title: Evaluation of spontaneous baroreflex response after 28 days head down tilt bedrest.
abstract: The spontaneous baroreflex response was evaluated during supine rest and head up tilt (60 degrees) before and immediately after a 28 day 6 degrees HDT bedrest in 6 healthy adult men (age 30-42 years). Sequences of 3 or more beats where RR-interval and systolic blood pressure changed in the same direction were used to evaluate baroreflex response slope (BRS). Prior to bedrest, the mean BRS and RR-interval were 18.0 +/- 3.9 ms/mm Hg and 926 +/- 61 ms at rest and 10.5 +/- 2.5 ms/mm Hg and 772 +/- 63 ms during the first 10 min of 60 degrees tilt. Following bedrest, these values changed to 15.6 +/- 2.7 ms/mm Hg and 780 +/- 53 ms at rest, and to 6.5 +/- 1.2 ms/mm Hg and 636 +/- 44 ms during tilt. Thus, (1) the spontaneous baroreflex can be evaluated in human subjects during experiments of orthostatic stress; (2) the baroreflex slope was reduced on going from supine to the head up tilt position; and (3) 28 days of bedrest reduced the spontaneous baroreflex slope.
authors.affiliation: Department of Kinesiology, University of Waterloo, Canada.
authors.forename: R L
authors.initials: RL
authors.lastname: Hughson
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: G C
authors.initials: GC
authors.lastname: Butler
authors.forename: A
authors.initials: A
authors.lastname: Guell
authors.forename: C
authors.initials: C
authors.lastname: Gharib
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D017704:Baroreflex / Q000502:physiology*; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology*; D005081:Exercise Therapy; D018475:Head-Down Tilt; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007024:Hypotension, Orthostatic / Q000209:etiology; D008150:Lower Body Negative Pressure; D008297:Male; D016683:Supine Position