[Combinations of methods for the monitoring of the cerebral microcirculation]

Any single method for measuring changes in local cerebral blood flow (LCBF) or blood vessels during physiological stimuli has individual strengths and deficiencies. The coupling of multiple methods based on different physical principles permits simultaneous measurements and tests of interrelated cerebrovascular changes and mechanisms. The present paper describes combined recordings of LCBF by H2 clearance with inhalation (H2Cl-Inh) and with steady electrochemical generation (H2Cl-Gen), by laser Doppler flowmetry (LDF) and by dimensional changes in surface vessels with videomicroscopy through acute cranial windows in rats anesthetized with urethane 1g/kg or urethane (0.6 g/kg) plus chloralose (0.05 g/kg)ip. For H2Cl-Gen recordings paired or quadred Pt sharped block of electrodes (diameter 0.04-0.06 mm) with distance between single electrode 0.3-0.5 mm, was inserted to brain tissue in barrel cortex. One electrode was used for H2 generation and others for LCBF recordings and their position in brain tissue was examined morphologically. Increase local blood flow in barrel cortex and arterial dilation were stimulated by inhalation of 7% CO2 and mechanical stimulation of the contralateral whiskers. H2Cl-Inh was a "gold standard" for quantitative measurements of LCBF within a tissue radius 0.3-0.5 mm from the recording electrode during related tests during steady states at the same site. H2Cl-Gen was very sensitive to transient changes in flow and could record latencies. H2Cl-Gen was calibrated for quantitative measurements of changes in LCBF by pairing with H2Cl-Inh responses to CO2 inhalation. The laser Doppler miniature probe recorded the time course and normalized intensity changes within an approximate 1 mm3 volume of cortex but with more background noise and less sensitivity compared to H2Cl-Gen. Bright illumination of the cranial window increased LCBF by both methods in these experiments. The diameters of surface arterioles and venues were measured in single video frames with date-time markers for correlation with electrical recordings. Changes in diameter were small and were slower compared to H2Cl-Gen and LDF in the present recordings. Received data permit to conclude that there are two optimal combinations of methods were (1) H2Cl-Gen and H2Cl-Inh for both dynamic sensitivity and quantitative LCBF during systemic and neuronal stimulation, and (2) H2Cl-Gen, LDF, and videomicroscopy for multidimensional monitoring of cerebral circulation.