Editing Biofeedback (section)

===Electrocardiogram===
The [[electrocardiogram]] (ECG) uses electrodes placed on the torso, wrists, or legs, to measure the electrical activity of the heart and measures the [[interbeat interval]] (distances between successive [[R-wave]] peaks in the [[QRS complex]]). The interbeat interval, divided into 60 seconds, determines the heart rate at that moment. The statistical variability of that interbeat interval is what we call heart rate variability.<ref>{{cite book | vauthors = Berntson GG, Quigley KS, Lozano D | date = 2007 | chapter = Cardiovascular psychophysiology. | veditors = Cacioppo JT, Tassinary LG, Berntson GG | title = Handbook of psychophysiology | edition = 3rd | location = New York | publisher = Cambridge University Press }}</ref> The ECG method is more accurate than the PPG method in measuring heart rate variability.<ref name="Combatalade, D. 2009"/><ref name=":0">{{cite journal | author = Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology | title = Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology | journal = Circulation | volume = 93 | issue = 5 | pages = 1043–65 | date = March 1996 | pmid = 8598068 | doi = 10.1161/01.cir.93.5.1043 }}</ref>

Biofeedback therapists use [[heart rate variability]] (HRV) biofeedback when treating [[asthma]],<ref>{{cite journal | vauthors = Lehrer PM, Vaschillo E, Vaschillo B, Lu SE, Scardella A, Siddique M, Habib RH | title = Biofeedback treatment for asthma | journal = Chest | volume = 126 | issue = 2 | pages = 352–61 | date = August 2004 | pmid = 15302717 | doi = 10.1378/chest.126.2.352 }}</ref> [[COPD]],<ref>{{cite journal | vauthors = Giardino ND, Chan L, Borson S | title = Combined heart rate variability and pulse oximetry biofeedback for chronic obstructive pulmonary disease: preliminary findings | journal = Applied Psychophysiology and Biofeedback | volume = 29 | issue = 2 | pages = 121–33 | date = June 2004 | pmid = 15208975 | doi = 10.1023/B:APBI.0000026638.64386.89 | s2cid = 21774729 }}</ref> depression,<ref name="Preliminary results of an open labe">{{cite journal | vauthors = Karavidas MK, Lehrer PM, Vaschillo E, Vaschillo B, Marin H, Buyske S, Malinovsky I, Radvanski D, Hassett A | display-authors = 6 | title = Preliminary results of an open label study of heart rate variability biofeedback for the treatment of major depression | journal = Applied Psychophysiology and Biofeedback | volume = 32 | issue = 1 | pages = 19–30 | date = March 2007 | pmid = 17333315 | doi = 10.1007/s10484-006-9029-z | s2cid = 31614375 }}</ref> anxiety,<ref>{{cite journal | vauthors = Trousselard M, Canini F, Claverie D, Cungi C, Putois B, Franck N | title = Cardiac Coherence Training to Reduce Anxiety in Remitted Schizophrenia, a Pilot Study | journal = Applied Psychophysiology and Biofeedback | volume = 41 | issue = 1 | pages = 61–9 | date = March 2016 | pmid = 26346569 | pmc = 4749648 | doi = 10.1007/s10484-015-9312-y }}</ref> [[fibromyalgia]],<ref>{{cite journal | vauthors = Hassett AL, Radvanski DC, Vaschillo EG, Vaschillo B, Sigal LH, Karavidas MK, Buyske S, Lehrer PM | display-authors = 6 | title = A pilot study of the efficacy of heart rate variability (HRV) biofeedback in patients with fibromyalgia | journal = Applied Psychophysiology and Biofeedback | volume = 32 | issue = 1 | pages = 1–10 | date = March 2007 | pmid = 17219062 | doi = 10.1007/s10484-006-9028-0 | s2cid = 17033799 }}</ref> [[heart disease]],<ref>{{cite journal | vauthors = Cowan MJ, Pike KC, Budzynski HK | title = Psychosocial nursing therapy following sudden cardiac arrest: impact on two-year survival | journal = Nursing Research | volume = 50 | issue = 2 | pages = 68–76 | year = 2001 | pmid = 11302295 | doi = 10.1097/00006199-200103000-00002 }}</ref> and unexplained [[abdominal pain]].<ref>{{cite journal | vauthors = Humphreys PA, Gevirtz RN | title = Treatment of recurrent abdominal pain: components analysis of four treatment protocols | journal = Journal of Pediatric Gastroenterology and Nutrition | volume = 31 | issue = 1 | pages = 47–51 | date = July 2000 | pmid = 10896070 | doi = 10.1097/00005176-200007000-00011 | doi-access = free }}</ref> Research shows that HRV biofeedback can also be used to improve physiological and psychological wellbeing in healthy individuals.<ref name = "Barrios-Choplin_1997">{{cite journal | vauthors = Barrios-Choplin BO, McCraty RO, Cryer B |date=July 1997 |title=An inner quality approach to reducing stress and improving physical and emotional wellbeing at work|journal=Stress Medicine |volume=13 |issue=3 |pages=193–201 |doi=10.1002/(sici)1099-1700(199707)13:3<193::aid-smi744>3.0.co;2-i }}</ref>

HRV data from both polyplethysmographs and electrocardiograms are analyzed via mathematical transformations such as the commonly-used [[fast Fourier transform]] (FFT).<ref name=":0" /> The FFT splits the HRV data into a [[Spectral density|power spectrum]], revealing the waveform's constituent frequencies.<ref name="Combatalade, D. 2009" /> Among those constituent frequencies, high-frequency (HF) and low-frequency (LF) components are defined as above and below .15&nbsp;Hz, respectively. As a rule of thumb, the LF component of HRV represents sympathetic activity, and the HF component represents parasympathetic activity. The two main components are often represented as a LF/HF ratio and used to express sympathovagal balance.<ref name="Combatalade, D. 2009" /> Some researchers consider a third, medium-frequency (MF) component from .08&nbsp;Hz to .15&nbsp;Hz, which has been shown to increase in power during times of appreciation.<ref>{{cite journal | vauthors = McCraty R, Atkinson M, Tiller WA, Rein G, Watkins AD | title = The effects of emotions on short-term power spectrum analysis of heart rate variability | journal = The American Journal of Cardiology | volume = 76 | issue = 14 | pages = 1089–93 | date = November 1995 | pmid = 7484873 | doi = 10.1016/s0002-9149(99)80309-9 }}</ref>