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 and 1.5 by the end of May. The latest model is now available on the AppStore for MacOS: version 1.7.
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.
Have you ever wondered why intracranial pressure elevation (ICP) is accompanied by systolic spikes in the middle cerebral artery flow velocity signal?
Model simulation shows that the penetration force of arterial acceleration (a brief arterial stiffening at stroke onset) overcomes ICP, whereas later phases of systole (ejection phase) and diastole do not. The video of the model simulation shows how systolic spikes prevail when ICP is gradually increasing.
In the simulation above the intracranial pressure is gradually increased. Notice the simulated waveform of middle cerebral artery flow velocity: blue curve at the right (red curve is simulated arterial blood pressure).