Localised cerebral phosphorus-31 MR spectroscopy in man before and immediately after coronary bypass surgery with
J A Wilson1, S D Taylor-Robinson, D J Bryant
1Department of Anaesthesia, Imperial College School of Medicine, Hammersmith Hospital, London, UK.
Insights
Hypothermic cardiopulmonary bypass during coronary artery bypass surgery may cause brain changes. Phosphorus-31 magnetic resonance spectroscopy (31P MRS) revealed altered brain metabolites after surgery, suggesting increased metabolic activity during rewarming.
Area of Science:
- Neurology
- Cardiovascular Surgery
- Biochemistry
Background:
- Coronary artery bypass surgery (CABG) often uses hypothermic cardiopulmonary bypass (CPB).
- Neuropsychological deficits are common after cardiac surgery, potentially due to cerebral ischemia during rewarming.
- Phosphorus-31 magnetic resonance spectroscopy (31P MRS) is a non-invasive technique to assess brain energy metabolism.
Purpose of the Study:
- To investigate changes in cerebral energy metabolism using 31P MRS in patients before and immediately after hypothermic CPB.
- To identify specific metabolite alterations associated with CPB and rewarming.
Main Methods:
- Localized cerebral 31P MRS was performed on four neurologically normal patients before and after CABG.
- Key metabolites including phosphomonoesters (PME), inorganic phosphate (Pi), phosphodiesters (PDE), phosphocreatine (PCr), and beta-adenosine triphosphate (betaATP) were quantified.
- Metabolite ratios and relative percentages were calculated to assess metabolic changes.
Main Results:
- All patients showed a significant decrease in the Pi/betaATP ratio and an increase in the PCr/Pi ratio post-surgery.
- Percentage changes in PME, PCr, betaATP, and Pi varied among patients.
- A marked decrease in percentage Pi was observed in all four subjects after CPB.
Conclusions:
- The observed metabolite changes suggest rebound phosphorylation and increased metabolic activity in the brain during rewarming from hypothermic CPB.
- 31P MRS can detect immediate post-operative cerebral metabolic alterations following cardiac surgery.
- These findings may contribute to understanding the mechanisms of post-cardiac surgery neuropsychological deficits.
Abstract:
Coronary artery bypass surgery classically is undertaken with hypothermic cardiopulmonary bypass (CPB). There is a high incidence of neuropsychological defects after cardiac surgery, which may be related to cerebral ischaemia during the rewarming period. In this study, phosphorus-31 magnetic resonance spectroscopy (31P MRS) was used to identify changes in cerebral 31P MR spectra in patients before and immediately after hypothermic CPB. Four neurologically normal patients undergoing coronary artery bypass surgery were studied. Localised cerebral 31P MRS (TR 5000 ms) was performed at 1.5 Tesla on each patient the day before and within an hour of completion of surgery. Peak areas for phosphomonoesters (PME), inorganic phosphate (Pi), phosphodiesters (PDE), phosphocreatine (PCr) and beta ATP (betaATP) were measured. Metabolite peak area ratios and relative percentages of each 31P MR resonance with respect to the total 31P MR signal were calculated. In the post-operative MR spectra, each patient displayed a marked reduction in Pi/betaATP and increase in PCr/Pi ratios. Spectral changes in percentage metabolite signals following surgery varied both in magnitude and pattern between patients. In two patients there was an increased postoperative percentage PME and percentage PCr with a decrease in percentage betaATP. The converse was found in the other two patients, but all four subjects displayed a markedly decreased percentage Pi after CPB. These metabolite changes probably reflect rebound phosphorylation in the immediate postoperative period and suggest increased metabolic activity in the hyperaemic brain on rewarming from hypothermic CPB.
![Investigating Cardiac Metabolism in the Isolated Perfused Mouse Heart with Hyperpolarized [1-13C]Pyruvate and 13C/31P NMR Spectroscopy](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F63188.jpg&w=3840&q=50)
