Wearable sensors and systems have evolved to the point that they can be considered ready for clinical application. The use of wearable monitoring devices that allow continuous or intermittent monitoring of physiological signals is critical for the advancement of both the diagnosis as well as treatment of diseases. Wearable systems are totally non-obtrusive devices that allow physicians to overcome the limitations of ambulatory technology and provide a response to the need for monitoring individuals over weeks or months.
They typically rely on wireless miniature sensors enclosed in patches or bandages or in items that can be worn, such as ring or shirt. The data sets recorded using these systems are then processed to detect events predictive of possible worsening of the patientâ€™s clinical situations or they are explored to access the impact of clinical interventions.
Each time the heart muscle contracts,blood is ejected from the ventricles and a pulse of pressure is transmitted through the circulatory system.
This pressure pulse when traveling through the vessels,causes vessel wall displacement which is measurable at various points.inorder to detect pulsatile blood volume changes by photoelectric method,photo conductors are used.normally photo resistors are used, for amplification purpose photo transistors are used.
Light is emitted by LED and transmitted through the artery and the resistance of photo resistor is determined by the amount of light reaching it.with each contraction of heart,blood is forced to the extremities and the amount of blood in the finger increases.it alters the optical density with the result that the light transmission through the finger reduces and the resistance of the photo resistor increases accordingly.The photoresistor is connected as a part of voltage divider circuit and produces a voltage that varies with the amount of blood in the finger.This voltage that closely follows the pressure pulse
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