Submitted on February 16, 2008
Accepted on July 30, 2008
Cardiovascular Changes of Conscious Rats after simulated microgravity with and without daily −Gx Gravitation
Li-Fan Zhang1*, Jiu-Hua Cheng1, Xin Liu2, Shouyan Wang3, Yang Liu2, Hong-Bing Lu2, and Jin Ma4
1 Aerospace Physiology, Fourth Military Medical University, Xi'an, Shaanxi, China
2 Computer Application, Fourth Military Medical University, Xi'an, Shaanxi, China
3 Institute of Sound and Vibration Research, University of Southampton, Southampton, United Kingdom
4 Aerospace Physiology, Fourth Military Medical University, United States
* To whom correspondence should be addressed. E-mail: zhanglf{at}fmmu.edu.cn.
This study was designed to test the hypothesis that post-suspension cardiovascular manifestation in conscious rats after a medium-term (28-day) tail-suspension (SUS) is hypertensive and tachycardiac and which can be prevented by a countermeasure of daily 1-h dorsoventral (-Gx) gravitation provided by standing (STD). To assess associated changes in cardiovascular regulation, BP and HR variability was analyzed by spectral analysis computed by parametric autoregressive (AR) method and by nonlinear recurrence quantification analysis (RQA) and approximate entropy (ApEn) measure. The results showed that conscious SUS rats manifested hypertensive and tachycardiac response before and after being released from suspension compared with the controls and the countermeasure of 1 h/d -Gx prevented the hypertensive response. Auto- and cross-spectral analysis and transfer function analysis did not show significant changes in cardiovascular variability. However, SUS decreased the three RQA indices (RC%, DT%, and Lmax) of systolic BP, whereas STD alleviated these changes. ApEn values of HR data sets were significantly higher in the SUS and SUS+STD groups compared with those of the control group before and after release from suspension. The present study has demonstrated that daily -Gx for as short as 1 h is sufficient to prevent post-suspension cardiovascular alteration in conscious rats after a medium-term SUS. Nonlinear measures, but not spectral analysis, might provide promising data to estimate the overall changes in cardiovascular autonomic regulation due to microgravity exposure.
