Heart rate variability are needed to address the LF component (with a lower bound of 0.04 Hz). Although time domain methods, especially the SDNN and RMSSD methods, can be used to investigate recordings of long durations, a substantial part of the long-term variability is day–night differences. Thus, long-term recordings analyzed by time domain methods should contain at least 18 hours of analyzable ECG data that include the whole night. Although cardiac automaticity is intrinsic to various pacemaker tissues, heart rate and rhythm are largely under the control of the autonomic nervous system. The parasympathetic influence on heart rate is mediated via release of
"What Is This Heart?" of 69, based on 32 reviews, which indicates "generally favorable reviews". Ian Cohen of Pitchfork Media gave a very positive review of the album stating, ""What Is This Heart?" makes you initially susceptible and vulnerable, and that’s risky when modern discourse seeks metaphorical blood, allowing people to disclose more than ever without actually revealing anything. So make no mistake, the title of this album is a challenge as well, as How to Dress Well’s modern masterpiece is conducted with the most eternal transparency—Krell asks “what is this heart” and lets you look right into his own." "What Is This Heart?"