Yamamoto Y, Hoshikawa Y, Miyashita M
Laboratory for Exercise Physiology and Biomechanics, Graduate School of Education, University of Tokyo, Japan.
J Appl Physiol (1985). 1996 Sep;81(3):1223-9. doi: 10.1152/jappl.1996.81.3.1223.
It has been shown that fluctuation of human heartbeat intervals [heart rate variability (HRV)] reflects variations in cardiac autonomic nervous system activity. The present study was designed to investigate whether the acute exposure to moderate levels of simulated altitude and the resultant hypoxia could modify HRV during exercise. Seven healthy men completed one resting measurement in the upright sitting position and two submaximal steady-state cycle ergometer exercises at intensities equivalent to 25 and 50% of their estimated maximal work rate. Experiments were conducted in random order at altitude equivalents of 500, 1,500, 2,500, and 3,500 m within 2 h of exposure to that altitude. Beat-to-beat HRV was measured continuously during the tests. HRV data were analyzed by "coarse-graining spectral analysis" (Y. Yamamoto and R.L. Hughson, Physica 68D: 250-264, 1993) to break down their total power (PT) into harmonic and nonharmonic (fractal) components. The harmonic component was further divided into low (0.0- to 0.15-Hz; PL)- and high (> 0.15-Hz; PH)-frequency components, and the indicators of relative sympathetic (SNS) and parasympathetic (PNS) nervous system activities were calculated by PL/PH and PH/PT, respectively. The fractal component was used to calculate the spectral exponent (beta) to evaluate the overall "irregularity" of HRV. The effects of exercise intensity (increase in heart rate, SNS indicator, and beta and decrease in PNS indicator) were significant (P < 0.05) at all altitude levels. The altitude effects (increase in heart rate and SNS indicator and decrease in PNS indicator) were found only during exercise at 3,500 m (P < 0.05). There was no significant effect of altitude on beta (P > 0.05). These data indicate that acute effects of altitude exposure on HRV were found 1) during exercise at moderate altitude (> 2,500 m) and 2) mainly for the harmonic components of HRV.
研究表明，人类心跳间期的波动[心率变异性（HRV）]反映了心脏自主神经系统活动的变化。本研究旨在调查急性暴露于中等水平的模拟海拔高度及由此产生的缺氧是否会在运动期间改变HRV。七名健康男性在直立坐姿下完成一次静息测量，并在相当于其估计最大工作率25%和50%的强度下进行两次次最大稳态周期测力计运动。实验在暴露于该海拔高度2小时内，于海拔相当于500、1500、2500和3500米的高度随机进行。在测试过程中连续测量逐搏HRV。通过“粗粒化频谱分析”（Y. Yamamoto和R.L. Hughson，《物理学》68D：250 - 264，1993）分析HRV数据，将其总功率（PT）分解为谐波和非谐波（分形）成分。谐波成分进一步分为低（0.0至0.15赫兹；PL）和高（>0.15赫兹；PH）频率成分，相对交感神经（SNS）和副交感神经（PNS）系统活动指标分别通过PL/PH和PH/PT计算。分形成分用于计算频谱指数（β）以评估HRV的整体“不规则性”。在所有海拔水平，运动强度的影响（心率增加、SNS指标增加、β增加以及PNS指标降低）均具有显著性（P < 0.05）。仅在3500米运动期间发现海拔高度的影响（心率增加、SNS指标增加以及PNS指标降低）（P < 0.05）。海拔高度对β无显著影响（P > 0.05）。这些数据表明，海拔暴露对HRV的急性影响表现为：1）在中等海拔（>2500米）运动期间；2）主要针对HRV的谐波成分。
