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INTRODUCTION TO PHYSBE – PHYSIOLOGICAL SIMULATION BENCHMARK
EXPERIMENT USING SIMULINK
PHYSBE is a classic model of the human circulatory system. The specifications for the model were first published by John McLeod in 1966 in an article titled,
"PHYSBE...a physiological simulation benchmark experiment" [1] . PHYSBE models blood flow as a transport mechanism, and can be used to simulate the flow of oxygen, nutrients, heat, or chemical tracers within the bloodstream.
[2] It is also a good example of a non-linear continuous system.
To open the model (and the graphical user interface), just type 'physbe' at the MATLAB command prompt.
The PHYSBE demo has been built using Simulink v3.0. It will not function with earlier versions of Simulink. The MathWorks web site contains a PHYSBE webpage which describe the entire system in detail.
Figure 1 : Simulink Block Diagram for PHYSBE
Figure 1 shows the block diagram for PHYSBE software. To run the simulation, click ‘Start’ in ‘Simulation’ menu . Before starting the simulation, user can set input parameters using PHYSBE Control Centre as shown in Figure 2.
To understand the function of block diagram in Simulink, refer to ‘Library
Browser ’ in ‘View’ menu.

Figure 2 : PHYSBE Control Center
In this lab module, we only interested in the left heart, which is indicated by row
‘L. Heart’.
For the purpose of this lab module, the PHYSBE program is set to simulate for
60 seconds which means that it will show the result of 60 seconds simulation.
After starting the simulation, the program will be busy simulating until a sound produced which indicates the end of simulation.
The simulation time can be altered by entering the ‘Configuration Parameters’ in
‘Simulation’ menu.
Figure 3 : ‘Configuration Parameters’ menu

Figure 4 : Configuration Parameters
To adjust simu lation time, change the value in ‘Start time’ or ‘Stop time’ text box.
References
1. McLeod J, PHYSBE...a physiological simulation benchmark experiment ,
SIMULATION , 324-329, vol.7, no.6, 1966.
2. McLeod J, PHYSBE...a year later , SIMULATION , 37-45, vol.10, no.1,
1968.
3. http://www.mathworks.com/products/demos/simulink/physbe/

INSTRUCTION
TASK 1
1. Load the physbe program.
2.
Two windows will come out which are ‘PHYSBE Control Center’ and
‘physbe’.
3.
On the ‘physbe’ window, double-click the ‘Analysis Subsystem’ box. A window named ‘physbe/Analysis Subsystem’ will appear.
4.
In ‘physbe/Analysis Subsystem’ there are two diagrams labeled ‘Heart
Pressure’ and ‘Heart Volume’. Double-click both diagrams.
5. Start the Simulation.
QUESTION
1. What is the name of diagram labeled ‘Heart Pressure’ and ‘Heart Volume’ and what is the function of that diagram in Simulink?
2. Sketch the plot for ‘Heart Pressure’ and ‘Heart Volume’ that you obtain after running the simulation on diagram given below. Purple plot with solid line and yellow plot with dashed line.

Figure 1
Figure 2
3. From the plot, which color indicates left heart and right heart respectively.
Give reasons for your answer.
TASK 2
(Please read APPENDIX at the end of this lab sheet before proceed to task 2)
1. Change ‘Start time’ in ‘Configuration Parameters’ to 59.0.
2. Plot the P-V plot.
3. Go to window labeled ‘Figure 2’ and you will see a plot. This is the P-V
relationship plot.
4. Estimate the value of end-diastolic volume (EDV) and end-systolic volume
(ESV).
5. Write you finding on the table given. Repeat step 2 to 4 for different values of left heart input resistance, Ri and output resistance, Ro as given in the table. Before repeating step 2, don’t forget to start again the simulation by

clicking ‘Start’ in the ‘Simulation’ menu each time you change the Ri and
Ro values.
Ri
0.0588 0.0125
0.25
0.4
Ro
0.0125
0.0125
0.0125
0.25
0.4
0.5
0.5
ESV EDV SV EF
0.5
0.25
0.25
0.25
0.5
6. Calculate also the stroke volume and ejection fraction and write it in the
SV and EF column respectively.
QUESTION
1. Comment on how change in input resistance (Ri) and output resistance
(Ro) value could affect volume parameters in the P-V plot. Include reasons and explanation for each of your comments.

2. As a biomedical engineer, how do you find the benefit of PHYSBE program?
TASK 3
In this part you will need to build some Simulink model. Before that, spend some time on the ‘Library Browser’ in ‘View’ menu and look at ‘Math Operation’ and
‘Commonly Used Blocks’. Also study the model of the left heart. Go to ‘physbe’ window and doubleclick the ‘Left Heart’ box to view the model of left heart.
1. Suppose you have data on blood flow rate through the left ventricle. You need to know volume of blood flowing into the left part of heart. Draw a
Simulink model to obtain volume.
Notes : You are only required to sketch the model in this lab sheet without having to simulate it.
2. Let say you are given a set of data which tells the amount of blood flowing out of the heart through aorta. Suppose volume of blood pump out through

aorta is constant for each heart beat. Draw a Simulink model to calculate cardiac output.
Remember again that cardiac output is amount of blood pumped out from the left ventricle through aorta in liter/minute.
Name a device that you can use to obtain flow rate of blood that flows
into and out from the heart.
APPENDIX
1.
All command has to be written in the MatLab ‘Command Window’. Before executing the ‘plot’ command, make sure you program the MatLab to plot
in second figure because the first figure had been used for PHYSBE
Control Center.
>> figure(2)
>> plot(simout(:,2),simout(:,3))
2. Some useful equations :
Flow , F
 dV dt
Where F is flow rate and V is volume.