Basics of applied physics for the Anaesthesiologists like Avagadro principle,venturi and pressure regulators are dealt here

1. BASIC PHYSICS FOR THE
ANAESTHESIOLOGISTS
RATHER APPLIED PHYSICS
dr.r.selvakumar.
professor of anaesthesiology
k.a.p.viswanatham govt medical college
trichy

2. WE HATE PHYSICS…
THAT’S WHY WE SELECTED
MEDICINE
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3. BUT… THERE IS A LITTLE BIT OF
PHYSICS IN ALLACTIVITIES OF
OUR DAY TO DAY LIFE….

4. JUST NOW I’VE FITTED THE MACHINE
WITH A NEW N2O CYLINDER….
HOW LONG WILL IT LAST…?
CAN I TAKE A CASE WHICH MAY LAST
FOR 6 HOURS….?
How the physics knowledge helps the Anaesthesiologists?

5. 1.HOW TO CALCULATE THE AMOUNT OF
N2O GAS IN A CYLINDER..?
•STORAGE OF N2O IN A CYLINDER
•PARTLY AS GAS ,PARTLY AS LIQUID
STORY OF O2 – IDEAL GAS
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6. MOLECULAR WEIGHT
ADDITION OF ATOMIC WEIGHT
ATOMIC WEIGHT OF NITROGEN – 14, OXYGEN – 16
MOLECULAR WEIGHTOF N2O – 14+14+16 = 44
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7. GRAM MOLECULAR WEIGHT
MOLECULAR WEIGHT EXPRESSED IN GRAMS.
AVAGADRO HYPOTHESIS:
ONE GRAM MOLECUALR WEIGHT OF ALL GASES WILL CONTAIN THE
SAME NUMBER OF MOLECULES AND OCCUPY THE SAME VOLUME ( 22.4 L)
AT S.T.P
32 g OF O2 = 44 g OF N2O = 28 g OF N2 =22.4 LITERS
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8. AMOUNT OF N2O GAS IN A CYLINDER
TARE WEIGHT OF THE CYLINDER = 12.5 K.G
CYLINDER WEIGHT WITH N2O = 15 K.G
SO.. WEIGHT OF THE N2O = 2.5 K.G = 2500G
44G OF N2O = 22.4 L
THEREFORE 2500 G = 22.4/44 x 2500 = 1272 L
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9. 2. HOW DOES THE ALVEOLAR GAS
EXCHANGE OCCURS….?
O2 AND CO2 MOVE IN OPPOSITE
DIRECTION BECAUSE OF
PARTIAL PRESSURE GRADIENT.
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10. WHAT DO YOU MEAN BY
PARTIAL PRESSURE?
@ @
@
@
@
$ $
$
@ @
@
@
@ $
$
IN A MIXTURE OF GASES,THE PRESSURE EXERTED BY EACH GAS
IS THE SAME AS THAT WHICH IT WOULD EXERT IF IT ALONE
OCCUPIED THE CONTAINER
$
5 PSI 3 PSI 8 PSI

11. DALTON’S LAW OF PARTIAL PRESSURE
THE PROPORTION OF THE PRESSURE EXERTED BY A GAS
IN THE TOTAL PRESSURE IS EQUATED WITH THE VOLUME
IT OCCUPIES
@ @
@
@
@
$
$
$
PRESSURE OF @ GAS = 5 PSI
PRESSURE OF $ GAS = 3 PSI
TOTAL PRESSURE = 8 PSI
What is the % contribution of pressure of @ gas
In the total pressure?
5/8 x 100 = 62.5%
So, gas @ will occupy
62.5% of the total volume

12. THE % OF O2 IN THE ROOM AIR = 21% BY VOLUME
THAT MEANS…IT CONTRIBUTES 21% OF THE
TOTAL ATMOSPHERIC PRESSURE
21/100 X 760 = 159.6 mm of Hg. pO2 in room air = 159.6
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13. Gaseous
Component
Percentage in
Air
% x 760 (mm
Hg)
Partial
Pressure
exerted (mm
Hg)
Symbol
Nitrogen 79.04 0.7904 x 760 600.7 PN
Oxygen 20.93 0.2093 x 760 159.1 PO2
Carbon
Dioxide
0.03 0.0003 x 760 0.228 PCO2
Total 100 760
Partial Pressure of Atmospheric Gases Calculation
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15. WHAT WILL HAPPEN IN Mt EVEREST…?
ATMOSPHERIC PRESSURE = 253 mm of Hg.
PARTIAL PRESSURE OF O2 = 21/100 X 253 = 53 mm of Hg
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16. * *
** **
*** ** ***
* * *
* * * **
3. DIFFUSION OF GAS IN A LIQUID
GAS GOES INTO SOLUTION
SATURATION POINT
THE PRESSURE EXERTED BY THE GAS IN THE LIQUID
IS CALLED AS “TENSION”
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17. DIFFFUSION OF GAS IN A LIQUID
100 PSI 200 PSI
* *
* * *
* *
* *
* * * **
* ** **
*** ***
**** **
*** ***
*
*
*
THE AMOUNT OF GAS DISSOLVED IN A GIVEN LIQUID
IS DIRECTLY PROPORTIONAL TO THE PARTIAL PRESSURE OF
THE GAS IN EQUILIBRIUM WITH THE LIQUID
HENRY’S LAW
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18. DIFFUSION OF GAS IN A LIQUID
PARTIAL PRESSURE OF THE GAS
TEMPERATURE
NATURE OF THE GAS
TYPE OF LIQUID
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19. PARTITION COEFFICIENT
1 litre of BLOOD
1 litre
N2O
0.47 L N2O
RATIO OF THE AMOUNT OF SUBSTANCE PRESENT IN ONE PHASE
COMPARED WITH ANOTHER,THE TWO PHASES BEING OF EQUAL VOLUME
AND IN EQUILIBRIUM
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20. PARTITION CO-EFFICIENT
THE AMOUNT OF DISSOLVED GAS TO RAISE THE SAME
PARTIAL PRESSURE AS IN THE CONTAINER MAY NOT BE
THE SAME……
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21. ++++
++++
+++
*******
*******
**** ***
***
# # # #
# ## #
# ## ##
++ +
+
*******
****
****
# # ### ##
#####
####
########
N2O
0.47
HALOTHANE
2.3
ETHER
12
SOLUBILITY OF ANAESTHETICS IN BLOOD
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22. THATS WHY, INDUCTION WITH ETHER IS SLOW……
Partial pressure in the alveoli builds up
very slowly as most of the ether goes into
solution in the blood.
Only when blood gets fully saturated, the
Partial pressure in the alveoli and then brain rises…..
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23. BOURDON PRESSURE
GAUGE
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4. WHICH PART OF THE BOYLE’S MACHINE
UTILISES THE SAME PRINCIPLE AS THIS TOY…?

24. BOURDON PRESSURE GAUGECBE-SZ

25. IN A CONTAINER,PRESSURE EXERTED BYA COMPRESSED GAS
EXERTS ITS EFFECT EQUALLY ON ALL SIDES OF THE CONTAINER.
IF THE CONTAINER IS MADE SUCH A WAY THAT IT CAN EXPAND OR
STRAIGHTEN OUT IN A DIRECTION, IT WILL DO SO AS LONG AS THE
PRESSURE IS MAINTAINED INSIDE.
ONCE THE PRESSURE IS RELEASED, THE CONTAINER WILL RETAIN ITS
ORIGINAL SHAPE
PRINCIPLE OF BOURDON PRESSURE GAUGE
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26. ------------------------
---------------------------------------
BASIC PRINCIPLE OF PRESSURE REGULATORS
TALL CONTAINER
PRESSURE = P
AREA OF ACTING
FORCE = a
SHORT,
WIDE
CONTAINER
Pressure = p
Area = A
P
a
p
A
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5. HOW THE CYLINDER PRESSURE IS REDUCED
TO LOWER LEVEL IN THE BOYLE’S MACHINE…?

27. BASIC PRINCIPLE OF PRESSURE REGULATOR
AT EQUILIBRIUM
FORCE ACTING IN THE TALL
CONTAINER
=
FORCE ACTING IN THE
SHORT,WIDE CONTAINER
P x a = p x A
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28. A LARGE FORCE ACTING ON A SMALL SURFACE AREA
CAN BE BALANCED BY
A SMALL FORCE ACTING ON A LARGE SURFACE AREA
BASIC PRINCIPLE OF
PRESSURE REGULATORS
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29. CYLINDER
PRESSURE = P
SMALL DIAPHRAGM
AREA = a
LARGE DIAPHRAGM
AREA = A
REDUCED PRESSURE = p
FLOW
METER
SCHEME OF A SIMPLE PRESSURE REGULATOR
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30. SIMPLE PRESSURE REGULATOR
FORCE ACTING TO OPEN
THE SMALL DIAPHRAGM = P x a
AT EQUILIBRIUM….
FORCE ACTING TO CLOSE
THE SMALL DIAPHRAGM = p x A
BALANCED BY
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31. EXAMPLE:
CYLINDER PRESSURE = 2000 psi
SURFACE AREA OF
SMALL DIAPHRAGM = 10 mm
PRESSURE OF THE GAS
IN THE REGULATOR = p
SURFACE AREA OF
LARGE DIAPHRAGM = 100 mm
2000 X 10 = p X 100
p = 2000 X 10 /100
p = 200 psi
SO, IF THE CYLINDER PRESSURE IS 2000, THE REGULATOR WILL REDUCE
IT TO 200 psi.
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32. 2000 X 10 = p X 100
p = 2000 X 10 /100
p = 200 psi
IN OTHER WORDS, THE RATIO OF THE SURFACE AREA
OF THE TWO DIAPHRAGMS DECIDE THE RATIO OF
PRESSURE REDUCTION
HERE IT IS 10 : 100 – SO, PRESSURE REDUCTION IS 1/10
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33. CYLINDER
PRESSURE = P
SMALL DIAPHRAGM
AREA = a
LARGE DIAPHRAGM
AREA = A
REDUCED PRESSURE = p
FLOW
METER
SCHEME OF A MODIFIED PRESSURE REGULATOR
S1
S2
P X a X S1 = p X A X S2
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34. MODERN REGULATOR:
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35. PRESSURE OF THE SPEEDING FLUID
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6.WHAT DO YOU MEAN BY VENTURI PRINCIPLE…?

36. CBE-SZ

37. BASIC PRICIPLE OF VENTURI INJECTOR

38. BASIC PRINCIPLE OF A NEBULISER

39. VENTI MASKS FOR OXYGEN THERAPY

40. CBE-SZ
Some more applications
Of Venturi principle….
Bunsen burner
Insect sprayer

41. THE BRILLIANCE OF ANCIENT CHOLA KING, RAJA RAJA CHOLAN
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42. IRRIGATION SYSTEM OF THE CAUVERY BASIN
WATER LET-OUT SYSTEM FROM THE LAKES

44. DANIEL BERNOULLI - 1738
GIOVANNI BATTISTA VENTURI - 1746 - 1822
RAJA RAJA CHOLAN - 985 - 1014
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45. THANK YOU
dr.r.selvakumar. m.d.d.a.dnb
professor of anaesthesiology,
k.a.p.viswanatham govt. medical college,
trichy