Cardiac Monitoring Using Laser Speckle

TL;DR: In this article, the authors used laser speckle interferograms of the left and right side of the chest of anormal healthy subject, recorded at the Fourier transform plane on a fine grain photographic plate, while the subject held his breath.

Abstract: Laser speckle is an interference phenomena which is always present when a laser isused. Time -average speckle interferograms of the left and right side of the chest of anormal healthy subject were recorded at the Fourier transform plane on a fine grainphotographic plate, while the subject held his breath. The interferogram was analysedby the point wise method and a graph was drawn between the position and the displacementsat corresponding points on the chest wall. The associated displacements of the chestwall due to heart action are correlated with cardiac function.IntroductionCardiac monitoring can be carried out using various techniques such as electrocardio-graphy, phonocardiography, echocardiography etc. Studies of the heart using thesetechniques have contributed greatly towards understanding cardiac function and diagnosingcardiac disorders. In this present study we have attempted to exploit the associateddisplacement of the chest wall due to the heart action, end to correlate it with cardiacfunction using laser speckle techniques. This paper reports on our preleminary results.The mechanical process of the cardiac cycle cause the propagation of displacementwaves through the body tissues. Arriving at the chest wall, these waves form motionpatterns, containing information on the source and the propagation medium. There are anumber of methods such as stethoscopic or microphonic technique or using transducers ina matrix configuration on the surface of the body, to compare the signals and to locatethe different vibration maxima. The signal strength obtained is dependant on the forcewith which the stethoscope or microphone is pressed against the chest wall, and addi-tionally this has a loading effect on the phenomena being monitored which then causeschanges in the signal. An optical method does not suffer from such defects and can giveaccurate spatial information regarding the chest wall movement. Hok et al have usedholographic interferometry to obtain fringe patterns which describe the chest wall