Method and apparatus for in vivo blood gas analysis

Claim 5

A method in accordance with claim 2 wherein said carrier gas is characterized relative to said dissolved blood gases by either a slow rate of diffusion through said membrane or a low solubility in blood, or both.

Claim 6

The method in accordance with claim 2 wherein said volume of carrier gas containing said equilibrated blood gases substantially exceeds the portion analyzed.

Claim 7

The method in accordance with claim 4 wherein said volume of carrier gas including said equilibrated blood gas exceeds the portion analyzed by at least a factor of ten.

Claim 8

The method is accordance with claim 2 in which the steps of removing and isolating a portion of the volume of said carrier gas containing said equilibrated gases from the remaining carrier gas is carried out by first reducing the pressure in means connected to said membrane member for sampling a discrete portion of said volume, thereby causing the said portion to move from said member to said sampling means, connecting said sampling means to a gas analyzer and subsequently forcing the said portion containing said equilibrated gases from said sampling means to said gas analyzer by introducing into said sampling means carrier gas from an auxilliary source.

Claim 9

The method in accordance with claim 6 which comprises the steps of detecting the peak amount of said equilibrated gas distributed in said portion of carrier gas as said portion moves from the membrane member to said sampling means, and actuating valve means to admit a discreet amount of said portion including said equilibrated gases to said gas analyzer when said peak is positioned in said sampling means in a preselected position in relation to the intake of said gas analyzer.

Claim 10

The method in accordance with claim 7 wherein said peak generates a signal, detecting and utilizing said signal to actuate said valve means.

Claim 11

The method in accordance with claim 7 wherein said carrier gas is characterized by a thermal conductivity which is substantially different from that of the blood gas to be measured.

Claim 12

The method in accordance with claim 9 wherein helium is employed as a carrier gas.

Claim 13

The method in accordance with claim 9 wherein the space rate of change to thermal conductivity in said portion of carrier gas including said equilibrated blood gases is represented by a "bell shaped" curve, detecting a signal corresponding to the space rate of change in said thermal conductivity represented by the change in slope of said curve, and utilizing said signal to actuate said valve means to receive said portion including said equilibrated blood gases at a position represented by the flat top portion of said curve.

Claim 18

In a system in accordance with claim 13 wherein said means connected to the exhaust terminal of said catheter for removing said volume of carrier gas including said equilibrated blood gas from said passage to said means for analyzing the blood gases comprises: an auxilliary source of carrier gas, pumping means constructed and arranged to induce evacuation and exhaust cycles in said system, a gas purging valve connected to said pumping means; a conduit system including a sampling valve having at least two positions for transmission therethrough; during the evacuation cycle of said system: said sampling valve operable in a first position for connecting the exhaust terminal of said catheter to said pumping means to receive at least a portion of said volume of said carrier gas including said equilibrated blood gas in said sampling valve, and in a second position for connecting said auxilliary carrier source through said sampling valve to said means for analyzing said equilibrated blood gas, whereby said portion is forced into said blood gas analyzing means; and during the exhaust cycle of said system: said purging valve connectable for purging said pumping means of gas in preparation for the next evacuation cycle.

Claim 19

A system in accordance with claim 14 wherein said pumping means comprises automatic vacuum pumping means, and said system comprises detecting means connected adjacent one terminal of said sampling valve and responsive to detect the peak of equilibrated blood gases in said volume of carrier gas passing from said semipermeable membrane member to said sampling valve, and to generate a signal in response to the passage of said peak, and means responsive to said detecting means and actuated by said signal for operating said sampling valve to connect said auxilliary carrier source through said sampling valve to said gas analysis means.

Claim 20

A system in accordance with claim 15 wherein the space rate of change of the thermal conductivity of said volume of equilibrated blood gas varies as a function of the distribution of dissolved blood gas therein, and wherein said detecting means is sensitive to the space rate of change of thermal conductivity in said volume.

Claim 21

A system in accordance with claim 16 wherein said function is a "bell shaped" curve having a flattened peak, and wherein said defecting means is responsive to a change of slope of said "bell shaped" curve to actuate said sampling valve to introduce a portion of said volume including said equilibrated blood gases represented by the flat portion of said peak into said means for analyzing blood gas.

Claim 22

A system in accordance with claim 13 wherein said means for analyzing the blood gases comprises a gas chromatograph.

Claim 23

A system in accordance with claim 13 wherein the membrane member comprising said catheter comprises tubular means constructed for insertion percutaneously into the blood vessel in a direction extending along the principal axis thereof and simultaneously providing a continuous gas permeable conduit in contact with the blood of said subject between said input and output terminals, said input and output terminals both the the proximal end of said tubular means, and connecting means to said input and output terminals comprising a housing including input and output gas receptacles respectively constructed and arranged for connection in circuit relation to said source of carrier gas at said input receptacle and to said means for analyzing the blood gases at said output receptacle.

Claim 24

The combustion in accordance with claim 19 wherein said semipermeable tubular membrane member consists essentially of a polysiloxane polymer.

Claim 25

A system in accordance with claim 19 wherein said gas permeable conduit has a substantially uniform cross-section and permeability along its length between said terminals.

Claim 26

The combination in accordance with claim 19 wherein said semipermeable tubular membrane member comprises a plurality of lumens interconnected to provide a continuous uniform gas permeable conduit between said input and output terminals having a length in contact with the blood which substantially exceeds the length of said membrane member.

Claim 27

The combination in accordance with claim 22 wherein said semipermeable tubular membrane member comprises at least two parallel lumens of substantially uniform cross-section and permeability forming a gas permeable conduit substantially double the length of said tubular membrane member and joined together by connecting means at their distal ends to provide a reversal of gas flow from one to the other, the proximal ends of said lumens respectively connected to said input and output terminals.

Claim 28

The combination in accordance with claim 22 wherein each of said lumens has a cross-sectional dimension not exceeding about 0.011 inch and said membrane has an overall cross-sectional dimension not exceeding about 0.028 inch.

Claim 29

The combination in accordance with claim 19 wherein said membrane member comprises an external membrane tube coaxial with another tube, said tubes being inter-connected at their distal ends.