Hassanein Youmna Elsayed, Rogers Bruce, Ibrahim Dania, Fleitas-Paniagua Pablo R, Murias Juan M, Townsend Nathan E
College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, QATAR.
College of Medicine, University of Central Florida, Orlando, FL.
Med Sci Sports Exerc. 2025 Apr 28. doi: 10.1249/MSS.0000000000003744.
Purpose: Heart rate (HR) variability thresholds (HRVT) based on detrended fluctuation analysis alpha 1 (DFA a1) generally show reasonable alignment of thresholds estimations based on gas exchange responses under normoxic conditions. This study examined whether acute hypoxia would affect the agreement between HRVTs and the gas exchange equivalents during incremental cycling. Methods: Twelve participants (5 females) completed an incremental ramp test in normobaric hypoxia (FIO2 ≈ 13.5%) and normoxia. Gas exchange and ventilatory responses alongside a high sampling rate electrocardiogram for DFA a1 computation were used to determine thresholds. Comparisons were made between the oxygen consumption (V̇O2) and HR at the gas exchange threshold (GET) and respiratory compensation point (RCP) with the responses at the first and second HRVTs (HRVT1 and HRVT2 respectively). Results: Mean V̇O2 and HR values were not statistically different for GET:HRVT1 (normoxia:1.74±0.41 vs 1.74±0.48 L·min-1,133±18 vs 133±16 bpm; hypoxia:1.47±0.21 vs 1.45±0.37 L·min-1, 135±14 vs 133±15 bpm) and RCP:HRVT2 (normoxia:2.38±0.55 vs 2.37±0.48 L·min-1, 158±13 vs 158±14 bpm, hypoxia:2.07±0.32 vs 1.90±0.43 L·min-1 and 156±13 vs 152±15 bpm) in any condition. All normoxic comparisons passed equivalence testing but only GET:HRVT1 responses passed during hypoxia. Pearsons r correlation coefficients were 0.86 to 0.96 in normoxia and 0.58 to 0.79 in hypoxia. Bland Altman analysis indicated higher degrees of bias and limit of agreements (LOA) during hypoxic testing. Conclusions: Although the V̇O2 and HR at HRVTs retained alignment with GET/RCP in both normoxia and hypoxia, the degrees of correlation, and equivalence were weaker and the bias and LOA were larger in hypoxia. Therefore, whilst using HRVT alone for training boundary guidance in hypoxia is a potential option, further investigation including incorporating complimentary surrogate markers is recommended.
基于去趋势波动分析α1（DFAα1）的心率（HR）变异性阈值（HRVT）通常显示在常氧条件下基于气体交换反应的阈值估计具有合理的一致性。本研究探讨急性低氧是否会影响递增式骑行过程中HRVT与气体交换当量之间的一致性。方法：12名参与者（5名女性）在常压低氧（FIO2≈13.5%）和常氧条件下完成递增式斜坡试验。使用气体交换和通气反应以及用于DFAα1计算的高采样率心电图来确定阈值。对气体交换阈值（GET）和呼吸补偿点（RCP）时的耗氧量（V̇O2）和HR与第一和第二HRVT（分别为HRVT1和HRVT2）时的反应进行比较。结果：在任何条件下，GET:HRVT1（常氧：1.74±0.41对1.74±0.48L·min-1，133±18对133±16次/分钟；低氧：1.47±0.21对1.45±0.37L·min-1，135±14对133±15次/分钟）和RCP:HRVT2（常氧：2.38±0.55对2.37±0.48L·min-1，158±13对158±14次/分钟，低氧：2.07±0.32对1.90±0.43L·min-1，156±13对152±15次/分钟）时的平均V̇O2和HR值无统计学差异。所有常氧比较均通过等效性检验，但低氧期间只有GET:HRVT1反应通过。常氧时皮尔逊r相关系数为0.86至0.96，低氧时为0.58至0.79。布兰德-奥特曼分析表明低氧测试期间偏差程度和一致性界限（LOA）更高。结论：尽管常氧和低氧条件下HRVT时的V̇O2和HR与GET/RCP保持一致，但低氧时相关性和等效性程度较弱，偏差和LOA较大。因此，虽然单独使用HRVT作为低氧训练边界指导是一种潜在选择，但建议进一步研究，包括纳入补充替代标志物。
