NONINVASIVE MEASUREMENT OF CARDIAC OXYGENATION AND HEMODYNAMICS DURING TRANSIENT EPISODES OF CORONARY-ARTERY OCCLUSION AND REPERFUSION IN THE PIG

1. The non-invasive method of near-infrared spectroscopy was used to m easure myocardial oxygenation and haemodynamics in response to left an terior descending coronary artery occlusion in a porcine model. 2. Nea r-infrared spectroscopy measures changes in haemoglobin (and myoglobin ) oxygenation and blood volume to yield information on tissue perfusio n and flow. It also measures the redox state of cytochrome aa(3), 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 cha nges in deoxyhaemoglobin, oxyhaemoglobin and cytochrome aa(3) measured during occlusion were all highly significant compared with baseline v ariation. In all occlusions (n=13) a rapid decrease in oxyhaemoglobin concentration (-75.83+/-3.27 gamma mol/l, mean+/-SEM) with a simultane ous increase in deoxyhaemoglobin of 9.27+/-1.69 mu mol/l was measured. The total haemoglobin concentration also fell by -71.3+/-5.32 mu mol/ l. Cytochrome aa(3) was also reduced during occlusion (-8.35+/-1.044) mu mol/l. 4. Over the range 24-60 s occlusion, the magnitude of the fa ll in total haemoglobin and oxyhaemoglobin correlated with the duratio n of occlusion (P<0.003 and 0.013 respectively). For total haemoglobin only the magnitude of the fall correlated with the increase upon rele ase of occlusion (r=0.89, P<0.003). 5. Release of occlusion (n=8) resu lted 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 finall y oxyhaemoglobin at 29.75+/-5.96 s. The difference between the timing of the maxims after reperfusion is significant (P<0.002 and P<0.007 re spectively). Moreover, the time for the deoxyhaemoglobin signal to rea ch maximum values was found to correlate with the duration of occlusio n (P<0.04). This could be indicative of the PO2 of the ischaemic tissu es and an immediate off-loading of oxygen from oxyhaemoglobin. The res ults are reliable, reproducible and sensitive enough to detect the kin etics of haemoglobin oxygenation from a beating heart in situ.