It sounds paradoxical but computer simulation programs turn out to be very useful in higher education or industrial training for learning how to interact with a simulated model. For example: a computer simulation program of the blood pressure regulation mechanism of the human body, enables a medical student to construct a mental model of the relation between blood pressure, cardiac output, and peripheral resistance and to find that they are linear.

The model include at least 60 variables which can be displayed (at the right) and 25 important parameters which can be used for interventions in the model (at the left).

In this applet 7 variables will be displayed: arterial pressure, urine output, cardiac output, etc. The simulation time is displays in minutes. 10 days is 14400 minutes.

The applet has 8 possibilities for intervention: parameters for creeting diseases, parameters for therapies, and a case-selector: case 1, 2 and 3.

For actual use this pre-prototype applet you need our manuals whith the instructions, exercises, cases, texts, explinations, etc. (R. Min, the cardiovascular system, the heart as a pump; the computer simulation program CARDIO; Springer Verlag Berlin; 1991; also published on the web: see button Backgrounds.)

All variables, modelparameters, constants and possible interventions (name, mnemonic, units and remarks:

1. Clinical variables, for diagnosis and treatment. These variables are the only ones available during clinical simulations:

• Arterial Pressure AP (100 mmHg).
• Heart Rate HR (70 beats/min).
• Urine output UO (1 ml/min).
• Arterial O2 pressure PO2 (100 mmHg).
• Blood Urea Nitrogen BUN (10 mg%).
• Edema ED (Normally zero, can have values +, ++, +++, ++++).

2. Physiological Variables. These variables are used during physiological studies. Some units are familiar, some are normalized, i.e. usual value is 1.

• Cardiac Output CO (5000 ml/min).
• Total Peripheral Resistance TPR (.02 mmHg/ml/min).
• Blood Volume BV (5000 ml).
• Extracellular Fluid Volume ECFV (15000 ml).
• Mean Circulatory Filling Pressure MCFP (7 mmHg).
• Right Atrial Pressure RAP (0 mmHg).
• Resistance to Venous Return RVR (.0014 mmHg/ml/min).
• Water Intake WIN (1 ml/min).
• Autonomic Outflow SYMPS (1.0 x normal).
• Basic Heart Strength HSB (1.0 x normal).
• Total Cardiac Function HF (1.0 x normal).
• Renal Mass RM (1.0 x normal).
• Basic Renal Artery Resistance RARB (1.0 x normal).

3. Interventions. These are meant to mimic possible therapeutic procedures. Usually a value of 0 represents no intervention, while 1.0 represents the maximum possible value. All values between 0 and 1.0 are permitted, representing graded therapy.

• Diuretic DI (0-->1). Increases urine flow via tubular mechanisms.
• Vasoconstriction NOREPI (0-->1). Represents administration of an alpha-adrenergic agent).
• Adrenergic Blockade BLOCK (0-->1). Such as guanethidine, these agents decrease sympathetic outflow.
• Cardiac Glycosides DIGI (0-->1). Digitalis is typical; agents increase heart strength.
• Systemic vasodilator DILAT (0-->1). Dilates systemic and renal arteries.
• Management of H2O Intake WIN (1.0 ml/min is normal value and this can be adjusted up or down).
• Rapid Infusion of Fluids ECFV (15000 ml is normal value and this can be adjusted representing rapid infusion).
• Surgical Repair of Renal Artery Stenosis RARB (Normally, the basic renal artery resistance is 1.0, but if it is pathologically high, it can be lowered via surgical repair).

4. Additional Interventions for physiological demonstration. These variables are normally not within the domain of the physician

• Renal Mass RM (Normally 1.0). It can be lowered to simulate nephrectomy (.5 represents unilateral nephrectomy).
• Rapid Hemorrhage ECFV (ECFV can be reduced in step fashion).
• Slow Hemorrhage BL (ml/min) (is normally 0), but can be given a value to represent the rate of fluid loss (as in peritoneal hemorrhage).
• A-V fistula AVF (0-1). Opens a moderate to severe A-V fistula.
• Selective Venous Constriction VENCON (Normally 1.0). Can be increased to selectively constrict the veins.
• Selective Arterial Constriction VASCON (Normally 1.0). Can be used to selectively constrict non renal peripheral arteries.
• Basic Heart Strength HSB (Normally 1.0). Changes cardiac function curve.
• Metabolic Demand MD (Normally 1.0). Increased during exercise.

5. Additional Physiological Variables. These variables are important to the accurancy of the model but are not often followed.

• Unstressed Blood Volume (basic) BV0 (Normally 3500 ml).
• Extracellular Fluid Volume (in liters) EL (EL=ECFV/1000). For convenience in the "edema" calculation.
• Glomerular Capillary Pressure GP (Normally 60 mmHg).
• Chemoreceptor contribution Sympathetic Outflow CHEMO (Normally = 0) can increase with falling PO2 to a maximum of 0.5.
• Basic Baroreceptor Influence BAROB (Normally = 1). This is the value before adoptation..
• Adaptation ADP (Normally = 0). The part of BAROB that is lost because of adaptation..
• Adaptation Time Constant BAROK (Normally = 0.00035) k = 1/T in minutes, therefore T=2 days.
• Autonomic Outflow Multiplier AO (Normally = 1.0). Falls to 0.5 with no sympathetic activity.
• Baroreceptor Influence After Adaptation BARO (Normally = 1.0). BARO=BAROB-ADP.
• Basic Cardiac Output COB (Normally = 5000 ml/min). This is CO produced for a given RAP if heart function is normal.
• Metablic Blood Flow COM (Normally = 5000 ml/min)This flow plus shunt flow equals total cardiac output.
• Basic Total Peripheral Resistance TPRB (Normally = 0.02 mmHg/ml/min). This is TPR before the delay involved in changing resistance and before other extrinsic influence.
• Delayed resistance TPRD (Normally = 0.02 mmHg/ml/min). This is TPRB delayed by time constant 1/TPRDK.
• Vascularity time constant TPRDK (Normally = 0.00028) (= 2 1/2 days).
• Pressure Gradient for venous return DELP (Normally = 7.0 mmHg). DELP=MCFP - RAP.
• Difference between metabolic flow and Metabolic demand DELCO (Normal = 0 ml/min).
• Renal Artery resistance RAR (Normally = 1.67 units). Procedures a GP of 60 when AP = 100.
• Effect of arterial pressure on heart function APM (Normally=1.0 units). Value goes up showing decreased heart fuction at high arterial pressure.
• Quantity of BUN QBUN (Normally 1900 normal units). Used to calculate BUN.
• Heart Strength HS (Normally = 1.0), inludes effects of arterial pressure, autonomics, drugs - - - - everything but PO2.
• Basic Urine Output UOB (Normally = 1.0 ml/min). Urine produced before adjustment for decreased renal mass and diuretics.
• Metabolic Resistance TPRM (Normally = 0.02). The part of TPR involving metabolic, non-shunt flow paths.
• Excessive sympathetic activity PHEO (Normal = 0). When 2.0, produces syndrome of pheochromocytoma.
• Dietary protein PRDIET (Normally = 1). Can be reduced to zero.
• Urea Formation BUNI (Normally = 10). Can be changed with diet.
• Urea Excretion BUNO (Normally = 10). Depends on urine formation.

6. Initial conditions. These variables supply the values of certain important variables as solution of the model is begun.

• Initial Extracellular Fluid Volume ECFV0 (15000 ml).
• Initial Total Peripheral resistance TPR0 (normally 0.02).