Modifications and Extensions

Although the human cardiovascular model upon which RCVSIM is based accounts for a wide variety of hemodynamic behaviors, it certainly cannot address arbitrary cardiovascular research objectives. For example, if the researcher is interested in analyzing how stroke volume is compromised at very high heart rates ($>\,\sim$150 bpm) in the absence of cardiovascular regulation, the model, as described in Section 2, would not be adequate because contracting atrial compartments are not explicitly included. In such cases, the researcher may utilize the RCVSIM source code as a basis for facilitating the construction of a model which can address his research objective. An outline of the major steps necessary for the researcher to create different lumped parameter pulsatile heart and circulation models and add new bandlimited regulatory systems (e.g., arterial chemoreflex) and resting physiologic perturbations (e.g., central oscillator) is provided below. Note that additional steps may also be necessary depending upon the particular extension.

• Creating lumped parameter models of the pulsatile heart and circulation.
  1. Name the new lumped parameter model (preparation) and assign a unique number to it. This number will be used in conditional statements which must be added to the code in order to distinguish the desired preparation to be executed from the other possible preparations (see, for example, the rk4.m source code).
  2. Extend the MATLAB parameter vector (th) to include any additional, necessary parameters. Add the new parameters (in the correct format) to the parameter file (see Section 5.2). Expand the function read_param.m so that it can read these new parameters. If the researcher would like to implement the new preparation in the MATLAB environment, the function header_def.m must also be altered accordingly (see Appendix A).
  3. Create a function called preparation_init_cond.m to generate the initial pressures, volumes, and flow rates. Call this newly created function at the same point in simulate.m as the function call for intact_init_cond.m.
  4. Create a function called preparation_eval_deriv.m to calculate the derivative of the pressure values at a desired time step. Call this newly created function from rk4.m analogous to the function calls for intact_eval_deriv.m.
  5. Add code for calculating volumes and flow rates at the point in simulate.m in which these waveforms are computed for the other preparations.
  6. If necessary, pre-allocate additional memory for the simulated data in simulate.m, expand matrices to be written in MIT format in simulate.m and rcvsim.m, and extend code for generating the MIT format header file in rcvsim.m.
  7. Adjust parameter update code in simulate.m including conserve_vol.m.
  8. Add preparation_init_cond.m and preparation_init_cond.m to the make files (make.m and makem.m) and recompile the code.
     
     
     
     
• Adding bandlimited regulatory system/resting physiologic perturbation.
  1. Name the new regulatory system/resting physiologic perturbation. This name will serve as a flag indicating whether the new addition is to be activated or not. The MATLAB vector flag at the start of simulate.m should be extended to incorporate this name.
  2. Extend the MATLAB parameter vector (th) to include any additional, necessary parameters. Add the new parameters as well as the new flag name (in the correct format) to the parameter file (see Section 5.2). Expand the function read_param.m so that it can read these new parameters and flag name. If the researcher would like to implement the new model in the MATLAB environment, the function header_def.m must also be altered accordingly (see Appendix A).
  3. Initialize the necessary variables at the beginning of simulate.m.
  4. Create a function to compute the mandated change to the adjustable parameter. Call this function every 0.0625 s. If this function requires a simulated waveform as input, then this waveform must be averaged over the previous 0.25 s every 0.0625 s prior to the function call.
  5. If a parameter other than $F(t)$, $R_a(t)$, $Q_v^0(t)$, and $C_{l,r}^{es}(t)$ is adjusted, then the following steps must be undertaken:
     1. Pre-allocate additional memory for the adjustable parameter matrix ap in simulate.m.
     2. Expand the thc vector in simulate.m to include the new parameter to be adjusted.
     3. Linearly interpolate the newly adjustable parameter.
     4. Assign the mandated adjustment to the ap matrix in simulate.m.
     5. Expand the ap matrix to be written in MIT format in simulate.m and rcvsim.m.
     6. Adjust the parameter update code in simulate.m accordingly.
     7. Extend code for generating the MIT format header file in rcvsim.m to include the newly adjustable parameter.
  6. Add the new function to the make files (make.m and makem.m) and recompile the code.