Repeated measurements of cerebral blood flow in rats. Comparisons between the hydrogen clearance method and laser Doppler flowmetry

Changes in cerebral blood flow (CBF), in chloralose-anaesthetized spontaneously hypertensive rats, were measured simultaneously with the hydrogen clearance (HC) method and laser Doppler flowmetry (LDFM) in order to examine the correlation between results obtained with the two techniques. To induce changes in CBF the rats were bled and CBF measured at different levels of mean arterial pressure. As would be expected, with the platinum electrode at the depth of about 1 mm in the somatosensory cortex, HC gave biexponential curves reflecting clearance in two distinct compartments. During control situation the HC method gave the following values (mean +/- SE, n = 20, ml min-1 100 g-1): fast (fCBF) 158.6 +/- 11.5, slow (sCBF) 29.1 +/- 1.6 with a weighted mean flow (mCBF) of 83.3 +/- 7.4. These fCBF and sCBF values correspond well to those of others obtained with [14C]iodoantipyrine autoradiography in the cerebral cortex and corpus callosum, and better than the results of other studies using HC in rats. Our results, comparing data from HC and LDFM, show a linear relationship between relative values of blood flow changes, the coefficients being 0.658, 0.876 and 0.878 for the correlation between the LDFM data and relative changes in fCBF, sCBF and mCBF, respectively. All three regression lines were significantly different from the line of identity. Much of the discrepancy between the two methods may be related to limitations inherent in each of them, despite efforts to minimize their effects. Thus the depth sensitivity of LDFM in the brain may be greater than expected. In conclusion, the laser Doppler method seems, nevertheless, to be most useful for continuous estimations of changes in cerebral blood flow.