pressure volume curve of the respiratory system 吳健樑 馬偕醫院 胸腔內科
TRANSCRIPT
Pressure Volume Curve of the Respiratory System
吳健樑馬偕醫院 胸腔內科
Transmural Pressure of the Respiratory System
PA
Alveolar pressure
PIpIntraleural pressure
PTpTranspulmonary pressure
Pressure around the Balloon (Lung)
1. PTP = PA – PIP
2. PA = 0, if no air is flowi
ng into the balloon
3. PIP is subatmospheric
due to the recoil of the
lung away from the jar
4. PTP= 0 – (-10) cmH2O
= 10 cmH2O
Pressure Volume Curve of the Lung
100
75
50
25
100
0
20
40
60
80
0-20 10 20 30-10
Pressure
Volume
Vital Capacity%
TLC%
Pressure (cmH2O)
Lung recoil is due to- surface tension- elastic and collagen fibers of the lung
Resting lung
FRC
Pressure Volume Curve of the Lung
1.0
0.5
-10 -20 -30
Pressure around lung (cmH2O)
Volume (L)
Pressure Volume Curve of the Lung
1. P-V curve defines the elastic property of the lung
2. Compliance = change in volume per unit change of pressure
3. Compliance quantifies the elastic property
Calculation of Compliance
Pressure (cmH2O)
Vo
lum
e (m
l)
1.0
0.5
-10 -20 -30
Pressure around lung (cmH2O)
Volume (L)
․
․
․․
Compliance of the Lung
1. The slope is the compliance
2. The line 1 represents high compliance
3. The line 2 is low compliance
1
2
Mechanics of Chest Wall
• Chest wall = all structures surrounding the
lung that move during breathing
– i.e. rib cages, diaphragm, abdomen wall &
contents and mediastinal contents.
• Sometimes like a spring
• Sometimes like a balloon
Pressure Volume Curve of Chest Wall (I)
Pressure Volume Curve of Chest Wall (II)
100
75
50
25
100
0
20
40
60
80
0-20 10 20 30-10
Pressure
Volume
Vital Capacity%
TLC%
Pressure (cmH2O)
Resting lung
FRC
• Chest wall recoils in two directions• CW recoils outward below 75% of VC• CW recoils inward at volume > 75% of VC
Residual volume
Pressure Volume Curve of Chest Wall
Pressure
Volume
Vital Capacity%
TLC%
Pressure (cmH2O)
100
75
50
25
100
0
20
40
60
80
0-20 10 20 30-10
Resting lung
FRC
Residual volume
Pressure Volume Curve of the Respiratory System
Hysteresis of Air filled Alveolus
What Factors Contribute to Compliance
• Connective tissue of lung
• Surface tension
• Surfactant
What Factors Contribute to Compliance
• Connective tissue of lung
• Surface tension
• Surfactant
Surface TensionThe weight in the bubble is the collapsing pressure of the bubble
Law of Laplace (inward pressure of bubble):P =2 T/r (T:surface tension; r: radius)
MV
SurfactantSurfactant is produced by type II alveolar cell. The type II cells have characteristic microvilli (MV).
Functions of Surfactant
• Surfactant is a DPPC (DiPalmitoyl Phosphatidyl Choline) protein with a hydrophobic at one end and hydrophilic at the other.
• Reduce surface tension by intermolecular repulsive force
Repulsive Force of Surfactant Molecule
SurfactantDepletedlung
Influence of Surfactant on PV Curve of Lung
What Does Compliance Mean
• Compliance– easier to in/deflate– steep curve: less pressure needed for
unit volume change
• Compliance – difficult to in/deflate– flat curve
Commonly Used Methods for Measuring PV Curve
• Supersyringe method
• Flow interrupter
• Low-flow method
The supersyringe techniqueDisconnection
Time consuming
Volume loss
P-V curveMethodology
The supersyringe technique
P-V curveMethodology
The multiple occlusion technique
Complexity
Volume history
Recorded in 8.38 +/- 1.19 min…
Servillo, 2000
P-V curveMethodology
Quin Lu, 1999
The low flow technique
Popular (many validation studies)
The Pres should be known
And substracted…
Not usable in case of leak
Pmax should be adjusted
No way for the deflation
P-V curveMethodology
Comparison of PV curves by Different Methods(Qin et al ARRCCM 1999)
Compliance (mL/cmH20): Volume/ pressure
Why it is important?1. Physiology: how much work to produce a volume.
2. Prognosis: Low/high CRS = poor prognosis
3. Treatments: PEEP/VT/recruitment maneuvers
Why is it complex?1. One point is not enough…
2. Affected by chest wall, abdomen, tube resistances…
3. Dynamic versus quasi-static…
4. Inflation or deflation curve…
Clinical Uses of P-V Curve
1. Allow initial estimate of lung pathology2. Presence of lower inflection point suggePresence of lower inflection point sugge
sts compression atelectasis rather than sts compression atelectasis rather than consolidationconsolidation
3. Recruitment proportional to the applied Recruitment proportional to the applied PEEP linear P-V curvePEEP linear P-V curve
4. An inflection point of the chest wall may An inflection point of the chest wall may lead to erroneous interpretation of PV culead to erroneous interpretation of PV curve of respiratory system.rve of respiratory system.
Normal
Restrictive(ARDS)
Obstructive(COPD)
P-V curveThe “Classical” Approach
P-V Curves in Different Stages of ARDS
Airway Pressure, cmH2O
Vol
ume
(%)
20
80
60
100
40
3015 20 25105 35 40
Recovery stageEarly stageIntermediate stageFibrotic stage
Clinical Uses of P-V Curve
1. Allow initial estimate of lung pathologyAllow initial estimate of lung pathology2. Presence of lower inflection point indicat
es the opening pressure of the atelectatic alveoli
3. Recruitment proportional to the applied Recruitment proportional to the applied PEEP linear P-V curvePEEP linear P-V curve
4. An inflection point of the chest wall may An inflection point of the chest wall may lead to erroneous interpretation of PV culead to erroneous interpretation of PV curve of respiratory system.rve of respiratory system.
Nonrecruitable
AtelectaticRecruitable
Normal
Pathophysiology
Acute Respiratory Distress Syndrome
Non-recruitable
AtelectaticRecruitable
Normal
Acute Respiratory Distress Syndrome
Effects of PEEP
PEEP
M. Tobin, NEJM 2001
P-V curve
Compliance (mL/cmH20): Volume/ pressure
The 3 segmental analysis of the Venegas (JAP, 1998) model
Best compliance
Over
distention of
lung units
Collapse of
peripheral
airways and
lung units
Ventral
Dorsal
Gas-Tissue Ratio Distribution in Lung Region
Gattinoni et al. JAMA 1993;269:2122
Gattinoni L, AJRCCM 2001
P-V curveThe “Modern” Approach
The sponge model and the superimposed pressure (SP)…
gas tissue
0
0.2
0.6
0.4
‧ ‧ ‧ ‧ ‧ ‧ ‧‧ ‧‧‧
●●0
0.2
0.6
0.4
● ● ● ● ● ●●
●
●
●●
0
0.2
0.6
0.4● ●
●● ●
● ●● ●
0 204 8 12 16
Gas
/Tis
sue
Rat
i on
Gas
/Tis
sue
Rat
i on
Gas
/Tis
sue
Rat
i on
PEEP, cmH2O
Gas/Tissue Ratio as A Function of PEEP
Gattinoni et al. JAMA
Pflex
Clinical Uses of P-V Curve
1. Allow initial estimate of lung pathologyAllow initial estimate of lung pathology2. Presence of lower inflection point indicatPresence of lower inflection point indicat
es the opening pressure of the atelectaties the opening pressure of the atelectatic alveolic alveoli
3. Recruitment proportional to the applied PEEP linear P-V curve
4. An inflection point of the chest wall may An inflection point of the chest wall may lead to erroneous interpretation of PV culead to erroneous interpretation of PV curve of respiratory system.rve of respiratory system.
P-V curveThe “Modern” Approach
SP0 SP5 SP10SP15
P-V curveThe “Modern” Approach
UIP = end of recruitment
LIP = start of recruitment
Recruitment zone
CT findings of Lung recruitment during Inspiration
Pressure – Volume Curves in ARDS caused by Pulmonary and Extrapulmonary disease
P-V curveThe “Modern” Approach
Peter C. Rimensberger
CRITICAL CARE MEDICINE 1999;27:1946-1952
Maggiore, AJRCCM 2001
P-V curveThe “Modern” Approach
De-recruitment even at high PEEP.
No correlation between VDER and the LIP.
The steeper the curve in ZEEP (potential for recruitment) and the highest the volume recruited by PEEP
Clinical Uses of P-V Curve
1. Allow initial estimate of lung pathologyAllow initial estimate of lung pathology2. Presence of lower inflection point indicatPresence of lower inflection point indicat
es the opening pressure of the atelectaties the opening pressure of the atelectatic alveolic alveoli
3. Recruitment proportional to the applied Recruitment proportional to the applied PEEP linear P-V curvePEEP linear P-V curve
4. An inflection point of the chest wall may lead to erroneous interpretation of PV curve of respiratory system.
V
Pst,rs
V
Pst,cw Pst,L
Surgical ARDS
Medical ARDS
UIP(VT =0.5)UIP(VT =0.7)
LIP =18 LIP =16
Impaired Lung and Chest wall mechanics in PV curves in ARDS
Ranieri et al AJRCCM 1997
The P-V curveConclusions
Understanding the PV curve:
The LIP: start of recruitment
The UIP: end of recruitment
Middle part: recruitment zone
Methodology:
Inflation and deflation
Pressure ramp method (?)
Clinical implications:
Recruitment maneuver
Optimum PEEPMaximum volume at equivalent pressure
Minimal hysteresis
Minimum slope
Adjust PEEP Level Based on Pflex
UIP
LIP
P-V loops on monitoring screen of MV
Plot of P-V loop from scalars of pressure and volume
P-V Loop: different resistance
C1 C2 C3
P-V loops: change in compliances
P-V loops: change in resistance
Work of Breathing
Esophageal Balloon
• The balloon should be 5 -10 cm long and 3.2 – 4.8 cm perimeter• The volume is 0.5 ml
LatexBalloon
Position of Esophageal Balloon
Methods of Confirmation of Optimal Balloon Placement
1. Dynamic occlusion test
– Compare the change in Pm and Pes during serial inspiratory efforts against occluded airway
2. Stomach placement
– Insert catheter into stomach first, then pull back into esophagus until negative pressure waveform
Pm (cmH2O)
Pes
(cm
H2O
)
0
10
5
50 10
Tracing of Volume, Pes and Pm during a dynamic occlusion test
Clinical Uses of Esophageal Pressure Measurement
• To determine the presence of dynamic intrinsic PEEP
• To assess the lung mechanics and respiratory mechanics (work of breathing)
• To interpret pulmonary properly vascular pressures during hemodynamic monitoring
Determination of Dynamic PEEPi using Esophageal Pressure
Pressure Waveform Indicating The Presence of auto-PEEP
Different Static and Dynamic auto-PEEP
-4 0
Esophageal pressure (cmH2O)
Ccw
-5
200
-2
400
600
Esophageal pressure (cmH2O)
Vo
lum
e (m
l)
Plots of Esophageal pressure vs volume during Unassisted and Passive br
eathing
CL,dyn
-5
200
0
400
600
Esophageal pressure (cmH2O)
Vol
ume
(ml)
Esophageal pressure vs volume during unassisted ventilation
Elastic work
Resistive work
CL,dyn Ccw
Influence of Pleural Pressure on Hemodynamic Monitoring
5 15 15-5 -5 15
LALA LA
HighPleural
Pressure
Normal LowMyocardialCompliance
Ppl = PEEP x {CL/ CL + CCW}