Nonlinear dynamics applied to blood pressure control

Hypertension is a very frequent disease, known to trigger a range of severe cardiovascular problems. The elucidation of its pathophysiology requires i nvestigation of the mechanisms responsible for the maintenance of blood pre ssure in the normal system, and their possible failure in hypertension. Som e of these control mechanisms display nonlinear features, indicating that t he blood pressure signal might be characterized by nonlinear dynamics. Our aim was thus to investigate the nonlinear properties of the blood pressure signal under normal conditions, and in a cardiovascular system prone to hyp ertension. Blood pressure was investigated in young spontaneously hypertensive rats (S HR), versus their age-matched normotensive progenitors (WKY). The correlati on dimension was computed as quantification of blood pressure control compl exity,The parameters required for the calculation procedure of the correlat ion dimension were carefully determined. The results were tested with surro gate data statistics, assuming linear autocorrelated Gaussian noise as the null hypothesis. Non-integer correlation dimension values were found in both strains, with l ower Values for SHR than far WKY, in particular following alpha -blockade. In all cases, a statistically significant difference was found between the real and surrogate data. These results show that the nonlinear dynamics par ameter D-2 can be used to detect differences in BP control between prehyper tensive SHR and WKY rats as early as 6-7 weeks after birth. (C) 2001 Elsevi er Science B.V. All rights reserved.