| abstract |
A dynamic method and apparatus for determining the rate of expiration of a selected fluid constituent expired by a living subject during respiration. The apparatus includes a fluid path system which conducts the expired air to a first fluid detector which produces a first signal operable as a function of concentration for the selected fluid constituent. The signal registered by the detector is used for later comparison with a second signal which provides the basis for determining the expiration rate of fluid constituent originally present in the expired air. To make this determination, the fluid constituent is removed from the expired air, with the expired air being advanced to a mixing chamber where a second detection means senses the fluid concentration. The respective signals from the first and second detection means are compared and integrated and additional fluid constituent is added to the expired air at the mixing chamber by a metering pump until the respective signals are equal, indicating equivalent concentrations. Since the flow rate of fluid constituent replenished is a function of rate of expiration for the selected fluid constituent, this value can be used to obtain the value of the latter. Such a system can be readily adapted to existing anesthesia delivery systems, as well as other respiratory monitoring apparatus. Fluids which are subject to measurement by such a method and apparatus include CO2, anesthetics, alcohols, water vapor and numerous gases. |