Heart rate variability (HRV) considered as an indicator of the autonomic activity, shows differences between NREM and REM sleep. However, when evaluating during NREM sleep, some authors evaluate without considering the different stages, while others do it. There are discrepancies between values obtained from stages N2 and N3. Our objective was to evaluate whether differences exist between stages N2 and N3 based on several metrics of HRV that reflect the autonomic activity. Additionally, we analyzed the structure of these metrics through principal component analysis (PCA) at each sleep stage. Polysomnograms were recorded in 24 healthy subjects. We found significant differences in the LF and THM metrics with higher values in stage N2. The relative power of HF metric showed a significant difference with higher value in stage N3, however, this metric showed inconsistencies related to other HF representations. Two factors were extracted with PCA and their structure was stable across sleep stages. One factor accounted for 92% of the variance during stage N2 with moderate to high loadings for metrics most strongly associated with the parasympathetic activity. A second factor accounted for 91% of the variance during stage N3 with moderate to high loadings for metrics associated with parasympathetic and blood pressure control. Physiological mechanisms regulated by central commands that may involve neurons in the hypothalamus, pons, and midbrain may explain the differences in LF and THM metrics. The combination of stages N2 and N3 as NREM should be done according to the type of HRV metrics used.

心律变异性（HRV）被视为自主神经活动的指标，显示了NREM和REM睡眠之间的差异。但是，当在NREM睡眠期间进行评估时，有些作者评估时没有考虑不同的阶段，而另一些作者则这样做。从阶段N2和N3获得的值之间存在差异。我们的目标是根据反映自主活动的HRV的多个指标评估阶段N2和N3之间是否存在差异。此外，我们在每个睡眠阶段通过主成分分析（PCA）分析了这些指标的结构。在24位健康受试者中记录多导睡眠图。我们发现，在阶段N2中，LF和THM指标具有较高的值，但存在显着差异。在N3阶段，HF度量的相对功率显示出较大的差异，但值较高。此度量标准显示与其他HF表示形式相关的不一致。用PCA提取了两个因子，它们的结构在整个睡眠阶段都稳定。一个因素占N2阶段变异的92％，对于与副交感神经活动最相关的指标，中等至高负荷。第二个因素占阶段N3期间方差的91％，与副交感神经和血压控制相关的指标有中等到高负荷。由中央命令调节的生理机制可能涉及下丘脑，脑桥和中脑的神经元，这可以解释LF和THM指标的差异。应根据所使用的HRV指标的类型将阶段N2和N3合并为NREM。用PCA提取了两个因素，它们的结构在整个睡眠阶段都稳定。一个因素占N2阶段变异的92％，对于与副交感神经活动最相关的指标，中等至高负荷。第二个因素占阶段N3期间方差的91％，与副交感神经和血压控制相关的指标有中等到高负荷。由中央命令调节的生理机制可能涉及下丘脑，脑桥和中脑的神经元，这可以解释LF和THM指标的差异。应根据所使用的HRV指标的类型将阶段N2和N3合并为NREM。用PCA提取了两个因素，它们的结构在整个睡眠阶段都稳定。一个因素占N2阶段变异的92％，对于与副交感神经活动最相关的指标，中等至高负荷。第二个因素占阶段N3期间方差的91％，与副交感神经和血压控制相关的指标有中等到高负荷。由中央命令调节的生理机制可能涉及下丘脑，脑桥和中脑的神经元，这可以解释LF和THM指标的差异。应根据所使用的HRV指标的类型将阶段N2和N3合并为NREM。一个因素占N2阶段变异的92％，对于与副交感神经活动最相关的指标，中等至高负荷。第二个因素占阶段N3期间方差的91％，与副交感神经和血压控制相关的指标有中等到高负荷。由中央命令调节的生理机制可能涉及下丘脑，脑桥和中脑的神经元，这可以解释LF和THM指标的差异。应根据所使用的HRV指标的类型将阶段N2和N3合并为NREM。一个因素占N2阶段变异的92％，对于与副交感神经活动最相关的指标，中等至高负荷。第二个因素占阶段N3期间方差的91％，与副交感神经和血压控制相关的指标有中等到高负荷。由中央命令调节的生理机制可能涉及下丘脑，脑桥和中脑的神经元，这可以解释LF和THM指标的差异。应根据所使用的HRV指标的类型将阶段N2和N3合并为NREM。由中央命令调节的生理机制可能涉及下丘脑，脑桥和中脑的神经元，这可以解释LF和THM指标的差异。应根据所使用的HRV指标的类型将阶段N2和N3合并为NREM。由中央命令调节的生理机制可能涉及下丘脑，脑桥和中脑的神经元，这可以解释LF和THM指标的差异。应根据所使用的HRV指标的类型将阶段N2和N3合并为NREM。