Respiratory rhythm detection with photoplethysmographic methods

A transmittance type infrared photoelectric plethysmograph (PPG) is described that performs time and frequency analysis of the peripheral finger volume pulse using an IBM 386 computer. It was revealed that in addition to the heart action the respiratory rhythm and waveform could be obtained from the peripheral volume pulse signal. This result was confirmed with the aid of a true respiration signal from a thermistor in different experiments: (1) varying breathing rates; (2) breathing-stop. The authors conclude that their new method may be useful for clinical noninvasive breath monitoring