[Changes in pulsatility of the middle cerebral artery during the hyperemic phase after carotid compression. Studies with simultaneous bilateral transcranial Doppler].

AIM

The aim of the present study was to investigate the hypothesis that the transient hyperaemic response (THR), i.e. the TCD measured increase in MCA blood flow velocity, indicate an intact cerebral autoregulation.

METHOD

THR tests were performed repeatedly in 6 healthy volunteers during simultaneous bilateral TCD recording of the MCA Doppler spectrum. The changes in the pulsatility index (PI) and the pulsatility transmission index (PTI) during the THR were compared with their baseline values.

RESULTS

THR was observed in all subjects on each side. PTI of the MCA decreased during the THR. PI did not change on the side of carotid compression, but increased in the contralateral MCA.

CONCLUSION

The results suggest that the cerebrovascular resistance is decreased during the THR and that the THR indicates a functioning cerebral autoregulation. While PI is strongly influenced by upstream haemodynamic forces, PTI seems to be an indicator of cerebrovascular resistance downstream to the sample volume.