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Am J Physiol Regul Integr Comp Physiol (May 7, 2008). doi:10.1152/ajpregu.00070.2008
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Submitted on January 30, 2008
Accepted on May 2, 2008

Dynamic time-varying analysis of heart rate and blood pressure variability in cats exposed to short-term chronic intermittent hypoxia

Sergio Rey1, Mika P Tarvainen2, Pasi A Karjalainen2, and Rodrigo Iturriaga1*

1 Neurobiology, Pontificia Universidad Catolica de Chile, Santiago, Chile
2 Physics, University of Kuopio, Kuopio, Finland

* To whom correspondence should be addressed. E-mail: riturriaga{at}bio.puc.cl.

Chronic intermittent hypoxia (CIH) contributes to the development of hypertension in patients with obstructive sleep apnea and animal models. However, the early cardiovascular changes that precede CIH-induced hypertension are not completely understood. Nevertheless, it has been proposed that one of the possible contributing mechanisms to CIH-induced hypertension is a potentiation of carotid body (CB) hypoxic chemoreflexes. Therefore, we studied the dynamic responses of heart rate, blood pressure and their variabilities during acute exposure to different levels of hypoxia after short-term preconditioning with CIH (4 days) in cats. In addition, we measured baroreflex sensitivity (BRS) on the control of heart rate by non-invasive techniques. To assess the relationships among these indexes and CB chemoreflexes, we also recorded CB chemosensory discharges. Our data show that short-term CIH reduced BRS, potentiated the increase in heart rate induced by acute hypoxia and was associated with a dynamic shift of heart rate variability (HRV) spectral indexes towards the low frequency band. In addition, we found a striking linear correlation (r= 0.97) between the low-to-high frequency ratio of HRV and baseline CB chemosensory discharges in the CIH-treated cats. Thus, our results suggest that cyclic hypoxic stimulation of the CB by short-term CIH induces subtle but clear selective alterations of HRV and BRS in normotensive cats.







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