/*
 * Guyton Model: stress_relaxation
 * 
 * Model Status
 * 
 * This CellML model has been validated. Due to the differences
 * between procedural code (in this case C-code) and declarative
 * languages (CellML), some aspects of the original model were
 * not able to be encapsulated by the CellML model (such as the
 * damping of variables). This may affect the transient behaviour
 * of the model, however the steady-state behaviour would remain
 * the same. The equations in this file and the steady-state output
 * from the model conform to the results from the MODSIM program.
 * 
 * Model Structure
 * 
 * Arthur Guyton (1919-2003) was an American physiologist who became
 * famous for his 1950s experiments in which he studied the physiology
 * of cardiac output and its relationship with the peripheral circulation.
 * The results of these experiments challenged the conventional
 * wisdom that it was the heart itself that controlled cardiac
 * output. Instead Guyton demonstrated that it was the need of
 * the body tissues for oxygen which was the real regulator of
 * cardiac output. The "Guyton Curves" describe the relationship
 * between right atrial pressures and cardiac output, and they
 * form a foundation for understanding the physiology of circulation.
 * 
 * The Guyton model of fluid, electrolyte, and circulatory regulation
 * is an extensive mathematical model of human circulatory physiology,
 * capable of simulating a variety of experimental conditions,
 * and contains a number of linked subsystems relating to circulation
 * and its neuroendocrine control.
 * 
 * This is a CellML translation of the Guyton model of the regulation
 * of the circulatory system. The complete model consists of separate
 * modules each of which characterise a separate physiological
 * subsystems. The Circulation Dynamics is the primary system,
 * to which other modules/blocks are connected. The other modules
 * characterise the dynamics of the kidney, electrolytes and cell
 * water, thirst and drinking, hormone regulation, autonomic regulation,
 * cardiovascular system etc, and these feedback on the central
 * circulation model. The CellML code in these modules is based
 * on the C code from the programme C-MODSIM created by Dr Jean-Pierre
 * Montani.
 * 
 * This particular CellML model describes the effect of stress
 * relaxation on basic venous volume (V0). This model calculates
 * the effect over a period of time caused by excess volume (or
 * too little volume) in the venous tree to cause changes in the
 * volume holding capacity of the venous tree when it is fully
 * filled with blood but at zero pressure. In this model, there
 * are two separate parallel stress relaxations of the veins. One
 * of these has a short time constant (SRK) and the other has a
 * long time constant (SRK2).
 * 
 * model diagram
 * 
 * [[Image file: full_model.png]]
 * 
 * A systems analysis diagram for the full Guyton model describing
 * circulation regulation.
 * 
 * model diagram
 * 
 * [[Image file: stress.png]]
 * 
 * A schematic diagram of the components and processes described
 * in the current CellML model.
 * 
 * There are several publications referring to the Guyton model.
 * One of these papers is cited below:
 * 
 * Circulation: Overall Regulation, A.C. Guyton, T.G. Coleman,
 * and H.J. Granger, 1972, Annual Review of Physiology , 34, 13-44.
 * PubMed ID: 4334846
 */

import nsrunit;
unit conversion on;
unit minute=60 second^1;
unit per_minute=.01666667 second^(-1);
//Warning:  unit mmHg_ renamed from mmHg, as the latter is predefined in JSim with different fundamental units.
unit mmHg_=133.322 kilogram^1*meter^(-1)*second^(-2);
unit per_mmHg2=5.6259564E-5 kilogram^(-2)*meter^2*second^4;
unit monovalent_mEq=.001 mole^1;
unit monovalent_mEq_per_minute=1.6666667E-5 second^(-1)*mole^1;
unit monovalent_mEq_per_litre=1 meter^(-3)*mole^1;
unit monovalent_mEq_per_litre_per_minute=.01666667 meter^(-3)*second^(-1)*mole^1;
unit litre2_per_monovalent_mEq_per_minute=1.6666667E-5 meter^6*second^(-1)*mole^(-1);
unit L_per_minute=1.6666667E-5 meter^3*second^(-1);
unit L_per_minute_per_mmHg=1.2501063E-7 kilogram^(-1)*meter^4*second^1;

math main {
	realDomain time minute;
	time.min=0;
	extern time.max;
	extern time.delta;
	real VVE litre;
	VVE=0.743224;
	real VV7(time) litre;
	when(time=time.min) VV7=0.00366525;
	real SR dimensionless;
	SR=1;
	real SRK minute;
	SRK=5;
	real VV6(time) litre;
	when(time=time.min) VV6=0.0101913;
	real SR2 dimensionless;
	SR2=1;
	real SRK2 minute;
	SRK2=10000;

	// <component name="environment">

	// <component name="stress_relaxation">

	// <component name="short_term_stress_relaxation">
	VV7:time=(((VVE-(.74 litre))*SR-VV7)/SRK);

	// <component name="long_term_stress_relaxation">
	VV6:time=(((VVE-(.74 litre))*SR2-VV6)/SRK2);

	// <component name="parameter_values">
}