Continuous and non-invasive study of brain oxygenation in the calf by nearinfrared spectroscopy

Near infrared spectroscopy (NIRS) was used to detect changes in brain oxyge nation in five tranquilised calves that were placed on a hypoxic gas mixtur e (10 per cent O-2/90 per cent N-2) and hyperoxic gas mixture (30 per cent O-2/70 per cent N-2) for five minutes at each concentration. A NIRO 500 (Ha mamatsu, Japan) was used for;he NIRS, with the incident light source and se parate detector (optodes) placed on shaved skin on the most dorsal surface of the frontal bone. Sequential arterial blood gas sample analyses provided confirmation of the appropriate change in systemic oxygenation status. By the end of the five-minute-period of breathing 10 per cent oxygen, NIRS of the calf head detected highly significant changes in haemoglobin oxygenatio n reflective of hypoxaemia, with oxyhaemoglobin decreasing by 23.5 units (P <0.01) and deoxyhaemoglobin increasing by 45.6 units, (P<0.01) from the bas eline of breathing room air. Total haemoglobin (oxyhaemoglobin + deoxyhaemo globin) showed a significant increase of 22.1 units (P<0.05) but there was no significant change in NIRS determined cytochrome aa(3) oxygenation. Conc omitant blood gas alterations included significant decreases in PaO2 (-27.8 mmHg, P<0.01), haemoglobin saturation (-29.0 per cent, P<0.05), and PaCO2( -7.8 mmHg, P<0.05) and significantly increased blood pH (0.059, P<0.05). At the end of the five minutes of breathing 30 per cent oxygen NIRS of the ca lf head detected significantly increased oxyhaemoglobin (13.1 units, P<0.01 ) and decreased deoxyhaemoglobin (-13.7 units, P<0.05) when compared with b aseline breathing of room aim. Total haemoglobin and cytochrome aa(3) were unchanged from baseline. The accompanying arterial blood gas changes includ ed significant increases in PaO2 (30.9 mmHg, P<0.05), arterial O-2 saturati on (11.7 per cent, P<0.05), and significantly decreased pH (-0.026, P<0.05) . This study showed that NIRS can be used to continuously and non-invasivel y detect cerebral oxygenation changes in the live calf in response to both increased and decreased systemic arterial oxygen. Additionally, despite ind uction of profound hypoxaemia, cytochrome aa3 in the brain did not appear t o become reduced.