WO2005104062A1 - Simulateur de poumon - Google Patents

Simulateur de poumon Download PDF

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Publication number
WO2005104062A1
WO2005104062A1 PCT/GB2005/001602 GB2005001602W WO2005104062A1 WO 2005104062 A1 WO2005104062 A1 WO 2005104062A1 GB 2005001602 W GB2005001602 W GB 2005001602W WO 2005104062 A1 WO2005104062 A1 WO 2005104062A1
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WO
WIPO (PCT)
Prior art keywords
lung simulator
diaphragm
lung
simulator
pneumatic
Prior art date
Application number
PCT/GB2005/001602
Other languages
English (en)
Inventor
Mark Edwards
Ka-Lok Carroll Lee
Original Assignee
Kings College London
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kings College London filed Critical Kings College London
Publication of WO2005104062A1 publication Critical patent/WO2005104062A1/fr

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09B—EDUCATIONAL OR DEMONSTRATION APPLIANCES; APPLIANCES FOR TEACHING, OR COMMUNICATING WITH, THE BLIND, DEAF OR MUTE; MODELS; PLANETARIA; GLOBES; MAPS; DIAGRAMS
    • G09B23/00—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes
    • G09B23/28—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for medicine
    • G09B23/288—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for medicine for artificial respiration or heart massage

Definitions

  • the present invention relates to a pneumatic lung simulator which can simulate the respiratory system.
  • Lung simulators are used for testing and evaluating new types of ventilators and for modelling the behaviour of patients for training purposes.
  • Pneumatic lung simulators are known and must be capable, through adjustment, of simulating a wide range of patient pulmonary physiology, ranging from paediatric to adult patients with various types and states of pulmonary disease.
  • lung simulators have been created using piston arrangements.
  • the resistance is provided by a range of methods that restrict the flow from the volume (e.g. calibrated orifice, different weights of gauze). Compliance is then added by either mechanical springs, which prevent the compliance value being changed dynamically or using pressure feedback, which is difficult to control.
  • a lung simulator is required which provides accurate simulation of the lung in a range of conditions and patients.
  • a training test lung is described in U.S. Patent No. Re. 29,317.
  • the training test lung simulates human lungs by providing a pair of expansible chambers or bellows which are secured at one end to a frame and at the other end to a pair of movable end plates.
  • the bellows are interconnected by a Y-shaped fitting to assistant ventilation equipment for inflation.
  • the movable end plates pivot relative to the frame as the bellows are inflated and the free end of the pivotable plate cooperates with printed indicia on a panel adjacent thereto, to provide a visual readout of the inspired tidal volume.
  • Pulmonary compliance is simulated by adjustable springs which intercom ect the pivotable plates and the stationary frame.
  • Respiratory flow resistance is simulated by calibrated flow resistant tubes disposed in the flow path extending between the expansible bellows and the assistant ventilator.
  • Computer controlled lung simulators are known in which some lung parameters for an individual patient or disease type can be entered so that, as algorithms are developed, they can be compared against the same condition and their effectiveness quantified.
  • known test lungs are not able to facilitate a patient machine interaction which results in a patient's efforts being downloaded by the machine over a range of lung dynamics to provide a more comprehensive knowledge of the way the test lung operates.
  • a pneumatic lung simulator which comprises (i) a sealed enclosure having a controllable outlet; (ii) a movable diaphragm mounted so as to be able to compress and decompress air in the enclosure; (iii) a means for applying a force to the movable diaphragm in a direction that compresses and decompresses air in the enclosure to simulate human lungs in spontaneous breathing; (iv) a means for measuring the displacement of the diaphragm and (v) a means for measuring the flow of air through the outlet.
  • the diaphragm is a cone diaphragm, the wide end of which is attached to a rim of flexible material which allows the cone to move, which rim is attached to a metal frame and in which the narrow end of the cone diaphragm is attached to a coil mounted adjacent to a magnet, the coil being attached to a suspension which comprises a ring of flexible material attached to the frame which allows the coil to move freely back and forth.
  • the magnet is a permanent magnet and the coil is mounted between the poles of the magnet or is substantially surrounded by the magnet.
  • An example of such a structure is that of a conventional loud speaker which can be adapted to be used in the present invention.
  • an enclosure is sealed to the output of the loudspeaker cabinet, the enclosure having a volume which simulates that of a human lung and an outlet which can be varied.
  • the suspension of the coil is equivalent to lung compliance; the outlet from the enclosure is equivalent to the resistance to flow caused by the airways and trachea.
  • the force applied to the cone can be seen as the patient's effort to exchange tidal volume against these natural dynamics.
  • a preferred loudspeaker is that which is known as a subwoofer which was selected for its specific characteristics of high magnetic motor force, that allows representative pressures to be achieved and the large surface area of the cone combined with high excursion capability and a particularly strong magnetic motor force typical of this type of loudspeaker.
  • Other advantages of this device are good input/output linearity across the excursion range, direct electronic control, highly dynamic capability and the absence of fluid seals or mechanical sticksion. As subwoofers are mass produced items, they are readily available and lead times are short making this design quick and cost effective to implement.
  • Normal audio amplifiers have a prefilter to prevent any DC component of the input signal causing undesired heating effects in the speaker due to a continuous offset.
  • the nominal cut-off is 10Hz.
  • this prefilter prevents the use of a standard audio amplifier and hence a custom linear amplifier was built.
  • the influence of mask leaks can also be studied in a realistic manner by connecting the output from the lung volume to the trachea of a Laerdal respiratory trainer.
  • the lung volume is simulated by the enclosure which can be a Perspex (RTM) box that is sealed to the loudspeaker e.g. subwoofer, casket. This ensures the integrity of the enclosure seal and allows access for adjustment and calibration.
  • RTM Perspex
  • a displacement sensor which measures the displacement of the coil and pressure sensors to monitor the change in pressures.
  • Displacement (and hence volume) data for the speaker can be provided using a LNDT (Linear Variable Differential Transformer), which is fitted to the back of the cone. This measurement gives the precise moment of inspiration/expiration change, which is important for the analysis of patient machine synchrony, as well as providing accurate volume data without the problems associated with flow integration.
  • Functional residual capacity (FRC) can be adjusted by adding further volumes to expansion ports on the enclosure.
  • a pressure sensor to give data inside the lung volume and a pressure sensor in the outlet pipe to give mask pressure e.g. ⁇ 70 cm H 2 O.
  • a bidirectional flow sensor ⁇ 200 1/min used for flow measurement and integrated to check the volume information provided by the displacement sensor.
  • the inputs to the simulator are preferably controlled by computer and the results fed to the computer; this enables there to be the minimum hardware necessary to be used and uses the processing power of the computer for the implementation of data logging/control, filtering etc.
  • Parameter settings can be tuned online, recorded data stored to file and test scripts located in a single environment giving the ability for online and offline data manipulation to allow a suitable range of tidal volumes to be simulated.
  • the apparatus of the invention can be used in anaesthiology by operating it in the reverse direction.
  • Anaesthetic agents are commonly administered by mixing a carrier gas such as air or oxygen mixed with the anaesthetic e.g. by passing the gas through a vapourizer containing liquid anaesthetic and a metered amount of anaesthetic is administered to the patient and the apparatus of the invention can be used to administer the metered amount of anaesthetic.
  • the apparatus is used to anaesthetize a patient by connecting the outlet to the patient and using the apparatus to pump anesthetic into the air breathed in by the patient i.e. movement of the diaphragm pumps anaesthetic into the air breathed in so the patient breathes in anaesthetic e.g. the apparatus functions as a bellows.
  • Fig. 1 is a schematic view of the apparatus
  • Fig. 2 is a block diagram of the apparatus that is a simulation of the system in Simulink;
  • Fig. 3 is a force diagram of the apparatus and Figs 4 to 9 are graphs of results obtained in the example.
  • a subwoofer loudspeaker comprised a conical diaphragm (1) which was attached at its narrow end to coil (3) suspended by suspension (7) to speaker frame or basket (6).
  • the coil (3) was mounted within permanent magnet (4).
  • a Perspex (RTM) enclosure (2) was sealed to the frame (6) by air tight seals (8). There was a controlled air outlet (5) in enclosure (2).
  • a variable electric current is applied to coil (3) which causes the diaphragm to pump air into and out of the enclosure (2).
  • the volume of air pumped, the frequency and direction of the pumping and the resistance to the flow of air can be varied by varying the current and the air outlet.
  • There are sensors to monitor the air flow and the apparatus is controlled by a computer which monitors and measures the behaviour of the simulated lung.
  • a functional block diagram of the apparatus is shown in Fig. 2, and a mass-spring-damper force analogy is shown in Fig. 3 which allows the system to be partitioned in this way to separate the forces required to modify compliance from the force required to achieve the volume profile (patient effort).
  • a 15" subwoofer made by Eclipse, Model 15" Ti Pro had the cloth covering the output of the cone removed and a Perspex (RTM) enclosure of volume 5 litres sealed to its casket.
  • the enclosure had a variable outlet which was controlled by a motorised iris.
  • a linear variable differential transformer was fitted to the back of the cone which gave the precise moment of inspiration/expiration change.
  • ⁇ 70 cm H O pressure sensor to give data inside the lung volume and a ⁇ 70 cm H 2 O pressure sensor in the outlet pipe to give mask pressure.
  • the output of the sensors was fed to a computer which controlled the current to the subwoofer coil to control the frequency, direction and displacement of the subwoofer cone and measured the feedback.
  • the sensors were connected to a standard multifunction card (National Instruments DAQCard-6024) and analogue and digital outputs from the card used to control the power amplifier and valve drivers. All the sensor power requirements were provided directly from the multi-function card avoiding the need for external power supplies and creating a portable laptop based system that can be taken to other sites. Simulink was used with the Real-Time Windows Target toolbox to provide real-time implementation of the application.
  • Tests were carried out to first display the ability to set lung parameters and examine the effects on the unsupported system and then to investigate the level of support required to provide optimal unloading of the active effort that the patient would need to make, based on a range of lung parameters and the results are shown in the graphs of Figs. 4 to 9.
  • the graphs of Fig 4 show the effect that a change in lung compliance has on the force.
  • the graphs show the force output from the control system to achieve a litre volume change against the stated lung compliances. Lower lung compliances require a greater force to achieve the same volume change.
  • This Figure shows that the effort increase is proportional to the increase in compliance as the mathematical model predicts. For a fully elastic exhalation, all patient effort is removed after the lung volume target is achieved. This causes the step change in the first graph and results in no negative component of force being present during exhalation. The slope of the curve is higher for lower lung compliances as there is more elastic force to return to the residual volume.
  • the controlled exhalation shown in the second graph of Fig. 4 has a negative portion that represents the patient effort required to breathe out.
  • the values are a function of airway resistance and breath rate. A high breath rate combined with high resistance will result in a large exhalation effort being made which will fatigue the patient.
  • Fig 5 shows the effect that a change in lung resistance has on the force required to achieve the volume change.
  • the resistance used is of an orifice style restriction.
  • the valve resistance is calibrated by controlling the flow through the orifice to 60 L/min and the value given is based upon the measurement of the pressure drop across the valve over a range of valve positions. This calibration was then cross-checked against Pneuflo (RTM) calibrated resistances for accuracy.
  • the controlled exhalation seen in the second graph of Fig. 5 again shows the patient force going negative. This represents the force required to breathe out against the airway resistance. Static resistance of the airway plus the resistance added by dynamic airway collapse and the breath rate determine the force required for exhalation.
  • test lung controller is designed to meet a tidal volume change over a defined duration and profile. Effort is increased to follow the volume profile that is set and when external pressure support is provided the controller compensates by reducing the force in proportion to the level of support. However, if the ventilator support pressure is too high the target volume profile will be exceeded and the lung controller will resist the ventilator by increasing the test lung drive, which then works against the ventilator.
  • the force from the control system is zero (apart from the force required to maintain the compliance setting). It can be seen that the ventilator support incrementally unloads force but when exhalation is controlled, the controller force goes negative to expel the remaining air from the lung space. This is caused by the airway resistance and rate of breathing as stated before but also the force due to Intrinsic Positive End Expiration Pressure (iPEEP) setting on the ventilator which is designed to provide a resistance for the patient to breathe against to prevent alveoli collapse from trapping air in the lower branches of the lung.
  • iPEEP Intrinsic Positive End Expiration Pressure
  • Another capability of this system is to compare the level of support offered at the facemask to what actually happens in the lung. This is clinically important due to the danger that barotrauma presents to a patient with severe lung parameters who needs a high level of pressure support. It is possible to see how the support is applied in terms of the ramp rate at which pressure increases and also the maximum pressure that is experienced at the mask and in the lung volume. This measurement of mask pressure and pressure from within the lung volume can be compared to the support level set on the ventilator as can be seen in Fig 7.
  • the minimum iPEEP pressure setting on the ventilator used is 4cm H 2 O which is the cause of the irregular waveform on the 5 cm H O support setting as there is only 1cm H O range within which the ventilator can operate.
  • the higher settings clearly show the ramp rate at which the pressure support is applied. Above 15cm H 2 O support there ceases to be any negative pressure observed in the lung.
  • the graphs in Fig 8 show how the ventilator supported system is unloaded of the effort required to achieve tidal volume change.
  • the top graph shows that the unsupported system required a peak of over 200N whereas the supported system unloads the active force required by 70%.
  • the ventilator pressure support ramps up towards the set point of 20cm H 2 O.
  • the support pressure measured at the mask has a different profile to the pressure inside the lung. This is due to the rate of change of volume being drawn through the airway resistance.
  • Fig 9 shows the flow triggering of the external pressure support into inspiration (arrow). At the point where flow crosses zero the pressure support ramp starts. This graph also shows that the pressure support cycles off before flow crosses zero into expiration. This is a technique used by ventilator manufacturers to prevent the pressure support continuing into expiration by removing the pressure support after a percentage drop in flow.
  • NIPPV Non Invasive Pressure ventilation

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  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
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  • Medical Informatics (AREA)
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  • Heart & Thoracic Surgery (AREA)
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  • Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)

Abstract

L'invention concerne un simulateur de poumon basé sur un caisson de basse. Ledit simulateur est obtenu par fixation d'une enceinte présentant une sortie variable sur le panier de caisson de basse afin de simuler la capacité pulmonaire et utilisation du mouvement du diaphragme pour simuler la respiration d'un patient.
PCT/GB2005/001602 2004-04-27 2005-04-27 Simulateur de poumon WO2005104062A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0409282A GB0409282D0 (en) 2004-04-27 2004-04-27 Lung simulator
GB0409282.1 2004-04-27

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WO2005104062A1 true WO2005104062A1 (fr) 2005-11-03

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010027436B3 (de) * 2010-07-09 2011-07-21 Schaller, Peter, Dr., 01326 Lungensimulator
WO2013143933A1 (fr) 2012-03-28 2013-10-03 Laerdal Global Health As Simulateur de poumons

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3808706A (en) * 1973-01-29 1974-05-07 Michigan Instr Inc Pneumatic lung analog
US4430893A (en) * 1981-11-16 1984-02-14 Michigan Instruments, Inc. Pneumatic lung analog for simulation of spontaneous breathing and for testing of ventilatory devices used with spontaneously breathing patients
US5403192A (en) * 1993-05-10 1995-04-04 Cae-Link Corporation Simulated human lung for anesthesiology simulation
FR2800288A1 (fr) * 1999-11-03 2001-05-04 App Medical De Prec Amp L Procede et dispositif pour simuler la respiration humaine
US6273728B1 (en) * 1997-09-04 2001-08-14 The University Of Florida Life support simulation system simulating human physiological parameters

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3808706A (en) * 1973-01-29 1974-05-07 Michigan Instr Inc Pneumatic lung analog
US4430893A (en) * 1981-11-16 1984-02-14 Michigan Instruments, Inc. Pneumatic lung analog for simulation of spontaneous breathing and for testing of ventilatory devices used with spontaneously breathing patients
US5403192A (en) * 1993-05-10 1995-04-04 Cae-Link Corporation Simulated human lung for anesthesiology simulation
US6273728B1 (en) * 1997-09-04 2001-08-14 The University Of Florida Life support simulation system simulating human physiological parameters
FR2800288A1 (fr) * 1999-11-03 2001-05-04 App Medical De Prec Amp L Procede et dispositif pour simuler la respiration humaine

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010027436B3 (de) * 2010-07-09 2011-07-21 Schaller, Peter, Dr., 01326 Lungensimulator
WO2013143933A1 (fr) 2012-03-28 2013-10-03 Laerdal Global Health As Simulateur de poumons

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GB0409282D0 (en) 2004-06-02

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