Reflectance spectrophotometry in the gastrointestinal tract: Limitations and new applications

OBJECTIVES: Reflectance spectrophotometry (RS) assesses blood flow changes by measuring an index of Hb concentration (IHB) and index of Hb oxygen saturation (ISO 2). We tested the following hypotheses: 1) endoscopic RS measurements obtained by two observers and with the aid of fiber optic and video endoscopes are similar, and 2) the method is suitable for documenting mesenteric venoconstriction associated with systemic hypoxia and blood flow autoregulation associated with hemorrhagic hypotension. METHODS: Study 1: two investigators obtained baseline gastric mucosal RS measurements in anesthetized rats (n = 3) before and after stepwise reduction of blood pressure induced by arterial hemorrhage. Study 2: subjects were examined by both fiber optic and video endoscopes. Endoscopic RS measurements were obtained at 20 cm from the anal verge. Study 3: video endoscope was used to obtain RS measurements in oxygen-dependent patients on and off oxygen treatment. Study 4: the procedures in study 1 were repeated in five additional rats by one of the investigators. RESULTS: Study 1: there was good agreement between the measurements of IHB and ISO 2 between the two investigators. Study 2: video endoscope-assisted measurements were consistently lower. Study 3: cessation of oxygen treatment produced a significant drop in oxygen saturation (pulse oximetry), decline in ISO 2, and rise in IHB. Study 4: when blood pressure varied between 90% and 40% of baseline, gastric mucosal blood flow (IHB) was maintained at ∼70% of baseline level. CONCLUSIONS: We confirmed that reproducible measurement can be obtained by different investigators using standardized techniques. Standardization of endoscopic equipment is also necessary to overcome the significant limitation of endoscopic equipment on RS measurements. RS measurements can document mesenteric venoconstriction associated with systemic hypoxia and blood flow autoregulation associated with hemorrhagic hypotension.