Abstract: A system is disclosed to prevent the build up of pressure within a patient circuit when an oxygen flush is activated in a ventilator powered anesthesia system. In the event the user activates the oxygen flush at a time that the ventilator is in the inhalation cycle providing a breath to the patient, a valve is automatically opened to vent the patient circuit to the atmosphere, thereby preventing that additional oxygen flow to the patient circuit from resulting in an undesirable pressure build up that could affect the lungs of the patient.

Abstract: A needle valve having improved economy of manufacture and assembly is disclosed in which the tapered end of the needle moves axially with respect to a valve seat having a cylindrical opening but does not rotate. An adjusting means, in turn, is rotated to cause the axial movement of the needle and an alignment means, preferably a sphere, is interposed between the needle and the adjusting means to provide alignment between the two components. The needle itself is also spring biased away from the valve seat.

Abstract: An ultrasonic flowmeter which measures gas velocity including a pair of ultrasonic transducers oppositely located around a conduit at a predetermined angle to the flow direction. Each transducer alternates between acting as a transmitter and a detector of ultrasonic frequencies, thus as one transducer transmits, the other receives. A measurement is made of the time of flight of the ultrasonic signal between the transmitter transducer and the receiver transducer and a microcomputer calculates the velocity of the gas by a known mathematical relationship utilizing the difference between the time of flight of the ultrasonic signals traveling upstream and those traveling downstream. The time of flight is determined by the phase shift or difference in phase angle between the signal at the transmitter transducer and the signal detected by the receiver transducer. To prevent ambiguity arising when the phase angle difference exceeds 360.degree.

Abstract: An instrument for withdrawing equilibrated blood gases in vivo, which comprises a tubular gas permeable membrane inserted through a cannular into the blood stream. In preferred form, the tubular membrane comprises a continuous conduit in contact with the blood. An inlet supply gas terminal is constructed for connection to a carrier gas source, and an outlet gas terminal, for connection to an appropriate analyzer. In preferred forms of the invention, a heater maintains the equilibrated gases at above normal body temperature as they pass to the analyzer; and a port is provided for drawing blood samples from the area being analyzed without dislodging the catheter.

Abstract: Method and apparatus for withdrawing and analyzing gases dissolved in liquid, more specifically, equilibrated blood gas samples in vivo. A catheter including a semipermeable membrane, connected to include a volume of carrier gas at atmospheric pressure, is introduced percutaneousluy into the bloodstream. After a predetermined period, equilibratin occurs between the blood gases and the carrier gas. By means of displacement in the volume or reduction in the pressure, the carrier gas including the equilibrated gas is then removed from the semipermeable membrane to another area for analysis. A corresponding volume of carrier gas is replaced in the semipermeable membrane from an inlet supply.