CCISS,Vascular and BP Reg: Canadian space life science research on ISS

A comprehensive goal of the Canadian Space Agency studies (CCISS, Vascular and BP Reg) has been to investigate the efficacy of current exercise countermeasures to maintain cardiovascular and cerebrovascular health on return to Earth after up to 6-months in space. Results from the CCISS experiments revealed no significant change of in-flight heart rate during daily activities or sleep, and small, but variable between astronauts, post-flight elevation. The between astronaut differences were exaggerated during measurement of spontaneous baroreflex slope, which was reduced post-flight (P<0.05) during paced breathing with 3 astronauts having significant correlations between reduced baroreflex and reduced RR-interval (consistent with reduced fitness). Cerebrovascular autoregulation and CO₂ response were mildly impaired after flight. Some loss of in-flight fitness of astronauts in Vascular was reflected by the increase in HR at a work rate of 161±46 W of 12.3±10.5 bpm, 10.4±5.9 bpm and 13.4±5.7 bpm for early-flight, late-flight and R+1, respectively. On return to gravity, changes in resting heart rate for supine (5.9±3.5 bpm), sit (8.1±3.3 bpm) and stand (10.3±10.0 bpm) were small but variable between individuals (from −5 bpm to +20 bpm in post-flight standing) and not related to the change in exercise heart rate. In Vascular astronauts, pulse wave transit time measured to the finger tended to be reduced post-flight and carotid artery distensibility was significantly reduced (P=0.03, and n=6). The heart rate and baroreflex data suggest that some astronauts return with cardiovascular deconditioning in spite of the exercise regimes. However, greater arterial stiffness is common among all astronauts studied to date. The new CSA project, BP Reg, will monitor inflight blood pressure in an attempt to identify astronauts in greater need for countermeasures. Future research should focus on whether Vascular changes in astronauts might make them an appropriate model to study the mechanisms of arterial aging on Earth.     

Cardiac and vascular adaptation to 0g with and without thigh cuffs (Antares 14 and Altair 21 day Mir spaceflights)

Cardiovascular Actaptation was evaluated on 2 astronauts: one wearing thigh cuffs from flight day 1 to 8 (14d flight), the second without cuffs (21d flight). Ultrasound investigations were performed at rest and during LBNP. Results: Without thigh cuffs the cardiovascular Actaptation consists in (1) the development of a hypovolemia with an increase of the heart rate and the cardiac output, (2) the decrease of the vascular tone in the deep (mesenteric and splanchnic) and peripheral (Lower limbs) vascular areas. The use of thigh cuffs maintains the volemia and the cardiac output at the preflight level (without heart rate increase) and prevents the loss of vascular tone in the deep and peripheral areas. Moreover the adaptative process changes since the cuffs are removed and even the volemia seems to be unaffected at this stage the vascular tone decreases to a comparable extend as during the flight without cuffs. Nevertheless during the flight without cuffs or 3 days after removing the cuffs hemodynamic signs of decreased orthostatic tolerance are present during the inflight and the 3 days post flight LBNP. Presently the possible contribution of the thigh cuffs to the reduction of the vascular deconditioning has not been tested yet.     

模拟失重对心血管自主神经调节功能的影响

载人航天或模拟失重后，航天员会出现运动能力与立位耐力降低，其发生机理与多种因素的改变有关．为进一步验证这种变化与中枢神经系统调节功能障碍的可能相关，本文研究模拟失重过程中心脏与外周血管自主神经调节功能的动态变化及与卧床后立位耐力降低的关系．结果表明，6名被试者的HRV谱的总功率（TP）及低频（LF）、高频（HF）成份均减少，而LF：HF比值在卧床后期有增大趋势．卧床后HUT初始6min所有被试者心率明显快于卧床前的相应值．说明模拟失重后心脏迷走神经反应与外周血管交感神经活动水平降低，心脏交感神经活动水平逐渐升高．但卧床后HUT时心血管自主神经调节反应基本正常．     

立位加下身负压时的心血管反应

本实验采用了立位加下身负压方法(负-立方法)模拟航天员返回地面后受到的重力刺激,检查了20名健康受试者在单纯立位和负-立时的心血管反应。按照受试者在负-立时的心率、外周阻力和耐受时间,将受试者分为四种不同的反应类型,其耐力和潜力是血管型>混合型>心脏型>欠调型。结果表明负-立方法是一种很好的心血管功能检查方法,可应用于航天员心血管功能选拔。