title: Combat casualties undergoing lifesaving interventions have decreased heart rate complexity at multiple time scales.
abstract: OBJECTIVE
  We found that heart rate (HR) complexity metrics such as sample entropy (SampEn) identified patients with trauma receiving lifesaving interventions (LSIs). We now aimed (1) to test a multiscale entropy (MSE) index, (2) to compare it to single-scale measures including SampEn, and (3) to assess different parameter values for calculation of SampEn and MSE.
  
  
  METHODS
  This was a study of combat casualties in an emergency department in Iraq. Electrocardiograms of 70 acutely injured adults were recorded. Twelve underwent LSIs and 58 did not. Lifesaving interventions included endotracheal intubation (9), tube thoracostomy (9), and emergency transfusion (4). From each electrocardiogram, a segment of 800 consecutive beats was selected. Offline, R waves were detected and R-to-R interval time series were generated. Sample entropy, MSE, and time-domain measures of HR variability (mean HR, SD, the proportion of pairs of consecutive NN intervals that differ by more than 20 and 50 milliseconds, square root of the mean of the squares of differences between adjacent NN intervals) were computed.
  
  
  RESULTS
  Differences in mean HR (LSI: 111 ± 33, non-LSI: 90 ± 17 beats/min) were not significant. Systolic arterial pressure was statistically but not clinically different (LSI: 123 ± 19, non-LSI: 135 ± 19 mm Hg). Sample entropy (LSI: 0.90 ± 0.42, non-LSI: 1.19 ± 0.35; P < .05) and MSE index (LSI: 2.58 ± 2.55, non-LSI: 5.67 ± 2.48; P < .001) differed significantly.
  
  
  CONCLUSIONS
  Complexity of HR dynamics over a range of time scales was lower in high-risk than in low-risk combat casualties and outperformed traditional vital signs.
authors.affiliation: US Army Institute of Surgical Research, Fort Sam Houston, TX. Electronic address: divego99@gmail.com.
authors.forename: Leopoldo C
authors.initials: LC
authors.lastname: Cancio
authors.forename: Andriy I
authors.initials: AI
authors.lastname: Batchinsky
authors.forename: William L
authors.initials: WL
authors.lastname: Baker
authors.forename: Corina
authors.initials: C
authors.lastname: Necsoiu
authors.forename: José
authors.initials: J
authors.lastname: Salinas
authors.forename: Ary L
authors.initials: AL
authors.lastname: Goldberger
authors.forename: Madalena D
authors.initials: MD
authors.lastname: Costa
mesh_terms: D000328:Adult; D001803:Blood Transfusion; D004562:Electrocardiography; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal; D054542:Iraq War, 2003-2011; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods; D013907:Thoracostomy; D014947:Wounds and Injuries / Q000503:physiopathology* / Q000628:therapy*
keywords: Electrocardiography; Entropy; Heart rate; Iraq War 2003; Nonlinear dynamics; Wounds and injuries