Measurements of gastric mucosal blood flow by hydrogen gas clearance

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Abstract
The validity of the use of H2 gas clearance to measure gastric mucosal blood flow (GMBF) was investigated in the intact stomach of anesthetized dogs. With a modified, more sensitive Pt electrode, the H2 gas concentration to a nonflammable gas mixture was reduced. GMBF was repeated measured when the dogs inhaled gas containing 100, 10, and 3-5% H2. GMBF measured using 100% H2 demonstrated close correlation with inhaled gases containing 10% H2 (r = 0.84, slope = 0.89) and 3-5% H2 (r = 0.91, slope = 0.88). At a nonflammable concentration of 3% H2, it was safe to add 20% O2 into the gas mixture. The addition of O2 into the inhaled gas eliminated the transient hypoxia noted otherwise. It was possible to reduce the gas flow rate from 5-10 to 1-3 l/min. Regression analysis of GMBF determined by inhalation of 5% H2 at these flow rates revealed a significant linear correlation (r = 0.95, slope = 1.13). In 10 dogs GMBF was determined by using these low concentrations of H2 at the low flow rates also showed a good agreement (r = 0.93, slope = 0.65) with that measured by radioacitve microspheres. These 2 methods also demonstrated comparable changes in GMBF induced by i.v. infusion of histamine and vasopressin. With the modified technique H2 gas clearance could be a safe and accurate tool for quantitating gastric mucosal blood flow.