Cardiac out put and its regulation

Cardiac Output
Dr Raghuveer Choudhary

Objectives
❖ Define stroke volume, end-systolic volume, and end-diastolic volume.
❖ Define cardiac output, venous return, cardiac index & cardiac reserve.
❖ Understand the concept of preload and afterload.
❖ Understand the factors affecting the EDV (the venous return).
❖ Understand the factors affecting the ESV.
❖ Know how cardiac contractility & heart rate changes affect CO.
❖ Identify the factors that affect heart rate.
❖Know the method for measurement of CO (The direct Fick’s method)
.
❖ Describe the factors affecting the SV&CO

CARDIAC OUTPUT
Cardiac output is defined as:
The volume of the blood pumped out by each
ventricle per minute.
Cardiac output = Stroke volume x Heart rate
CO = SV x HR
= 70 x 70
= 4900ml/min (5000ml/min)

1- Cardiac Output
It is the amount of blood pumped by each ventricle
per minute.
It keeps the arteries full of blood.
An increase in cardiac output results in increased
blood pressure.
Anything that decreases cardiac output also
decreases blood pressure, because there is less
pressure on the vessel walls.
Cardiac Output = Heart Rate X Stroke Volume
Anything that affects heart rate or stroke volume
affects cardiac output and thus blood pressure.
08/08/2021 7

STROKE VOLUME (SV)
Volume of blood pumped out by each
ventricle per beat.
70ml / beat (70 to 80ml / beat)
SV = EDV – ESV
END-DIASTOLIC VOLUME (EDV)
Volume of blood present in the ventricular
cavity at the end of ventricular diastole.
EDV = 120 to 130ml

END-SYSTOLIC VOLUME (ESV)
Volume of blood present in the
ventricular cavity at the end of
ventricular systole.
ESV = 40 to 50ml
SV = EDV – ESV
More EDV, more SV
More ESV, less SV

EJECTION FRACTION
Percentage (fraction) of EDV ejected out by
each ventricle per beat.
• It is 60 to 65% of EDV
• Ejection Fraction is a valuable index of
ventricular function

CARDIAC INDEX
It is the cardiac output with respect to body
surface area, i.e; cardiac output per square
meter of body surface area.
70 kg adult male = 1.7 sq m of body surface area.
CO 5
CI = ------------------------ = ------------
Body Surface area 1.7
= 3 lit /min/ m2
80 years man :- CI = 2.4 lit/min/m2
10 years child :- CI = 4 lit/min/m2

During the first 3 hours after meals, the CO increases by ≈ 30% to enhance blood flow in
the intestinal circulation.
Later months of pregnancy are accompanied by 30% increase in CO due to increased
uterine blood flow.
At environmental temperature above 30°C, the CO is increased due to increased skin
blood flow. Also at low environmental temperature CO is increased due to shivering that
increases blood flow to the muscles.
Increased sympathetic activity during anxiety and excitement (enhances the CO up to
50% - 100%.)
Sitting or standing from the lying position deceases the CO by 20-30%.

CO is crucial since it is also the amount of blood that flows into
the circulation and is responsible for transporting substances to
and from the tissues. Thus, the body has strict control
mechanisms that maintain adequate CO.

↑VR → ↑EDV → ↑initial length → ↑force on
contraction → ↑SV → ↑CO
when it exceeds physiological limits: ↑↑EDV →
sarcomere disruption & loss of its function →
↓force of contraction → ↓SV

the force of contraction)
the force of contraction)

Normally, Rt atrial pressure (RAP)
fluctuates with atrial contraction and
respiration.
When the mean RAP is about 0 mmHg,
the CO in an adult is about 5 L/min.
Because of the steepness of the cardiac
function curve, very small changes in
RAP (just a few mmHg), can lead to
large changes in cardiac output.

Sympathetic stimulation affects both the heart and the systemic circulation:
(1) It makes the heart a stronger pump.
(2) in the systemic circulation, it increases the Psf because of contraction of the
peripheral vessels, especially the veins, and it increases the resistance to venous
return.

It is expressed as tension which must be developed in the wall of ventricles
during systole, i.e the load the heart needs to overcome to open the
semilunar ( Aortic and pulmonary ) valves and eject blood to
aorta/pulmonary artery.
- Left ventricular afterload represents the force that the muscle must
generate to eject the blood into the aorta.
- When the aortic pressure (afterload) is reduced, the velocity of shortening
of the LV myocardial fibers increases ( the ventricles will contract easily
). Hence, the LV can eject blood more rapidly → ↑SV → ↓ESV.
- The opposite is true with increased LV afterload.

CARDIAC OUTPUT MEASUREMENT
DIRECT METHOD
• Animal anesthetized
• Direct cannulation of great vessels
• Electromagnetic / Doppler flowmeter

MEASUREMENT OF CARDIAC OUTPUT
Direct Methods
• Cardiac output can be measured directly by placing an
electromagnetic flow meter in the ascending aorta or by using a
cardiometer. These are accurate methods of measuring cardiac
output.
• However, these direct methods are applicable only in experimental
animals or in humans (in patients) undergoing open thoracic
surgery.
• In humans, cardiac output is usually determined by using Doppler
combined with echocardiography.

Indirect Methods
1. Fick method
2. Indicator dilution method
3. Thermo-dilution method
4. Ballistocardiography
5. Echocardiography
6. X-ray method
7. Pulse-pressure method

Fick Method
Definition: Fick principle is defined as the amount of a substance taken
up by an organ or by the whole body per unit of time is equal to the
arteriovenous difference of the substance times blood flow.
Procedure:
• Cardiac output can be measured by measuring the amount of oxygen
consumed by the body in a given period and dividing this value by
the arteriovenous difference of oxygen across the lungs.
• The oxygen consumption of the body is measured by spirometry.
• As the arterial content of oxygen is same in all parts of the body, for
measuring oxygen content of the arterial blood, the blood is obtained
from any peripheral artery.
• The venous blood is collected from the pulmonary artery by placing a
catheter into it through the heart.

Measurement of cardiac output
• Fick Method
adding 10 beads per minute

• Fick Method
adding 10 beads per minute
concentration is 2 beads per litre
Flow =
Rate added
Concentration
=
10 beads/min
2 beads/litre
= 5 litres/min

OXYGEN FICK METHOD:
Fick’s Principle
The amount of a substance taken up by an organ or the
whole body in a unit time is equal to arteriovenous
difference times the blood flow.

• Fick Method
lung
rate of O2 consumption
Flow =
rate of O2 consumption
[O2] leaving – [O2] entering
=
250 ml/min
190 – 140 ml/litre
= 5 litres/min
O2 concentration of
blood leaving lung
O2 concentration of
blood entering lung

Table 31–3 Effect of Various Conditions on Cardiac Output.
Condition or Factora
No change Sleep
Moderate changes in environmental temperature
Increase Anxiety and excitement (50–100%)
Eating (30%)
Exercise (up to 700%)
High environmental temperature
Pregnancy
Epinephrine
Decrease Sitting or standing from lying position (20–30%)
Rapid arrhythmias
Heart disease

The cardiac output is calculated as:
O2 consumption (mL/min)
Output of left ventricle = ——————————————
(AO2 )  (VO2)
Advantages
1. Result is accurate
2. No chemical is injected
Disadvantages
1. Catheterization should be done by expert hand
2. Hospitalization is required for catheterization
3. Patient may be apprehensive of catheterization that increases
cardiac output
4. Simultaneous measurement of oxygen consumption makes the
process difficult.
5. It is difficult to measure cardiac output by this method in
ambulatory patients and during exercise.

DYE DILUTION (HAMILTON’S
DILUTION) METHOD
(Indicator Dilution Method)
• Evan’s blue (T-1824)
• Albumin labeled with I131
• Cardiogreen
• Brilliant violet red

Indicator Dilution Method
Principle: A known amount of an indicator is injected into circulation
usually through an arm vein and the concentration of the indicator is
measured in serial samples of the arterial blood. The output of the heart
is equal to the amount of indicator injected divided by its average
concentration in arterial blood after a single circulation through
the heart.
Procedure
• This method is popularly known as Hamilton’s dye dilution
method.
• The dye injected is usually the Evans’ blue or indocyanine green.
• Before injection of the dye, 10 ml of peripheral venous blood is
withdrawn and divided equally into two samples.
• In one sample of 5 ml, enough quantity of the dye is injected to give
a concentration of 0.5 mg/100 ml. (used as standard).
• The other sample is used as blank.

• One ml of the dye solution containing 5 mg is injected rapidly into the basilic
vein.
• From a limb artery, the blood samples are collected at an interval of 2 s in
serial tubes.
• The tubes are then centrifuged together with the standard and blank tubes,
following which the concentration of dye is determined
photocolorimetrically.
• The concentration of the successive samples is plotted on a semi-log paper.
The resulting concentration of dye in the arterial blood changes with time.
• First, the concentration rises as the indicator carried by the fast-moving
blood reaches the arterial sampling point
• Second, reaches a peak as majority of indicator substance arrives at the
sampling point

• Finally, the concentration falls as indicator carried by slow moving
blood arrives at the point.
• Thus, the result obtained gives a curve with an ascending limb, a
peak, and a descending limb. But the descending limb ends with a
rise.
• The slope of descending limb is extrapolated to the abscissa. The
point on the time scale at which it touches the abscissa, gives the
time of first passage of the dye through the artery (t).
Advantages: Accurate method.
Disadvantages
• Should not be repeated in short time as the concentration of the dye
of the earlier use may give errors.

Thermodilution Method
Principle
• Same as indicator dilution technique. In this method, the cold
saline is used as the indicator. A double lumen catheter is used.
• Following catheterization, the cold saline is injected into the right
atrium through one side of the catheter.
• A thermistor is placed in the other end of the other side of the
catheter.
• The change in temperature of the blood is recorded in the
pulmonary artery through the thermistor placed in the catheter.
• The change in temperature is inversely proportional to the amount of
blood flowing through the pulmonary artery.

Advantages
1. Saline is harmless
2. Cold is dissipated, so recirculation is not a problem
3. Can be repeated many times, if needed
4. Usually preferred for children as saline is nontoxic5. Useful in
severely sick patients (serious patients in intensive care units)
Disadvantages
1. Cardiac catheterization is required.

OTHER METHODS
1) Echocardiography:This is a noninvasive technique in which ultrasonic waves
emitted from a transducer detects waves reflected from various parts of the
heart. When it is combined with Doppler technique it determines the velocity and
volume of flow of blood through various cardiac valves.
Principle
• Ultrasound waves are transmitted into the chest and the reflection of these
waves off the various parts of the heart is analyzed.
• A transducer, which is a small microphone-like device, is held against the
chest. The transducer sends and receives the ultrasound waves.
• By moving the transducer to various positions on the chest, different
structures of the heart and the blood flow are analyzed.
• The computer software assembles the reflected ultrasound waves to create an
image of the heart. These images appear on a television screen.

Parameters Seen
1. Size and shape of the heart
2. Pumping efficiency of the heart:
3. Valve abnormalities
Advantages
• It is a non-invasive test.
• Accurate diagnosis and develop a treatment plan that is best.
• It is a safe and painless way
• Transthoracic echocardiography is used in critically ill patients
Limitations
• The major limitation is that it is often difficult to obtain good quality images from
persons who have broad chests, are obese, or are suffering from chronic lung
disease.

2) Ballistocardiography
• In this method, the vibrations generated by each heart-beat are received and
converted into waveforms by a transducer that records the cardiac activities
on an ink recorder.
• From the recording, cardiac output is calculated by using a special formula by
analyzing the recorded waves.
• However, cardiac output measured by this method is not an accurate one.
3) X-ray Method
• In this method, a radio-opaque dye is injected intravenously and then the size
of the heart is detected by serial x-rays in systole and diastole from which
cardiac output is measured using computer programme.
4) Pulse-Pressure Method
• Pulse pressure (difference between systolic and diastolic pressures) provides a
rough idea of cardiac output.

INDIRECT METHODS
• Oxygen Fick Method
• Dye Dilution Method
• Thermal Dilution Method
• Doppler’s Method
• Ballistocardiography
• Echocardiography
• Radionucleotide angiography

• Fick Method
– Devised in 1870, not use practically until 1950’s
– Easy to get representative arterial blood sample
• eg femoral artery, brachial artery
– Difficult to get representative venous blood sample
• renal venous blood contains ~ 170 ml O2 / litre of blood
• cf coronary venous blood ~ 70 ml O2 / litre
• therefore need mixed venous blood
• ie from right ventricle or pulmonary trunk
– Very accurate – the “gold standard” for measuring CO
– But is invasive, and discontinuous

PROCEDURE
• 100% O2 is breathed in from a spirometer for 5-10
minutes.
• O2 concentration from arterial blood can be
measured from any peripheral artery.
• O2 concentration from mixed venous blood is
measured by passing a catheter via subclavian or
medial cubital vein to right atrium & then venous
blood is obtained either from right ventricle or
pulmonary trunk.

LIMITATIONS
• Requires a trained person
• Slow method
• Chances of ventricular fibrillation
• Can’t be used during exercise

Dye must be :
Easily available, non-toxic, easy to
measure, should not bring any change in the
circulation.
• Known quantity (I=5mg) of dye injected into arm
vein, SVC or right atrium
• Concentration of the dye (C) in the arterial blood
is monitored continuously by drawing blood from
any peripheral artery (mg/L).

• Time between 1st appearance and then
disappearance (t) is noted (seconds).
Flow = Volume per unit time (F=V/t)
Mass of indicator (I)
Volume = ------------------------
Concentration (C)
I/C
Flow = -------
t
I x 60
= -------
C x t

• Indicator dilution method
Sample dye
concentration
Concentration
(g/L)
Time (min)
inject bolus
of dye
0 0.5

• A plot of dye concentration (C) on y-axis against
time (t) along x-axis is made.
• It should be plotted on a semi-logarithmic paper.
A straight line is obtained which can easily be
extrapolated to baseline.
• Average concentration of dye (C) is obtained
from area under the curve.

• Amount of dye added = 5 mg
• Average dye concentration = 2 mg/L
• Therefore the volume that diluted the dye = 5mg = 2.5 L
• Time it took to go past = 0.5 min
• ie flow rate = 2.5 L = 5 L/min
• General equation:
~
mass of dye (Q g)
average dye conc (X g/L) x time of passage (t min)
2 mg/L
0.5 min
Flow rate =
Concentration
(g/L)
Time (min)
0 0.5
average conc (X) = 2 mg/L
time of passage (t) = 0.5 min
~

ADVANTAGES:
• Quick method
• Can be used during exercise
• Non-invasive (in comparison with Oxygen Fick
Method)

THERMAL DILUTION METHOD
• Change in temperature is an indicator
• Cold saline into right atrium
• Swan-Ganz catheter (Double lumen catheter)
• Thermistor- To record change in temperature
Advantages:
• Problem of re-circulation solved
• Unlike dye, saline is harmless

Doppler echocardiography
• Pulsed ultrasound waves emitted
• Directed parallel to flow of blood eg down supra-
sternal notch into ascending aorta
• Wavelength of sound is altered as it is reflects
off moving red blood cells
• Change in pitch indicates velocity of red blood
cells
• Estimate of aortic cross-section gives blood flow
ie cardiac output
• Pseudo-colouring used to indicate turbulence

Cardiac out put and its regulation

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