Cardiovascular applications of the ALOPEX optimization technique

Abstract

ALOPEX is a general optimization process incorporating a cost function containing a large number of parameters which may be simultaneously adjusted until the cost function reaches an optimum (maximum or minimum); local extremes are avoided by introducing random noise into the procedure. In this paper, ALOPEX is incorporated into a simple haemodynamic study in which an electric analogue model of the left ventricle is used to develop equations of myocardial stroke work. Pilot experiments were undertaken in rabbits (n = 5) to gauge the effectiveness of this optimizing technique. In the control state, calculated stroke work for the rabbit was determined to be 50 ± 7 mmHg ml, while ALOPEX predicted a stroke work of 51 ± 7 mmHg ml. ALOPEX is capable of following changing cardiovascular states when pharmacological agents are introduced. For example, after nitroprusside treatment, stroke work was reduced by 38 ± 6% (P < 0.05) while ALOPEX predicted a 42 ± 4% reduction from baseline (P < 0.05). Methoxamine treatment increased stroke work by 74 ± 34%, while ALOPEX predicted a 73 ± 43% increase above control values. There were no statistical differences between calculated and ALOPEX predicted values. Individual model parameters such as maximum left ventricular elastance (E_max) and left ventricular end diastolic volume (EDV) were also predicted correctly by ALOPEX. We have found that the ALOPEX optimization technique is useful in predicting components of multi-parametric functions. In particular, we have shown it to be adaptable to a simple haemodynamic model.