title: Upright cardiac output measurements in the transition to weightlessness during parabolic flights.
abstract: OBJECTIVE
  Aims of this study were: 1) to determine cardiac output by inert gas rebreathing (CO(reb)) during transition into 0 Gz in the standing position; and 2) to compare impedance cardiography (ICG) and pulse contour method (PCM) with CO(reb) as a reference method.
  
  
  METHODS
  We measured baseline CO(reb) and heart rate (HR) on the ground, and CO(reb), CO(pcm), CO(icg), and HR in standing and supine positions in the transition to weightlessness in six subjects. We conducted repeated measures ANOVA, Bland and Altman analysis, and analysis of percentage error of each data set.
  
  
  RESULTS
  CO(reb) rose from 5.03 +/- 0.7 upright ground control to 11.45 +/- 3.6 L x min(-1) in 0 Gz. HR and stroke volume (SV) rose from 83 +/- 14 to 113 +/- 19 bpm and from 61 +/- 6 to 99 +/- 18 ml, respectively. Mean CO(reb), CO(pcm), and CO(icg) across all conditions were 10.45 +/- 3.04, 7.42 +/- 1.71, and 6.57 +/- 2.46 L x min(-1), respectively. Overall Bland and Altman analysis showed poor agreement for CO(pcm) and CO(icg) compared to CO(reb).
  
  
  CONCLUSIONS
  Large bias for both comparisons indicated that both PCM and ICG underestimate the true CO value. Paired CO values of individual subjects showed a better correlation between methods and a broad bias range, indicating a preponderant role for large between-subjects variability. Repeated CO(reb) determinations in 1 Cz (i.e., when the cardiovascular system is in a steady state) should be used for calibration of the PCM and of ICG data. PCM and ICG can then be used to track CO dynamics during rapid changes of acceleration profiles.
authors.affiliation: German Aerospace Center (DLR), Institute of Aerospace Medicine, Space Physiology, Cologne, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Limper
authors.forename: Peter
authors.initials: P
authors.lastname: Gauger
authors.forename: Luis E J
authors.initials: LE
authors.lastname: Beck
mesh_terms: D000328:Adult; D002302:Cardiac Output; D005260:Female; D006334:Heart Function Tests / Q000379:methods*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D005741:Noble Gases; D013026:Space Flight; D013318:Stroke Volume; D018474:Weightlessness Simulation
chemical_list: D005741:Noble Gases