title: Cardiovascular responses to upright and supine exercise in humans after 6 weeks of head-down tilt (-6 degrees).
abstract: Seven healthy men performed steady-state dynamic leg exercise at 50 W in supine and upright postures, before (control) and repeatedly after 42 days of strict head-down tilt (HDT) (-6 degrees) bedrest. Steady-state heart rate (fc), mean arterial blood pressure, cardiac output (Qc), and stroke volume (SV) were recorded. The following data changed significantly from control values. The fc was elevated in both postures at least until 12 days, but not at 32 days after bedrest. Immediately after HDT, SV and Qc were decreased by 25 (SEM 3)% and 19 (SEM 3)% in supine, and by 33 (SEM 5)% and 20 (SEM 3)% in upright postures, respectively. Within 2 days there was a partial recovery of SV in the upright but not in the supine posture. The SV and Qc during supine exercise remained significantly decreased for at least a month. Submaximal oxygen uptake did not change after HDT. We concluded that the cardiovascular response to exercise after prolonged bedrest was impaired for so long that it suggested that structural cardiac changes had developed during the HDT period.
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institute, Stockholm, Sweden. Patrik.Sundblad@fyfa.ki.se
authors.forename: P
authors.initials: P
authors.lastname: Sundblad
authors.forename: J
authors.initials: J
authors.lastname: Spaak
authors.forename: D
authors.initials: D
authors.lastname: Linnarsson
mesh_terms: D001510:Bed Rest; D001794:Blood Pressure; D002302:Cardiac Output; D015444:Exercise; D018475:Head-Down Tilt / Q000009:adverse effects*; D006339:Heart Rate; D006439:Hemodynamics; D006801:Humans; D018476:Hypokinesia / Q000209:etiology / Q000503:physiopathology*; D007866:Leg / Q000503:physiopathology; D008297:Male; D005082:Physical Exertion; D011187:Posture; D013318:Stroke Volume