title: Assessment of a new prototype hydrogel CO( 2 ) sensor; comparison with air tonometry.
abstract: OBJECTIVE
  Gastrointestinal ischemia is always accompanied by an increased luminal CO(2). Currently, air tonometry is used to measure luminal CO(2). To improve the response time a new sensor was developed, enabling continuous CO(2) measurement. It consists of a pH-sensitive hydrogel which swells and shrinks in response to luminal CO(2), which is measured by the pressure sensor. We evaluated the potential clinical value of the sensor during an in vitro and in vivo study.
  
  
  METHODS
  The response time to immediate, and stepwise change in pCO(2) was determined between 5 and 15 kPa, as well as temperature sensitivity between 25 and 40 degrees C at two pCO(2) levels. Three sensors were compared to air tonometry (Tonocap) in healthy volunteers using a stepwise incremental exercise test, followed by a period of hyperventilation and an artificial CO(2)-peak.
  
  
  RESULTS
  The in vitro response time to CO(2) increase and decrease was mean 5.9 and 6.6 min. The bias, precision and reproducibility were +5%, 3% and 2%, resp. Increase of 1 degrees C at constant pCO(2) decreased sensor signal by 8%. In vivo tests: The relation with the Tonocap was poor during the exercise test. The response time of the sensor was 3 min during hyperventilation and the CO(2) peak.
  
  
  CONCLUSIONS
  The hydrogel carbon dioxide sensor enabled fast and accurate pCO(2) measurement in a controlled environment but is very temperature dependent. The current prototype hydrogel sensor is still too unstable for clinical use, and should therefore be improved.
authors.affiliation: Gastroenterology, Medical Spectrum Twente Hospital, Ariensplein 1, PO Box 50000, Enschede, 7500 KA, Netherlands. rinzetersteege@hotmail.com
authors.forename: Rinze W F
authors.initials: RW
authors.lastname: ter Steege
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: Herber
authors.forename: Wouter
authors.initials: W
authors.lastname: Olthuis
authors.forename: Piet
authors.initials: P
authors.lastname: Bergveld
authors.forename: Albert
authors.initials: A
authors.lastname: van den Berg
authors.forename: Jeroen J
authors.initials: JJ
authors.lastname: Kolkman
mesh_terms: D000388:Air / Q000032:analysis; D002245:Carbon Dioxide / Q000032:analysis*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005753:Gastric Mucosa / Q000378:metabolism*; D006801:Humans; D020100:Hydrogels / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008365:Manometry / Q000295:instrumentation* / Q000379:methods; D010865:Pilot Projects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013686:Telemetry / Q000295:instrumentation* / Q000379:methods; D014159:Transducers
chemical_list: D020100:Hydrogels; D002245:Carbon Dioxide