Near infrared monitoring of perfusion and oxygen availability in abdominal organs and skeletal muscle during hypoxia

Near infrared spectroscopy was used to quantify blood content and oxygenation dynamics in abdominal organs and skeletal muscle of 18 anesthetized rabbits during hypoxic hypoxia. Liver, kidney and hindlimb muscle were exposed surgically. Laser diode pulses (775, 8 10, 862 and 904 nm) transmitted across the tissues were detected by means of a photomultiplier. The amount and redox level of tissue hemoglobin were estimated from the near infrared signals and monitored during 5 mm long hypoxic challenges (10% and 6% FiO₂) and subsequent recovery periods. In the kidney, exposure to 10% FiO2 resulted in rapid and symmetrical changes in oxygenated and reduced hemoglobin with 50% of the variations occurring within 1 mm and a plateau after 3 min. Total hemoglobin did not change and hemoglobin oxygenation returned to baseline within 1 mm of hypoxia cessation. Exposure to 6% FiO₂ doubled the decrease in oxygenated hemoglobin and induced a sustained vasoconstriction which decreased total hemoglobin content 2 min after initiation of hypoxia. Comparable patterns were observed in the liver and skeletal muscle with the following exceptions: Local vasoconstriction was generally not observed at 6% FiO₂, return to baseline oxygen availability was much slower in skeletal muscle than in the other organs.