GLOBAL CEREBRAL BLOOD-FLOW DURING INFUSION OF ADENOSINE IN HUMANS - ASSESSMENT BY MAGNETIC-RESONANCE-IMAGING AND POSITRON EMISSION TOMOGRAPHY

Adenosine, an endogenous vasodilator, induces a cerebral vasodilation at hypotensive infusion rates in anaesthetized humans. At lower doses (< 100 mu g kg(-1) min(-1)), adenosine has shown to have an analgesic effect. This study was undertaken to investigate whether a low dose, c ausing tolerable symptoms of peripheral vasodilation affects the globa l cerebral blood flow (CBF). In nine healthy volunteers CBF measuremen ts were made using axial magnetic resonance (MR) phase images of the i nternal carotid and vertebral arteries at the level of C2-3. Quantitat ive assessment of CBF was also obtained with positron emission tomogra phy (PET) technique, using intravenous bolus [O-15]butanol as tracer i n four of the subject at another occasion. During normoventilation (5. 4 +/- 0.2 kPa, mean +/- s.e.m.), the cerebral blood flow measured by m agnetic resonance imaging technique, as the sum of the flows in both c arotid and vertebral arteries, was 863 +/- 66 mL min(-1), equivalent t o about 64 +/- 5 mL 100 g(-1) min(-1). The cerebral blood flow measure d by positron emission tomography technique, was 59 +/- 4 mL 100 g(-1) min(-1). All subjects had a normal CO2 reactivity. When adenosine was infused (84 +/- 7 mu g kg(-1) min(-1)) The cerebral blood flow, measu red by magnetic resonance imaging was 60 +/- 5 mL 100 g(-1) min(-1). T he end tidal CO2 level was slightly lower (0.2 +/- 0.1 kPa) during ade nosine infusion than during normoventilation. In the subgroup there wa s no difference in cerebral blood flow as measured by magnetic resonan ce imaging or positron emission tomography. In conclusion, adenosine i nfusion at tolerable doses in healthy volunteers does not affect globa l cerebral blood flow in unanaesthetized humans.