Central Frequency of Low Frequency Component of RR Estimates Sympathetic Activity during Dynamic Exercise, Standing and Controlled Breathing Maneuvers

Salvador Carrasco-Sosa and Alejandra Guillén-Mandujano
Universidad Autónoma Metropolitana-I


It is known that low-frequency power of RR intervals (PLFRR) fails to track sympathetic activity changes during dynamic exercise (DE). Recently, we documented that the central frequencies of low-frequency components (CFLF) of RR (CFLFRR), systolic, and diastolic pressure (CFLFDP) correctly indicated sympathetic activation during static exercise. To provide further evidence of the indicating capabilities of CFLF, in 25 healthy subjects we assessed, the effects of supine position (SP), DE executed at 100 W, standing (ST) and controlled breathing (CB) –each maneuver lasting 5 min– on the time-courses of CFLFRR, CFLFDP, PLFRR, high-frequency power of RR (PHFRR), PLFRR/PHFRR and CFLFRR/PHFRR ratios, all estimated by a time-frequency distribution. Comparisons and correlations among spectral measures were obtained. With respect to SP, mean values of CFLFRR (Table) and PHFRR increased (p<0.001) in CB and decreased progressively in ST (p<0.001) and DE (p<0.001); CFLFRR/PHFRR decreased in CB (p<0.03) and increased progressively in ST (p<0.001) and DE (p<0.001); PLFRR only decreased pronouncedly in DE (p<0.001); CFLFDP augmented during CB and ST (Table). Mean values of PLFRR/PHFRR were not different between ST and DE. In SP, CB, and ST, CFLFRR was greater than CFLFDP (Table). The CFLFRR-PHFRR correlation was 0.77±0.08. The progressive CFLFRR decrement from a maximum in CB, followed by SP and ST to a minimum in DE, together with its strong correlation with the robust autonomic marker PHFRR and the better discriminating capability of CFLFRR/PHFRR than PLFRR/PHFRR, support that CFLFRR performs adequately as a sympathetic activity measure, relevantly in DE, and that it could replace PLFRR for computing the sympathovagal balance. The striking finding that CFLFRR is greater than CFLFDP in CB, SP, and ST, although in DE are similar, corroborates our previous report that the modulatory frequency of the cardiac sympathetic outflow is greater than the vasomotor one.