TestChest Physiological Model
28Pages

TestChest® Physiological Model presented by the neosim Academy

neosim academy c/o neosim AG Susenbühlstrasse 12 CH-7000 Chur Switzerland www.neosim.ch Written by Josef X. Brunner, PhD, Chur, c/o neosim AG, Susenbühlstrasse 12, CH7000 Chur, Switzerland Reviewed by A. Timothy Chen, PhD, Hong Kong c/o Trinity Trading Company Ltd, Unit A, 13/F, Goodwill Industrial Bldg. No. 36-44, Pak Tin Par Street, Tsuen Wan, New Territories Hong Kong This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting,...

“TestChest is very impressive in terms of physiological reality, especially spontaneous breathing”. Dr. Lise Piquilloud, PD & MER, Médecin associée CHUV Lausanne, Switzerland, moderator at the 3 day simulation training session held with TestChest® during the ESICM congress 2017 in Vienna, Austria

INTRODUCTION TestChest® is a real-time teaching and training tool for mechanical ventilation management. It supports any kind of artificial respiration in anesthesia, intensive care, emergency medicine and home care. This booklet describes the physical representation of the physiological models built into TestChest®. The information provided herein is intended for clinicians who wish to exploit the full capabilities of TestChest® and is not intended to be a textbook of physiology. In order to make the physiological models of TestChest® feasible, some simplifications were necessary. These...

neosi m. • spontaneous breathing by providing pre-determined changes of respiratory rate and respiratory activity • interaction with haemodynamics and thus allows to test closed-loop controlled ventilators by providing SpO2, and Pulse Pressure Variation POP in response to the ventilator setting

OVERVIEW TestChest® is a fully interactive, physical lung model with two access points: airways and peripheral circulation (artificial finger). The airways provide the opportunity for both, therapy and diagnosis while the artificial finger provides the result of the therapy: oxygen saturation and hemodynamic stability. TestChest® is loaded with a set of parameters to define a certain patient and then acts completely independent and in interaction with the environment such as a ventilator, an anesthesia machine or even an ambu-bag. This principle is illustrated in Figure 1. Figure 1:...

Patient parameters and output variables of the physiological model An overview of the basic physiological model is given in Figure 2, lung mechanics are provided in Figure 3, and 4 and the relationship between lung collapse and venous admixture is given in Figure 7. Figure 2: Lung/heart model. Details of lung mechanics are given in Figure 3, description of each parameter and output variable is given in text. Parameters are, for example, compliance and resistance – variables are, for example, airway flow and pressures. A list of parameters and variables are provided further down below.

LUNG MECHANICS Lung mechanics are usually described as multi-compartment models with mechanical elements like springs and dash-pots (friction) or with electrical elements like resistors and capacitors. Independent of these descriptive elements, lung mechanics is always described in lumped parameter models and never in its anatomical complexity. The equation of motion describes the interdependence of the variables (pressure, flow, volume) and the impact of the parameters compliance and resistance as shown in Figure 3. Figure 3: Elements constituting the equation of motion; “const” is an...

Compliance is measured in volume per pressure and can be constant or sigmoid. Lung compliance CL and chest wall compliance CW are arranged in series and together form the respiratory compliance C rs. 1/Crs = 1/ CW + 1/ CL Resistance Raw is pressure drop per unit of flow, is never constant but often assumed to be constant. Pleural pressure is pressure in the pleural cavity. Although varibale along the gravitational axis, only one pressure is usually taken to represent a “mean” pleural pressure. Figure 4: Pressure-volume curve for static conditions; explanations see text The lungs can have...

neosim. pressure-volume curve with the equilibrium position at 2000ml (zero PEEP i.e. FRC@0PEEP, open airways, no muscle tension, zero airway pressure). This FRC@0PEEP, also called minimal FRC (FRCmin) is a parameter in TestChest® . Lung collapse is modelled by setting FRCmin lower than FRC predicted (FRCpred). Figure 4 shows the ideal-typical sigmoid pressure-volume curve starting with VLee equal to FRC at zero PEEP. Compliance is the slope at each point of the pressure-volume curve and as follows: Crs : compliance of the respiratory system, between lower and upper inflection point C1:...

FRC@0 PEEP: The volume at zero pressure (meaning at atmospheric pressure) is called Functional Residual Capacity FRC. Since mechanically ventilated patients may have an elevated lung volume by virtue of ventilator pressures, the end-expiratory Lung Volume (VLee) is also used. Calculation of VLee is done as follows in TestChest® : The end-expiratory lung volume VLee follows a decrease of measured VL immediately (simulation of immediate collapse), yet takes some time to follow an increase in lung volume with the time constant of about 3 seconds. Lung collapse: in supine position, a small part...

SPONTANEOUS ACTIVITY Intercostal and diaphragmatic muscle tissue contribute to effective ventilation. The movement is quite complex and can depend on many factors, including exercise, stress, disease, filling level of the bladder, etc. To simplify matters, however, usually one single representative muscle is used as depicted in Figure 3. Respiratory muscle activity is sometimes measured in patients by the occlusion pressure P0.1. For this reason, TestChest® allows to enter P0.1. The user can adjust spontaneous activity by entering the respiratory activity P0.1 and the respiratory rate f....