Comparison of blood flow measurements by hydrogen gas clearance and laser Doppler flowmetry in the rat duodenum

This report examines the relationship between hydrogen gas clearance and laser Doppler flowmetry measurements in the duodenum of fasted, anesthetized rats under conditions of 1) reduced perfusion due to graded levels of hemorrhagic hypotension or 2) hyperemia due to perfusion with step doses of acid. There was a significant correlation between hydrogen gas clearance and laser Doppler flowmetry measurements (r = 0.73, p less than 0.01; n = 32 data points in 16 rats). The change in laser Doppler flowmetry values from the period immediately before to the period during the 3 min of acid perfusion was significantly correlated with the dose of acid used (r = 0.51, p less than 0.01; n = 27 rats). The changes in hydrogen gas clearance and laser Doppler flowmetry values from the 30-min period before to the 30-min period after acid perfusion were not correlated with the dose of acid used (r = 0.30 and 0.33, respectively). We conclude that in the rat duodenum 1) the significant linear correlation between hydrogen gas clearance and laser Doppler flowmetry when blood flow is reduced suggests that the countercurrent exchange mechanism is unlikely to modulate significantly hydrogen gas clearance measurements, and 2) the dose-related acid-induced duodenal hyperemia is transient rather than persistent when the rat duodenum is exposed to hydrochloric acid (0.03 to 0.1 N) for 3 min.