Reliability-enhanced apparatus operation for re-breathing and methods of effecting same

#1. Field of the Invention

#The present invention relates to breathing circuits affording a re-breathing capability and, more specifically, to reliability and safety enhancements to apparatus employed to divert an exhaled breath volume for re-breathing by a patient and to subsequently remove such volume from the breathing circuit after re-breathing.

#2. Description of the Related Art

#FIG. 1 is a schematic drawing of a conventional breathing circuit including a pneumatically operated re-breathing valve;

#FIG. 2 is a semi-schematic drawing of breathing circuit components including a pressure-actuated airway valve for re-breathing and an associated flow and CO2 sensor arrangement modified in accordance with the present invention; and

#FIG. 3 is a drawing of three sets of exemplary flow and CO2 waveforms during the inspiratory period and a portion of the expiratory period illustrating a leak, re-breathing and normal operation of the airway valve.

#Referring now to FIG. 2 of the drawings, an exemplary pneumatically actuated airway valve 550 is depicted in association with a combined air flow and CO2 sensor 560, such as that described in previously referenced U.S. Pat. No. 5,789,660. One particularly preferred airway valve is disclosed in various embodiments in U.S. patent application Ser. No. 09/173,517 filed Oct. 15, 1998, assigned to the assignee of the present invention and incorporated herein by this reference. The airway valve as disclosed in the foregoing patent application is spring-biased to a normal mode, requiring application of a positive pneumatic pressure to shift to a re-breathing mode and divert an exhalation into a tubing loop. Of course, the present invention is not limited to the valve as disclosed in the foregoing patent application. Two pressure signals from the flow sensor portion of combined sensor 560 providing a differential indicative of air flow rate between airway valve 550 and the patient are detected by transducers in flow processing unit 562, which outputs a flow signal to patient monitor processing unit 522. A CO2 processing unit 564 processes the output from the CO2 sensor portion of combined sensor 560 and outputs a CO2 concentration signal to patient monitor processing unit 522.

#Airway valve 550 may be selectively actuated by valve control system 100, which comprises control line tubing 102 connected to a pressure source 104. Pressure source 104 may comprise either a positive or negative pressure source as known in the art, but preferably comprises a positive pressure source 104 such as a vessel containing compressed air or, more preferably, a pump to provide same at a suitable magnitude on demand. Such a pressure source 104 in the form of compressed air is commonly made available as needed through lines extending to a plurality of locations via pneumatic taps distributed throughout a health care installation such as a hospital or convalescent care facility. However, line pressure is usually high enough so that a regulator is required, making a pump preferable.

#Pressure source 104 may feed control line tubing 102 through a valve 106, which may comprise a conventional spring-loaded, two-position solenoid vent valve normally in an open state to vent control line tubing 102 to ambient air pressure. If a pump is employed as pressure source 104, two events must occur in order to shift airway valve 550 to the re-breathing mode: first, the pump must be actuated (for example, electrically, by closure of a switch) and second, the solenoid valve 106 must be electrically actuated to create a closed system between pressure source 104 and airway valve 550. It is preferred that the solenoid valve be closed before the pump is actuated, although this is not required.