Abstract: An improved tonometric catheter can be configured to have one or more pressure transmitting chambers for sensing the internal pressure such as the internal abdominal pressure of a subject. The tonometric catheter is inserted into the patient such as a nasogastric catheter. The pressure sensing chamber in the form of a balloon is insufflated with a pressure transmitting medium when the balloon is in the desired location. After insufflation of the chamber the catheter is connected to a pressure transducer or manometer which then provides an output reading the internal pressure of the subject. The tonometric catheter with a pressure sensing chamber is useful for sensing the internal abdominal pressure such as during laparoscopic surgery. The sensing of internal pressure can also be used at other locations along the gut or in the cranium. The monitoring of internal pressure is also useful in conjunction with the monitoring of internal pH.