下面两篇文章“视角”不同。不妨都试一下。

译者注：高心率变异性（ heart rate variability， HRV） 与健康状况相关，而低HRV 与病况相关。（High HRV is associated with healthy condition, while low HRV is associated with pathological conditions.）

每分钟 5.5 次呼吸且吸气与呼气比率相等会增加心率变异性

Breathing at a rate of 5.5 breaths per minute with equal inhalation-to-exhalation ratio increases heart rate variability

https://pubmed.ncbi.nlm.nih.gov/24380741/

目的：之前的研究发现，每分钟 6 次或 5.5 次呼吸 (bpm) 的呼吸模式与比自主呼吸频率更大的心率变异性 (HRV) 相关。 然而，呼吸频率与吸、呼气比（I:E 比，即吸入：呼出比例）相结合对 HRV 指数的影响并不清楚。 本研究旨在探讨四种不同呼吸模式之间 HRV 指数以及焦虑和放松主观感受的差异。

方法：选取47名健康大学生进行研究，采用随机序列平衡的拉丁方实验设计（Latin square experimental design）。 参与者被要求以两种不同的呼吸频率（每分钟6 次和5.5 次呼吸）和两种不同的 I:E 比率（5:5 和 4:6）进行呼吸。 在基线（自主呼吸）和四种不同的呼吸模式下测量 HRV 指数以及焦虑和放松水平。

结果：结果显示，与其他呼吸模式相比，5.5 bpm 的 I:E 比为 5:5 的模式产生更高的NN （normal-to-normal？）间隔标准偏差和更高的低频功率。 此外，与基线相比，四种不同的呼吸模式与放松感显着增加相关。

结论：研究证实，I:E 比为 5:5 的 5.5 bpm 呼吸模式比其他呼吸模式能实现更高的HRV。 这一发现可以应用于未来的 HRV 生物反馈或呼吸训练。

【译者：简单地说，就是每分钟呼吸5.5次，吸入和呼出时间相同，是最佳的。】

Abstract

Objectives: Prior studies have found that a breathing pattern of 6 or 5.5 breaths per minute (bpm) was associated with greater heart rate variability (HRV) than that of spontaneous breathing rate. However, the effects of combining the breathing rate with the inhalation-to-exhalation ratio (I:E ratio) on HRV indices are inconsistent. This study aimed to examine the differences in HRV indices and subjective feelings of anxiety and relaxation among four different breathing patterns.

Methods: Forty-seven healthy college students were recruited for the study, and a Latin square experimental design with a counterbalance in random sequences was applied. Participants were instructed to breathe at two different breathing rates (6 and 5.5 breaths) and two different I:E ratios (5:5 and 4:6). The HRV indices as well as anxiety and relaxation levels were measured at baseline (spontaneous breathing) and for the four different breathing patterns.

Results: The results revealed that a pattern of 5.5 bpm with an I:E ratio of 5:5 produced a higher NN interval standard deviation and higher low frequency power than the other breathing patterns. Moreover, the four different breathing patterns were associated with significantly increased feeling of relaxation compared with baseline.

Conclusion: The study confirmed that a breathing pattern of 5.5 bpm with an I:E ratio of 5:5 achieved greater HRV than the other breathing patterns. This finding can be applied to HRV biofeedback or breathing training in the future.

（呼吸过程中）呼气与吸气比率的增加会增强健康成年人的高频心率变异性

Increased exhalation to inhalation ratio during breathing enhances high-frequency heart rate variability in healthy adults

https://pubmed.ncbi.nlm.nih.gov/34289128/

心率变异性 (HRV) 是心脏和情绪健康的公认替代指标；它反映自主神经系统交感神经和副交感神经活动之间的平衡。 我们研究了在不改变健康个体固有呼吸频率的情况下，控制呼气与吸气比率 (E:I) 对 HRV 的影响。 我们假设相对于吸气较长的呼气(E:I > 1；即呼气时间长于吸气时间) 会使 HRV 指标向与副交感神经活动增加一致的方向转变。 28 名受试者（16 名年轻人 [6M，年龄 = 21～28]；12 名老年人 [6M，年龄 = 66～80]）完成了测试任务。在测试期间，他们根据其内在呼吸频率调整呼吸速度，但改变了呼气和吸气的开始时间，根据 1:1 声音提示（呼气和吸气持续时间相等）或 2:1 提示（呼气时间是吸气时间的两倍）。 然后进行 1:1 节奏呼吸，以检查残留效应。 基于胸部运动的实际 E:I 比率的估计值对于 1:1 节奏为 1.08（0.16），对于 2:1 节奏为 1.33（0.20），两者之间存在显着差异。 源自心电图的 HRV 指标包括正常心跳 (RMSSD) 和高频 (HF) HRV 之间连续差异的均方根。 按“组”进行的 HRV 指标分析表明，与 1:1 节奏相比，2:1 节奏下的 RMSSD 和 HF-HRV 更高。 时间序列分析显示，2:1 节奏结束后 HF-HRV 升高，并在四分钟内保持升高状态。 这些发现表明，在不改变呼吸频率的情况下，相对于吸气，呼气持续时间较长，RMSSD 和HF-HRV 急剧增加，这与心脏迷走神经张力的增强一致。

【译者：试一下， 把呼气时间延长到你吸气时间的两倍。】

Abstract

Heart rate variability (HRV) is a well-established surrogate of cardiac and emotional health that reflects the balance between sympathetic and parasympathetic activity of the autonomic nervous system. We examined the impact of manipulating exhalation to inhalation ratio (E:I) on HRV, without altering the intrinsic breathing rate of healthy individuals. We hypothesized that a longer exhalation relative to inhalation (E:I > 1) would shift HRV metrics in a direction consistent with increased parasympathetic activity. Twenty-eight individuals (16 young [6M, age = 21-28];12 older adults [6M, age = 66-80]) completed a task during which they paced breathing according to their intrinsic respiratory rate, but altered onset of exhalation and inhalation according to 1:1 sound cue (equal exhalation and inhalation duration) or 2:1 cue (exhalation twice as long as inhalation). Paced 1:1 breathing followed these task conditions to examine residual effects. Estimates of actual E:I ratio based on thoracic movement were 1.08(0.16) for 1:1 task and 1.33(0.20) for 2:1 task, which were significantly different from one another. HRV metrics derived from electrocardiogram included root mean square of the successive differences between normal heartbeats (RMSSD) and high-frequency (HF) HRV. Analyses of HRV metrics by block showed that RMSSD and HF-HRV were higher in the 2:1 task condition compared to 1:1. Time series analysis showed that HF-HRV increased after the end of the 2:1 task block and remained elevated for four minutes. These findings suggest that longer duration of exhalation relative to inhalation, without altering breathing rate, acutely increased RMSSD and HF-HRV, consistent with enhancement of cardiac vagal tone.