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Background Although it is well documented that the use of a pH-stat strategy during hypothermic cardiopulmonary bypass improves cerebral blood flow, an α-stat strategy has been almost exclusively used during retrograde cerebral perfusion. We investigated the effects of pH-stat and α-stat management on brain tissue blood flow and oxygenation during retrograde cerebral perfusion in a porcine model to determine if the use of a pH-stat strategy during retrograde cerebral perfusion improves brain tissue perfusion. Methods Fourteen pigs were managed by an α-stat strategy (alpha-stat group, n=7) or by a pH-stat strategy (pH-stat group, n=7) during 120 minutes of hypothermic retrograde cerebral perfusion. Retrograde cerebral perfusion was established through the superior vena cava. Brain tissue blood flow and oxygenation were measured continuously with a laser flowmeter and near infrared spectroscopy, respectively. Brain tissue water content was determined at the end of the experiments. Results During cooling, brain tissue blood flow was significantly higher with use of the pH-stat strategy than with the α-stat strategy (86% ± 10% versus 40% ± 3% of baseline). During retrograde cerebral perfusion, brain tissue blood flow was also significantly higher (about three times higher) in the pH-stat group than in the alpha-stat group (15% ± 4% versus 5% ± 1% of baseline at 60 minutes of retrograde cerebral perfusion). Tissue oxygen saturation appeared to be higher during retrograde cerebral perfusion in the pH-stat group than in the alpha-stat group. Brain tissue blood flow during rewarming remained significantly higher with the use of pH-stat than with the use of α-stat. Brain tissue water contents were similar in both groups. Conclusions In our pig model, the use of a pH-stat strategy during retrograde cerebral perfusion significantly improves brain tissue perfusion. Therefore, to improve retrograde cerebral blood flow during retrograde cerebral perfusion, it may be preferable to use a pH-stat strategy, rather than an α-stat strategy.

Purpose: To examine neuronal activation in the spinal cord due to secondary hyperalgesia resulting from intrajoint capsaicin injection, and the effect of physiotherapy manipulation, using functional magnetic resonance imaging (fMRI), in α-chloralose anesthetized rats. Materials and Methods: FMRI of the rat lumbar spinal cord was performed at 9.4 Tesla. Stimuli included injection of 25 μL of capsaicin (128 μg/mL in 7.5% dimethyl sulfoxide [DMSO]) into the right forepaw or 75 μL into the right ankle joint followed by a light touch stimulus, with and without physiotherapy manipulation. Results: Activation of pain areas of the spinal cord (dorsal horn) was found in all animals after injection of capsaicin into the plantar surface of the rat hindpaw and ankle joint. Overlay maps depicting activations and deactivations showed significant reproducibility between experiments. Greater overlay of activations were observed for intrajoint compared to intradermal capsaicin injection. The distribution of activations after stimulation of the hindpaw using a light touch stimulus was somewhat more varied; activation of the dorsal horn was evident, with greater overlap resulting when joint mobilization was not performed. Conclusion: Results suggest a trend toward decreased areas of activation in the spinal cord associated with pain, as a result of hyperalgesia, following physiotherapy joint mobilization. J. Magn. Reson. Imaging 2003;18:152–159. © 2003 Wiley-Liss, Inc.