1. Basic Pulmonary Mechanics during Mechanical Ventilation
Equation of Motion
dP = R x Flow + dV / C st

2. Points of Discussion Equation of motion Airway pressures Compliance
Resistance
Pressure-Time
Flow-Time
Pressure-volume loop
Flow-volume loop

3. Spontaneous Breathing
Exhalation
Inspiration

4. Precondition of InspirationPb Pa
Gas Flow
Pa < Pb
Spontaneous breath
Pb > Pa
Mechanical ventilation

5. Lung Mechanics resistance = Dpressure / Dflow
transairway
pressure
transrespiratory
pressure
transthoracic
pressure
compliance = Dvolume / Dpressure
volume
The equation of motion says that the pressure necessary to deliver a breath has two components; the pressure to overcome elastic recoil of the lungs and chest wall and the pressure to cause flow through the airways. The left hand side of the equation can be expanded to show that ventilating pressure may be made up of muscle pressure and/or airway pressure generated by the ventilator. The right hand side of the equation can be expanded to show that elastic recoil pressure is the product of elastance times volume while resistive pressure is the product of resistance and flow.

6. Tube + Spring Model
Resistive Forces
Elastic Forces

7. “The Feature of the Tube” Pressure Difference = Flow Rate x Resistance
Airway Resistance
“The Feature of the Tube”
R =
D P
D F
Pressure Difference = Flow Rate x Resistance

8. Pressure Difference = Volume Change / Compliance
Cs =
D V
Volume
Pressure
D V
D P
D P
Pressure Difference = Volume Change / Compliance

9. Compliance and Resistance
Cs=
D V
D P
R =
D P
D F
In the ventilator circuit, the peak inspiratory pressure is a combination of the resistance related pressure and the compliance related pressure. An end inspiratory pause eliminates the flow related pressure and thus reflects on the compliance related pressure.

10. DYNAMIC CHARACTERISTICS:
Equation of Motion
DYNAMIC CHARACTERISTICS:
dP = dV / Cdyn
RESISTANCE:
dPresistive = R x Flow
STATIC COMPLIANCE:
dPdistensive = dV / Cst
dP = dPresist. + dP dist.
dP = R x Flow dV / C st

11. Equation of Motion
dP = R x Flow + dV / C st

12. Components of Inflation Pressure
PIP }
Transairway Pressure (PTA)
Paw (cm H2O)
Pplateau
(Palveolar)
Inspiratory Pause
Expiration
Begin Inspiration
Time (sec)
Begin Expiration

13. Exhalation Valve Opens
PIP }
Transairway Pressure (PTA)
Exhalation Valve Opens
Paw (cm H2O)
Pplateau
(Palveolar
Expiration
Begin Inspiration
Time (sec)
Begin Expiration
Paw (cm H2O)
Time (sec)
PIP
Inflation Hold
(seconds)
Distending
(Alveolar)
Pressure
Airway Resistance
Expiration
Begin Inspiration
Begin Expiration

14. Spontaneous vs. Mechanical
Inspiration
Paw
(cm H2O)
Spontaneous
Expiration
Expiration
Inspiration
Time (sec)

15. PIP vs Pplat Paw (cm H2O) Time (sec) High Raw Normal High Flow
Low Compliance
PPlat
Time (sec)

16. Lengthen Inspiratory Time Increase peak pressure
Mean Airway Pressure
Lengthen Inspiratory Time
Increase peak pressure
Increase PEEP
Increase Rate
Increase Flow
Another helpful feature is monitoring during trigger.
Here is a diagram of a pressure wave showing all the parameter settings that can effect MAP.
Mean Airway Pressure (MAP) is the average pressure applied to the airway during a respiratory cycle. It is calculated as the area under the pressure wave for one repiratory cycle.
In premature babies, you need to use quite short inspiratroy time settings in order to achieve synchrony - typically a Ti of s.
However as you can see in the diagram, this reduces the area under the pressure wave and may therefore reduce your MAP which effects oxygenation.
What you can do to compensate for this loss of MAP due to shorter Ti (given that your ventilator has no problem with inadvertent PEEP), is increase the flow rate. Increasing the flow creates a quicker rise of pressure at the airway - more time at peak pressure and thus increases MAP.

17. Inspiratory Flow Pattern
Beginning of expiration
exhalation valve opens
Peak inspiratory flow rate
PIFR
Inspiration
Inspiratory
Time TI
Expiratory Time TE
Flow (L/min)
Total cycle time
TCT
Time (sec)
Beginning of inspiration
exhalation valve closes
Expiration
Peak Expiratory Flow Rate PEFR

18. Flow vs Time
Inspiration
Time (sec)
Flow (L/min)
Expiration

19. Flow Patterns
SQUARE
DECELERATING
ACCELERATING
SINE

20. Flow Patterns and Effects of Volume
SQUARE
DECELERATING
ACCELERATING
SINE

21. Mechanical vs Spontaneous
Inspiration
Expiration

22. Inspiratory Tidal Volume
Volume vs. Time
Inspiratory Tidal Volume
Volume (ml)
Inspiration
Expiration TI
Time (sec)

23. FRC and PV Loop Normal Compliance TLC FRC FRC VOLUME Negative Positive
DISTENDING PRESSURE
Normal Compliance
FRC
FRC

24. Components of Pressure-Volume LoopVT
Expiration
Volume (mL)
Inspiration
PIP
Paw (cm H2O)

25. PEEP and P-V Loop VT
PIP
Volume (mL)
PEEP
Paw (cm H2O)

26. Thank You