Carbogen-induced changes in rat mammary tumour oxygenation reported by near infrared spectroscopy

We have evaluated the ability of steady-state, radially-resolved, broad-ban d near infrared diffuse reflectance spectroscopy to measure carbogen-induce d changes in haemoglobin oxygen saturation (SO2) and total haemoglobin conc entration in a rat R3230 mammary adenocarcinoma model in vivo. Detectable s hifts toward higher saturations were evident in all tumours (n = 16) immedi ately after the onset of carbogen breathing. The SO2 reached a new equilibr ium within 1 min and remained approximately constant during 200-300 s of ad ministration. The return to baseline saturation was more gradual when carbo gen delivery was stopped. The degree to which carbogen increased SO2 was va riable among tumours, with a tendency for tumours with lower initial SO2 to exhibit larger changes. Tumour haemoglobin concentrations at the time of p eak enhancement were also variable. In the majority of cases, haemoglobin c oncentration decreased in response to carbogen, indicating that increased t umour blood Volume was not responsible for the observed elevation in SO2. W e observed no apparent relationship between the extent of the change in tum our haemoglobin concentration and the magnitude of the change in the satura tion. Near infrared diffuse reflectance spectroscopy provides a rapid, non- invasive means of monitoring spatially averaged changes in tumour haemoglob in oxygen saturation induced by oxygen modifiers.