Parasympathetic activity during parabolic flight, effect of LBNP during microgravity.
OBJECTIVE
During parabolic flight, in the standing position, changes are partly due to an acute shift in fluid between the lower extremities, the head and the thorax (Vaïda P, et al. J Appl Physiol 1997; 82:1091-7; and Bailliart O, et al. J Appl Physiol 1998; 85:2100-5). We hypothesized that modifications of parasympathetic activity associated with changes in hydrostatic pressure gradients induced by changes in gravity could be detected by analysis of short time periods.


METHODS
We assessed heart rate variability (HRV) in 11 healthy volunteers by indices of temporal analysis (NN, SDNN, RMSSD) and normalized indices such as coefficients of variation CV-SDNN and CV-RMSSD and ratio SDNN/RMSSD. A lower body negative pressure (LBNP) at -50 mm Hg was randomly applied during the microgravity phase (0 Gz) to counteract the lack of hydrostatic pressure in the lower part of the body.


RESULTS
NN, CV-SDNN and CV-RMSSD decreased during hypergravity phases and increased during microgravity and during early normogravity (1 Gz) period at the end of parabolas. With LBNP changes are less pronounced at 0 Gz and in the 1 Gz post parabolic period.


CONCLUSIONS
We concluded that parasympathetic nervous activity is recordable by temporal analysis of HRV during short periods of time. LBNP applied during 0 Gz phase reduced the parasympathetic activation at 0 Gz and post parabolic 1 Gz.
Capderou
A
A
Laboratoire de Physiologie CCML, Le Plessis-Robinson, Université Paris XI, UPRES EA2397, France. capderou@ccml.com
Bailliart
O
O
Maison-Blanche
P
P
Kedra
A W
AW
Atkov
O
O
Techoueyres
P
P
Lachaud
J L
JL
Vaïda
P
P
D000328:Adult; D000704:Analysis of Variance; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000502:physiology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology; D008150:Lower Body Negative Pressure; D008297:Male; D008875:Middle Aged; D010275:Parasympathetic Nervous System / Q000502:physiology*; D011187:Posture / Q000502:physiology; D013026:Space Flight; D018561:Space Simulation / Q000009:adverse effects; D014893:Weightlessness / Q000009:adverse effects*