Modifications of spontaneous cerebral blood flow oscillations during cardiopulmonary bypass

Summary

Spontaneous slow waves are present in the systemic circulation including the intracranial compartment. They are supposed to reflect the cerebral autoregulation. We hypothesised that in the absence of cardio respiratory variability, during cardiopulmonary bypass (CPB), we should reveal extreme physiologic controls.

Material/methods. Ten patients were included. Arterial blood pressure (ABP, radial invasive), extracorporeal circuitry pressure and cerebral blood flow velocity (CBFV, middle cerebral artery) were recorded. We analysed the slow waves in the B (8 to 50) and the UB (> 50 to 200) bands (in milli-Hz). The analysis, before and during CPB, was performed in the tine domain (correlation coefficient, entropy, mean quantity of mutual information, relative entropy) and in the frequency domain (spectrogram, frequency spectrum, coherence).

Results. CPB dramatically changed monitored signals decreasing their entropy and revealing a dominant CBFV 70 mHz-frequency and a dominant ABP 9 mHz-frequency. There was no association between the signals ( p<0.05). Before CPB we found complex patterns where B and UB waves were present.

Conclusion. We hypothesised that CPB provoked a highly protective mechanism, reducing the fluctuations of CBF, by a deactivation of B waves, revealing monotonous UB waves.