Basic Pulmonary Mechanics during Mechanical Ventilation
Equation of Motion
dP = R x Flow + dV / C st
Points of Discussion
1.Equation of motion2.Airway pressures3.Compliance4.Resistance5.Pressure-Time6.Flow-Time7.Pressure-volume loop8.Flow-volume loop
Inspiration Inspiration
Spontaneous Breathing
Exhalation Exhalation
Precondition of Inspiration
• Pa < Pb– Spontaneous
breath• Pb > Pa
– Mechanical ventilation
Pb
Pa
Gas Flow
compliance = Dvolume / Dpressure
volume
transairwaypressure
transthoracicpressure
transrespiratorypressure
Lung Mechanics resistance = Dpressure / Dflow
flow
Tube + Spring Model
Elastic Forces
Resistive Forces
“The Feature of the Tube”
R = D
P D F
Airway Resistance
Pressure Difference = Flow Rate x Resistance
Pressure Difference = Volume Change / Compliance Pressure Difference = Volume Change / Compliance
Volume
Pressure
D V
D P
Cs = D VD P
Compliance
Cs= D
VD P
R = D P D
F
Compliance and Resistance
Equation of Motion
DYNAMIC CHARACTERISTICS:dP = dV / Cdyn
DYNAMIC CHARACTERISTICS:dP = dV / Cdyn
RESISTANCE:dPresistive = R x Flow
RESISTANCE:dPresistive = R x Flow
STATIC COMPLIANCE:dPdistensive = dV / Cst
STATIC COMPLIANCE:dPdistensive = dV / Cst
dP = dPresist. + dP dist.
dP = R x Flow + dV / C st
Equation of Motion
dP = R x Flow + dV / C st
Components of Inflation PressureComponents of Inflation Pressure
Begin Expiration
Pa
w
(cm
H2O
)
Time (sec)
Begin Inspiration
PIP
Pplateau
(Palveolar)
Transairway Pressure (PTA)}
Expiration
Inspiratory Pause
Begin Inspiration Begin Expiration
Paw
(cm
H2O
)
Time (sec)
Airway
Resi
stance
Distending (Alveolar)
Pressure Expiration
Inflation Hold(seconds)
Begin Expiration
Paw
(c
m H
2O)
Time (sec)
Begin Inspiration
PIP
Pplateau
(Palveolar
Transairway Pressure (PTA)
}Exhalation Valve Opens
Expiration
PIP
Spontaneous vs. Mechanical
Mechanical
Time (sec)
SpontaneousPaw (cm H2O)
Inspiration
ExpirationExpiration
Inspiration
PIP vs PplatPIP vs Pplat
NormalHigh Raw
High FlowLow Compliance
Time (sec)
Paw
(c
m H
2O
)
PIP
PPlat
PIP
PIP PIP
PPlatPPlat
PPlat
Mean Airway Pressure
Increase FlowIncrease peak pressureLengthen Inspiratory TimeIncrease RateIncrease PEEP
Inspiratory Flow Pattern Inspiratory Flow Pattern
Inspiration
Expiration
Time (sec)
Flo
w (
L/m
in)
Beginning of inspirationexhalation valve closes
Peak inspiratory flow ratePIFR
Beginning of expirationexhalation valve opens
Total cycle timeTCT
Inspiratory Time
TI
Expiratory Time TE
Peak Expiratory Flow Rate PEFR
Flow vs TimeFlow vs Time
Inspiration
Expiration
Time (sec)
Flo
w (
L/m
in)
Flow PatternsFlow Patterns
ACCELERATING
DECELERATING
SINE
SQUARE
Flow Patterns and Effects of Volume
Flow Patterns and Effects of Volume
ACCELERATINGDECELERATING SINESQUARE
Mechanical vs SpontaneousMechanical vs Spontaneous
Inspiration
Expiration
Spontaneous
Mechanical
Volume vs. TimeVolume vs. Time
Inspiration
Expiration
Time (sec)
Vo
lum
e (m
l)
Inspiratory Tidal Volume
TI
FRC and PV Loop
FRC
VO
LU
ME
TLC
Negative Positive0
DISTENDING PRESSURE
Normal Compliance
FRC
Components of Pressure-Volume LoopComponents of Pressure-Volume Loop
Volume (mL)
Insp
irat
ion
Expirat
ion
PIP
VT
Paw (cm H2O)
PEEP and P-V LoopPEEP and P-V Loop
Volume (mL)
VT
PIPPaw (cm H2O)
PEEP
THANK YOU
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