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J Appl Physiol 84: 1795-1800, 1998;
8750-7587/98 $5.00
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Vol. 84, Issue 5, 1795-1800, May 1998

Use of nonlinear methods to assess effects of clonidine on blood pressure in spontaneously hypertensive rats

Denis Mestivier1, Hubert Dabiré2, Michel Safar2, and Nguyen Phong Chau1

1 Institut National de la Santé et de la Recherche Médicale U444, Centre de Bio-informatique, University of Paris 7-Denis Diderot, 75251 Paris cedex 05; and 2 Institut National de la Santé et de la Recherche Médicale U337, Faculté de Médecine Broussais Hôtel-Dieu, 75270 Paris cedex 06, France

In spontaneously hypertensive rats (SHR), chronic infusion of clonidine failed to decrease blood pressure and blood pressure variability. We used nonlinear methods to get a deeper insight on the effects of clonidine on blood pressure dynamics. For 24 h and 4 wk, clonidine (0.1 mg · kg-1 · day-1 sc) was infused by minipumps in the conscious SHRs, and, for comparison, a vehicle was infused in SHRs and in Wistar-Kyoto rats. Blood pressure was recorded for 30 min before and after treatments. We used the Lyapunov exponent, approximated by the inverse of the lmax index derived from the recurrence plot method, to characterize nonlinear dynamics. Before treatment, lmax index of blood pressure was lower (P < 0.01) in the SHRs than in the Wistar-Kyoto rats. Clonidine significantly increased lmax (P < 0.01) to the level observed in normotensive rats, at 24 h and up to 4 wk after infusion. We conclude that clonidine has a significant chronic effect on blood pressure dynamics, as evidenced by nonlinear methods. Our study also suggests that the mechanisms governing blood pressure variations are nonlinear.

recurrence plot; lmax index; Lyapunov exponent; cardiovascular dynamics


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