title: Breathing at a rate of 5.5 breaths per minute with equal inhalation-to-exhalation ratio increases heart rate variability.
abstract: OBJECTIVE
  Prior studies have found that a breathing pattern of 6 or 5.5 breaths per minute (bpm) was associated with greater heart rate variability (HRV) than that of spontaneous breathing rate. However, the effects of combining the breathing rate with the inhalation-to-exhalation ratio (I:E ratio) on HRV indices are inconsistent. This study aimed to examine the differences in HRV indices and subjective feelings of anxiety and relaxation among four different breathing patterns.
  
  
  METHODS
  Forty-seven healthy college students were recruited for the study, and a Latin square experimental design with a counterbalance in random sequences was applied. Participants were instructed to breathe at two different breathing rates (6 and 5.5 breaths) and two different I:E ratios (5:5 and 4:6). The HRV indices as well as anxiety and relaxation levels were measured at baseline (spontaneous breathing) and for the four different breathing patterns.
  
  
  RESULTS
  The results revealed that a pattern of 5.5 bpm with an I:E ratio of 5:5 produced a higher NN interval standard deviation and higher low frequency power than the other breathing patterns. Moreover, the four different breathing patterns were associated with significantly increased feeling of relaxation compared with baseline.
  
  
  CONCLUSIONS
  The study confirmed that a breathing pattern of 5.5 bpm with an I:E ratio of 5:5 achieved greater HRV than the other breathing patterns. This finding can be applied to HRV biofeedback or breathing training in the future.
authors.affiliation: Department of Psychology, Kaohsiung Medical University, No 100, Shiquan 1st Rd., Kaohsiung City 807, Taiwan. Electronic address: psyiml@kmu.edu.tw.
authors.forename: I M
authors.initials: IM
authors.lastname: Lin
authors.affiliation: Department of Psychology, Kaohsiung Medical University, No 100, Shiquan 1st Rd., Kaohsiung City 807, Taiwan. Electronic address: qaziiizaq@yahoo.com.tw.
authors.forename: L Y
authors.initials: LY
authors.lastname: Tai
authors.affiliation: Institute of Gerontology, National Cheng Kung University, No. 1, University Road, Tainan City 701, Taiwan. Electronic address: dibe1011@yahoo.com.tw.
authors.forename: S Y
authors.initials: SY
authors.lastname: Fan
mesh_terms: D001007:Anxiety / Q000503:physiopathology / Q000523:psychology; D004562:Electrocardiography; D045853:Exhalation / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D056152:Respiratory Rate / Q000502:physiology; D013997:Time Factors; D064232:Visual Analog Scale; D055815:Young Adult
keywords: Breathing pattern; Heart rate variability; Inhalation-to-exhalation ratio