4. Open-loop simulation in Simulink

This example demonstrates how to run the Python Anesthesia Simulator inside Simulink through MATLAB’s Python interface. The files associated with this example can be downloaded by clicking on the following link:

• main simulation file

• callPython function

• Simulink file

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4.1. Script Overview

File: main_sim_openloop.m

The script performs the following steps:

1. Clears the MATLAB workspace

2. Configures the Python environment to use the simulator backend

3. Defines simulation and patient parameters

4. Runs a Simulink model (sim_openloop.slx)

5. Plots the simulation outputs (BIS and drug infusion rates)

6. Clears the Python interface to free memory

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4.2. 1. Workspace Initialization

clear all
close all
clc

These commands reset the MATLAB session by removing all variables, closing figures, and clearing the console.

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4.3. 2. Configure Python Environment

Before running the simulation, specify which Python interpreter MATLAB should use.

env = pyenv('Version', ...
    'your_path\your_environment\Scripts\python.exe');

Replace the path above with the location of your virtual environment’s python.exe.

Example (Windows):

env = pyenv('Version', 'C:\Users\michele\python_anesthesia_env\Scripts\python.exe');

Example (macOS/Linux):

env = pyenv('Version', '/Users/your_username/python_anesthesia_env/bin/python');

⚠️ The environment must have the python_anesthesia_simulator package installed (pip install .).

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4.4. 3. Define Simulation Parameters

simulation_time = 3600;   % 1 hour

age    = 18;      % years
height = 170;     % cm
weight = 60;      % kg
sex = 0;       % 0 = female, 1 = male

sampling_time = 1;   % [s]

These parameters are passed to the Python simulator through the Simulink model.

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4.5. 4. Run Simulink Model

y = sim('sim_openloop.slx');

The Simulink model sim_openloop.slx must contain:

• A MATLAB Function Block that calls the function:

  [bis, co, map, tol, nmb] = PythonStep(u_p,u_r,u_n,u_a,age,height,weight,sex,sampling_time);
  

• The PythonStep block internally calls callPython.m, which manages communication with Python.

4.5.1. Required Files

File	Role
callPython.m	Creates and maintains a Python Patient object
PythonStep.m	Simulink wrapper for callPython.m
sim_openloop.slx	Simulink model running the simulation

✅ Simulation Mode must be set to “Normal”
(Python calls are not supported in Accelerator or Code Generation modes.)

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4.6. 5. Plot Simulation Results

After running the model, the script visualizes:

• BIS (depth of anesthesia)

• Propofol infusion rate

• Remifentanil infusion rate

subplot(3,1,1)
plot(y.bis, 'k', 'LineWidth', 1.2)
title('BIS')

subplot(3,1,2)
plot(y.u_prop, 'k', 'LineWidth', 1.2)
title('Propofol Infusion Rate')

subplot(3,1,3)
plot(y.u_remi, 'k', 'LineWidth', 1.2)
title('Remifentanil Infusion Rate')

Each subplot corresponds to one of the patient’s key signals, plotted over the simulation time.

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4.7. 6. Clear Persistent Python Objects

At the end of the script:

clear callPython

This command clears the persistent variables stored in callPython.m, which hold the Python Patient instance.
It ensures that the next simulation starts with a fresh Python object.

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4.8. Example Workflow

1. Open MATLAB and ensure your Python environment is active:

   pyenv('Version','C:\path\to\env\Scripts\python.exe')
   

2. Open and configure sim_openloop.slx (Normal mode).

3. Run the simulation:

   main_sim_openloop
   

4. Inspect the BIS and drug infusion plots.

5. Reset the Python interface when done:

   clear callPython
   

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4.9. Output Signals

Signal	Description	Units
y.bis	Bispectral Index (depth of hypnosis)	–
y.u_prop	Propofol infusion rate	mg/s
y.u_remi	Remifentanil infusion rate	µg/s

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4.10. Notes

• Works only in Normal Simulation Mode.

• pyenv must point to a valid Python environment containing the simulator.

• Each run initializes or reuses a persistent Python Patient instance.

• Use clear callPython between runs to fully reset the model.