11 A Simple Time Domain Estimate for Determining the Baroreceptor Reflex Mediated Heart Rate Response in Newborns

Abstract

Top of pageAbstract Introduction: The baroreceptor reflex mediated heart rate response is generally estimated by complex cross-spectral analysis (transfer function gain) between R-R interval and systolic blood pressure (SBP) fluctuations in the low frequency (LF, 0.04–0.15 Hz) band: The baroreceptor reflex sensitivity (BRS, ms/mmHg) (Andriessen, P. et al. Pediatr Res 2003;53:89–97). Aim: To evaluate the BRS with a simple time domain (t-BRS) estimate rather than a complex frequency domain (f-BRS) estimate. Methods: Forty-two infants (postconceptional age, range: 28–42 wk) were studied in the first days after birth whose intensive care management required an arterial catheter. Data analysis was performed on 192-s-long stationary segments during the quiet sleep state. f-BRS was estimated using transfer function analysis (LF transfer gain) based on cross-spectral analysis of R-R interval and SBP density curves, using 5 half-overlapping fast Fourier transform 64-s segments, at coherence values > 0.5 indicating statistical reliability. t-BRS was estimated by the ratio of SD of (R-R)i intervals (square root of variance or root-mean-square for the mean) divided by the SD of SBP beat-to-beat values in the 192-s-long segments. Statistics: linear regression analysis and difference of mean as function of mean of both methods with its 95% limits of agreement (Bland-Altman). Results: Time domain assessment of BRS (t-BRS) correlated significantly with LF cross-spectral analysis (f-BRS): r2 = 0.85; t-BRS = f-BRS + 1; p<0.01. The mean difference of both methods (f-BRS - t-BRS) was -1 mmHg/ms. The 95% limits of agreement were between -5 and +3 mmHg/ms. Conclusions: The baroreceptor reflex mediated heart rate response can reliable estimated by this simple time domain estimate and may be useful to determine in critical ill patients with signs or symptoms of cardiovascular instability. Low BRS implicates poor short-term regulation of BP fluctuations. Intensive care management should aim at reducing interventions causing blood pressure changes in these patients.