Capnostat and oxystat. Electronic devices to automatically maintain the end-tidal $$P_{CO_2 } $$ and $$P_{O_2 } $$ of a subject connected to a closed respiratory circuit at adjustable levels

Abstract

Summary In respiratory physiology it is often desirable to maintain the end-tidal\(P_{CO_2 } \) and\(P_{O_2 } \) 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\(P_{CO_2 } \) and\(P_{O_2 } \). 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\(P_{O_2 } \) instead of inspiratory\(P_{O_2 } \) 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\(P_{CO_2 } \) or\(P_{O_2 } \). An optic as well as an acoustic alarm is provided and will be switched on whenever no end-tidal\(P_{O_2 } \) is detected for an adjustable time.