Methods and apparatus for enhancing reliability of, and monitoring the operation of airway valves to enhance patient safety. Pneumatic control line pressure (positive or negative) for actuation of the airway valve may be specified at a given magnitude or within a selected range and monitored continuously. Reduced or excessive pressure may be compensated by actuation of a pressure source or a bleed valve, and monitoring may be effected so as to warn the user of any deviation from the range, or deviations of selected magnitudes or frequencies or a combination thereof. The inspired volume of CO.sub.2 may be monitored using air flow and CO.sub.2 sensing, with detection of excessive CO.sub.2 volume triggering a warning. Similarly, measured end-tidal or end-inspired CO.sub.2 or other appropriate measures of CO.sub.2 concentration may be employed as a warning trigger. Other driving energy sources for airway valves, and monitoring thereof, are also disclosed. In addition, alternative devices and approaches for initiation of re-breathing, and their monitoring, are disclosed.