Abstract: A method of determining the mixed venous PCO.sub.2 (PvCO.sub.2) is disclosed, the method comprising the steps of:(a) measuring the PCO.sub.2 of the gases inhaled and exhaled by the patient under controlled conditions without rebreathing;(b) causing the patient to inhale a test gas containing at least a small concentration of CO.sub.2 and continuing to measure the PCO.sub.2 of the inspired and expired gases, the patient taking at least two breaths without rebreathing;(c) determining the PCO.sub.2 of the inspried gases (P.sub.I CO.sub.2) and the end tidal PCO.sub.2 of expired gases (PECO.sub.2);(d) determing the differences between the end tidal PCO.sub.2 and inspired PCO.sub.2 under control and test conditions, and relating it to the inspired PCO.sub.2 used in the determination of the difference. This relationship can be used to calculate the mixed venous PCO.sub.2.

Abstract: A method of determining the mixed venous PCO.sub.2 (PvCO.sub.2) is disclosed, the method comprising the steps of: (a) measuring the PCO.sub.2 of the gases inhaled and exhaled by the patient under controlled conditions without rebreathing; (b) causing the patient to inhale a test gas containing at least a small concentration of CO.sub.2 and continuing to measure the PCO.sub.2 of the inspired and expired gases, the patient taking at least two breaths without rebreathing; (c) determining the PCO.sub.2 of the inspired gases (P.sub.I CO.sub.2) and the end tidal PCO.sub.2 of expired gases (PECO.sub.2); (d) determing the differences between the end tidal PCO.sub.2 and inspired PCO.sub.2 under control and test conditions, and relating it to the inspired PCO.sub.2 used in the determination of the difference. This relationship can be used to calculate the mixed venous PCO.sub.2.

Abstract: A mouthpiece through which a person may breathe has a sealing flange for introduction into the mouth. The sealing flange has an upper portion for lying against the hard palate and a lower portion for fitting between the lower lip and the anterior surface about the lower teeth and gums. The juxtaposition in the mouth of the upper portion against the hard palate and the lower portion seated in the lower vestibule portion of the mouth results in the sealing flange forming an effective seal and the sealing flange being comfortably held in place in the mouth even when the mouth is open to the extent of the normal relaxed muscle tone of the mouth. To facilitate the seal when the mouthpiece is introduced into the mouth, a tooth tray is provided. Another aspect of the invention permits the mouthpiece to envelop the nostrils such that when the mouthpiece is in place all inspired and expired air must pass through the mouthpiece.

Abstract: A fire damper of the kind in which at least one flap is pivoted in a duct between a first position in which the flap closes the duct and a second position in which the duct is open. A suitably powered winching motor is adapted to control the movement of the flap through a linkage including a fusible link so that when the motor is energized the flap is moved to its second position or open position provided that the fusible link is still intact whereas when the motor is de-energized the flap is moved to its first or closed position.