The impedance of extremeeties such as fingers, arms and legs changes with the blood flow in and out, so this provides another method for plethysmography.
The arterial pulse wave has a very low amplitude and is superimposed on the venous blood volume changes. Pulse wave measurements are possible in many locations including the head (this measurement is called rheoencephalography). Pulse waves can also be measured in the fingers and toes with photoplethysmography.
The shape of the pulse wave is determined, in part, by the elasticity of the blood vessels. A trained technician can analyze the shape of the curve to get early information about a developing arterial vascular disease. The pulse wave analysis can often detect changes very early, and is noninasive, very easy to use, and one of the most economical techniques available today. The pulse wave is changed by different diseases:
- Design a circuit for impedance measurement
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