# Pressure Volume Curve of the Respiratory System

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Pressure Volume Curve of the Respiratory System

Transmural Pressure of the Respiratory System

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

Pressure Volume Curve of the Lung

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

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)

Calculation of Compliance
Volume (ml) Pressure (cmH2O)

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)

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)

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

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)

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 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)

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

Influence of Surfactant on PV Curve of Lung
Depleted lung

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

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

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

The supersyringe technique
P-V curve Methodology The supersyringe technique

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

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

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

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…

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.

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

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

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.

Acute Respiratory Distress Syndrome
Pathophysiology Nonrecruitable Normal Atelectatic Recruitable

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

P-V curve M. Tobin, NEJM 2001

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

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

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

‧ 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

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.

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

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

CT findings of Lung recruitment during Inspiration

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

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

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

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.

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

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

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

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 Latex Balloon

Position of Esophageal Balloon

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

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

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

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)

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

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