Cardiac Output And
Hemodynamic Measurements
Iskander Al-Githmi, MD, FRCSC,
FCCP
Asst. Professor of Surgery
King Abdulaziz University
Adolf Eugen Fick ( 1829 – 1901)
Historical Perspective
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Adolf Fick: 1829- 1901
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
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
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
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
Cardiac output influencing factors
Ventricular Preload
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
Frank-Starling’s Mechanism
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
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
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)
Cardiac output influencing factors
Afterload
• Related to ventricular wall stress
Laplace Law:
Tension (T)= Pr/t
• Afterload per se does not
Alter preload
Clinical Measurement of Afterload
• Right ventricular afterload
- Pulmonary vascular resistance (PVR)
- PVR = MPAP- PAWP / CO x 80
- Normal:< 250 dynes/ sec /cm-5
Clinical Measurement of Afterload
• Left ventricular afterload
-Systemic vascular resistance (SVR)
-SVR = MAP- RAP / CO x 80
Normal: 800 – 1200 dynes / sec / cm-5
Ventricular compliance
Compliance = V/P
• Given a change in the pressure cause a change
in the volume
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
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
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
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
Methods of calculating and measuring
cardiac output
Thermodilution Curve
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
Non Invasive Methods
Doppler Method
• Based on measuring the length of blood flowvelocity 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.
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
Questions
Question 1
During a cardiac output reading the thermistor of
the PAC measures the temperature of the:
a. Blood
b. Injectate
c. Pulmonary artery blood
d. Mixing of blood and injectate
Questions
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Question 2
Which of the following statements is correct
As it relates to cardiac output curve ?
a. The larger the curve, the larger the output
b. The smaller the curve, the smaller the output
c. The larger the curve, the smaller the output
Questions
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Question 3
When patients take a spontaneous breath,
Venous return and cardiac output:
a. Increase
b. Decrease
Questions
Question 4
A 50- year-old male with myocardial ischemia presents with
the following:
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HR 128 BPM
CO 6.2 L/min
MAP 88 mmHg
SVO2 51%
CVP 6 mmHg
PAWP 16
SaO2 94%
Is the cardiac output for his tissue is adequate ?
Questions
Question 5
Same patient after treatment with NTG and morphine, his
numbers are as follow:
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HR 115 BPM
CO 5.1L/min
MAP 84 mmHg
PAWP 13 mmHg
SVO2 61%
CVP 5 mmHg
SaO2 95%
Is he better or worse ?