title: Use of Bioimpedance to Assess Changes in Hemodynamics During Acute Administration of CPAP.
abstract: BACKGROUND
  Attempts to investigate the mechanisms by which continuous positive airway pressure (CPAP) therapy improves heart function in patients with obstructive sleep apnea (OSA) have been limited by the lack of non-invasive methods to assess cardiac performance. We used transthoracic electrical bioimpedance (TEB) to assess acute hemodynamic changes including heart rate (HR), stroke volume (SV), cardiac output (CO) and cardiac index (CI) during PAP titration in (1) post-operative cardiac surgery patients, (2) patients with severe OSA, and (3) normal healthy volunteers.
  
  
  METHODS
  Post-operative cardiac surgery patients were studied via TEB and pulmonary artery catheter (PAC) during acute titration of positive end-expiratory pressure (PEEP) while mechanically ventilated. Patients with severe OSA were studied non-invasively by TEB during acute CPAP titration in supine stage 2 sleep, and normal subjects while awake and recumbent.
  
  
  RESULTS
  In post-operative cardiac surgery patients (n = 3), increasing PEEP to 18 cmH2O significantly reduced SV and CI relative to baseline. There was no difference between TEB and PAC in terms of ability to assess variations in hemodynamic parameters. In patients with severe OSA (n = 3), CPAP titration to optimal pressure to alleviate obstructive apneas reduced HR, SV, CO and CI significantly compared to without CPAP. In three healthy subjects, maximal tolerated CPAP reduced SV and CO significantly compared to baseline.
  
  
  CONCLUSIONS
  Acute administration of CPAP causes a decrease in CO and CI, apparently a consequence of a reduction in SV. TEB appears to be an accurate and reproducible non-invasive method of detecting changes in hemodynamics.
authors.affiliation: Department of Medicine, Queen's University, Kingston, Ontario, Canada.
authors.forename: Genevieve C
authors.initials: GC
authors.lastname: Digby
authors.affiliation: Department of Medicine, Queen's University, Kingston, Ontario, Canada; Sleep Disorders Laboratory, Kingston General Hospital, Kingston, Ontario, Canada.
authors.forename: Helen S
authors.initials: HS
authors.lastname: Driver
authors.affiliation: Department of Medicine, Queen's University, Kingston, Ontario, Canada; Sleep Disorders Laboratory, Kingston General Hospital, Kingston, Ontario, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Fitzpatrick
authors.affiliation: Department of Surgery, Queen's University, Kingston, Ontario, Canada.
authors.forename: Glorianne
authors.initials: G
authors.lastname: Ropchan
authors.affiliation: Department of Medicine, Queen's University, Kingston, Ontario, Canada; Department of Physiology, Queen's University, Kingston, Ontario, Canada.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Parker
keywords: Continuous positive airway pressure; Obstructive sleep apnea; Pulmonary artery catheters; Transthoracic electrical bioimpedance