Arterial baroreflexes and cardiovascular modeling.

Many cardiovascular models involve prediction of changes that occur when a subject is perturbed in some way, to move from one state to another. A successful, predictive model should involve at least two elements: First, the model should include some index of the intensity of the perturbation that elicits the response; effective responses should, in some fashion, be linearly or nonlinearity related to perturbations. Second, the model should factor in subjects' abilities to meet the challenges posed by the perturbations. This review indicates that these two basic components of a successful model may be difficult to incorporate. In the simple case of passive upright tilt, blood pressure measurements may not accurately indicate the stimulus, because blood pressure reductions are reversed by rapidly occurring reflex blood pressure increases. Since not all subject populations respond identically to hemodynamic challenges, it also may be important to characterize baroreflex responsiveness, and include such a term in a model. Although vagal and sympathetic baroreflex responses to stereotyped challenges can be measured accurately, recent research points to extraordinary variability of baroreflex responsiveness. The complexities discussed in this review should be considered, whether they are, or even can be incorporated into cardiovascular models.