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 &amp;gt; 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 &amp;gt; 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 &amp;gt; 0.002 and P &amp;gt; 0.007 respectively). Moreover, the time for the deoxyhaemoglobin signal to reach maximum values was found to correlate with the duration of occlusion (P &amp;gt; 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.</jats:p

Plethysmographic validation of near infrared spectroscopic monitoring of cerebral blood volume.

The validation of measurement of cerebral blood volume (CBV) and cerebral blood flow (CBF) using near infrared spectroscopy (NIRS) against jugular venous occlusion plethysmography is described. Repeated measurements in six infants were made using both techniques simultaneously. A close relationship between the two measurements of change in CBV was obtained in five infants. There was also a close relationship for measurement of CBF in four infants. This study confirms the possibility of using NIRS to monitor CBV continuously in the premature infant. This parameter may prove to be of greater clinical value than the intermittent measurement of CBF

Cyclical fluctuations in cerebral blood volume.

Cyclical fluctuations of cerebral blood flow velocity have been reported previously using Doppler ultrasound. The same phenomena was detected during investigations of changes in cerebral blood volume using near infrared spectroscopy. Rhythmic fluctuations of cerebral blood volume at a frequency of 3.5 cycles/minute is reported here