TRANSCRANIAL DOPPLER SONOGRAPHIC MEASUREMENTS OF MIDDLE CEREBRAL-ARTERY FLOW VELOCITY DURING HYPERBARIC-OXYGEN EXPOSURES

In the present study, experimental exposures to hyperbaric oxygen (HBO 2) were performed (30-min exposure to 2.8 bar (280 kPa) pure oxygen). During all phases of the experiment, blood flow velocity in the right middle cerebral artery was monitored with transcranial Doppler (TCD) s onography. Time courses of heart rate, blood pressure, respiratory rat e, end-tidal CO2, and TCD mean velocity (V-mean) are described for a g roup of 23 subjects during uncomplicated exposure to HBO2 and for thre e subjects who showed signs of central nervous system (CNS) O-2 toxici ty, including one subject with a HBO2-induced generalized tonic-clonic seizure. Hyperbaric oxygen decreased V-mean, an effect that could not completely be explained by changes in end-tidal CO2. The findings of the present study are in agreement with the concept that an increase i n partial oxygen pressure is the primary factor underlying CNS O-2 tox icity. Of the variables analyzed, the TCD V-mean is the most valuable variable for monitoring a HBO2 exposure. The V-mean showed the most pr onounced change during HBO2 application, and in one subject a sudden i ncrease in V-mean during HBO2 exposure heralded toxicity before clinic al signs. It should be realized, however, that the small series of sub jects with toxicity in this study does not allow us to draw definite c onclusions.