Aberrant Behaviour

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Blood Gas Model:

Inevitably, the blood:gas model has limitations although in general, it is able to simulate quite extreme conditions. The design of the model requires the imposition of some constraints and, as a result, may produce 'anomalous' behaviour under some circumstances.

Some of the more important constraints are:

•	That the PCO2 in any compartment is constrained to 500 mm Hg.

•	That the maximum inducible base deficit is constrained to -15.

•	That the peak (sustained) oxygen utilisation rate is constrained to about 800 mls/minute.*

•	That gas exchange does not occur in the ideal compartment if it does not have blood flow.

•	That temperature is constrained to the range 15 - 40 degrees C.

The supervisor should avoid producing rapid, marked changes in some variables as this will result in transient, 'anomalous' behaviour for some minutes. In particular, instantaneous changes in body temperature of more than a few degrees and rapid changes in haematocrit of more than a few % should both be avoided. If such changes are made, the partial pressures of the respiratory gases in all compartments will take some time to reach a new steady state and for many minutes, the reported blood gas values will be clearly erroneous.

* This compares very unfavourably with the sustained VO2 achieved by Alberto Contador who apparently was able to utilise ~ 7000 mls/minute for over half an hour in a recent Tour De France!!.

Absence of Haptic technology:

The present implementation includes no haptic technology. In general, this has no implications on the fidelity of the simulation. However, in real life, the rpm controllers of ECMO pumps exhibit considerable force-feedback (so that it is relatively difficult to produce sudden, marked changes in pump output). Clearly, this is not the case in the simulated environment and, unless care is taken in control adjustment, sudden, unrealistic, changes in pump output can be produced.