title: Comparison of acute cardiovascular responses to water immersion and head-down tilt in humans.
abstract: The hypothesis was tested that acute water immersion to the neck (WI) compared with 6 degrees head-down tilt (HDT) induces a more pronounced distension of the heart and lower plasma levels of vasoconstrictor hormones. Ten healthy males underwent 30 min of HDT, WI, and a seated control (randomized). During WI, left atrial diameter and stroke volume increased to the same extent as during HDT. Cardiac output increased by 1 l/min more during WI than during HDT. (P < 0.05). Plasma atrial natriuretic peptide increased during WI (P < 0.05) but not during HDT, whereas plasma norepinephrine, vasopressin, and renin activity were suppressed similarly. Mean arterial pressure decreased by 9 mmHg (P < 0.05) during HDT and was unchanged during WI, and heart rate decreased more during HDT (P < 0.05). Arterial pulse pressure increased considerably more during HDT than during WI. In conclusion, the hypothesis was not confirmed because the cardiac atria were similarly distended by acute HDT and WI and the release of vasoconstrictor hormones were suppressed to the same extent.
authors.affiliation: Neurology Division, St. Marianna University School of Medicine, Kawasaki, Kanagawa 216-8511, Japan. shira@marianna-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Shiraishi
authors.forename: Morten
authors.initials: M
authors.lastname: Schou
authors.forename: Mikkel
authors.initials: M
authors.lastname: Gybel
authors.forename: Niels Juel
authors.initials: NJ
authors.lastname: Christensen
authors.forename: Peter
authors.initials: P
authors.lastname: Norsk
mesh_terms: D000328:Adult; D009320:Atrial Natriuretic Factor / Q000097:blood; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D002496:Central Venous Pressure / Q000502:physiology; D004562:Electrocardiography; D018475:Head-Down Tilt / Q000502:physiology*; D006321:Heart / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D007101:Immersion / Q000503:physiopathology*; D008297:Male; D009318:Natriuresis / Q000502:physiology; D009490:Neurosecretory Systems / Q000502:physiology; D009994:Osmolar Concentration; D013318:Stroke Volume / Q000502:physiology; D014661:Vasoconstriction / Q000502:physiology; D018474:Weightlessness Simulation
chemical_list: D009320:Atrial Natriuretic Factor