Medical gas recirculation system

An apparatus for providing and circulating to a medical device a medical gas mixture comprising at least two components, said apparatus comprising:

• a main gas circuit for recirculating the medical gas mixture and comprising:
• a constant speed circulation pump for pumping gas through the main circuit and increasing the gas pressure from a lower pressure to a higher pressure,
• a pressure maintaining valve downstream of the pump and dividing the main circuit into a higher pressure section and a lower pressure section,
• a medical gas outlet in the higher pressure section,
• a spent gas inlet in the lower pressure section,
• a first feed gas supply inlet,
• a second feed gas supply inlet downstream of the gas outlet and upstream of the pressure reduction valve,
• concentration determining means for measuring the concentration of at least one component of the recirculating medical gas mixture and generating a signal indicative of said concentration,
• circuit volume regulating means for varying the volume of the main circuit at a location in the lower pressure section for maintaining a predetermined gas flow to the pump and generating a signal indicative of said volume, and
• means for venting gas from the main circuit;
• a first feed gas supply conduit for supply to the first feed gas inlet of a first feed gas of predetermined composition;
• first feed gas supply flow control means for controlling the flow of first feed gas through the first gas supply conduit in response to the signal from the concentration determining means to maintain constant the medical gas composition at the pump inlet;
• a second feed gas supply conduit for supply to the second feed gas inlet of a second feed gas of predetermined composition different from the first feed gas;
• second feed gas supply flow control means for controlling the flow of second feed gas through the second gas supply conduit in response to the signal from the circuit volume regulating means to maintain constant the recirculating medical gas composition;
• and
• a medical device supply circuit for connecting the medical device to the main circuit to receive a portion of the medical gas from the medical gas outlet thereof and to return spent gas to the spent gas inlet thereof and comprising:
• flow control means for controlling flow of the medical gas to the medical device and
• purification means for removing contaminant(s) from the spent gas.