Near-infrared spectroscopy (NIRS) can be used as a non-invasive monitoring technique for regional cerebral oxygenation (rScO₂). We studied basal rScO₂, after atropin blockade and after hypertensive testing by phenylephrin in a cardiac muscarinic receptor overexpression rabbit strain with severe cardiac pauses (H) compared to a normal rabbit strain (N).

Results

– rScO₂ values are systematically higher in H rabbits compared to N rabbits: (H=75.6%±5.6 vs N=60.7%±5.7, n=6 in each group, P<0.05);

– Atropin decrease rScO₂ in both groups, but this reduction is more marked in H rabbits (Fig. 1);

– During the phenylephrin test, the cardiac pauses in the H group are longer than in the N group (H: 24 285ms±8 837 [n=6] vs N: 3 566ms±1 455 [n=8]).

We observed a progressive hypoxia with rScO₂ decrease in both groups during the test. Unexpectedly, the rScO₂ reduction is not as pronounced in H rabbits with severe cardiac pauses as in the N group (Fig. 1).

These data support the hypothesis that: A higher rScO₂ by NIRS could reflect a higher central muscarinic receptor density, protecting brain against hypoxia. RScO₂ could be a non-invasive muscarinic receptor overexpression marker, useful in vasovagal syncope study.