Patent US 5,316,010

An apparatus for measuring changes in intrathoracic pressure and upper airway resistance which occurs in humans during sleep and includes a photoelectric plethysmographic transducer associated with the suprasternal fossa to measure movement of the skin surface which correlates with changes in intrathoracic pressure and upper airway resistance. The transducer includes a housing having a flexible diaphragm bonded to the skin surface at the suprasternal fossa. A photodiode is mounted on the diaphragm within the housing and a light emitting diode is mounted within the housing in spaced relation to the photodiode. The housing is fixedly secured in position whereby movement of the skin surface varies the output voltage of the photodiode which provides a signal that enables measurement of changes in intrathoracic pressure and upper airway resistance in humans during sleep.