title: Determination of heart rate variability with an electronic stethoscope.
abstract: BACKGROUND
  Heart rate variability (HRV) is widely used to characterize cardiac autonomic function by measuring beat-to-beat alterations in heart rate. Decreased HRV has been found predictive of worse cardiovascular (CV) outcomes. HRV is determined from time intervals between QRS complexes recorded by electrocardiography (ECG) for several minutes to 24 h. Although cardiac auscultation with a stethoscope is performed routinely on patients, the human ear cannot detect heart sound time intervals. The electronic stethoscope digitally processes heart sounds, from which cardiac time intervals can be obtained.
  
  
  METHODS
  Accordingly, the objective of this study was to determine the feasibility of obtaining HRV from electronically recorded heart sounds. We prospectively studied 50 subjects with and without CV risk factors/disease and simultaneously recorded single lead ECG and heart sounds for 2 min.
  
  
  RESULTS
  Time and frequency measures of HRV were calculated from R-R and S1-S1 intervals and were compared using intra-class correlation coefficients (ICC).
  
  
  CONCLUSIONS
  The majority of the indices were strongly correlated (ICC 0.73-1.0), while the remaining indices were moderately correlated (ICC 0.56-0.63). In conclusion, we found HRV measures determined from S1-S1 are in agreement with those determined by single lead ECG, and we demonstrate and discuss differences in the measures in detail. In addition to characterizing cardiac murmurs and time intervals, the electronic stethoscope holds promise as a convenient low-cost tool to determine HRV in the hospital and outpatient settings as a practical extension of the physical examination.
authors.affiliation: Division of Cardiovascular Medicine, State University of New York Downstate Medical Center, Brooklyn, NY 11203-2098, USA.
authors.forename: Haroon
authors.initials: H
authors.lastname: Kamran
authors.forename: Isaac
authors.initials: I
authors.lastname: Naggar
authors.forename: Francisca
authors.initials: F
authors.lastname: Oniyuke
authors.forename: Mercy
authors.initials: M
authors.lastname: Palomeque
authors.forename: Priya
authors.initials: P
authors.lastname: Chokshi
authors.forename: Louis
authors.initials: L
authors.lastname: Salciccioli
authors.forename: Mark
authors.initials: M
authors.lastname: Stewart
authors.forename: Jason M
authors.initials: JM
authors.lastname: Lazar
mesh_terms: D000328:Adult; D000368:Aged; D002309:Cardiology / Q000295:instrumentation*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D019023:Stethoscopes; D055815:Young Adult