Department of Electrical Engineering, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven, The Netherlands. Philips Research, High Tech Campus, 5656 AE Eindhoven, The Netherlands. Sleep Medicine Center Kempenhaeghe, P.O. Box 61, 5590 AB Heeze, The Netherlands.
Physiol Meas. 2020 Jul 8;41(6):065010. doi: 10.1088/1361-6579/ab9481.
Respiratory activity is an essential parameter to monitor healthy and disordered sleep, and unobtrusive measurement methods have important clinical applications in diagnostics of sleep-related breathing disorders. We propose a respiratory activity surrogate extracted from wrist-worn reflective photoplethysmography validated on a heterogeneous dataset of 389 sleep recordings.
The surrogate was extracted by interpolating the amplitude of the PPG pulses after evaluation of pulse morphological quality. Subsequent multistep post-processing was applied to remove parts of the surrogate with low quality and high motion levels. In addition to standard respiration rate performance, we evaluated the similarity between surrogate respiratory activity and reference inductance plethysmography of the thorax, using Spearman's correlations and spectral coherence, and assessed the influence of PPG signal quality, motion levels, sleep stages and obstructive sleep apnea.
Prior to post-processing, the surrogate already had a strong similarity with the reference (correlation = 0.54, coherence = 0.81), and reached respiration rate estimation performance in line with the literature (estimation error = 0.76± 2.11 breaths/min). Detrimental effects of low PPG quality, high motion levels and sleep-dependent physiological phenomena were significantly mitigated by the proposed post-processing steps (correlation = 0.62, coherence = 0.88, estimation error = 0.53± 1.85 breaths/min).
Wrist-worn PPG can be used to extract respiratory activity, thus allowing respiration monitoring in real-world sleep medicine applications using (consumer) wearable devices.
呼吸活动是监测健康和紊乱睡眠的一个重要参数，非侵入性测量方法在睡眠相关呼吸障碍的诊断中具有重要的临床应用。我们提出了一种从佩戴在手腕上的反射光体积描记法中提取的呼吸活动替代物，该替代物在一个包含 389 个睡眠记录的异质数据集上得到了验证。
替代物是通过评估脉搏形态质量后对 PPG 脉冲的幅度进行插值提取的。随后应用多步后处理步骤去除替代物中质量低和运动水平高的部分。除了标准呼吸率性能外，我们还使用 Spearman 相关系数和频谱相干性评估了替代呼吸活动与胸部感应体积描记法的参考呼吸活动之间的相似性，并评估了 PPG 信号质量、运动水平、睡眠阶段和阻塞性睡眠呼吸暂停的影响。
在进行后处理之前，替代物已经与参考物具有很强的相似性（相关性=0.54，相干性=0.81），并且达到了与文献一致的呼吸率估计性能（估计误差=0.76±2.11 次/分钟）。通过所提出的后处理步骤，可以显著减轻 PPG 质量低、运动水平高和睡眠相关生理现象的不利影响（相关性=0.62，相干性=0.88，估计误差=0.53±1.85 次/分钟）。
佩戴在手腕上的 PPG 可用于提取呼吸活动，从而允许使用（消费）可穿戴设备在真实世界的睡眠医学应用中进行呼吸监测。
