Measurement of regional cerebral blood flow with 133xenon and a multiple-crystal scintillation camera

Evaluation of the cerebral hemodynamic response to rhythmic handgrip

The response of the cerebral circulation to exercise has been studied with transcranial Doppler ultrasound (TCD) because this modality provides continuous measurements of blood velocity and is well suited for the exercise environment. The use of TCD as an index of cerebral blood flow, however, requires the assumption that the diameter of the insonated vessel is constant. Here, we examine this assumption for rhythmic handgrip using a spectral index designed to measure trends in vessel flow. Nineteen normal subjects were studied during 5 min of volitional maximum rhythmic right handgrip at 1 Hz. TCD velocities from both middle arteries (left and right), blood pressure, and end-tidal PCO(2) were recorded every 10 s. A spectral weighted sum was also calculated as a flow index (FI). Averages were computed from the last 2 min of handgrip. Relative changes in velocity, FI, and pressure were calculated. The validity of FI was tested by comparing the change in diameter derived from equations relating flow and diameter. Mean blood pressure increased 23.8 +/- 17.8% (SD), and velocity increased 13.3 +/- 9.8% (left) and 9.6 +/- 8.3% (right). Although the mean change in FI was small [2.0 +/- 18. 2% (left) and 4.7 +/- 29.7% (right)], the variation was high: some subjects showed a significant increase in FI and others a significant decrease. Diameter estimates from two equations relating flow and luminal area were not significantly different. Decreases in FI were associated with estimated diameter decreases of 10%. Our data suggest that the cerebral blood flow (CBF) response to rhythmic handgrip is heterogeneous and that middle cerebral artery flow can decrease in some subjects, in agreement with prior studies using the Kety-Schmidt technique. We speculate that the velocity increase is due to sympathetically mediated vasoconstriction rather than a ubiquitous flow increase. Our data suggest that the use of ordinary TCD velocities to interpret the CBF response during exercise may be invalid.

Intraoperative use of laser Doppler in the study of cerebral microvascular circulation

Laser Doppler (LD) flowmetry has been used for evaluation of microcirculatory flow in a variety of human tissues, including skin, muscle, retina and recently the brain. In the present paper, intraoperative Laser Doppler recordings have been performed in 72 cases, in basal conditions and after stimulation. The morphology of basal recordings obtained from normal cortical areas were analyzed and three different rhythmical variations were identified; these rhythmical variations are described and explained. Several kinds of stimulation have been used: hypotensive drugs, mannitol, nimodipine, eupaverine, hypercapnia, decompressive manoeuvres and temporary occlusion of the ICA in the neck. Laser Doppler recordings obtained during and after these stimulations are reported and explained. The results have been evaluated in order to verify the reliability and the reproducibility of this technique in the study of the cerebral microvascular circulation intraoperatively.

Intraoperative measurement of cortical blood flow adjacent to cerebral AVM using laser Doppler velocimetry

Standard methods for measurement of cerebral blood flow (CBF) are not optimal for continuous intraoperative recording. Laser Doppler velocimetry has been used for evaluation of microcirculatory flow in a variety of human tissues, including skin, muscle, and retina. The authors report the use of this technique for measuring flow in human cerebral cortex. The physiological changes associated with excision of a cerebral arteriovenous malformation are interpreted using CBF recorded intraoperatively with the laser Doppler probe.

Methods for assessment of the effect of drugs on cerebral blood flow in man

The cerebral circulation is not an unimportant vascular bed but it is difficult one to investigate. Methodological difficulties are the main reasons for the paucity of clinical pharmacology studies to date. Of the methods currently available those of the McHenry (1964) and Wyper et al. (1976) appear to be the most useful to the clinical investigator. Increasing use of multiple detectors even with inhalation techniques may give evidence of regional drug effects upon the cerebral circulation. Improvements in methodology in the last few years, particularly the development of atraumatic methods are likely to act as an important spur to research in this field.