a tonometric device for use in hollow viscus tonometry and remote sensing of patient fluid parameters is disclosed . the device is capable of monitoring certain critical fluid properties of interest , such as oxygen gases and carbon dioxide gases in the wall tissue itself of the patient &# 39 ; s organ , rather than monitoring such properties in a lumen of the organ . a walled sampling chamber , which is preferably an inflated balloon member , is provided on an elongated tube , with provisions for positioning the sampling chamber in direct contact with a wall portion of the patient &# 39 ; s internal organ .