title: Decreased heart rate variability responses during early postoperative mobilization--an observational study.
abstract: BACKGROUND
  Intact orthostatic blood pressure regulation is essential for early mobilization after surgery. However, postoperative orthostatic hypotension and intolerance (OI) may delay early ambulation. The mechanisms of postoperative OI include impaired vasopressor responses relating to postoperative autonomic dysfunction. Thus, based on a previous study on haemodynamic responses during mobilization before and after elective total hip arthroplasty (THA), we performed secondary analyses of heart rate variability (HRV) and aimed to identify possible abnormal postoperative autonomic responses in relation to postural change.
  
  
  METHODS
  A standardized mobilization protocol before, 6 and 24 h after surgery was performed in 23 patients scheduled for elective THA. Beat-to-beat arterial blood pressure was measured by photoplethysmography and HRV was derived from pulse wave interbeat intervals and analysed in the time and frequency domain as well as by non-linear analysis using sample entropy
  
  
  RESULTS
  Before surgery, arterial pressures and HR increased upon standing, while HRV low (LF) and high frequency (HF) components remained unchanged. At 6 and 24 h after surgery, resting total HRV power, sample entropy and postural responses in arterial pressures decreased compared to preoperative conditions. During standing HF variation increased by 16.7 (95 % CI 8.0-25.0) normalized units (nu) at 6 h and 10.7 (2.0-19.4) nu at 24 h compared to the preoperative evaluation. At 24 h the LF/HF ratio decreased from 1.8 (1.2-2.6) nu when supine to 1.2 (0.8-1.8) nu when standing.
  
  
  CONCLUSIONS
  This study observed postoperative autonomic cardiovascular dysregulation that may contribute to limited HRV responses during early postoperative mobilization.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT01089946.
authors: Section of Surgical Pathophysiology, Copenhagen University Hospital, Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen, Denmark. oeivind.jans@regionh.dk.|The Lundbeck Centre for Fast-track Hip and Knee Arthroplasty, Rigshospitalet, Copenhagen, Denmark. oeivind.jans@regionh.dk.
authors: Øivind
authors: Ø
authors: Jans
authors: Coordinating Research Centre, Frederiksberg Hospital, Frederiksberg, Denmark. louise.brinth@regionh.dk.
authors: Louise
authors: L
authors: Brinth
authors: Section of Surgical Pathophysiology, Copenhagen University Hospital, Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen, Denmark. henrik.kehlet@regionh.dk.|The Lundbeck Centre for Fast-track Hip and Knee Arthroplasty, Rigshospitalet, Copenhagen, Denmark. henrik.kehlet@regionh.dk.
authors: Henrik
authors: H
authors: Kehlet
authors: Coordinating Research Centre, Frederiksberg Hospital, Frederiksberg, Denmark. jesper.mehlsen@regionh.dk.
authors: Jesper
authors: J
authors: Mehlsen
mesh_terms: D004434:Early Ambulation / Q000706:statistics & numerical data*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period