Testing Intestinal Function Possibilities Offered by 13 co 2 Breath Tests and Stable

Breath tests have in common the fact the subject is given a substrate in which C atoms normally present in the functional group are replaced by the stable isotope C. This functional group is cleaved enzymatically under specific circumstances, during either transit through the gastrointestinal tract, absorption, or further metabolism of the absorbed substrate. After cleavage, the labeled subgroups undergo a metabolic process that ends with the expiration of labeled co2. It is necessary that the speed-determining (rate-limiting) factor of the whole physiologic process is directly related to the genesis of co2. The co2 mixes with the body pool of CO2/HCO3" and is expired. In this way, the exhalation of co2 reflects the function to be investigated. The process is shown schematically in Fig. 1. For co2 measurement to be used to demonstrate a well-defined gastrointestinal function, an enzyme activity, or bacterial metabolism, the C substrate has to be chosen in such a way that the enzyme or function is the rate-limiting step in co2 production. When the excretion of the tracer in the breath is expressed as percent dose per hour or as cumulative percent dose excreted over a defined time period, a dynamic analysis of the variable examined is obtained over time. The co2 breath tests are excellent investigative methods, as their scientific basis is sound and well conceived, the results have been validated in an unequivocal way, and their application is accepted by a growing number of scientists.