Combined microlightguide spectrophotometry and microendoscopy for measurement of oxygen saturation in peripheral nerves

Microlightguide measurements of the spectral composition of backscattered l ight may be used to determine local tissue oxygen saturation and monitor ti ssue perfusion using intravenous injection of fluorescein dye as a contrast agent. We have used a combination of microlightguide spectrophotometry and microendoscopy to measure intravascular oxygen saturation (HbSaO(2) %) and monitor blood Bow in the sciatic nerve of 12 healthy male Sprague-Dawley r ats. The microlightguide and endoscope combination is a relatively new meas urement technique. The aims of this study were to determine whether microli ghtguide spectrophotometry and microendoscopy could be used to measure HbO( 2) and blood flow in peripheral nerves and to compare the measurements made using the flexible lightguide with the endoscope-lightguide combination. W e found no significant difference between the two types of measurement over similar regions of the nerve, mean SaO(2) % values 77.1% (95% CI = 75.4-78 .8) and 78.8% (95% CI = 77.5-80.1) respectively. During a period of hypoxia there was a similar fall in both arterial and nerve oxygen saturation. Fol lowing injection of fluorescein, the rate of increase in nerve fluorescence was used as a measure of perfusion, The combination of microlightguide spe ctrophotometry and microendoscopy allows the exact site of measurement to b e directly visualized. The minimally invasive nature of this technique may allow its application to the study of peripheral nerves in human subjects i n conditions such as diabetic neuropathy where vascular factors are thought to have an important role in aetiology.