Certain congenital birth defects can result in the shunting of central vascular blood from left (systemic) to right (pulmonary) or from right to left. Several that we have considered/will consider in Cardiovascular Physiology include atrial and ventricular septal defects, patent ductus arteriosus, transposition of the great vessels and Tetralogy of Fallot. Thus is a right to left shunt the shunted blood bypasses the lung oxygenator and passes directly into the systemic circulation.
A right to left shunt (R->L) can be simulated in web-HUMAN by setting the parameter FR2LS (see on-line variables list) to a non-zero value. This shunts the specified fraction of right heart's output to the left side, bypassing the lungs. FR2LS can be set from zero (default value = no shunt) to one (complete shunt).
Below you set FR2LS to 0.5 ("a moderate to severe shunt")* , run the model for 1 hour (1H) and evaluate several resulting data patterns. Check the on-line variables list for units and normal reference values for the variables listed below
| Variable | HUMAN code name | Units | Control Value | Value at 1 hour |
| Right to Left Shunt | FR2LS | 0.0 | 0.5 | |
| Cardiac Output | CO | |||
| Arterial Pressure | AP | |||
| Ventilation | VENT | |||
| Arterial Oxygen | PO2A | |||
| Arterial CO2 | PCO2A | |||
| Pulmonary Venous O2 Content | O2PV | |||
| Arterial O2 Content | O2A | |||
| Venous O2 Content | O2V |
1) Describe and explain the changes in the blood gas partial pressures.
2) From the profile of O2 content values localize the 'entry' point of the R->L shunt. Support your reasoning from the data.
3) Is tolerance to exercise compromised? (Use EXER = 2.0, XERMIN = 60, Run 30 min., 5 min. intervals, eyeball O2DEBT, use Patient's Chart to get exercise cessation time)
* adapted from experiments listed in Coleman and in Randall (see web-HUMAN docs for references)