Activating Central Vascular Shunts in web-HUMAN
web-HUMAN incorporates the capability of activating both right to left and left to right shunts (see Shunts 1 exercise). Right to left shunts (R->L), in which the shunted blood bypasses the lungs, are activated by setting the parameter FR2LS to values greater than zero (and less than one); the value selected determines what fraction of the right heart's output bypasses the lungs. Similarly, the parameter FL2RS (0-1) determines how much blood is shunted away from the systemic circulation back to the right side to be recirculated to the lungs (a left to right [L->R] shunt).

The "anatomy" of web-HUMAN Shunts
HUMAN is, of course, a mathematical simulation and as such does not always exactly mimic the actual anatomy of the subsystem it is modeling. In the case of "real world" central vascular anatomical shunts, the location of the shunt can often be diagnosed from cardiac catheterization data such as a step-up in blood O2 in an unexpected location. Thus a left to right (L->R) shunt through an atrial septal defect might result in right ventricular O2 content and saturation being significantly higher than right atrial O2 values; oxygenated blood has crossed back to the right side via the atrial septal opening. In this course (Cardiovascular Physiology) we have considered at least five such actual anatomical shunt situations (atrial and ventricular septal defects, patent ductus arteriosus, transposition of the great vessels and Tetralogy of Fallot).

The diagnostic problem stated
Interestingly in HUMAN Dr. Coleman has chosen to simulate the R->L and L->R shunts via anatomic pathways that do not occur in 'normal' congenital defects. You are asked below, based on the data gathered in web-HUMAN, to figure out for each of the two shunts from what anatomical location HUMAN picks up the shunt blood and into which anatomical location it 'dumps' it.

Procedure

I. Create a right to left shunt of 50% (FR2LS = 0.5) and then a left to right shunt (FL2RS = 0.5), run for 1 hour (1H) in each case.

II. After creating each shunt, use the on-line variables list (List all variables) to gather data on at least the following:

• 1) O2 content values (e.g. O2A is the arterial O2 content in ml O2/ml blood)
  
• 2) O2 partial pressure values - (e.g. PO2A is the arterial partial pressure of O2 in mmHg)
  
• 3) Flows - examine at least
  - Right heart output RHOUT
  - Flow through the lungs LUNGF
  - Cardiac output CO
  
• 4) Pressures
  Left atrial pressure
  Right atrial pressure

III. From the data patterns above determine the 'anatomical' location at which the shunt begins and the 'anatomical' location at which the shunt terminates.

IV. In each shunt obtain the value for lung O2 uptake. With O2 uptake and blood concentration values (obtained above) you now have enough information to calculate blood flows via the Fick method. Employing a Fick calculation verify each of the following values:

A] For the right->left shunt in I. above
- that the model's cardiac output matches the caculated Fick value

B] For the left->right shunt
- that the model's cardiac output matches the calculated Fick value
- that the pulmonary blood flow matches the calculated Fick value

web_HUMAN users outside the Skidmore Cardiovascular course should feel free to write us (rmeyers@skidmore.edu) to verify their conclusions and analysis logic.