Performance of low-frequency power of the maximal amplitude of the first derivative of arterial pressure waveform as a cardiac sympathetic activity index

We assessed the time-frequency spectra of the maximal amplitude of arterial pulse first derivative (dP/dt_max) series during four maneuvers provoking different sympathetic activity levels, and examined the relations between dP/dt_max spectral measures and those of heart rate, systolic pressure (SP), and respiratory variabilities. Thirty healthy subjects performed 5-min maneuvers: lying, controlled breathing, standing (S) and exercise (E). Time-frequency spectra of RR intervals (RR), SP, dP/dt_max and respiration (Res) time series were estimated to compute their low-frequency powers (LF_SP, LFdP/dt_max), high-frequency powers (HF_RR, HFdP/dt_max, HF_Res), and HFdP/dt_max-HF_Res time-frequency coherence. While LF_SP and LFdP/dt_max increased in S and E, HF_RR and RR level decreased. Correlations of HF_RR and RR level with LFdP/dt_max were very strong and greater than with LF_SP. HFdP/dt_max was maximal in E and showed significant coherences with HF_Res. LFdP/dt_max and LF_SP correctly indicate the increasing levels of sympathetic activation in S and E. Thus, LFdP/dt_max power can be considered a suitable noninvasive cardiac sympathetic activity-contractility index, complementary to LF_SP, which is associated to vasomotor sympathetic activity. HFdP/dt_max power is originated by a mechanical respiratory effect.