Department of Electronics, Information and Bioengineering, Politecnico di Milano, P.zza L. da Vinci 32, 20133, Milan, Italy.
Institute of Electronics, and Information and Telecommunication Engineering, Consiglio Nazionale delle Rircerche, Milan, Italy.
Eur J Appl Physiol. 2020 Jul;120(7):1699-1710. doi: 10.1007/s00421-020-04404-7. Epub 2020 Jun 3.
Prolonged weightlessness exposure generates cardiovascular deconditioning, with potential implications on ECG circadian rhythms. Head-down (- 6°) tilt (HDT) bed rest is a ground-based analogue model for simulating the effects of reduced motor activity and fluids redistribution occurring during spaceflight. Our aim was to evaluate the impact of 60-day HDT on the circadianity of RR and ventricular repolarization (QTend) intervals extracted from 24-h Holter ECG recordings, scheduled 9 days before HDT (BDC-9), the 5th (HDT5), 21st (HDT21) and 58th (HDT58) day of HDT, the 1st (R + 0) and 8th (R + 7) day after HDT. Also, the effectiveness of a nutritional countermeasure (CM) in mitigating the HDT-related changes was tested.
RR and QTend circadian rhythms were evaluated by Cosinor analysis, resulting in maximum and minimum values, MESOR (a rhythm-adjusted mean), oscillation amplitude (OA, half variation within a night-day cycle), and acrophase (φ, the time at which the fitting sinusoid's amplitude is maximal) values.
RR and QTend MESOR increased at HDT5, and the OA was reduced along the HDT period, mainly due to the increase of the minima. At R + 0, QTend OA increased, particularly in the control group. The φ slightly anticipated during HDT and was delayed at R + 0.
60-Day HDT affects the characteristics of cardiac circadian rhythm by altering the physiological daily cycle of RR and QTend intervals. Scheduled day-night cycle and feeding time were maintained during the experiment, thus inferring the role of changes in the gravitational stimulus to determine these variations. The applied nutritional countermeasure did not show effectiveness in preventing such changes.
长期的失重暴露会导致心血管适应不良，这可能对心电图的昼夜节律产生影响。头低位（-6°）卧床休息是一种模拟航天飞行中减少运动和体液再分布影响的地面模拟模型。我们的目的是评估 60 天头低位卧床对 24 小时动态心电图记录中 RR 和心室复极（QTend）间期昼夜节律的影响，这些记录分别在头低位卧床前 9 天（BDC-9）、第 5 天（HDT5）、第 21 天（HDT21）和第 58 天（HDT58）、头低位卧床后第 1 天（R+0）和第 8 天（R+7）进行。此外，还测试了一种营养对策（CM）在减轻头低位卧床相关变化方面的有效性。
通过余弦分析评估 RR 和 QTend 昼夜节律，得出最大值和最小值、MESOR（调整后的节律平均值）、振幅（OA，昼夜周期内的半变化）和峰相位（φ，拟合正弦波幅度最大的时间）值。
RR 和 QTend 的 MESOR 在 HDT5 时增加，OA 在头低位卧床期间减小，主要是由于最小值的增加。在 R+0 时，QTend 的 OA 增加，特别是在对照组。φ 在头低位卧床期间略有提前，在 R+0 时延迟。
60 天的头低位卧床通过改变 RR 和 QTend 间隔的生理昼夜周期来影响心脏昼夜节律的特征。在实验期间，维持了预定的日夜周期和喂养时间，因此推断重力刺激的变化决定了这些变化。所应用的营养对策并没有显示出在预防这些变化方面的有效性。
