Design of low cost apnea detector by modifying a simple pulse delay circuit interfacing with computer with audio input by freely available audio software

Human Respiration rate is measured for Clinical investigation of lungs for different diagnostic purposes. Human respiration rate can be measured by different methods that involves Piezoelectric Sensor, Laser Doppler Vibrometer & by using Pyroelectric Transducer, Impedance Pneumography Method, Capnography and PPG (Photo plethysmography) signal. However, all of these techniques are very cost effective. Whereas apnea that is loss of breathing, mainly during sleep, termed as sleep apnea. By different clinical investigation it has been observed that sleep apnea have the following risk factors e.g. excessive weight, enlarge tonsils or tongue, small jaw bone, gastro esophageal reflux, sinus problem and it also associated with heart disorder and stroke. We have designed a new system that can measure respiration rate and can also detect Apnea present in human beings by using NTC (Negative Temperature Coefficient) type thermistor, Wheatstone bridge, a differential amplifier (using IC-741) and a modifying pulse delay circuit. This system can be used to detect apnea along with display of its waveform in a computer screen. In this system the output signals are taken out and after performing some impedance matching it is used as audio input to a computer. A freely available software Audacity (latest version 2.1.3) downloaded from internet and installed to the computer for observing the waveform of the output signal. From this response, doctors can easily detect whether there are presence of apnea or not. The used thermistor is highly sensitive which changes it resistance -7KΩ per degree centigrade rise in temperature.