Have you ever had difficulty explaining to your students what is the difference between the propagation of a pressure wave and the actual movement of blood? In Neuromon's CardioVascularSimulationApp 1.14 we have incorporated the animation of a single stroke volume being pushed forward along the arterial tree. The model demonstrates that the stroke volume moves considerably slower than the blood pressure wave. The effect of arterial acceleration can easily be demonstrated by turning it off or on.
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.
Detailed waveform analysis of arterial blood pressure and blood flow to the brain reveals that the relation between these two may vary within the scope of a single heart beat. Increased intracranial pressure may severely impair diastolic flow whereas it may leave the first systolic peak or S1 largely unaffected. This peak S1 is hypothetically due to arterial acceleration (a brief peristaltic contraction in the body's conducting arteries). The differences in relation between pressure and flow translate to variation in the so called apparent resistance.
The working of the S1-PaR is demonstrated in Neuromon's cardiovascular simulation: S1-PaR explanation.
Read more in our publication published in Neuro Critical Care: an international collaboration between investigators in Brasil and the Netherlands.
During the first half of 2023 Neuromon has released new updates for its CardioVascularSimulation model: version 1.2 in January, followed by versions 1.3 in March, 1.4 in April 2023, 1.5 in May, 1.6 in July and 1.7 released January 2024. The latest model available on the AppStore for MacOS is version 1.14 published January 2026.
Apart from the well known model of hemodynamics, the latest releases features a Patient Condition window and a Patient Monitor window. Also, the tilt table test is introduced, demonstrating the effect of hydrostatic pressure on blood distribution within the body. After assuming an upright posture and without cardiovascular reflexes active the blood supply to the brain rapidly becomes inadequate and the patient may lose consciousness. Repeating the manoeuvre with cardiovascular reflexes active prevents this unwanted effect. For educational purposes the effect of cardiac arrest is added to the more than 16 other scenario's, such as carotid occlusion, intracranial pressure elevation, respiratory failure etc.
For an extensive documentation about the way the model works, what assumptions were made and which theories implemented, please consult: CardioVascularSimulation Documentation.
Compumedics DWL® has recently released an update of the Transcranial Doppler QL software V 3.6.8 . This update incorporates Z-score analysis of middle cerebral artery flow velocity within the NMA module.
A Z-score expresses how many standard deviations a given middle cerebral artery flow velocity measurement lies above or below the value expected for that age. Z-scores of different variables (Sys1, Sys2, D560 and HR) can be combined into a single radar plot to facilitate the rapid interpretation of intracranial hemodynamics in health and disease.
