Heart beat and blood volume
- The heart pumps blood around the all of the body.
- The blood volume at finger is synchronized with heart beat (fig. a).
- At each heart beat, the blood volume is increased and then decreased ( fig.b).
- If we can measure the blood volume changes, the heart beat can be measured.
Optical measuring heart beat
- The light from the light source (fig.a) is absorbed by tissue, bone, venous blood and arterial blood.
- The light absorption is in proportion to arterial blood volume (fig.b).
- The output of the light detector shows the blood volume changes synchronized with heart beats (fig.c).
- Usually, the measured AC component is named by pulse wave or PPG (Photo Plethysmo Gram).