title: Exercise with and without gravitational gradient:  evaluation with the new random access mass spectrometer (RAMS).
abstract: Gravity adds about 40-50 mmHg perfusion pressure to the arterial supply of the quadriceps muscles in the upright posture.  This could have important implications in supply of blood flow during exercise.  Recently, we have shown that when subjects exercise in the supine posture the rate of increase in VO2 is considerably slower then when cycling exercise takes place in the upright posture.  The most probable explanation for this slower adaptation was the altered perfusion gradient.  Indeed, when the perfusion gradient from heart to legs was restored by placing the lower part of the body of supine subjects in a negative pressure chamber, the rate of increase in VO2 returned to upright values.  The hypothesis advanced from these studies was that skeletal muscle blood flow was reduced at the onset of supine exercise.  Exercise in the microgravity environment of space should be similar to that in the supine posture.  The only experiments conducted in space to this date that have addressed the question of cardiorespiratory adaptation to changing work rates were performed on the German D2 mission using the methodology proposed by Stegemann and colleagues.  To conduct these experiments, it is necessary to utilize sensitive breath-by-breath technology.  Recently, NASA and the Russian space programs have commissioned a new mass spectrometer based system as part of the GASMAP project.  It was the purpose of this study to evaluate the new mass spectrometer under conditions in which the gravitational effects on the cardiorespiratory response were being challenged.
authors.affiliation: Department of Kinesiology, University of Waterloo, Canada.
authors.forename: R L
authors.initials: RL
authors.lastname: Hughson
authors.forename: J K
authors.initials: JK
authors.lastname: Shoemaker
authors.forename: M E
authors.initials: ME
authors.lastname: Tschakovsky
authors.forename: D
authors.initials: D
authors.lastname: Corsale
authors.forename: B H
authors.initials: BH
authors.lastname: Dietrich
mesh_terms: D000328:Adult; D004867:Equipment Design; D016552:Ergometry / Q000295:instrumentation; D005069:Evaluation Studies as Topic; D015444:Exercise / Q000502:physiology*; D005260:Female; D006112:Gravitation; D006801:Humans; D008297:Male; D013058:Mass Spectrometry / Q000295:instrumentation*; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D011187:Posture / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D016683:Supine Position