One of the main changes with aging is loss of elasticity. Arteries contain fibrinogen as well as elastin. With aging elastin degrades and arteries become wider (dilatation) and longer (elongation). Dilatation causes a decrease of intra-arterial blood flow velocity and elongation causes kinking and coiling so typical during angiography or duplex investigations of the elderly.
For the interpretation of blood flow velocities within the middle cerebral artery it is crucial to take age into account. In Trancranial Doppler (TCD) machines sold by Compumedics DWL this has been achieved by introducing Z-scores. Z-scores express how many standard deviations a given measurement lies above or below the value expected for that age. Z-scores can be calculated for the different components of the flow velocity waveform: Sys1, Sys2 and D560. Together with heart rate they can be combined into a single radar plot.
The normal values underlying the calculation of Z-scores are published in the Journal of Vascular Ultrasound 2024.