LOCALIZED CEREBRAL P-31 MR SPECTROSCOPY IN MAN BEFORE AND IMMEDIATELYAFTER CORONARY-BYPASS SURGERY WITH HYPOTHERMIC CARDIOPULMONARY BYPASS

Coronary artery bypass surgery classically is undertaken with hypother mic cardiopulmonary bypass (CPB). There is a high incidence of neurops ychological defects after cardiac surgery, which may be related to cer ebral ischaemia during the rewarming period. In this study, phosphorus -31 magnetic resonance spectroscopy (P-31 MRS) was used to identify ch anges in cerebral P-31 MR spectra in patients before and immediately a fter hypothermic CPB. Four neurologically normal patients undergoing c oronary artery bypass surgery were studied. Localised cerebral P-31 MR S (TR 5000 ms) was performed at 1.5 Tesla on each patient the day befo re and within an hour of completion of surgery. Peak areas for phospho monoesters (PME), inorganic phosphate (Pi), phosphodiesters (PDE), pho sphocreatine (PCr) and beta ATP (beta ATP) were measured. Metabolite p eak area ratios and relative percentages of each P-31 MR resonance wit h respect to the total P-31 MR signal were calculated. In the post-ope rative MR spectra, each patient displayed a marked reduction in Pi/bet a ATP and increase in PCr/Pi ratios. Spectral changes in percentage me tabolite signals following surgery varied both in magnitude and patter n between patients. In two patients there was an increased postoperati ve percentage PME acid percentage PCr with a decrease in percentage be ta ATP. The converse was found in the other two patients, but all four subjects displayed a markedly decreased percentage Pi after CPB. Thes e metabolite changes probably reflect rebound phosphorylation in the i mmediate postoperative period and suggest increased metabolic activity in the hyperaemic brain on rewarming from hypothermic CPB.