The document discusses various methods for measuring cardiac output, including Fick's method. It explains the concepts of hemodynamics using Ohm's law and Poiseuille's law to relate factors like blood pressure, flow, resistance, vessel diameter and viscosity. The document also describes types of blood flow such as laminar and turbulent flow, and how flow is affected by conditions like stenosis, anemia and atherosclerosis. Measurement methods discussed include direct methods using electromagnetic and Doppler flow meters, and indirect methods like Fick's principle and indicator dilution techniques.

1. Dr Sanad Ahmed
MBBS,MSc.,MRCP2

3.  The different methods used to measure the
cardiac out put.
 Measuring the cardiac out put using Fick’s
method.
 To understand the concept of haemo-
dynamics.
 Types of blood flow.

4. A. Direct methods:
1. Flowmeter:
 Invasive: cannulate the aorta, pulmonary
artery, or great veins entering the heart
 Electromagnetic or Ultrasonic Flowmeter
 experimental animals

5. B. Indirect methods:
1. Oxygen Fick method
2. The indicator dilution method.
3. Doppler and echocardiograph

6.  The blood flow through an organ is equal to
the amount of a substance produced or
consumed by that organ in a unit of time,
divided by the arterio-venous difference of
that substance

7.  COP of the right ventricle = Blood flow
through the lungs in a unite of time

8.  250 mL of oxygen are
absorbed from the
lungs into the
pulmonary blood each
minute.
 Blood entering the
right heart has an
oxygen concentration
of 140 mL per litre of
blood.
 Blood leaving the left
heart has an oxygen
concentration of 190
mL per litre of blood.

9.  Each litre of blood passing through the lungs
absorbs 50 mL of oxygen.
 The total quantity of oxygen absorbed into the
blood from the lungs each minute is 250 mL.
 The volume of blood that must pass through the
pulmonary circulation each minute to absorb this
amount of oxygen =250/50 = 5L.

10.  Therefore, the quantity of blood flowing
through the lungs each minute is
5 litres
= The cardiac output.
 COP of the right ventricle = COP of the left
ventricle.

11.  the cardiac output can be calculated by the
following formula:

12. In applying this Fick procedure for measuring
cardiac output in the human being
1. Mixed venous blood is obtained through a
catheter inserted up the brachial vein and
directed into the right ventricle or pulmonary
artery.
2. Systemic arterial blood can be obtained from
any systemic artery in the body.
3. The rate of oxygen absorption by the lungs is
measured from respired air using an oxygen
meter.

14.  Haemo-dynamics: is the study of
the relationship between blood
pressure , blood flow & vascular
resistance.
 Ohm’s low =
Current = voltage/ resistance
I = ∆V/R
 Flow =pressure difference/
resistance
Q= ∆P/R

15.  Q= ∆P/R
Direction of flow is from high to low
pressure.
Flow is inversely proportional to
resistance.
The major mechanism of controlling
blood flow in all of the CVS and in
tissues is by changing the resistance of
blood vessels (arterioles in particular).

16.  R= ∆P/Q
 The resistance of all the systemic
vasculature is called the Total
Peripheral Resistance (TPR).
 The arterioles are the site of highest
resistance .

17.  Poiseuille low: relates fluid flow in
a long narrow tube to viscosity
(η)and radius (r).
 According to Poiseuille formula the
resistance to blood flow (R)=

18. Resistance (R) is determined by:
Radius (r) raised to the power 4 = inverse
relation.
Viscosity (ŋ) = Direct relation
Length (L) = Direct relation
(factors in the blood vessels and in the blood)

19.  Note that the most important variable is
the diameter of the blood vessel.
Why?
1. Raised to the power 4 : if r decreased by
half the resistance increases 16 times.
2. It can be regulated rapidly (Neural,
hormonal and local factors).

20.  Polycythemia increases viscosity =
increase resistance.
Anemia decreases resistance and
improve flow.

21. Flow can be : laminar, turbulent or transitional in
nature.
Osborne Reynolds (1842 - 1912) observed the
nature of flow through a glass tube by injecting a
dye and watching its path as it was carried by the
fluid .

22.  Laminar flow / streamline flow:
 fluid flows in parallel layers, with no disruption
between the layers and adjacent layers slide past
one another.
 Flow at low velocities.

23. Laminar blood flow:
flow in blood vessels is
laminar up to
a critical velocity.
 In a laminar flow:
1.The velocity of flow increases from a
minimum (zero) at contact with blood vessel
wall to a maximum at the center of the blood
vessel.
2.It makes no sounds. It is silent.

24.  Turbulent flow:
 Irregular flow in which there are cross currents
perpendicular to the direction of flow with mixing
of the fluid streams.
 Turbulent flow requires more energy.
 Turbulent flow is noisy and it creates audible
sounds (murmurs and bruits ).

25. Turbulent flow:
 Depends on the density, diameter, velocity &
viscosity of fluid.
The probability of Turbulence is predicted by
Reynold’s number (Re)
Re = density X diameter X velocity
viscosity

26. Turbulent flow:
The higher is (Re ), the higher the probability of
turbulence.
Re < 2000 = laminar flow
Re > 3000 = Turbulence

27. Narrowing of a blood vessel (Atherosclerosis or
thrombus) , or valve stenosis or regurgitation =
Increased velocity (if flow is constant)
Velocity cm/min = Flow / area
= Turbulence = murmurs and bruit
Anemia decreases viscosity = turbulence = systolic
murmurs.

28. Measurement of blood flow
 Direct methods:
Electromagnetic flow meters.
Doppler flow meters.
 Indirect methods:
Fick's principle.
Indicator dilution technique.
Plethysmography for measuring blood flow
in extremities (venous occlusion
plethysmography).

31.  The different methods used to measure the
cardiac out put.
 Measuring the cardiac out put using Fick’s
method.
 To understand the concept of haemo-
dynamics.
 Types of blood flow.