Semi-closed anesthetic system

Claim 1

IN A SEMI-CLOSED, PARTIAL REBREATHING ANESTHETIC SYSTEM, THE COMBINATION OF A GAS-FLOW CIRCUIT, EXHALATION AND INHALATION VALVES, A RESERVOIR BAG, SAID RESERVOIR BAG BEING OPERATIVE WHEN COMPRESSED TO PRODUCE POSITIVE PRESSURE INFLATION OF A PATIENT, AND A RELIEF VALVE MEANS, SAID RELIEF VALVE MEANS HAVING A VALVE ELEMENT EXTERNALLY ADJUSTABLE TO OPEN AND CLOSED SETTINGS IN WHICH SAID VALVE ELEMENT, ALTERNATIVELY, IS POSITIVELY SEATED IN A CLOSED POSITION OR DISPOSED IN AN OPEN POSITION PROVIDING A SELECTED VENTING FLOW RESTRICTION, MEANS FOR ACTUATING SAID VALVE ELEMENT IN ITS OPEN POSITIONS IN RESPONSIVE TO A PREDETERMINED PRESSURE DIFFERENTIAL ACTING THEREON TO DISPLACE SAID VALVE ELEMENT TO SAID CLOSED POSITION, INDEPENDENTLY OF SAID EXTERNAL ADJUSTMENT, DURING POSITIVE PRESSURE INFLATION AND SIGNAL MEANS PROJECTED FROM SAID VALVE BY DISPLACEMENT OF SAID VALVE ELEMENT TO GIVE VISUAL INDICATION OF THE CLOSED POSITION OF SAID VALVE ELEMENT IN RESPONSE TO SAID PREDETERMINED PRESSURE DIFFERENTIAL AND EXTERNALLY OPERABLE TO MANUALLY UNSEAT SAID VALVE ELEMENT AGAINST SAID PREDETERMINED PRESSURE DIFFERENTIAL ACTING THEREON.