OPTICAL REMOTE-SENSING OF HEARTBEATS

The deflection of a human vein due to heartbeats is recorded by two optical methods. In the first method the skin is directly illuminated by a 2 mW, HeNe laser beam in the neighborhood of the vein. The reflected speckle pattern is recorded with a TV camera and afterwards digitized frame by frame. Its contrast is then calculated by computer software and plotted as a function of time. In the second method a small mirror glued to the skin is illuminated by the laser beam. The position of the light spot resulting from intersection of the reflected beam with an opaque observation plane is recorded by a CCD camera and plotted as a function of time. The instants of time corresponding to a maximum of the mirror rotation speed in the second graph coincide with the instants of time when the speckle contrast is a minimum in the first graph. As the mirror closely follows the vein displacements, this allows remote sensing of the heartbeats by a fully non-invasive method.