title: Cardiovascular changes of conscious rats after simulated microgravity with and without daily -Gx gravitation.
abstract: This study was designed to test the hypothesis that postsuspension cardiovascular manifestation in conscious rats after a medium-term (28-day) tail suspension (SUS) is hypertensive and tachycardiac and can be prevented by a countermeasure of daily 1-h dorsoventral (-G(x)) gravitation provided by standing (STD). To assess associated changes in cardiovascular regulation, blood pressure (BP) and heart rate (HR) variability were 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/day -G(x) 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 indexes [recurrence percentage (RC%), determinism percentage (DT%), and the longest diagonal line (L(max))] 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 -G(x) for as short as 1 h is sufficient to prevent postsuspension 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.
authors.affiliation: Department of Aerospace Physiology, Fourth Military Medical University, Xi'an, China. zhanglf@fmmu.edu.cn
authors.forename: Li-Fan
authors.initials: LF
authors.lastname: Zhang
authors.forename: Jiu-Hua
authors.initials: JH
authors.lastname: Cheng
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.forename: Shouyan
authors.initials: S
authors.lastname: Wang
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Hong-Bing
authors.initials: HB
authors.lastname: Lu
authors.forename: Jin
authors.initials: J
authors.lastname: Ma
mesh_terms: D000818:Animals; D001341:Autonomic Nervous System / Q000503:physiopathology*; D001794:Blood Pressure; D002319:Cardiovascular System / Q000294:innervation*; D006339:Heart Rate; D019417:Hindlimb Suspension / Q000009:adverse effects; D006973:Hypertension / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D008297:Male; D023421:Models, Animal; D008955:Models, Cardiovascular; D017711:Nonlinear Dynamics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012815:Signal Processing, Computer-Assisted; D013610:Tachycardia / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D013997:Time Factors; D018544:Weightlessness Countermeasures; D018474:Weightlessness Simulation / Q000009:adverse effects*