He Qinghua, Sun Zhiyuan, Li Yuandong, Wang Wendy, Wang Ruikang K
Department of Bioengineering, University of Washington, Seattle, WA 98105, USA.
Department of Ophthalmology, University of Washington, Seattle, WA98105, USA.
Biomed Opt Express. 2021 Apr 23;12(5):2919-2937. doi: 10.1364/BOE.423160. eCollection 2021 May 1.
We propose a smartphone-enabled remote multispectral photoplethysmography (SP-rmPPG) system and method to realize spatiotemporal monitoring of perfusion changes and pulsations of the oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) information of the effective blood volume within light interrogated skin tissue beds. The system is implemented on an unmodified smartphone utilizing its built-in camera and flashlight to acquire videos of the skin reflectance. The SP-rmPPG method converts the RGB video into multispectral cubes, upon which to decouple the dynamic changes in HbO2 and Hb information using a modified Beer-Lambert law and the selective wavelength bands of 500 nm and 650 nm. Blood pulsation amplitudes are then obtained by applying a window-based lock-in amplification on the derived spatiotemporal changes in HbO2 or Hb signals. To demonstrate the feasibility of proposed method, we conduct two experiments on the skin tissue beds that are conditioned by occlusive maneuver of supplying arteries: one using the popular blood cuff pressure maneuver on the upper arm, and another artificially inducing a transient ischemic condition on the facial skin tissue beds by finger pressing on the supplying external carotid artery. The cuff experiment shows that the measured dynamic information of HbO2 and Hb in the downstream agrees well with the parallel measurements of oxygenation saturation given by the standard pulse oximeter. We also observe the expected imbalance of spatiotemporal changes in the HbO2 and Hb between the right and left cheeks when the transient ischemic condition is induced in the one side of facial skin tissue beds. The results from the two experiments sufficiently demonstrate the feasibility of the proposed method to monitor the spatiotemporal changes in the skin hemodynamics, including blood oxygenation and pulsation amplitudes. Considering the ever-growing accessibility and affordability of the smartphone to the general public, the proposed strategy promises the early screening of vascular diseases and improving general public health particularly in rural areas with low resource settings.
我们提出了一种基于智能手机的远程多光谱光电容积脉搏波描记法（SP-rmPPG）系统及方法，以实现对光照射的皮肤组织床内有效血容量的氧合血红蛋白（HbO2）和脱氧血红蛋白（Hb）信息的灌注变化和搏动进行时空监测。该系统在未改装的智能手机上实现，利用其内置摄像头和手电筒获取皮肤反射率视频。SP-rmPPG方法将RGB视频转换为多光谱立方体，然后使用修正的比尔-朗伯定律和500 nm及650 nm的选择性波长带对HbO2和Hb信息的动态变化进行解耦。然后通过对推导的HbO2或Hb信号的时空变化应用基于窗口的锁相放大来获得血液搏动幅度。为了证明所提方法的可行性，我们在通过供应动脉闭塞操作处理的皮肤组织床上进行了两个实验：一个是在上臂使用流行的血压袖带压力操作，另一个是通过手指按压供应的颈外动脉在面部皮肤组织床上人为诱发短暂缺血状态。袖带实验表明，下游测量的HbO2和Hb的动态信息与标准脉搏血氧仪给出的氧饱和度平行测量结果吻合良好。当在一侧面部皮肤组织床上诱发短暂缺血状态时，我们还观察到左右脸颊之间HbO2和Hb的时空变化出现预期的不平衡。这两个实验的结果充分证明了所提方法监测皮肤血流动力学时空变化（包括血液氧合和搏动幅度）的可行性。考虑到智能手机对普通大众的可及性和可承受性不断提高，所提策略有望实现血管疾病的早期筛查，并改善公众健康，特别是在资源匮乏的农村地区。
