Fiber optic sensing of tissue pH to assess low blood flow states

Tissue pH is a regional measure of anaerobic metabolism and low blood flow state that can be measured using near infrared (NIR) spectroscopy (700 - 1100 nm). NIR light passes through the skin to probe muscle and tissue at depths of 5 - 10 mm. We have used a fiber optic probe to collect light both through skin and directly from internal organs during surgical procedures, to investigate the measurement of tissue pH in a number of settings. We have demonstrated the successful optical measurement of tissue pH during complete blood flow cessation (vessel occlusion) and during reduced blood flow conditions such as hemorrhagic shock. We have shown, in a series of animal studies, that optically measured tissue pH is accurate under conditions of variable blood flow, temperature, hematocrit and oxygen saturation.