Measurement of cerebral blood flow in rats and mice by hydrogen clearance during hyperbaric oxygen exposure

The hydrogen (H2) clearance method was adapted for the measurement of regional cerebral blood flow (rCBF) in anesthetized rats and mice during hyperbaric oxygen (HBO2) exposure. Polarographic platinum electrodes 0.1 mm in diameter were used to record H2 clearance curves from the parietal cortex (PC), substantia nigra (SN), and caudate putamen nucleus (CPN) after inhalation of 2.5% H2 in air. The system for H2 breathing under hyperbaric conditions was designed for remote operation from outside the chamber. The rCBF values (measured every 10 min) were calculated from the H2 clearance curves using the initial slope method. During air breathing control, rCBF values were similar to values reported using other methods. Considering all control rats together, blood flow (ml.100 g-1.min-1) was 89 +/- 3.6 in the SN, 78 +/- 4.7 in the CPN, and 76 +/- 6.7 in the PC. Blood flow (ml.100 g-1.min-1) for air-breathing mice was 108 +/- 11.4 in the SN and 74 +/- 8.8 in the CPN. During HBO2 exposure to 3 atm abs, rCBF in rats fell within 30 min by 26-39% (P < 0.05) and by 27-29% in mice (P < 0.05). HBO2 exposure to 4 atm abs induced maximal rCBF decreases in rats within 60 min by 37% (P < 0.01) in the SN and by 47% (P < 0.01) in the CPN. Breathing CO2 during HBO2 exposure to 4 atm abs reversed the vasoconstriction and led to a rCBF increase of 80-96% in rats. The H2 clearance method seems to be an accurate and sensitive technique for the repeated measurement of local CBF under hyperbaric conditions.