Central Vascular Shunts 1
Right to Left Shunt
(version 3/19/02)

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)