title: Validation of thoracic impedance cardiography by echocardiography in healthy late pregnancy.
abstract: BACKGROUND
  Assessment of stroke volume (SV) is often necessary in clinical and research settings. The clinically established method for SV assessment in pregnancy is echocardiography, but given its limitations, it is not always an appropriate measurement tool. Thoracic impedance cardiography (ICG) allows continuous, non-invasive SV assessment. However, SV determination relies on assumptions regarding the thoracic shape that may mean the algorithm is not valid in pregnancy. The available data regarding the validity of ICG against an established reference standard using modern SV algorithms are both limited and conflicting. We aimed to test the validity of ICG in a clinically realistic setting in late pregnancy using echocardiography.
  
  
  METHODS
  Twenty-nine women in late pregnancy underwent standard echocardiography assessments with simultaneous ICG measurement. Agreement between devices was tested using Bland-Altman analysis.
  
  
  RESULTS
  Bland-Altman analysis of the relationship between ICG and echocardiography demonstrated that the 95% limits of agreement exceeded acceptable or expected ranges. Measures of maternal and fetal anthropometry do not account for the lack of agreement.
  
  
  CONCLUSIONS
  Absolute values of SV as determined by ICG are not valid in pregnancy. Further work is required to examine the ability of ICG to assess relative changes in maternal haemodynamics in late pregnancy.
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, University of Auckland, Level 12, Support Building, Auckland City Hospital, Private Bag 92019, Auckland, New Zealand. j.mcintyre@auckland.ac.nz.|New Zealand Respiratory and Sleep Institute, Auckland, New Zealand. j.mcintyre@auckland.ac.nz.
authors.forename: Jordan P R
authors.initials: JP
authors.lastname: McIntyre
authors.affiliation: Respiratory Measurement Laboratory, Auckland District Health Board, Auckland, New Zealand. KEllyett@adhb.govt.nz.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Ellyett
authors.affiliation: Department of Paediatrics, University of Auckland, Auckland, New Zealand. e.mitchell@auckland.ac.nz.
authors.forename: Edwin A
authors.initials: EA
authors.lastname: Mitchell
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand. g.quill@auckland.ac.nz.
authors.forename: Gina M
authors.initials: GM
authors.lastname: Quill
authors.affiliation: Department of Paediatrics, University of Auckland, Auckland, New Zealand. j.thompson@auckland.ac.nz.
authors.forename: John Md
authors.initials: JM
authors.lastname: Thompson
authors.affiliation: Department of Epidemiology and Biostatistics, School of Population Health, University of Auckland, Auckland, New Zealand. aw.stewart@auckland.ac.nz.
authors.forename: Alistair W
authors.initials: AW
authors.lastname: Stewart
authors.affiliation: Department of Medicine, University of Auckland, Auckland, New Zealand. r.doughty@auckland.ac.nz.
authors.forename: Robert N
authors.initials: RN
authors.lastname: Doughty
authors.affiliation: Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, University of Auckland, Level 12, Support Building, Auckland City Hospital, Private Bag 92019, Auckland, New Zealand. p.stone@auckland.ac.nz.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Stone
mesh_terms: D000328:Adult; D002307:Cardiography, Impedance / Q000379:methods / Q000592:standards; D057186:Comparative Effectiveness Research; D004452:Echocardiography / Q000379:methods / Q000592:standards; D005260:Female; D006439:Hemodynamics; D006801:Humans; D011247:Pregnancy; D011263:Pregnancy Trimester, Third / Q000502:physiology*; D012015:Reference Standards; D015203:Reproducibility of Results; D013318:Stroke Volume / Q000502:physiology*