A transfer function method for the continuous assessment of baroreflex control of renal sympathetic nerve activity in rats.
The present study examined whether the gain of the transfer function relating cardiac-related rhythm of renal sympathetic nerve activity (RSNA) to arterial pressure (AP) pulse might serve as a spontaneous index of sympathetic baroreflex sensitivity (BRS). AP and RSNA were simultaneously recorded in conscious rats, either baroreceptor-intact (control, n = 11) or with partial denervation of baroreflex afferents [aortic baroreceptor denervated (ABD; n = 10)] during 1-h periods of spontaneous activity. Transfer gain was calculated over 58 adjacent 61.4-s periods (segmented into 10.2-s periods). Coherence between AP and RSNA was statistically (P < 0.05) significant in 90 +/- 3% and 56 +/- 10% of cases in control and ABD rats, respectively. Transfer gain was higher (P = 0.0049) in control [2.39 +/- 0.13 normalized units (NU)/mmHg] than in ABD (1.48 +/- 0.22 NU/mmHg) rats. In the pooled study sample, transfer gain correlated with sympathetic BRS estimated by the vasoactive drug injection technique (R = 0.75; P < 0.0001) and was inversely related to both time- (standard deviation; R = -0.74; P = 0.0001) and frequency-domain [total spectral power (0.00028-2.5 Hz); R = -0.82; P < 0.0001] indices of AP variability. In control rats, transfer gain exhibited large fluctuations (coefficient of variation: 34 +/- 3%) that were not consistently related to changes in the mean level of AP, heart rate, or RSNA. In conclusion, the transfer function method provides a continuous, functionally relevant index of sympathetic BRS and reveals that the latter fluctuates widely over time.
Kanbar
Roy
R
Université de Lyon, France. roy.kanbar@sante.univ-lyon1.fr
Oréa
Valérie
V
Chapuis
Bruno
B
Barrès
Christian
C
Julien
Claude
C
D000818:Animals; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D003627:Data Interpretation, Statistical; D003714:Denervation; D006339:Heart Rate / Q000502:physiology; D007668:Kidney / Q000294:innervation* / Q000502:physiology*; D007677:Kidney Function Tests; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000502:physiology*