Jm. Clark et al., RELATIONSHIP OF XE-133 CEREBRAL BLOOD-FLOW TO MIDDLE CEREBRAL ARTERIAL FLOW VELOCITY IN MEN AT REST, Journal of cerebral blood flow and metabolism, 16(6), 1996, pp. 1255-1262
Cerebral blood flow (CBF) was measured by Xe-133 clearance simultaneou
sly with the velocity of blood flow through the left middle cerebral a
rtery (MCA) over a wide range of arterial Pco(2) in eight normal men.
Average arterial Pco(2), which was varied by giving 4% and 6% CO2 in O
-2 and by controlled hyperventilation on O-2, ranged from 25.3 to 49.9
mm Hg. Corresponding average values of global CBF15 were 27.2 and 65.
0 ml 100 g min(-1), respectively, whereas MCA blood-flow velocity rang
ed from 42.8 to 94.2 cm/s. The relationship of CBF to MCA blood-flow v
elocity over the imposed range of arterial Pco(2) was described analyt
ically by a parabola with the equation: CBF = 22.8 - 0.17 x velocity 0.006 x velocity(2) The observed data indicate that MCA blood-flow ve
locity is a useful index of CBF response to change in arterial Pco(2)
during O-2 breathing at rest. With respect to baseline values measured
while breathing 100% O-2 spontaneously, percent changes in velocity w
ere significantly smaller than corresponding percent changes in CBF at
increased levels of arterial Pco(2) and larger than CBF changes at th
e lower arterial Pco(2). These observed relative changes are consisten
t with MCA vasodilation at the site of measurement during exposure to
progressive hypercapnia and also during extreme hyperventilation hypoc
apnia.