Provided that the relevant parameters are properly set, the researcher may view cardiac function and venous return curves immediately after they have been calculated (on-line viewing) by running the rcvsim executable which will make a function call to Gnuplot. Since the time required for generating a cardiac function or venous return curve is relatively short (within a few seconds), the on-line viewing capability will usually suffice. However, it is possible that the researcher may also desire to view the curves off-line. Since the curves are written to file in ASCII, multi-column format, the researcher may view them any time after completion of the simulation by directly executing gnuplot at the Linux prompt. A description of how to set the relevant parameters is given below. See also Examples 8-13 in Section 5.5 which illustrate how to view the cardiac function and venous return curves both on-line and off-line. (Note that this section requires some familiarity with Gnuplot which may be garnered by typing man gnuplot at the Linux prompt.)
In order for the rcvsim executable to generate a cardiac function or venous return curve, either the heart-lung unit preparation or systemic circulation preparation must be implemented by assigning the preparation parameter under the status parameters a numerical value of 1 or 2. Provided that this has been done, then the numerics parameter under the display parameters determines whether the cardiac function/venous return curve is to be viewed on-line. If the numerics parameter is assigned the numerical value of -1, then the curve will not be displayed as soon as it is calculated but may be subsequently viewed off-line. If the numerics parameter is set to a numerical value between 0 and 3 inclusive which correspond to different plotting formats (see Figure 9), then the cardiac function/venous return curve will be automatically displayed immediately following the completion of the simulation. The different plotting formats can be best understood by recognizing that the on-line display of the curves is specifically implemented by writing gnuplot commands to a file in the /tmp directory and executing these commands through a function call to gnuplot. The single plot per window formats (corresponding to numerical values of 0 and 2) will delete this file if it exists, write a new file to the /tmp directory, and thus display only the cardiac function/venous return curve of the current simulation. The multiple plots per window formats (corresponding to numerical values of 1 and 3) will add plotting instructions to the existing file in the /tmp directory and thus display the curve of the current simulation as well as all other curves that are instructed to be displayed in the file. In this way, multiple cardiac output and venous return curves can be overlayed on the same axes. The mPra x-axis formats (corresponding to numerical values of 0 and 1) will display either cardiac function or venous return curves. The mPa x-axis formats (corresponding to numerical values of 2 and 3) will display average cardiac output as a function of average systemic arterial pressure and is thus applicable only to the heart-lung unit preparation.
Whether cardiac function and venous return curves are to be viewed on-line or off-line, the simulation time is determined by the time parameter under integration and sampling parameters or the time it takes to complete the calculation of the entire curve, which ever is less. Hence, the time parameter should always be set to a value that is greater than the time it takes to calculate the entire curve (1000 seconds is usually more than enough).
In order to generate venous return curves, the Crds parameter under pulsatile heart and circulation parameters must be properly selected. This parameter determines the increments in which the Crd parameter is stepped from the value assigned to the Crs parameter to 60 ml/mmHg. Hence, this parameter determines the number of points to be calculated on the venous return curve. For example, if this parameter is set to five and all other parameters are also set to their default values, then 12 points on the venous return curve will be calculated. If the Crds parameter is set to a value greater than 60-Crs, then the Crd parameter will be held constant throughout the simulation and only one point on the venous return curve will be generated.
In order to generate cardiac function curves, the Pvs and Pas parameters under pulsatile heart and circulation parameters must be properly selected. Analogous to the Crds parameter, these parameters indicate the increments in which the Pv and Pa parameters are stepped. If the simulation of a cardiac output curve is desired, the Pa parameter should be held constant by setting the Pas parameter to a very large value (1000 mmHg will usually be more than sufficient), and the Pvs parameter should be set to a sufficiently small value in order to permit the generation of a reasonably smooth curve (2 mmHg will usually do). If the generation of a curve of average cardiac output versus average systemic arterial pressure is required, the Pv parameter should be held constant by setting the Pvs parameter to a very large value (100 mmHg will usually be more than sufficient), and the Pas parameter should be set to a sufficiently small value in order to allow the generation of a reasonably smooth curve (30 mmHg will usually do). Finally, note that the researcher may assign sufficiently small values to both Pvs and Pas such that a family of cardiac output curves at different systemic arterial pressures will be generated.