Spontaneous baroreflex sensitivity in children and young adults calculated in the time and frequency domain.

Spontaneous baroreflex receptor sensitivity (BRS) was calculated in 22 healthy normotensive children and young adults (age 14 +/- 5 years) using the sequence technique (time domain) and the alpha-coefficient or the gain of the transfer function between coherent oscillations (frequency domain). BRS estimated by the sequence technique (median: 16.7 ms/mm Hg) was significantly higher than BRS calculated from the gain of the transfer function using all frequencies (median: 13.0 ms/mm Hg; p = 0.009). However, there was a high correlation between these methods (r = 0.92). The reproducibility coefficient (RC) was high for all methods, but the coefficient of variability (VC) was best for the sequence technique and the gain of the transfer function, but significantly worse for the estimates of the alpha-coefficient in the low or high frequency band. The differentiation between increasing or decreasing blood pressure (BP) ramps did not give further information showing the same BRS values. The best BRS estimates will be achieved by using three consecutive beats without lag by the sequence technique and by using only frequencies with a proven correlation of BP and pulse interval (PI) and then calculating the gain of the transfer function using coherent oscillations.