Relationship of ¹³³Xe Cerebral Blood Flow to Middle Cerebral Arterial Flow Velocity in Men at Rest

Abstract

Cerebral blood flow (CBF) was measured by 133Xe clearance simultaneously with the velocity of blood flow through the left middle cerebral artery (MCA) over a wide range of arterial PCO2 in eight normal men. Average arterial PCO2, which was varied by giving 4% and 6% CO2 in O2 and by controlled hyperventilation on O2, 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 ranged from 42.8 to 94.2 cm/s. The relationship of CBF to MCA blood-flow velocity over the imposed range of arterial PCO2 was described analytically by a parabola with the equation: CBF = 22.8 - 0.17 x velocity + 0.006 x velocity2 The observed data indicate that MCA blood-flow velocity is a useful index of CBF response to change in arterial PCO2 during O2 breathing at rest. With respect to baseline values measured while breathing 100% O2 spontaneously, percent changes in velocity were significantly smaller than corresponding percent changes in CBF at increased levels of arterial PCO2 and larger than CBF changes at the lower arterial PCO2. These observed relative changes are consistent with MCA vasodilation at the site of measurement during exposure to progressive hypercapnia and also during extreme hyperventilation hypocapnia.

Transcranial doppler sonography and internal jugular bulb saturation during hyperventilation in patients with fulminant hepatic failure

“…However, during extreme hypocapnia, the cerebral vessels may dilate. 15 In the present study, PaCO 2 was only moderately decreased and therefore such vasodilatation was unlikely to occur.…”

“…Most clinical studies agree that the diameter of large arteries remains almost constant during arterial carbon dioxide (CO 2 ) tension changes. [10][11][12][13][14][15][16] The aim of the present study is to compare absolute and regional CBF determined by the xenon 133 ( 133 Xe) washout technique with TCD velocity and the internal jugular bulb oximetry (svJO 2 ) as a measurement of cerebral CO 2 reactivity in patients with FHF.…”

Effect of Short-Term Hyperventilation on Cerebral Blood Flow Autoregulation in Patients With Acute Bacterial Meningitis

“…We used an infusion of norepinephrine to increase MAP in the patients. A constant diameter of the middle cerebral artery during norepinephrine infusion has been reported in healthy volunteers 25,26 and in patients with neurological diseases 27 as well as in patients with acute liver failure. 28 Changes in the diameter of the insonated artery do not explain the increase in V mean because a-v DO 2 would then have been expected to remain unchanged despite changes in V mean .…”

Dynamic Cerebral Autoregulation in Acute Lacunar and Middle Cerebral Artery Territory Ischemic Stroke

“…The MCA V mean is assumed to represent flow velocity in the center of the vessel, and, when flow is laminar, MCA V mean follows 133 Xe clearancedetermined CBF. 23 Thus, the constancy of vessel diameter links changes in MCA V to those in CBF. When nonlaminar blood flow in the affected cerebral arteries is considered, MCA V mean may change out of proportion to flow, and, therefore, the analysis was restricted to normally shaped Doppler signals.…”