title: Acute hemodynamic responses to weightlessness during parabolic flight.
abstract: Pilots and astronauts experience fluid shifts in variable gravity. Acute effects of fluid shifts on the cardiovascular system were monitored on NASA's KC-135 aircraft during parabolic flight. The variability of R-R intervals in the electrocardiogram was measured as an indication of vagal cardiac neural activity. R-R intervals were measured during the gravity transition from 2-G to 0-G produced by parabolic flight to assess the involvement of the autonomic nervous system in regulating the acute effects of fluid shifts. In seven subjects, a BoMed noninvasive continuous cardiac output monitor (NCCOM 3) monitored thoracic fluid index (TFI, ohms), heart rate (bpm), and cardiac output (1/min). Data were stored on a lap-top computer with the subject in one of four postures: sitting, standing, supine, and semi-supine, during one of four sets of eight to ten parabolas. Five seconds of data were averaged: before parabola onset (1.3-G); parabola entry (1.9-G); 0-G; and parabola exit (1.7-G). Three to eight parabolas were averaged for subjects in each posture; the mean for each posture was calculated. In each of five additional subjects, the coefficient of variation was calculated by dividing mean value by the standard deviation of 3 to 15 R-R intervals. Eight to ten parabolas were averaged for each postural set. Compared with values collected before 0-G, standing values during 0-G showed that the thoracic fluid index decreased 2.5 ohms, heart rate decreased 22 bpm, and cardiac output increased 1 L/min. During sitting, thoracic fluid index decreased 1.25 ohms, heart rate decreased 10 bpm, whereas cardiac output increased 0.5 L/min.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: NASA/Johnson Space Center, Houston, Texas 77058.
authors.forename: C N
authors.initials: CN
authors.lastname: Mukai
authors.forename: C M
authors.initials: CM
authors.lastname: Lathers
authors.forename: J B
authors.initials: JB
authors.lastname: Charles
authors.forename: B S
authors.initials: BS
authors.lastname: Bennett
authors.forename: M
authors.initials: M
authors.lastname: Igarashi
authors.forename: S
authors.initials: S
authors.lastname: Patel
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology; D001826:Body Fluids / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D004562:Electrocardiography; D005260:Female; D006112:Gravitation; D006321:Heart / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture; D013909:Thorax / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology; D014893:Weightlessness / Q000009:adverse effects*