Key result
A 13-day head-down bed rest significantly decreased heart rate approximate entropy during lower body negative pressure testing in healthy young women (P<0.05).
Why the study?
Does head-down bed rest decrease complex physiological heart rate variability during LBNP testing in healthy young adult women?
Does head-down bed rest decrease complex physiological heart rate variability during LBNP testing in healthy young adult women?
p-value: p=< 0.05
Short-term head-down bed rest decreases complex heart rate variability during LBNP testing, suggesting approximate entropy is a sensitive marker of physiological variability loss.
Head-down bed rest may reduce complex heart rate variability; leaves open its value as a spaceflight autonomic model.
Head-down bed rest is used to model physiological changes during spaceflight. We postulated that bed rest would decrease the degree of complex physiological heart rate variability. We analyzed continuous heart rate data from digitized Holter recordings in eight healthy female volunteers (age 28-34 yr) who underwent a 13-day 6 degree head-down bed rest study with serial lower body negative pressure (LBNP) trials. Heart rate variability was measured on 4-min data sets using conventional time and frequency domain measures as well as with a new measure of signal "complexity" (approximate entropy). Data were obtained pre-bed rest (control), during bed rest (day 4 and day 9 or 11), and 2 days post-bed rest (recovery). Tolerance to LBNP was significantly (P < 0.02) reduced on both bed rest days vs. pre-bed rest. Heart rate variability was assessed at peak LBNP. Heart rate approximate entropy was significantly (P < 0.05) decreased at day 4 and day 9 or 11, returning toward normal during recovery. Heart rate standard deviation and the ratio of high- to low-power frequency did not change significantly. We conclude that short-term bed rest is associated with a decrease in the complex variability of heart rate during LBNP testing in healthy young adult women. Measurement of heart rate complexity, using a method derived from nonlinear dynamics ("chaos theory"), may provide a sensitive marker of this loss of physiological variability, complementing conventional time and frequency domain statistical measures.
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Goldberger et al. (1994) studied Healthy volunteers (n=8). Head-down bed rest vs. Pre-bed rest was evaluated on Heart rate approximate entropy at peak LBNP (p=< 0.05). A 13-day head-down bed rest significantly decreased heart rate approximate entropy during lower body negative pressure testing in healthy young women (P<0.05).
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