Estimates of pulse wave velocity and measurement of pulse transit time in the human cerebral circulation

Knowledge of the velocity with which pressure and flow waves travel within the arterial tree has been fundamental to the understanding of important hemodynamic parameters, such as vessel wall elastance, impedance and reflection coefficients for the systemic circulation. To our knowledge, however, this pulse wave velocity (PWV) has not been previously measured for the human cerebral circulation. In this study, we estimate the PWV from 88 measurements during normocarbia and 95 measurements during hypocarbia in six healthy human volunteers. The measurements consisted of time delays between velocity waveforms obtained simultaneously from the cervical carotid artery and the ipsilateral middle cerebral artery. An estimation of the distance between these sites as 10 centimeters yielded a PWV of 12.8 m/s for both levels of pCO₂. Vessel elasticity could then be estimated between 17 and 34 dyne/cm² · 10⁶. These values of PWV are among the highest of those found in the peripheral circulation, and may have implications for the interpretation of the shape of the cerebral pressure and flow waveforms.