1. Pressure Volume Curve of the Respiratory System
吳健樑
馬偕醫院 胸腔內科

2. Transmural Pressure of the Respiratory System

3. Pressure around the Balloon (Lung)
PTP = PA – PIP
PA = 0, if no air is flowing into the balloon
PIP is subatmospheric due to the recoil of the lung away from the jar
PTP= 0 – (-10) cmH2O
= 10 cmH2O
PTp
Transpulmonary
pressure PA
Alveolar
pressure
PIp
Intraleural
pressure

4. Pressure Volume Curve of the Lung

5. Pressure Volume Curve of the Lung
100
Vital Capacity %
100 80 75
TLC % 60
Volume
Resting lung 50 40 20
FRC 25
Pressure
-20
-10 10 20 30
Pressure (cmH2O)
Lung recoil is due to
surface tension
elastic and collagen fibers of the lung

6. Pressure Volume Curve of the Lung
P-V curve defines the elastic property of the lung
Compliance = change in volume per unit change of pressure
Compliance quantifies the elastic property
Volume (L)
1.0
0.5
-10
-20
-30
Pressure around lung (cmH2O)

7. Calculation of Compliance
Volume (ml)
Pressure (cmH2O)

8. Compliance of the Lung The slope is the compliance
2. The line 1 represents high compliance
3. The line 2 is low compliance
Volume (L) ․
1.0 ․ 2 ․
0.5 ․ 1
-10
-20
-30
Pressure around lung (cmH2O)

9. 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

10. Pressure Volume Curve of Chest Wall (I)

11. Pressure Volume Curve of Chest Wall (II)

12. Pressure Volume Curve of Chest Wall
100
Vital Capacity %
100 80 75
TLC % 60
Volume 40
Resting lung 50 20
FRC 25
Pressure
Residual
volume
-20
-10 10 20 30
Pressure (cmH2O)
Chest wall recoils in two directions
CW recoils outward below 75% of VC
CW recoils inward at volume > 75% of VC

13. Pressure Volume Curve of the Respiratory System
Vital Capacity %
100 75 50 25 20 40 60 80
-20 10 30
-10
Resting lung
FRC
Residual
volume
TLC %
Volume
Pressure
Pressure (cmH2O)

15. Hysteresis of Air filled Alveolus

16. What Factors Contribute to Compliance
Connective tissue of lung
Surface tension
Surfactant

17. What Factors Contribute to Compliance
Connective tissue of lung
Surface tension
Surfactant

18. Surface Tension
The 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)

19. Surfactant
Surfactant is produced by type II alveolar cell. The type II cells have characteristic microvilli (MV). MV

20. 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

21. Repulsive Force of Surfactant Molecule

22. Influence of Surfactant on PV Curve of Lung
Depleted
lung

23. What Does Compliance Mean
easier to in/deflate
steep curve: less pressure needed for unit volume change
difficult to in/deflate
flat curve

24. Commonly Used Methods for Measuring PV Curve
Supersyringe method
Flow interrupter
Low-flow method

25. The supersyringe technique
P-V curve Methodology
The supersyringe technique
Disconnection 
Time consuming
Volume loss

26. The supersyringe technique
P-V curve Methodology
The supersyringe technique

27. The multiple occlusion technique
P-V curve Methodology
The multiple occlusion technique
Complexity
Volume history
Recorded in / min…
Servillo, 2000

28. P-V curve Methodology 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
Quin Lu, 1999

29. Comparison of PV curves by Different Methods
(Qin et al ARRCCM 1999)

30. Compliance (mL/cmH20): Volume/ pressure
Why it is important?
Physiology: how much work to produce a volume.
Prognosis: Low/high CRS = poor prognosis
Treatments: PEEP/VT/recruitment maneuvers
Why is it complex?
One point is not enough…
Affected by chest wall, abdomen, tube resistances…
Dynamic versus quasi-static…
Inflation or deflation curve…

31. Clinical Uses of P-V Curve
Allow initial estimate of lung pathology
Presence of lower inflection point suggests compression atelectasis rather than consolidation
Recruitment proportional to the applied PEEP linear P-V curve
An inflection point of the chest wall may lead to erroneous interpretation of PV curve of respiratory system.　

32. P-V curve The “Classical” Approach
Normal
Obstructive
(COPD)
Restrictive
(ARDS)

33. P-V Curves in Different Stages of ARDS
100 80 60
Volume (%)
Recovery stage
Early stage
Intermediate stage
Fibrotic stage 40 20 5 10 15 20 25 30 35 40
Airway Pressure, cmH2O

34. Clinical Uses of P-V Curve
Allow initial estimate of lung pathology
Presence of lower inflection point indicates the opening pressure of the atelectatic alveoli
Recruitment proportional to the applied PEEP linear P-V curve
An inflection point of the chest wall may lead to erroneous interpretation of PV curve of respiratory system.　

35. Acute Respiratory Distress Syndrome
Pathophysiology
Nonrecruitable
Normal
Atelectatic
Recruitable

36. Acute Respiratory Distress Syndrome
Effects of PEEP
PEEP
Non-
recruitable
Normal
Atelectatic
Recruitable

37. P-V curve
M. Tobin, NEJM 2001

38. Compliance (mL/cmH20): Volume/ pressure
The 3 segmental analysis of the Venegas (JAP, 1998) model
Over
distention of
lung units
Collapse of
peripheral
airways and
lung units
Best compliance

39. Gas-Tissue Ratio Distribution in Lung Region
Ventral
Dorsal
Gattinoni et al. JAMA 1993;269:2122

40. P-V curve The “Modern” Approach
The sponge model and the superimposed pressure (SP)…
gas
tissue
Gattinoni L, AJRCCM 2001

41. ‧ Gas/Tissue Ratio as A Function of PEEP Pflex Gattinoni et al. JAMA
0.2
0.6
0.4 ‧ ● 20 4 8 12 16
Gas/Tissue Ratio
as A Function
of PEEP
Gas/Tissue Ration
Pflex
Gas/Tissue Ration
Gas/Tissue Ration
Gattinoni et al. JAMA
PEEP, cmH2O

42. Clinical Uses of P-V Curve
Allow initial estimate of lung pathology
Presence of lower inflection point indicates the opening pressure of the atelectatic alveoli
Recruitment proportional to the applied PEEP linear P-V curve
An inflection point of the chest wall may lead to erroneous interpretation of PV curve of respiratory system.　

43. P-V curve The “Modern” Approach
SP5
SP0
SP10
SP15

44. UIP = end of recruitment LIP = start of recruitment
P-V curve The “Modern” Approach
UIP = end of recruitment
Recruitment zone
LIP = start of recruitment

45. CT findings of Lung recruitment during Inspiration

46. Pressure – Volume Curves in ARDS caused by Pulmonary and Extrapulmonary disease

47. P-V curve The “Modern” Approach
Peter C. Rimensberger
CRITICAL CARE MEDICINE 1999;27:

48. P-V curve The “Modern” Approach
The steeper the curve in ZEEP (potential for recruitment) and the highest the volume recruited by PEEP
De-recruitment even at high PEEP.
No correlation between VDER and the LIP.
Maggiore, AJRCCM 2001

49. Clinical Uses of P-V Curve
Allow initial estimate of lung pathology
Presence of lower inflection point indicates the opening pressure of the atelectatic alveoli
Recruitment proportional to the applied PEEP linear P-V curve
An inflection point of the chest wall may lead to erroneous interpretation of PV curve of respiratory system.　

50. Impaired Lung and Chest wall mechanics in PV curves in ARDS
Surgical ARDS  V
UIP(VT =0.7)
UIP(VT =0.5)
Medical ARDS
LIP =18
LIP =16  V 
Pst,rs 
Pst,cw 
Pst,L
Ranieri et al AJRCCM 1997

51. The P-V curve Conclusions
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 PEEP
Maximum volume at equivalent pressure
Minimal hysteresis
Minimum slope

52. Adjust PEEP Level Based on Pflex

54. UIP
LIP

55. P-V loops on monitoring screen of MV

56. Plot of P-V loop from scalars of pressure and volume

57. P-V Loop: different resistance

58. P-V loops: change in compliances

59. P-V loops: change in resistance

60. Work of Breathing

61. Esophageal Balloon The balloon should be 5 -10 cm long and 3.2 –
4.8 cm perimeter
The volume is 0.5 ml
Latex
Balloon

62. Position of Esophageal Balloon

63. Methods of Confirmation of Optimal Balloon Placement
Dynamic occlusion test
Compare the change in Pm and Pes during serial inspiratory efforts against occluded airway
Stomach placement
Insert catheter into stomach first, then pull back into esophagus until negative pressure waveform

64. Tracing of Volume, Pes and Pm during a dynamic occlusion test10
Pes (cmH2O) 5 5 10
Pm (cmH2O)

65. 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

66. Determination of Dynamic PEEPi using Esophageal Pressure

67. Pressure Waveform Indicating The Presence of auto-PEEP

68. Different Static and Dynamic auto-PEEP

69. Plots of Esophageal pressure vs volume during Unassisted and Passive breathing
CL,dyn
Ccw
600
400
Volume (ml)
200 -5 -2 -4
Esophageal pressure (cmH2O)
Esophageal pressure (cmH2O)

70. Esophageal pressure vs volume during unassisted ventilation
CL,dyn
Ccw
600
400
Volume (ml)
Elastic work
Resistive
work
200 -5
Esophageal pressure (cmH2O)

71. Influence of Pleural Pressure on Hemodynamic Monitoring5 15 -5 15 -5 15 LA LA LA
High
Pleural
Pressure
Low
Myocardial
Compliance
Normal
Ppl = PEEP x {CL/ CL + CCW}