The stethoscope is a medical acoustic device which is used to auscultate internal body sounds, mainly the heart and lungs. A digital stethoscope overcomes the limitations of a conventional stethoscope as the sound data is transformed into electrical signals which can be amplified, stored, replayed and, more importantly, sent for an expert opinion, making it very useful in telemedicine. With the above in view, a low cost digital stethoscope has been developed which is interfaceble with mobile communication devices. In this instrument sounds from various locations can be captured with the help of an electret condenser microphone. Captured sound is filtered, amplified and processed digitally using an adaptive line enhancement technique to obtain audible and distinct heart sounds.
Photoplethysmography (PPG), introduced in 1937, is routinely used for monitoring heart rate, blood perfusion and oxygen saturation of the blood in the intensive care units for the past several decades. It is also being used for the assessment of peripheral blood flow and venous filling time in noninvasive vascular laboratories. It works on the principle of light/infrared absorption in the body segment and detection and processing of transmitted light/infrared radiation.In the past few decades, there has been more emphasis on the pulse morphology. Analysis of higher harmonic components and derivation of cardiovascular indices have emerged as powerful tools for the assessment of arterial aging, endothelial function, and vascular compliance. The ease of operating and extreme low cost of PPG system has made it ideal for objective assessment of autonomic nervous system (ANS). This technique is presently being explored for the personal monitoring of blood glucose noninvasively.
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