Effect of PCO2 changes induced by head-upright tilt on transcranial Doppler recordings.
OBJECTIVE
Transcranial Doppler (TCD) monitoring of mean blood flow velocity (mV) during head-upright tilt can allow testing of cerebral autoregulation. Nonetheless, head-upright tilt can induce changes in the ventilation-perfusion relationship and/or respiratory activity that might influence TCD data.


METHODS
Forty-eight healthy volunteers underwent monitoring of mV and end-tidal CO2 in the horizontal position and during head-upright tilt.


RESULTS
Both mV and end-tidal CO2 significantly decreased in orthostasis (P < .01). Linear regression analysis showed a significant linkage between end-tidal CO2 and mV changes (r = .83, P < .01).


CONCLUSIONS
Changes in ventilation-perfusion ratio and in the respiratory pattern induced by head-upright tilt can significantly influence TCD data by determining a PCO2 decrease.
Cencetti
S
S
Department of Internal Medicine 1. S Maria Nuova Hospital, Florence, Italy.
Bandinelli
G
G
Lagi
A
A
D000328:Adult; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000032:analysis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D011187:Posture; D017585:Ultrasonography, Doppler, Transcranial; D014692:Ventilation-Perfusion Ratio
D002245:Carbon Dioxide