Improved Patient Outcomes by Normalizing Sympathovagal Balance: Differentiating Syncope—Precise Subtype Differentiation Leads to Improved Outcomes

Figure 1

A spectral domain comparison of the LFa and RFa method [8] and the LF and HF method [12, 13] (see Methods for abbreviations). The vertical broken line represents the respiratory frequency over the four-second measurement period. The respiratory frequency is independently computed in the respiratory activity spectrum (not shown) and then transferred here to the HRV spectrum to locate the RFa (parasympathetic) spectrum. In this way, the RFa spectrum is based on the breathing rate of the subject. In this example, the respiratory frequency is 0.125 Hz (equivalent to 7.5 breathes per minute). The LF spectrum is represented in dark grey from 0.04 Hz to 0.15 Hz [12, 13]. The HF spectrum is represented in light grey from 0.15 Hz to 0.40 Hz [12, 13]. The RFa spectrum, in this example, is from 0.065 Hz to 0.185 Hz [8]. The RFa is computed from a frequency range centered on the respiratory frequency (0.125 Hz, see above) and moves as the respiratory frequency moves [8]. The LFa spectrum, in this example, is from 0.04 Hz to 0.065 Hz. The LFa is computed as the (fixed) LF frequency range (0.04 Hz to 0.15 Hz) minus the portion of the RFa frequency range that overlaps the LF frequency range (in this example, 0.065 Hz to 0.15 Hz) [8]. LFa, in (beats per minute)² or bpm², represents sympathetic activity, and RFa, in bpm², represents parasympathetic activity [8, 14–17].