Respiratory Simulation Specialists

Tips & Tricks

A Look Inside a Var File

A Var file (.vr3) represents a particular model of the respiratory system at a particular point in time. To learn more about how Var files and Script files are used to build scenarios, please refer to Tips and Tricks #1 – Vars v. Scripts.

A Var file is comprised of two major groups of settings:

  • The first group of settings determine the lung model in terms of mechanical properties (e.g., resistance and compliance).
  • The second group of settings determine the patient effort model (e.g., breathing frequency and amplitude of the breath, including the possibility of a passive system, meaning apnea).

You can run the simulation with a sequence of Var files or just one.

For example, to set up a Var file to model a paralyzed adult patient with ARDS:

  • Model the mechanics using a resistance of 10 cm H2O/L/s and compliance of 25 mL/cm H2O.

TnT_3-1

  • On the screen that follows (Choose a Patient Effort Model), you would choose the passive model to represent paralysis.

TnT_3-2

Once you connect a ventilator to the simulator, you can then demonstrate, for example, how to calculate respiratory system mechanics using the ventilator’s waveform displays. The values you get by manual analysis should be very close to the ones you set for the lung model.

Alternatively, you could specify an active model by the parameters of the muscle pressure waveform:

A Look Inside a Var File_1

These are the main components of a Var file, but many advanced options exist for building patient models.

Special thanks to Rob Chatburn (Cleveland Clinic) for input developing this example.

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