Time-Courses of the Central Frequencies of Low-Frequency Components of RR Intervals, Systolic and Diastolic Pressure Variabilities in Response to Active Orthostatic Test

In 25 healthy subjects we assessed the effects provoked by 1-min of active orthostatic test (AOT) on time-courses of central frequencies and powers of low frequency components (CFLF, PLF) of RR (CFLFRR, PLFRR), systolic (CFLFSP, PLFSP) and diastolic (CFLFDP, PLFDP) pressures, estimated by a time-frequency distribution. Ensemble averages of the three PLF-CFLF pairs dynamics depicted an initial sudden change (ISC), followed by a recovery change (RC) and a final sudden change (FSC). The rapid changes were upwards for PLF and downwards for CFLF. Means of the maximal PLF surges and of minimal CFLF falls were greater and smaller ($p < 0.01$) than their respective control means. Mean correlations of the three PLF-CFLF relations ranged from $- 0.95+ 0.05\ to\ -0.97\pm 0.04$ in ISC, $-0.86\pm 0.13\ to\ -0.87\pm 0.15$ in R C and $-0.30\pm 0.59$ to $-0.41\pm 0.63$ in FSC. In all stages, means of CFLFRR were greater ($p < 0.04$) than those of CFLFDP. That the patterned responses of the three PLF-CFLF pairs time-courses present rapid initial and final changes, upstrokes for PLF and falls for CFLF, significantly inversely correlated, and the greater level of CFLFRR than CFLFDP, refine the time-course of cardiovascular sympathetic activation in AOT, possibly non-uniform, and suggest that CFLF are trustable quantitative sympathetic measures, with some specificity, CFLFRR for the cardiac and CFLFDP for the vasomotor one.