Focal gastric mucosal blood flow by laser-Doppler and hydrogen gas clearance: a comparative study

We compared focal gastric mucosal blood flow (GMBF) values simultaneously obtained by laser-Doppler flowmetry (LDF) and hydrogen gas clearance (HGC) from the same point in a chambered segment model of the gastric corpus in two sets of experiments (Experiments 1 and 2) involving nine anesthetized dogs (weighing 20-30 kg). We also investigated the feasibility of obtaining a conversion factor for LDF signal to absolute flow values. The GMBF values showed a highly significant linear correlation within individual experiments and for the combined data in experiments 1 (r = 0.7132, P less than 0.0001, n = 37) and 2 (r = 0.5660, P less than 0.0001, n = 61). The combined data did not corroborate a common regression line hypothesis in both experiments (Experiment 1: F = 6.59, P less than 0.0005; Experiment 2: F = 10.57, P less than 0.0005). There was a statistically significant difference between the slopes of the 5 and 4 linear regression lines obtained in Experiments 1 (F = 13.15, P less than 0.0005) and 2 (F = 21.14, P less than 0.0005), respectively. The LDF signal was stable and optical coupling is not a problem in this experimental model. HGC and GMBF values were reliable and highly reproducible within dog measurements. We conclude that LDF and HGC are comparable in the measurement of focal GMBF. Our data, however, did not suggest the existence of a conversion factor for LDF signal to absolute flow values from experiment to experiment. Conversion will have to be within individual experiments. Thus, LDF may only be useful in situations where qualitative changes in focal blood flow are investigated.