Effect of ventilation on breath hydrogen measurements
Perman, J.A.; Modler, S.; Engel, R.R.; Heldt, G.
Journal of Laboratory and Clinical Medicine 105(4): 436-439
1985
ISSN/ISBN: 0022-2143 PMID: 3920335 Document Number: 251663
Measurement of hydrogen (H2) sugar malabsorption. Standard breath H2 tests require comparison of H2 concentrations in expired air samples obtained innediately before and after delivery of a test substrate. Comparison of interval samples assumes that minute ventilation (.ovrhdot.VE) remains constant unless H2 is independent of .ovrhdot.VE. Because healthy individuals have variable .ovrhdot.VE, how H2 is influenced by changes in .ovrhdot.VE. H2 concentration was studied at different ventilatory rates in 8 healthy adults. It varied inversely with .ovrhdot.VE in all subjects. The effect of changes in .ovrhdot.VE on the relationship between H2 and CO2 concentrations in expired air samples was also compared. At constant .ovrhdot.VE, the relationship between H2 and CO2 was linear (r = 0.95, P < 0.001). As .ovrhdot.VE changed, the relationship between H2 and CO2 became nonlinear. Changes in .ovrhdot.VE altered methane concentrations in expired air samples from 2 subjects in a manner comparable to the effect on H2. Breath H2 concentrations apparently vary with ventilatory rate. Under conditions where frequent changes in .ovrhdot.VE are likely, independent measures for ensuring constant .ovrhdot.VE over sampling times are necessary. Use of CO2 as an internal standard to normalize H2 values to an alveolar concentration is appropriate only under conditions of constant .ovrhdot.VE.