Non-Invasive Measurement of Cardiac Oxygenation and Haemodynamics during Transient Episodes of Coronary Artery Occlusion and Reperfusion in the Pig

1. The non-invasive method of near-infrared spectroscopy was used to measure myocardial oxygenation and haemodynamics in response to left anterior descending coronary artery occlusion in a porcine model.

2. Near-infrared spectroscopy measures changes in haemoglobin (and myoglobin) oxygenation and blood volume to yield information on tissue perfusion and flow. It also measures the redox state of cytochrome aa₃, thus providing information about intracellular oxygen utilization.

3. Left anterior descending coronary artery occlusion was induced to produce periods of ischaemia lasting between 24 s and 13.5 min (n = 13). The changes in deoxyhaemoglobin, oxyhaemoglobin and cytochrome aa₃ measured during occlusion were all highly significant compared with baseline variation. In all occlusions (n = 13) a rapid decrease in oxyhaemoglobin concentration (−75.83 ± 3.27 μmol/l, mean ± SEM) with a simultaneous increase in deoxyhaemoglobin of 9.27 ± 1.69 μmol/l was measured. The total haemoglobin concentration also fell by −71.3 ± 5.32 μmol/l. Cytochrome aa₃ was also reduced during occlusion (–8.35 ± 1.044) μmol/l.

4. Over the range 24–60 s occlusion, the magnitude of the fall in total haemoglobin and oxyhaemoglobin correlated with the duration of occlusion (P > 0.003 and 0.013 respectively). For total haemoglobin only the magnitude of the fall correlated with the increase upon release of occlusion (r = 0.89, P > 0.003).

5. Release of occlusion (n = 8) resulted in an immediate increase in the concentration of deoxyhaemoglobin at 9.88 ± 1.06 s, then total haemoglobin at 13.62 ± 1.23 s and finally oxyhaemoglobin at 29.75 ± 5.96 s. The difference between the timing of the maxima after reperfusion is significant (P > 0.002 and P > 0.007 respectively). Moreover, the time for the deoxyhaemoglobin signal to reach maximum values was found to correlate with the duration of occlusion (P > 0.04). This could be indicative of the Po₂ of the ischaemic tissues and an immediate off-loading of oxygen from oxyhaemoglobin. The results are reliable, reproducible and sensitive enough to detect the kinetics of haemoglobin oxygenation from a beating heart in situ.