本研究之目的在以時域分析法比較常壓低氧對安靜時心率變異度之影響。九名大學體育系之男性學生（年齡：22±1.5歲；身高：174.1±4.4公分；體重：72.6±8.19kg），採坐姿休息配合呼吸低氧的方式進行心電圖訊號之收集，再以時域分析法比較常壓低氧環境對安靜時心率變異度之影響。所得結果如下：1、在平均心跳率方面（HR mean），在常壓低氧環境（16% O2）高於常壓常氧（21%O2）環境（81.75±7.16╱71.79±2；13.89%，P<0.01）。2、安靜時之各項心率變異度時域分析指標方面，每跳時間間隔（R-R interval），常氧及低氧環境下分別為845.05±25.79毫秒及742.53±61.95毫秒（P<0.05）。在相鄰兩心跳間期差值平方和均方差（RMSSD）方面分別為53.01±19.96毫秒及27.87±9.09毫秒（P<0.01）。在相鄰兩個心跳間期差值超過50毫秒的個數（NN50）方面分別為58.99±28.17及18.66±11.94（P<0.05）。在相鄰兩個心跳間期差值超過50毫秒的比例（PNN50）方面分別為26.97±14.63%及8.39±5.36%（P<0.01），常壓低氧環境安靜時之各項心率變異度時域分析指標顯著低於常氧環境（p<0.01）。結論：處於急性常壓低氧環境會造成安靜時心跳率上升及心率變異度之時域指標值下降。

　　　　　purpose: This study was to investigate the effects of normobaric hypoxia on resting HRV in male college students (n=9) (age: 22±1.5yr; heigh: 174.1±4.4; weight: 72.6±8.19kg) majoring in physical education. We investigated the changes between normoxia (21% O2) and hypoxia (16% O2) and used the time domain analysis index to compaired the different between this two conditions. Methods: electrocardiogram (EKG) signal was taken while the subject was in seat position in a quiet room and breathing the mixed gas (21%O2 + 79%N2 or 16%O2 + 84%N2). The HRV time domain index assessed by the R-R interval which was translated from the EKG signal. Results: Showed that in normobaric normoxia and hypoxia condition. The HRV time domain index were significant decreased in mean R-R interval (845.05±25.79ms & 742.53±61.95ms, P<0.01), RMSSD (53.01±19.96ms & 27.87±9.09ms, P<0.01), PNN50 (26.97±14.63% & 8.39±5.36%, P<0.01), SDNN (83.71±23.97ms & 52.47±18.18ms, P<0.05) and NN50 (58.88±28.17 & 18.66±11.94, P<0.05) but increase in mean HR (81.75±7.16 & 71.78±2bpm, P<0.01). Conclusions: normobaric hypoxia has significantly decrease the HRV time domain indexs and increase resting heart rate.