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Pressure-Volume Curves of Respiratory System PowerPoint Presentation

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Description : lecture about determine and interpretation PV loop of respiration

Tags : respiration, Respiratory System,Curves of Respiratory

Published on : Apr 02, 2022 | Views : 2388 | Downloads : 14

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Slide 1-

Pressure-volume curves of respiratory system
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Respiratory system Lung compliance : the determination of the lungs to distend. C = ∆V/∆P Lung elastance : the determination to return to the resting position. E = 1/C Airway pressure during inflation Volume Thoracic (lung and chest wall) compliance Thoracic resistance to flow
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…Isotropic expansion… static P-V curves  compliance curves Jong et al. Critical Care (2019) 23:74
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Respiratory system The quasi-static pressure-volume relationship : resistance to flow must be eliminated, measuring pressure and volume during a period of zero flow Diagnose lung disease Customize ventilator settings Follow the course of disease Evaluated prognoses Compliance
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Hysteresis Elastic structures when the volume change from an applied force is sustained for some time after the force is removed Unrecoverable energy, or delayed recovery of energy, that is applied to a system. Minimal with small volume changes, but that it increases as the volume excursion increases. Results from 4 processes: recruitment/ derecruitment Surfactant stress relaxation gas absorption Differences in expiratory and inspiratory air flow (for dynamic compliance) Mead J,et al. J Appl Physiol 1957;10(2): 191–196. Inspiration Expiration
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Expanding force Collapsing force
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Equation of Motion PAO : pressure at the airway opening (mouth or endotracheal tube) V : lung volume C : respiratory system compliance V˙: gas flow R : airway resistance V¨ : convective gas acceleration I : impedance Pmus : pressure generated by the respiratory muscles
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Static Compliance, Chord Compliance, Specific Compliance, and the Pressure-Volume Curve Static compliance: performing an end-inspiratory hold, a linear relationship Chord compliance : a line segment that connects 2 points on a curve. Specific compliance: normalized by a lung volume, usually total lung capacity (TLC) or functional residual capacity (FRC). Specific compliance better assess intrinsic elastic properties of the lung R Scott Harris MD.RESPIRATORY CARE.jan.2005;50(1)
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Adams AB,et al. Respir Care 2001; 46(7):686–693. The curve consistently shifted to the right at all inspiratory flows tested Increased volume while on positive end-expiratory pressure (PEEP)
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Static Versus Dynamic Pressure-Volume Curves “quasi-static” P-V curve. slow flow rate, but the flow rate must be 9 L/min “dynamic compliance” compliance calculated during a tidal breath at the points of zero flow on the dynamic P-V loop. more representative of the mechanical behavior during breathing Lu Q,et al.Am J Respir Crit Care Med 1999;159(1):275–282. Servillo G,et al.Am J Respir Crit Care Med 1997;155(5):1629–1636.
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Measurement for quasi-static P-V curve Super syringe Method Inflation with a constant flow (< 10 L/min). 2–3-second pauses. Airway pressure reaches 40 cm H2O, inflation is stopped and deflation is performed. simple and allows construction of both inflation and deflation curves. Disadvantages: Requires additional equipment. Disconnecting from the ventilator. Sedated and paralyzed.
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Measurement for quasi-static P-V curve Super syringe Method
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Measurement for quasi-static P-V curve Multiple-occlusion (ventilator) Method Periodically interrupting tidal breathing at different lung volumes. No ventilator-disconnection. Requires sedation and/or paralysis
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Inspiratory hold maneuver End-inspiratory pause 0.3-1 sec Static respiratory compliance (Crs) Respiratory Care November 2014, 59 (11) 1773-1794 Pex is at least as great as PEEP greater if air trapping occurs  auto-PEEP
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Expiratory-hold maneuver Mandatory ventilation. End-expiratory pause. Total PEEP = PEEPe + PEEPi Singer, BD. Corbridge, TC.. "Basic Mecahnical Ventilation" Southern Medical Journal" 102, no. 12 December 2009.
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P-V loop waveform Amanda M Dexter and Kimberly Clark.RESPIRATORY CARE.jan.2020;65(6) Terry M. Corona,et al.Journal of Veterinary Emergency and Critical Care.2011;21(5) Spontaneous breath Mandatory ventilator-driven breath Ventilator-assisted breath
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Physiologic Meaning Sigmoidal with upward concavity at low inflation pressure and downward concavity at higher inflation pressure. Reflects the balance of forces between the chest wall (diaphragm and rib cage) and the lung parenchyma. Total compliance is the sum of the individual compliances Normal values ; 100 mL/cm H2O for CRS 200 mL/cm H2O for CL 200 mL/cm H2O for CCW Agostoni E,et al. Handbook of physiology, 2nd ed. Bethesda: American Physiological Society;1986:113–130
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Physiologic Meaning Supine Posture Chest-wall curve moves to the right and rotates counterclockwise, increasing the compliance of the total respiratory system in the range above FRC. Abdominal compliance curve shifts to the right, similar shift of the respiratory-system curve to the right, lowering FRC, and slightly rotating the curve counterclockwise, increasing compliance Scurr C.et al.Scientific Foundations of Anesthesia.Heinemann,1982
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clinical application
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Clinical application Airleak Overdistension Inadequate PEEP Inadequate flow
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Stress index Am J Respir Crit Care Med 2007;176(8):761-767 Ranieri VM,et al. Am J Respir Crit Care Med 1994;149(1):19–27. In AC volume ventilation using a constant flow waveform observe the pressure time scalar. Normal, linear change in airway pressure Stress index =1 Upward concavity indicates decreased compliance and lung overdistension Stress index > 1 Downward concavity indicates increased compliance and potential alveolar recruitment Stress index < 1 Patient effort must be absent
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Inflation point Lower inflection point : Critical opening pressure of the alveoli. The initial rapid rise in pressure is a reflection of alveolar recruitment. It takes more pressure to re-inflate a collapsed alveolus than it takes to distend a deflated one.
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Inflation point Upper inflection point : represents the elastic recoil of the lung tissue and chest wall. Occurs when the ventilator cycles to expiration and the pressure drops back to PEEP.
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Am J Respir Crit Care Med Vol. 156. pp. 846–854, 1997 The disappearance of LIP observed with PEEP suggested that lungs were recruited. The pressure of a UIP apparition suggested alveolar overdistension at high levels of PEEP. Crs above LIP reflected the amount of recruitable lung. Alveolar closure in ALI occurs over a wide range of pressure. LIP is a poor predictor of alveolar closure.
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significant correlation the PV loop accurate surrogates of lung recruitment without the need for a CT scan, can be used at the bedside as sufficiently
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The protective strategy (including PEEP set with LIP) was associated with improved survival at 28 days, a higher rate of weaning from mechanical ventilation, and a lower rate of barotrauma PEEP according to PMC recruited some parts and overdistended others parts of lungs
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Conclusion Lower inflation point : minimal pressure required for alveolar recruitment PEEP 2 cmH2O above LIP, not more than UIP Stress index (Pressure-time curve) upward concavity indicates decreased compliance and lung overdistension Stress index downward concavity indicates increased compliance and potential alveolar recruitment