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This Article Full Text Full Text (PDF) All Versions of this Article: 295/3/R821    most recent 00582.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Chon, K. H. Articles by Cupples, W. A. PubMed PubMed Citation Articles by Chon, K. H. Articles by Cupples, W. A.

HEMODYNAMICS AND CARDIORENAL INTEGRATION

Analysis of nonstationarity in renal autoregulation mechanisms using time-varying transfer and coherence functions

Departments of ¹Biomedical Engineering and ²Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York; ³Department of Biology, University of Victoria, Victoria, BC, Canada; and ⁴Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark

Submitted 11 August 2007 ; accepted in final form 19 May 2008

The extent to which renal blood flow dynamics vary in time and whether such variation contributes substantively to dynamic complexity have emerged as important questions. Data from Sprague-Dawley rats (SDR) and spontaneously hypertensive rats (SHR) were analyzed by time-varying transfer functions (TVTF) and time-varying coherence functions (TVCF). Both TVTF and TVCF allow quantification of nonstationarity in the frequency ranges associated with the autoregulatory mechanisms. TVTF analysis shows that autoregulatory gain in SDR and SHR varies in time and that SHR exhibit significantly more nonstationarity than SDR. TVTF gain in the frequency range associated with the myogenic mechanism was significantly higher in SDR than in SHR, but no statistical difference was found with tubuloglomerular (TGF) gain. Furthermore, TVCF analysis revealed that the coherence in both strains is significantly nonstationary and that low-frequency coherence was negatively correlated with autoregulatory gain. TVCF in the frequency range from 0.1 to 0.3 Hz was significantly higher in SDR (7 out of 7, >0.5) than in SHR (5 out of 6, <0.5), and consistent for all time points. For TGF frequency range (0.03–0.05 Hz), coherence exhibited substantial nonstationarity in both strains. Five of six SHR had mean coherence (<0.5), while four of seven SDR exhibited coherence (<0.5). Together, these results demonstrate substantial nonstationarity in autoregulatory dynamics in both SHR and SDR. Furthermore, they indicate that the nonstationarity accounts for most of the dynamic complexity in SDR, but that it accounts for only a part of the dynamic complexity in SHR.

hemodynamics; myogenic; tubuloglomerular feedback; hypertension