1.
Physics of Ventilation
National Chairperson (Ex)
Intensive Care Chapter I A P
Founder Chairman.....
National conference on pediatric critical
care
Professor of pediatrics ( Hon )
JNMC:Wardha
Nagpur : INDIA
Dr Deopujari

2.
The evolution of Ventilator

3.
Three problems of ventilation

4.
Applied Physics
• Compliance
• Static compliance
• Dynamic compliance
• Resistance
• Work of breathing
Flow
Pressure
Volume
Surface area
What can we manipulate ?

5.
Evolution of Ventilators………………
What can we manipulate ?
1)Minute ventilation
2)Pressure gradient
3)Surface are
4)Pulmonary vasculature
5)Solubility
How can we do this ?

6.
Compliance
Compliance is a quotient between volume
and corresponding pressure change.
C =
V
P
Dynamic compliance
Static compliance

7.
The compliance of any structure is the ease is
with which the structure distends ( C= ∆ V / ∆ P)
C
O
M
P
L
I
A
N
C
E

8.
C.C.P.
C.O.P.
V
O
L
U
M
E
PRESSURE
c.c.p. = critical closing pressure
c.o.p. = critical opening pressure
PEEP

9.
Pressure
Volume
Optimal Benefit Of PEEP
EX.
INS.

10.
Peak pressure
Plateau pressure
Pressure
Inspiratory pause
Flow
Time
Cst =
Tidal volume.
Cc
Cst : static compliance
Cc : circuit compliance
end expiratory pressure (Pend-ex)
Pend-ex = Peep + P peep
Resistance
Compliance
Static compliance
Static pressure – end expiratory pressure

11.
Flow …………………….
Flow indicates circulation of an element
per unit of time through a given place
Flow….
Linear
Turbulent

12.
FLOW
Palv
Pmo
FLOW THROUGH A PIPE LIKE
STRUCTURE REQUIRES A
DRIVING PRESSURE (Palv-
Pmo) TO OVERCOME THE
FRICTIONAL RESISTANCE
FLOW DEPENDS ON
Pressure Difference and
Resistance V=P/R

13.
Pressure …………….
Represents the force that a volume of gas exercises upon a unit
area.
Kinetic theory states that gas molecules bomb the walls of a
container .
If volume remains constant , pressure varies in direct proportion
to Temperature.
If temperature remains constant , pressure varies in inverse
relation to Volume .
Increase in pressure decreases volume

14.
Resistance ……………
Resistance is defined as the relationship between pressure (p) and flow ( 0 )
Therefore important when there is air flow.
R = -----------
Resistance depends upon
Diameter of airway
Length of airway
Viscosity and density of air
Resistance during inspiration
Resistance during expiration
P
O

15.
And how can we do this ?

16.
• Conditional variables
• Control variables
• Phase variables
Trigger variables
Limit variables
Cycle variables
Base line
Mechanical Ventilation
Concept

17.
Conditional variables alone or in combination are
analyzed by Ventilator’s control logic.
The state of this variable determines as to which of
two types of breath would be delivered.
SIMV is based on timing window and accordingly the
ventilator delivers …………………………….
a pressure triggered ( patient ) or time triggered
( machine) breath.
In this situation the patient effort and time are
conditional variables for determining triggering.
CONDITIONAL
VARIABLE
Conditional variables
• Pressure
• Volume
• Flow
• Time

18.
Control variable manipulates the conditional to cause inspiration.
Pressure , volume , flow and time are control variables.
The behavior of control Variable remains constant in spite of changed
Ventilatory load.
CONRTOL VARIALBE

19.
Control variable manipulates the conditionals to cause inspiration.
PRESSURE , VOLUME , FLOW and time are control variables.
The behavior of control Variable remains constant in spite of changed
Ventilatory load.
CONRTOL VARIALBE
Pressure
Rectangular Exponential

20.
Control variable manipulates the conditional to cause inspiration.
Pressure , VOLUME , FLOW and time are control variables.
The behavior of control Variable remains constant in spite of changed
Ventilatory load.
Volume
Ramp Sinusoidal
CONRTOL VARIALBE

21.
Control variable manipulates the conditional to cause inspiration.
PRESSURE , VOLUME , FLOW and time are control variables.
The behavior of control Variable remains constant in spite of changed
Ventilatory load.
Flow
sinusoidalrectangle ramp
ramp exponential
CONRTOL VARIALBE

22.
During pressure support ventilation
though one selects a level of support
the Inspiration continues till
predetermined flow rate or termination
criteria is reached.
During PSV patient determines the
Rate ……………..
Inspiratory time…
Flow……………..
LIMIT
VARIBALE

23.
Peak pressure
Plateau pressure
Resistance
Compliance
End of inspiration
Volume
Flow
Pressure
Volume control

24.
End of insp. flow
Volume
Flow
Pressure
Pressure control
What does not change …….
1)Volume curve
2)Exp. Flow curve

25.
End of insp. flow
Volume
Flow
Pressure
Pressure control
Peak p.
Plateau p. Resist.
Compliance
End of insp. flow
Volume
Flow
Pressure
Volume control

26.
Volume limited and pressure limited ventilation ………….
Volume limited pressure limited
Advantages
Tidal Volume guaranteed
Precise control of Inspiratory flow
Easy detection of changed
respiratory impedance
Precise control pf pressure
Decelerating flow reported to
improve distribution of ventilation
decrease dead space ventilation
decrease PIP
match Inspiratory flow
Disadvantages
PIP vary
Inspiratory flow may not match the
patients needs
Variable tidal volume
Changes in impedance not easily
detected

27.
Modes of ventilation
or moods of ventilation

28.
P
R
E
S
S
U
R
e
F
L
O
w
V
O
L
U
M
e
A B C
A normal lung B decreased compliance C increased resistance
Controlled Ventilation…………….

29.
SIMV
Patient triggered ventilation
Synchronized to patient breath
if the threshold is met .
Patient controlled variables
Respiratory rate
Inspiratory time
Clinician controlled variables
PIP if pressure limited
Tidal volume if volume cycled
Inspiratory time if time cycled
Flow
SIMV rate
Flow cycling …….
Insp. Terminated at % of peak
flow rather than time…………
Synchronizes expiratory and
Insp. flow thus total synchrony
achieved.

30.
When SIMV is used, the patient receives three different types of breath:
The controlled (Mandatory) breath.
Assisted (synchronized) breaths.
Spontaneous breaths, which can be pressure supported.
A B C
A .Controlled and time triggered
B .Spontaneous
C .Synchronized and assisted
Flow
PaW
Volume
Trigger

31.
Spontaneous
breath
Assisted breath
Back up ventilation period
Controlled breath
Spontaneous
volume
Trigger
Spontaneous
breath
Pressure
Volume

32.
Pressure support
Pressure support ventilation is a spontaneous mode
of ventilation.
Inspiratory effort is assisted by the ventilator at an
airway pressure that remains constant during the
phase of inspiration.
Inspiration is terminated when the peak Inspiratory
flow reaches a preset level. (usually 25%)
Patient determines………………
• Rate
• Inspiratory time
• Airflow

33.
PRVC
A control mode, which
delivers a set tidal volume with
each breath at the lowest
possible peak pressure.
Delivers the breath with a
decelerating flow pattern that is
thought to be less injurious to
the lung……

34.
Volume Support
Equivalent to pressure support
set a “goal” tidal volume
the machine watches the delivered
volumes and adjusts the pressure
support to meet desired “goal”
within limits set by you.

35.
Airway Pressure Release Ventilation
Can be thought of as giving a patient
two different levels of CPAP
Set “high” and “low” pressures with
release time.
Length of time at “high” pressure
generally greater than length of time at
“low” pressure.
By “releasing” to lower pressure, lung
volume is allowed to decrease to FRC

36.
Certain other issues

37.
Fixed insp. Time
Termination sens. off
Termination sens. on
Flow
Pressure

38.
Inspiratory cycle off…………
Proper Inspiratory cycle termination
avoids lung hyperinflation and
Increased work of breathing
40 %
10 %
10 %
5%
1%

39.
PEEP PIP
Vt.
COMPLIANCE LINE
Pressure limited…
Over distension

40.
PEEP PIP
Vt.
COMPLIANCE LINE
Pressure limited…
PEEP PIP
Vt.
COMPLIANCE LINE
Volume limited…
Pressure – Volume loops
Low
compliance

41.
A
B C
D
Volume
Pressure in CM
B C
Volume
Pressure in CMA
D
Normal resistance
Increased resistance

42.
volume
Pressure

43.
Triggering ……………………

44.
Triggering ……………………
Neuro – Ventilatory coupling ………….
Central Nervous System
Phrenic Nerve
Diaphragmatic contraction
Chest Wall and Lung expansion
Air way pressure , flow and volume
NAVA Ventilator
Current
Technology
Ideal technology
Neurally Adjusted
Ventilatory Assist
EA di
Waveform

45.
Tidal volume ÷ P plat – PEEP Tidal volume ÷ PIP – PEEP PIP – P plat ÷ Flow rate PIP- P2 ÷ Flow rate
Static compliance
Dynamic
characteristics
Maximum resistance
index
Minimum resistance
index
Elastic and resistive
property of respiratory
System
Time constant
×
Resistive property

46.
Conditional variables
Control variables
Pressure : Volume : Flow
Phase Variables
Trigger : Limit : cycle : Base line

47.
You can comfortably SLEEP even in difficult situation
if you know your physiology well……………
Thanks
SLEEP