Analysis of Cerebrovascular Autoregulation Reactivity Index Electronic Monitoring Methods

Novel Method and Device for Fully Non-Invasive Cerebrovascular Autoregulation Monitoring

“…First, the CA status might be estimated by using the invasively measured ICP waves only. In this way the CA status might be evaluated by calculating the phase shifts between the reference slow or (and) respiratory waves extracted from the invasive ICP pulse waves and the informative slow or (and) respiratory ICP waves [23], [26]. Such approach is based on the assumption that the ABP pulse waves are modulated with the reference respiratory (and slow) waves which might be extracted from the envelope of the ICP pulse waves with a negligible delay.…”

“…The possibility to estimate non-invasively the CA status without using any additional ABP measurements is to use a new ultrasonic "time-of-flight" technique [19], [20], [23], which enables to perform continuous non-invasive monitoring of slow, respiratory and pulse intracranial waves. The non-invasive ultrasonic "time-of-flight" (TOF) method for intracranial blood volume measurement is based on the transmission of short ultrasonic pulses from one side of the skull to the other and on dynamic measurements of the TOF of ultrasonic pulses [19].…”

“…It is shown experimentally [23]- [25] that the slow, respiratory and pulse ICP waves are the consequences of the variations of the intracranial blood volume (IBV). The ultrasound speed in blood is higher than in other intracranial components [19], therefore the increase of blood volume during each heart beat cycle will result in the increase of averaged relative ultrasound speed ΔC(t)/C0 which is inversely proportional to TOF, i.e., ΔC(t)/C0 ~ 1/TOF(t).…”

“…So, all IBV waves can be monitored continuously, noninvasively and in real-time by using the TOF technique [23], [25]. By using this technique, the invasive ICP slow, respiratory and pulse wave monitor can be replaced by the non-invasive monitoring of the relative speed ΔC/C0 of the ultrasound passing through the volume of brain parenchyma, which also reflects the variations of the intracranial blood volume.…”