COMPARISON OF CEREBRAL BLOOD-FLOW MEASURED BY LASER-DOPPLER FLOWMETRYAND HYDROGEN CLEARANCE IN CATS AFTER CEREBRAL INSULT AND HYPERVOLEMICHEMODILUTION

LASER-DOPPLER FLOWMETRY PROVIDES a continuous measurement of blood flo w without violating the natural state of circulation. The linearity of the laser-Doppler and hydrogen clearance methods of blood flow measur ement were compared using a protocol that produced changes in cerebral blood flow that might be experienced in a neurosurgical setting. Cere bral blood flow was measured in both hemispheres of 12 adult cats duri ng the snaring of one common carotid artery, the intracisternal inject ion of 5 mg of 5-hydroxytryptamine creatinine sulfate, and hypervolemi c hemodilution, which produced a 25% reduction in blood hematocrit. Th e percentage of baseline laser-Doppler flowmetry and hydrogen clearanc e flows showed an acceptable degree of correlation (R(2) = 0.762) over the range of cerebral blood flows measured. More rigorous analysis us ing Bland and Altman's difference against mean test showed that 10 min utes after hemodilution, the two methods displayed a level of variatio n outside the limits of agreement (-21.85 to 22.03%). Laser-Doppler fl owmetry provided a noninvasive and continuous measure of blood Glow, i ncreasing the ability to observe instantaneous changes in cerebral mic rocirculation. However, laser-Doppler flowmetry did not record absolut e blood flow, was affected by cerebral tissue shrinkage, and did not a ccurately measure flow under conditions of changed blood hematocrit.