title: Stroke volume of the heart and thoracic fluid content during head-up and head-down tilt in humans.
abstract: BACKGROUND
  The stroke volume (SV) of the heart depends on the diastolic volume but, for the intact organism, central pressures are applied widely to express the filling of the heart.
  
  
  METHODS
  This study evaluates the interdependence of SV and thoracic electrical admittance of thoracic fluid content (TA) vs. the central venous (CVP), mean pulmonary artery (MPAP) and pulmonary artery wedge (PAWP) pressures during head-up (HUT) and head-down (HDT) tilt in nine healthy humans.
  
  
  RESULTS
  From the supine position to 20 degrees HDT, SV [112 +/- 18 ml; mean +/- standard deviation (SD)], TA (30.8 +/- 7.1 mS) and CVP (3.6 +/- 0.9 mmHg) did not change significantly, whereas MPAP (from 13.9 +/- 2.7 to 16.1 +/- 2.5 mmHg) and PAWP (from 8.8 +/- 3.4 to 11.3 +/- 2.5 mmHg; P < 0.05) increased. Conversely, during 70 degrees HUT, SV (to 65 +/- 24 ml) decreased, together with CVP (to 0.9 +/- 1.4 mmHg; P < 0.001), MPAP (to 9.3 +/- 3.8 mmHg; P < 0.01), PAWP (to 0.7 +/- 3.3 mmHg; P < 0.001) and TA (to 26.7 +/- 6.8 mS; P < 0.01). However, from 20 to 50 min of HUT, SV decreased further (to 48 +/- 21 ml; P < 0.001), whereas the central pressures did not change significantly.
  
  
  CONCLUSIONS
  During both HUT and HDT, SV of the heart changed with the thoracic fluid content rather than with the central vascular pressures. These findings confirm that the function of the heart relates to its volume rather than to its so-called filling pressures.
authors.affiliation: Department of Medicine, Medium Care Unit, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: J J
authors.initials: JJ
authors.lastname: van Lieshout
authors.forename: M P M
authors.initials: MP
authors.lastname: Harms
authors.forename: F
authors.initials: F
authors.lastname: Pott
authors.forename: M
authors.initials: M
authors.lastname: Jenstrup
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D000328:Adult; D001826:Body Fluids / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology; D002496:Central Venous Pressure / Q000502:physiology; D017097:Electric Impedance; D004562:Electrocardiography; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D011651:Pulmonary Artery / Q000502:physiology; D011669:Pulmonary Wedge Pressure / Q000502:physiology; D013318:Stroke Volume / Q000502:physiology*; D016683:Supine Position / Q000502:physiology; D013909:Thorax / Q000502:physiology