Reduced spontaneous baroreflex response slope during lower body negative pressure after 28 days of head-down bed rest.
Effects of 28 days of continuous 6 degrees head-down tilt bed rest on spontaneous vagally mediated baroreflex response slope were evaluated from beat-by-beat relationships between R-R interval and systolic arterial blood pressure. Twelve healthy men (age 27-42 yr) were assigned to either countermeasure (CM) or no-countermeasure (no-CM) groups. CM consisted of strenuous short-term exercise once per day 6 days/wk from days 7 to 28 and lower body negative pressure (LBNP) for 15 min on days 16, 18, 20, and 22-28. Spontaneous baroreflex slope was evaluated by application of linear regression to sequences of at least three beats in which systolic blood pressure and R-R interval changed in the same direction. Measurements were made pre-, mid- (day 15), and post-bed rest at rest and during progressive LBNP tests (3 min at each of -20, -30, -40, and -50 mmHg). R-R interval decreased progressively and significantly (P < 0.0001) over duration of bed rest. Spontaneous baroreflex slope at rest in pre-bed rest was 18.5 +/- 2.1 ms/mm Hg for CM and 14.9 +/- 1.6 ms/mmHg for no-CM. There was a significant reduction in baroreflex slope as a function of bed rest, and it was further reduced during LBNP (P < 0.0001). Between CM and no-CM groups differences existed, but these were present pre-bed rest and appeared unaffected by countermeasures.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Kinesiology, University of Waterloo, Ontario, Canada.
R L
RL
Hughson
A
A
Maillet
C
C
Gharib
J O
JO
Fortrat
Y
Y
Yamamoto
A
A
Pavy-Letraon
D
D
Rivière
A
A
Güell
D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology; D018493:Cardiovascular Deconditioning / Q000502:physiology; D002395:Catecholamines / Q000097:blood; D015444:Exercise / Q000502:physiology; D018475:Head-Down Tilt; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007024:Hypotension, Orthostatic; D008150:Lower Body Negative Pressure; D008297:Male; D009334:Neck Muscles / Q000502:physiology; D010953:Plasma Volume / Q000502:physiology; D018544:Weightlessness Countermeasures; D018474:Weightlessness Simulation
D002395:Catecholamines