The document provides comprehensive information on ventilator mechanics, including definitions of ventilation and respiration, compliance and resistance in the respiratory system, and types of mechanical ventilators. It explains different types of ventilator waveforms, their significance, and the impact of airway resistance and compliance on pressure-time relationships. Various flow patterns and their effects on breathing dynamics are also discussed, along with key equations and diagrams illustrating the respiratory system's mechanics.

1. VENTILATOR
GRAPHICS
Dr.Gunasekaran
Dr.Dhatchinamoorthy

2. Definitions
Ventilation - Movement of air into and out of the lungs
Respiration - Exchange of oxygen and carbon dioxide between an
organism and its environment
Internal and external respiration

3. Compliance
The relative ease with which the structure
distends.
It can be defined as the opposite, or
inverse, of elastance
Elastance is the tendency of a structure to
return to its original form after being
stretched or acted on by an outside force
C = ΔV/ΔP
Compliance of the respiratory system is
the sum of the compliances of both the
lung parenchyma and the surrounding
thoracic structures
Normal= 100ml/cm H2O(50-170)
• Resistance is a measurement of the
frictional forces that must be
overcome during breathing.
• The anatomical structure of the
airways and the tissue viscous
resistance offered by the lungs and
adjacent tissues and organs
• Raw = (PIP Pplateau)/flow (where
−
PIP is peak inspiratory pressure); or
Raw = PTA/flow
Resistance

4. Types of Mechanical ventilators:
• Negative-pressure ventilators
• Positive-pressure ventilators.

5. Types of Positive-Pressure Ventilators
1- Volume Ventilators.
2- Pressure Ventilators
3- High-Frequency Ventilators

6. Flow VOLUME Pressure
Time FiO2
R.R.
Control variable

7. Inspiration
Expiration
Time (sec)
Flow
(L/min)
Phase variables of a Breath
Trigger
Limit
Cycle
Trigger
Time
Pressure
Flow
Cycle
Time/
Volume
Pressure
Flow

8. Inspiratory Trigger
• Normally set automatically
• 2 modes:
• Airway pressure
• Flow triggering

9. Triggering
Time (sec)
Patient Machine
Pressure
(cmH20)

10. ● Sensitivity(trigger Sensitivity)
• The sensitivity function controls the amount of
patient effort needed to initiate an inspiration
• Increasing the sensitivity (requiring less negative
force) decreases the amount of work the patient
must do to initiate a ventilator breath.
• Decreasing the sensitivity increases the amount of
negative pressure that the patient needs to initiate
inspiration and increases the work of breathing.

12. Types of Waveforms
•Scalars and Loops:
• Scalars: Plot pressure, volume, or flow against time. Time is the x-axis
• Loops: Plot pressure or flow against volume. (P/V or F/V). There is no
time component.

13. Types of Ventilator
Waveforms:
Scalars and Loops
Scalars are waveform representations of pressure, flow or volume
on the y axis vs time on the x axis
pressure vs time
scalar
flow vs time
scalar
volume vs time
scalar
Inspiratory
arm
expiratory
arm

14. Types of Loops
P-V Loop F-V Loop
Expiratory
arm
Inspiratory
arm
Inspiratory
arm
Expiratory
arm

15. Understanding the flow-time waveform
• There are two components to the flow-time
waveform
– The inspiratory arm:
• Active in nature
• The character is determined by the ventilatory flow settings.
– The expiratory arm:
• Passive in nature
• The character is determined mainly by elastic recoil of the patients
lungs and airway resistance.
• Also affected by patient respiratory effort (if any)
• There are two commonly used types of flow
patterns available on most ventilators
– The ‘square wave’ or ‘constant flow’ pattern
– The ‘ramp’ (decelerating) type pattern

16. The ‘square wave’ flow pattern
The inspiratory flow rate
remains constant over
the entire inspiration.
time
flow
Inspiratory
arm
Expiratory
arm
The expiratory flow is
passive and is
determined by airways
resistance and the
elastic recoil of the lungs

17. The ‘decelerating ramp’ flow pattern
The inspiratory flow rate
decelerates as a function
of time to reach zero flow
at end inspiration
For a given tidal volume,
the inspiratory time is
higher in this type of flow
pattern as compared to
the square wave pattern
time
flow
Inspiratory
arm
Expiratory
arm

19. Understanding the basic
ventilator circuit diagram
ventilator
Diaphragm
These two systems are connected by
an endotracheal tube which we can
consider as an extension of the
patients airways.
The ventilator makes up the first part
of the circuit. Its pump like action is
depicted simplistically as a piston
that moves in a reciprocating fashion
during the respiratory cycle.
The patient’s own respiratory system
Makes up the 2nd
part of the circuit.
The diaphragm is also shown as a
2nd
piston; causing air to be drawn into
the lungs during contraction.
ET Tube
airways
Chest wall

20. Understanding airway pressures
The respiratory system can be thought of as a mechanical
system consisting of a resistive (airways) and elastic
(lungs and chest wall) element in series
Diaphragm
ET Tube
airways
Chest wall
PPL
Pleural pressure
Paw
Airway pressure
Palv
Alveolar pressure
Lungs + Chest wall
(elastic element)
Airways
(resistive element)
The contribution of airway
resistance
pressure depends on the rate
of airflow
and the underlying resistance
(caliber)
of the airways
Flow resistance
The contribution of the
elastic element
(lungs + chest wall)
depends on
the degree of lung
inflation and
the underlying compliance
of the
lungs and the chest wall
Volume
compliance
Paw = Flow Resistance + Volume
Compliance

21. Understanding basic respiratory mechanics
The total ‘airway’ resistance (Raw)
in the mechanically ventilated patient
is equal to the sum of the resistances offered
by the endotracheal tube (R ET tube)
and the patient’s airways ( R airways)
Thus the equation of motion for the respiratory system
is
P applied (t) = Pres (t) + Pel (t)

22. ventilator
Diaphragm
Ppeak
Pres
RET tube
Rairways
Pres
Pplat
Understanding the pressure-time waveform
using a ‘square wave’ flow pattern
time
pressure
After this, the pressure rises in a linear fashion
to finally reach Ppeak. Again at end inspiration,
air flow is zero and the pressure drops by an
amount equal to Pres to reach the plateau
pressure Pplat. The pressure returns to
baseline during passive expiration
Pres

23. Now let’s look at some different pressure-time
waveforms using a ‘square wave’ flow pattern
This is a normal pressure-time waveform
With normal peak pressures ( Ppeak) ;
plateau pressures (Pplat )and
airway resistance pressures (Pres)
time
pressure
Ppeak
Pres
Pplat
Pres
time
flow
‘Square wave’
flow pattern
Normal values:
Ppeak < 40 cm H2O
Pplat < 30 cm H2O
Pres < 10 cm H2O

24. Waveform showing increased airways resistance
time
pressure
Ppeak
Pres
Pplat
Pres
The increase in the peak airway pressure is driven
entirely by an increase in the airways resistance
pressure.
e.g. ET tube
blockage
Paw = Flow Resistance + Volume + PEEP
Compliance
time
flow
‘Square wave’
flow pattern
Normal

25. Waveform showing increased airways resistance
Ppeak
Pplat
Pres
‘Square
wave’ flow
pattern

26. Waveform showing high airway resistance
due to high flow rates
time
pressure
Ppeak
Pres
Pplat
Pres
The increase in the peak airway pressure is driven
entirely by an increase in the airways resistance
pressure caused by excessive flow rates.
Note the shortened inspiratory time and high flow
e.g. high flow
rates
Paw = Flow Resistance + Volume + PEEP
Compliance
time
flow
‘Square wave’
flow pattern
Normal
Normal (low)
flow rate

27. Waveform showing decreased lung compliance
The increase in the peak airway pressure is driven
entirely by the decrease in the lung compliance.
Increased airways resistance is often
also a part of this scenario.
time
pressure
Ppeak
Pres
Pplat
Pres
e.g. ARDS
Paw = Flow Resistance + Volume + PEEP
Compliance
Normal
time
flow
‘Square wave’
flow pattern

28. Waveform showing decreased lung compliance
Ppeak
Pplat
Pres
‘Square
wave’ flow
pattern

29. Now lets look at the same pressure-time tracings
using a ‘decelerating ramp’ flow pattern
High Raw:
(e.g. asthma)
Normal
High flow:
(Note short
Inspiratory
time)
Low CL:
e.g. ARDS
Normal
PIP
Normal
Pplat
High
PIP
High
PIP
High
Pplat
Normal
Pplat
Normal
Pplat
High
PIP
pressure
time

30. LOOPS
P-V Loop F-V Loop
Expiratory
arm
Inspiratory
arm
Inspiratory
arm
Expiratory
arm

31. P/V loop

32. Components of P/V loop

33. Abnormalities in P/V loop
Alveolar over
distention
Increased WOB

34. F/V Loop

35. Abnormalities in F/V loop
Increased R aw
Air leak

36. • Each additional assisted breath at prefixed tidal
volume or pressureTrigger: ventilator or patient
• Limit: Flow / volume or Pressure
• Cycling: volume or time
Assist Control

38. Pressur
e
Flow
Volume
(L/min)
(cm H2O)
(ml)
Time (sec)
SIMV Mode
Spontaneous Breath

39. SIMV + PS Ventilation

40. CMV

41. PSV
Time (sec)
Pressure
(cm H2O)
Volume
(mL)
Flow
(L/m)
Set PS
level
Rise
Rise
Time
Courtesy: Prof J V
Divatia

42. Volume Control
Pressure-Time waveform.
X. Inspiration time
Y. Pause time
Z. Expiration time
1. Start of Inspiration
2. Peak inspiratory pressure
3. Early inspiratory pause pressure
4. End inspiratory pause pressure
5. Early expiratory pressure
6. End expiratory pressure
Flow-Time waveform.
X. Inspiration time
Y. Pause time
Z: Expiration time
7. Peak inspiratory flow
8. Zero flow phase
9. Peak expiratory flow
10. Slope decelerating expiratory limb
11. End expiratory flow
Volume-Time waveform.
X. Inspiration time
Y. Pause time
Z. Expiration time
12. Start of inspiration
13. The slope represents current delivery of
inspiratory tidal volume
14. End inspiration
15. The slope represents current patient
delivery of expiratory tidal volume

43. Pressure Control
Pressure-Time waveform.
X. Inspiration time
Z. Expiration time
1. Start of Inspiration
2. Peak inspiratory pressure
3. End expiratory pressure
Flow-Time waveform.
X. Inspiration time
Z. Expiration time
4. Peak inspiratory flow
5. End inspiratory flow
6. Peak expiratory flow
7. End expiratory flow
Volume-Time waveform.
X. Inspiration time
Z.: Expiration time
8. Start of inspiration
9. End inspiration
10. End expiration

44. Thanks