Abstract: A tonometry catheter apparatus comprises an elongate, flexible, multilumen tube having a proximal end to be positioned outside the human body and a distal end to be positioned within a portion of the human body. Provided at the distal end are an ingress lumen through which gas may enter the tube, and an egress lumen through which gas may exit the tube. A hollow connecting member links the ingress lumen and the egress lumen to define a sampling circuit through which the gas may continuously recirculate. In one embodiment, the distal end of the tube is provided with a distensible, gas-permeable vessel in communication with the ingress and egress lumens. In an alternative embodiment, an extracorporeal gas-permeable membrane links the sampling circuit to a separate, gas-containing analyzing circuit. In each embodiment, a pump is provided for propelling gas through the circuits, and a sensor continuously quantifies the level of gas within the circuits.

Abstract: A tonometry catheter apparatus comprising an elongate flexible tube having a proximal extracorporeal end and a distal interacorporeal end. The distal end of the tube has a distensible, gas-permeable tonometry vessel, the vessel and the distal end defining therebetween a space which may be filled with a gas. An in-flow orifice lies in communication with the space, through which gas may enter the vessel. An in-flow lumen with a distal end and a proximal end is also provided, the distal end being in communication with the in-flow orifice. An out-flow orifice lies in communication with the space, through which the gas may exit the vessel. An out-flow lumen is disposed with a distal end and a proximal end, the distal end being in communication with the out-flow orifice. The proximal end of the tube has a pump for propelling gas into the vessel. A capnometer and a sensor quantify the level of carbon dioxide (CO.sub.2) gas exiting the vessel.