension
Pulmonary stenosis
RV and RA changes
CVP !!!! – preload

9. During times of physiologic stress, cardiac output will increase to ensure adequate tissue perfusion.
Fick’s principle illustrates this notion in equation form:
CO = VO2/ (a – v O2 difference) where VO2 represents oxygen use by tissue and a-V O2 is the difference in oxygen content of arterial and venous blood

10. What factors affect stroke volume
Cardiac output = stroke volume * heart rate
Preload
Contractility
Afterload

12. Preload – tailwind pushing the cycle
Speed of the bicycle - Venous return

13. Preload is equal to the ventricular wall stress at end-diastole.
It is determined by ventricular EDV, end-diastolic pressure (EDP), and wall thickness

14. Preload --take it as venous return !!
Blood Volume
Elasticity of heart – if it decreases , the heart loses its capacity to fill easily !!
Valves in small veins
Muscle pump : leg muscles contract – squeezed blood to the heart
Gravity –
Intrapericardial pressure
Respiratory pump
RAP – usually close to ZERO

15. Mean systemic filling pressure
Pressure in all parts of the systemic circulation when blood flow is stopped and the blood is redistributed to all the vessels
7 mmHg
Ultimate pressure that puts blood to the right atrium
venous return = Psf – RAP

16. Venous return may decrease
Bleeding
Obstruction of large veins
Sudden dilation of veins

17. Force of cardiac contraction (contractility)
Clearly, if the cyclist flexes his/her muscles a little and pushes harder on the pedals, then the bicycle will move faster.
This can be equated to an increased contractility of the heart muscle, resulting in increased cardiac output

19. Afterload
Afterload can be considered either as the stress imposed on the ventricular wall during systole or as the arterial impedance to the ejection of SV.
σ ∝ P×r /h - ( law of laplace)
σ = ventricular wall stress
P = ventricular pressure
r = ventricular radius h = wall thickness
Hypertension
Aortic stenosis

21. Heart rate cardiac conduction system, central nervous system,
autonomic nervous system
Cycle fastens – moves faster but after some time it fatigues to go down under
Around 175/ minute

22. As the long-distance cyclist will know, prolonged strenuous exercise can lead to high tissue oxygen demands, which can later result in impaired muscle contraction and poor performance.
Continuous prolonged inotropes !! ??

23. How does it feel to cycle down hill ??
This is what vasodilators do to decrease afterload !!

24. Push the pedal faster
Also make the road less bumpy and smooth !!
Sometimes we need both
Inodilators like milrinone
Inotropy and vasodilation

26. ANS, myocardial disease
Blood volume muscle pump
Resp pump gravity
Valves

27. Thank you all