Gronwald Thomas, Hoos Olaf, Hottenrott Kuno
Department of Performance, Neuroscience, Therapy and Health, MSH Medical School Hamburg, Hamburg, Germany.
Center for Sports and Physical Education, Julius Maximilians University of Würzburg, Würzburg, Germany.
Front Physiol. 2019 Aug 2;10:999. doi: 10.3389/fphys.2019.00999. eCollection 2019.
Measurements of Non-linear dynamics of heart rate variability (HRV) provide new possibilities to monitor cardiac autonomic activity during exercise under different environmental conditions. Using detrended fluctuation analysis (DFA) technique to assess correlation properties of heart rate (HR) dynamics, the present study examines the influence of normobaric hypoxic conditions (HC) in comparison to normoxic conditions (NC) during a constant workload exercise.
Nine well trained cyclists performed a continuous workload exercise on a cycle ergometer with an intensity corresponding to the individual anaerobic threshold until voluntary exhaustion under both NC and HC (15% O). The individual exercise duration was normalized to 10% sections (10-100%). During exercise HR and RR-intervals were continuously-recorded. Besides HRV time-domain measurements (meanRR, SDNN), fractal correlation properties using short-term scaling exponent alpha1 of DFA were calculated. Additionally, blood lactate (La), oxygen saturation of the blood (SpO), and rating of perceived exertion (RPE) were recorded in regular time intervals.
We observed significant changes under NC and HC for all parameters from the beginning to the end of the exercise (10% vs. 100%) except for SpO and SDNN during NC: increases for HR, La, and RPE in both conditions; decreases for SpO and SDNN during HC, meanRR and DFA-alpha1 during both conditions. Under HC HR (40-70%), La (10-90%), and RPE (50-90%) were significantly-higher, SpO (10-100%), meanRR (40-70%), and DFA-alpha1 (20-60%) were significantly-lower than under NC.
Under both conditions, prolonged exercise until voluntary exhaustion provokes a lower total variability combined with a reduction in the amplitude and correlation properties of RR fluctuations which may be attributed to increased organismic demands. Additionally, HC provoked higher demands and loss of correlation properties at an earlier stage during the exercise regime, implying an accelerated alteration of cardiac autonomic regulation.
心率变异性（HRV）的非线性动力学测量为监测不同环境条件下运动期间的心脏自主神经活动提供了新的可能性。本研究采用去趋势波动分析（DFA）技术评估心率（HR）动力学的相关性，考察常氧条件（NC）与常压缺氧条件（HC）在恒定负荷运动期间的影响。
9名训练有素的自行车运动员在功率自行车上进行持续负荷运动，强度对应于个体无氧阈，直至在NC和HC（15%氧气）条件下自愿力竭。个体运动持续时间标准化为10%的时间段（10%-100%）。运动期间连续记录HR和RR间期。除了HRV时域测量（平均RR、SDNN）外，还计算了使用DFA短期标度指数α1的分形相关性。此外，定期记录血乳酸（La）、血氧饱和度（SpO）和主观用力程度分级（RPE）。
我们观察到，运动开始至结束时（10%对100%），除NC期间SpO和SDNN外，所有参数在NC和HC条件下均有显著变化：两种条件下HR、La和RPE均升高；HC期间SpO和SDNN降低，两种条件下平均RR和DFA-α1降低。在HC条件下，HR（40%-70%）、La（10%-90%）和RPE（50%-90%）显著高于NC，SpO（10%-100%）、平均RR（40%-70%）和DFA-α1（20%-60%）显著低于NC。
在两种条件下，持续运动至自愿力竭均会导致总变异性降低，同时RR波动的幅度和相关性降低，这可能归因于机体需求增加。此外，HC在运动过程的早期引发了更高的需求和相关性丧失，这意味着心脏自主神经调节的加速改变。
