Extracting physiological information in experimental biology via Eulerian video magnification

Background: Videographic material of animals can contain inapparent signals, such as color changes or motion that hold information about physiological functions, such as heart and respiration rate, pulse wave velocity and vocalization. Eulerian video magnification allows enhancement of such signals to enable their detection. The purpose of this study is to demonstrate how signals relevant to experimental physiology can be extracted from non-contact videographic material of animals. Results: We applied Eulerian video magnification to detect physiological signals in a range of experimental models and in captive and free ranging wildlife. Neotenic Mexican axolotls were studied to demonstrate the extraction of heart rate signal of non-embryonic animals from dedicated videographic material. Heart rate could be acquired both in single and multiple animal setups of leucistic and normally colored animals under different physiological conditions (resting, exercised or anesthetized) using a wide range of video qualities. Pulse wave velocity could also be measured in the low blood pressure system of the axolotl as well as in the high pressure system of the human being. Heart rate extraction was also possible from videos of conscious, unconstrained zebrafish and from non-dedicated videographic material of sand lizard and giraffe. This technique also allowed for heart rate detection in embryonic chickens in ovo through the eggshell and in embryonic mice in utero, and could be used as a gating signal to acquire two-phase volumetric micro-CT data of the beating embryonic chicken heart. Additionally, Eulerian video magnification was used to demonstrate how vocalization induced vibrations can be detected in infrasound producing Asian elephants. Conclusions: Eulerian video magnification provides a technique to extract inapparent temporal signals from videographic material of animals. This can be applied in experimental and comparative physiology where contact based recordings (e.g. heart rate) cannot be acquired.背景：动物影像素材中往往蕴含不易察觉的信号，例如颜色变化或运动模式，这些信号可反映心率、呼吸频率、脉搏波速度以及发声等生理功能信息。欧拉视频放大（Eulerian Video Magnification）技术可增强这类信号，使其能够被检测识别。本研究旨在展示如何从非接触式动物影像素材中提取实验生理学相关的生理信号。 结果：我们将欧拉视频放大技术应用于多种实验动物模型以及圈养和野生自由活动的野生动物，以检测其中的生理信号。以幼态持续型墨西哥钝口螈为研究对象，验证了从专用影像素材中提取非胚胎动物心率信号的可行性。研究涵盖了白化型与正常体色的钝口螈，在单只或多只动物的实验设置下，通过多种画质的视频，均可获取不同生理状态（静息、运动或麻醉状态）下的心率数据。此外，我们既在低血压的钝口螈循环系统中测量了脉搏波速度，也在人类的高压循环系统中完成了该项测量。研究还从自由活动的清醒斑马鱼视频，以及沙蜥和长颈鹿的非专用影像素材中成功提取了心率信号。该技术还可穿透蛋壳实现鸡胚卵内心脏的心率检测，以及穿透子宫实现小鼠胚胎的心率检测，并且可作为门控信号，获取搏动中的鸡胚心脏的双相体积显微计算机断层扫描（micro-CT）数据。此外，利用欧拉视频放大技术，我们还实现了对次声波发声亚洲大象的发声诱导振动信号的检测。 结论：欧拉视频放大技术可从动物影像素材中提取不易察觉的时域信号，该方法可应用于无法采用接触式记录手段（如心率记录）的实验生理学与比较生理学研究场景中。