Effectiveness of Daily Short-Duration Standing in Preventing Post-Suspension Cardiovascular Dysfunction in Rats Assessed by Cardiovascular Signal Analysis

The aim of the present study was to clarify whether simulated microgravity-induced post-suspension cardiovascular deconditioning in rats could be prevented by daily short-duration standing (STD). Three groups of rats were used as subjects to perform the experiments. Compared to a control group of male Sprague-Dawley rats (CON), a group of rats with tail-suspension (SUS) for 28 d was used to simulate cardiovascular deconditioning due to microgravity. Another group of tailed-suspended rats with daily STD for 1 h was used to provide -Gx (dorso-ventral) gravitational loading as countermeasure. In addition to hemodynamic changes to head-up tilt, blood pressure variability (BPV) signals were also analyzed by spectral and nonlinear analysis. The results showed: 1) blood pressure immediately decreased after head-up tilt in all three groups. After several minutes, blood pressure could restore to the initial condition in both CON and SUS+STD group, but the recovery process was slower in the latter group. In contrast, the recovery process was the slowest in the SUS group and could not restore to the initial level completely. 2) In frequency domain, power spectra has similar pattern in CON and SUS+STD group. However, they are quite different in the SUS group in that spectra peak is obvious increased in very low frequency and spectra is narrower and higher in high frequency. 3) By nonlinear analysis of systolic blood pressure (SBP), it is clearly that approximate entropy (ApEn) value is similar in CON and SUS+STD groups, while the ApEn value of SUS group is higher as compared wit them. Our preliminary data have indicated that daily short-duration standing may help to prevent simulated microgravity-induced cardiovascular dysfunction in intact animal too. These results also suggest potential benefit of intermittent artificial gravity in preventing postspaceflight cardiovascular dysfunction