MODEL NUMBER: 0001 MODEL NAME: OneAlvLung.Assist SHORT DESCRIPTION: A compliant 1 compartment lung with resistance to air flow, driven by external positive pressure ventilator. END OF MML CODE FIGURE: | Pmouth R Plung || || o------------/\/\/\/\----o----||--------||| Pref Flow --> + || || Com | Vlung DETAILED DESCRIPTION: The equations governing airflow in and out of a one compartment lung are given by the following analogy to electrical circuits: Airway pressure is analogous to voltage. Air flow is analogous to current flow. Volume is analogous to charge. Resistance to air flow is analogous to electrical resistance. Compliance, the relationship between pressure and volume, is analogous to capacitance, the relationship between charge and voltage. The model shows that various quantities are governed by exponential decay with time constant tau=R*Com. The main assumption is that the human lungs can be approximated as a single compartment modeled by an RC circuit where the quantities of interest, air flow, volume of air, pressure, compliance, and resistance are analogous to current, charge, voltage, capacitance, and resistance respectively. GENERAL RESULTS: The ventilator, using a driving pressure of 10 mmHg gives an approximately normal tidal volume of 500 ml. Normally of course, the force is provided by expansion of the chest, creating a negative pressure in the intrapleural space, just the oppposite of this positive pressure ventilator. SHORTCOMINGS: 1. Air is assumed incompressible. The maximum error with a 10 mmHg driving force is only 10/760 or 1.3%. 2. There is no deadspace volume, so if there were to be gas exchange, this model would assume that all of the volume is available for exchange. 3. The shape of the volume/pressure plot is dependent on the time step length KEY WORDS: lung compliance, resistance, RC circuit, lung mechanics, airflow in trachea, tidal volume, positive pressure ventilation, reference, tutorial REFERENCES: M.G. Levitsky, Pulmonary Physiology, Sixth Edition, McGraw Hill, 2003. REVISION HISTORY: Original Author: GR Date: 09/22/08 Revised: JBB 03 Jan 2014 to use Pref for both inhalation and exhalation. BEJ:14jun23: updated keywords COPYRIGHT AND REQUEST FOR ACKNOWLEDGMENT OF USE: Copyright (C) 1999-2014 University of Washington. From the National Simulation Resource, Director J. B. Bassingthwaighte, Department of Bioengineering, University of Washington, Seattle WA 98195-5061. Academic use is unrestricted. Software may be copied so long as this copyright notice is included. This software was developed with support from NIH grants HL088516 and HL073598, NIBIB grant BE08417 and the Virtual Physiological Rat program GM094503 (PI: D.A.Beard). Please cite this grant in any publication for which this software is used and send an email with the citation and, if possible, a PDF file of the paper to: staff@physiome.org.

Volume at rest, Functional Residual Capacity

Volume of air in lung, total

Resistance of airway, a constant

Flow at mouth

Reference Pressure external to body and ventilator

Pressure in the lung

Pressure at the mouth

Test of FlowAir; FlowAir = TestF when ScalPvent * Pvent = 10 mmHg at t = 0

Compliance of the lung

Scalar of amplitude of Pvent (Ventilator pressure)

Time constant, sec, = resistance * compliance

Driving Pressure from Ventilator

Volume at rest, Functional Residual Capacity

Ohm's Law: current = driving force / resistance

Pressure at the mouth

Linear Pressure/Volume relation around VFRC

Flow at mouth