1. Cardiac Output And Hemodynamic Measurements
Iskander Al-Githmi, MD, FRCSC, FCCP
Asst. Professor of Surgery
King Abdulaziz University

2. Adolf Eugen Fick ( 1829 – 1901)

3. Historical Perspective
Adolf Fick:
Born in Sep. 1829, in Kassel, Germany
Earned MD in 1851
1855- Introduced a law of diffusion called Fick law of diffusion
1870- Was the first one to develop a technique for measuring cardiac output
Fick was died in Aug. 1901

4. Cardiac Cycle Phase 1: Atrial contraction
Phase 2: Isovolum contraction
Phase 3: Rapid ejection
Phase 4: Reduced ejection
Phase 5: Isovolum relaxation
Phase 6: Rapid filling
Phase 7: Reduced filling

5. Cardiac output
Volume of blood ejected from left ventricle in one minute
It is the determinant of global oxygen transport from the heart to the body
It reflects the efficiency of cardiovascular system
There no absolute value for cardiac output measurement

6. Cardiac output influencing factors
Ventricular Preload
- Volume of blood in the ventricle at the end of diastole
- Any changes in the ventricular preload will affect the ventricular stroke volume

7. Cardiac output influencing factors
Ventricular Preload

8. Frank- Starling Mechanism
The ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return
I.E ( the greater the diastolic volume or fiber stretch at the end of diastole the stronger the force of contraction at systole
The force of contraction will decline once this physiological limit has reached

9. Frank-Starling’s Mechanism

10. Cardiac output influencing factors
Preload assessment
It has been very difficult to measure the fiber length or volume at the bedside
It is clinically acceptable to measure preload as a pressure.
CVP is used to evaluate right ventricular preload
Pulmonary artery diastolic pressure or PCWP are used to evaluate the left ventricular preload

11. Cardiac output influencing factors
Contractility
Increased contractility, will shift Starling’s curve to the left
Decreased contractility will shift Starling’s curve to the right

12. Cardiac output influencing factors
Assessment of contractility
Stroke volume (SV)
SV = EDV - ESV
Stroke volume index (SVI)
SVI = CI / HR
Left ventricular stroke work index
LVSWI = MAP – PCWP x SVI x (0.0136)

13. Cardiac output influencing factors
Afterload
Related to ventricular wall stress
Laplace Law:
Tension (T)= Pr/t
Afterload per se does not
Alter preload

14. Clinical Measurement of Afterload
Right ventricular afterload
Pulmonary vascular resistance (PVR)
PVR = MPAP- PAWP / CO x 80
Normal:< 250 dynes/ sec /cm-5

15. Clinical Measurement of Afterload
Left ventricular afterload
-Systemic vascular resistance (SVR)
-SVR = MAP- RAP / CO x 80
Normal: 800 – 1200 dynes / sec / cm-5

16. Ventricular compliance
Compliance = V/P
Given a change in the pressure cause a change in the volume

17. Ejection Fraction
Is a fraction of blood ejected by the ventricle relative to its end-diastolic volume
EF= SV / EDV. 100
Ejection fraction is used as a clinical index to evaluate the inotropic status of the heart

18. Methods of calculating and measuring cardiac output
Simple method:
CO = SV x HR
SV = 2ml x pulse pressure
CO = [2ml x pulse pressure] x HR

19. Methods of calculating and measuring cardiac output
Fick Principle: “gold standard”
CO = VO2 / O2 art – O2 ven
Arterial O2 = Hb x 1.34 x O2 sat.
Venous O2 = Mixed venous blood
VO2 = Oxygen consumption
Fick Principle relies on the total uptake of a substances by peripheral tissue is equal to the product of blood flow to the peripheral tissue and arterial – venous concentration difference of the substances
Fick cardiac outputs are infrequently used because difficulties in collecting and analyzing exhaled gas conc. In critically ill patients because may not have normal VO2 value

20. Methods of calculating and measuring cardiac output
Thermodilution Method
Based on how fast the flowing blood can dilute the substances introduced into the circulation
Stewart-Hamilton Equation:
CO = I x 60 / cm x t x 1/k
Area under the curve is inversely proportion to the rate of blood flow. This flow is equivalent to cardiac output in the absence of shunt

21. Methods of calculating and measuring cardiac output
Thermodilution Curve

22. Thermal dilution method
Limitations
Affected by the phase of respiration and should be measured at the same point of respiratory cycle
Variations in the speed of cold water injection can result in altered measurement

23. Non Invasive Methods Doppler Method
Based on measuring the length of blood flow-velocity in the ascending aorta in unit time. Multiplied by the cross- sectional area of the aorta to give stroke volume. Multiplied to heart rate to give cardiac output.

24. Methods of calculating and measuring cardiac output
Impedance plethysmography
This technique was developed by NASA. Cardiac output can be measured across externally electrodes. It measures a changing impedance in the chest (blood volume). The rate of change of impedance is a reflection of cardiac output.
CO = Art. BP / total peripheral vasc. resistance