Exercise Tonometry for the Diagnosis of Chronic Gastrointestinal Ischemia

This thesis investigates the role of gastrointestinal exercise tonometry as a functional diagnostic test in patients suspected of chronic gastrointestinal ischemia. In contrast with all other diagnostic modalities (angiography, duplex sonography, CT- and MRangiography) that only provide information about vessel anatomy, vessel patency or blood flow, tonometry can actually demonstrate end-organ ischemia. Measurement of gastrointestinal luminal to blood PCO2 by means of tonometry has been shown to provide exactly that information: the presence or absence of ischemia. Until now it is the only clinically feasible, i.e. minimally invasive and bedside, technique for monitoring the adequacy of gastrointestinal (mucosal) perfusion in a wide variety of conditions such as (hemorrhagic) shock, sepsis, trauma, pancreatitis, cardiovascular and gastro-esophageal surgery. In chapter two a review of the current thoughts on tonometry is given. Uncertainties about physiological background, methodology, and clinical use have hindered tonometry from gaining the status of a routine diagnostic technique. Most of the initial problems however have been addressed and solved, for instance by the introduction of automated air tonometry, and recognizing that measurements have to be done in an empty stomach and after adequate gastric acid suppression. Gastric tonometry after food provocation has been used as diagnostic test for chronic gastrointestinal ischemia. This has resulted in varying and disappointing accuracies. In a pilot study by J.J. Kolkman, using physical exercise as an alternative provocative manoeuvre, gastric (saline) tonometry showed to be a promising test for the detection of symptomatic chronic gastrointestinal ischemia. In chapters two, three and four of this thesis questions arising from this pilot study are addressed, including the intensity of exercise needed for provocation of gastrointestinal ischemia, the best way to monitor this exercise intensity and the best location in the gastrointestinal tract for tonometric measurements.

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