Middle cerebral artery blood flow velocity was investigated by transcranial Doppler sonography in 20 healthy subjects during a 10 min orthostasis test. Mean maximal velocity proved to be significantly lower in upright compared to horizontal position, its mean amounting to 93 +/- 9% of the latter value over the first two minutes and to 89 +/- 9% during the remaining period of the test. The index of resistance calculated by dividing systolic by enddiastolic maximal velocity was significantly decreased to a mean of 96 +/- 11% and 97 +/- 11% respectively during the two periods of orthostasis, probably due to autoregulation.

Orthostasis significantly lowers middle cerebral artery blood flow velocity compared to horizontal position, likely due to autoregulation.

[Transcranial Doppler sonography in orthostasis].

Key Takeaway: Orthostasis significantly lowers middle cerebral artery blood flow velocity compared to horizontal position, likely due to autoregulation.