Capnostat and oxystat. Electronic devices to automatically maintain the end-tidal PCO2 and PO2 of a subject connected to a closed respiratory circuit at adjustable levels.

In respiratory physiology it is often desirable to maintain the end-tidal PCO2 and PO2 at adjustable levels independent of each other, e.g., when taking steady-state CO2 or O2 response curves, or when studying the ventilatory effects of exercise or drugs at constant levels of PCO2 and PO2. Based on the closed respiratory circuit described by Folgering et al. (1974), a new version was designed. The main new features of this version are that end-tidal PO2 instead of inspiratory PO2 can be kept constant, and that the correcting activity of both controllers (capnostat and oxystat) is proportional to the magnitude of the difference between the actual and the adjusted end-tidal PCO2 or PO2. An optic as well as an acoustic alarm is provided and will be switched on whenever no end-tidal PO2 is detected for an adjustable time.