Tutorial Stage 6: Exploring the variables

1. If you are running the student practical, close the window so that the startup menu appears. Select the button labelled 'Teacher'. The HOM window will appear, this time with additional features.
2. Display a graph of the haematocrit. There are several ways of doing this. On the left of the screen you will see a tree diagram of folders, starting with 'HOM', 'Environment' and 'Body'. This tree allows you to view any of the variables in HOM. Expand the 'Body' node, by clicking on the small plus sign to the left of the folder.
   
3. You should see many variables, with their values displayed alongside. The haematocrit is a property of blood, so expand the node labelled 'blood'. You will see that blood has a lot of constituents. About 10 items down you should see 'Hct'. Right-click on this, then select 'Display/Scroll graph'. This adds the haematocrit to the main set of graphs.
4. Close the graph of the haematocrit by clicking the red 'x' on the right hand side of the screen that is on the same line as Haematocrit.
   
5. There are alternative ways of getting the graph of Haematocrit: try pressing CTRL+Q to get the 'Quick add' dialog box. Start typing the first letters of the variable in this box. You can use the variable's full name, or the abbreviation. For example, try 'SV', or 'STR' to get the stroke volume. Press OK or hit ENTER to display the variable. You will notice that the variable is not graphed, but the value appears on the right. To show the graph, tick the checkbox on the right hand side of the screen.
6. To quickly change the value of the haematocrit, first select the variable 'Hct' in the tree on the left (as described in (3) above). In the bottom-right-hand corner of the screen you should see the haematocrit in percent, with a slider. Drag this slider to the right to increase the haematocrit.
   Note that, although variables can be modified like this, many of them undergo continuous calculations by the model. Therefore, you will eventually see the haematocrit return back to normal after several days. Other variables, such as sympathetic tone (Symp), are calculated much quicker, and will return to physiological equilibrium within seconds. Some variables, such as mean arterial pressure (AP) are calculated from other variables on every frame, and therefore your adjustments will have no effect.