Non-invasive Cerebrovascular Autoregulation Assessment Using the Volumetric Reactivity Index: Prospective Study

Abstract

This prospective clinical study of the non-invasive ultrasonic volumetric reactivity index VRx monitoring, based on ultrasonic time-of-flight measurements of IBV dynamics, showed significant coincidence of non-invasive VRx index with invasive PRx index. The ultrasonic time-of-flight method reflects blood volume changes inside the acoustic path, which crosses both hemispheres of the brain. This method does not reflect locally and invasively-recorded intracranial pressure slow waves, but the autoregulatory reactions of both hemispheres of the brain. Therefore, VRx can be used as a non-invasive cerebrovascular autoregulation index in the same way as PRx and can also provide information about the CA status encompassing all intracranial hemodynamics.

Comparative Study of Novel Noninvasive Cerebral Autoregulation Volumetric Reactivity Indices Reflected by Ultrasonic Speed and Attenuation as Dynamic Measurements in the Human Brain

“…Changes in IBV values are known to consist of slow respiratory and pulse waves and are associated with ICP changes [25]. Hence, the similarity among the channel's pulse wave, vasoconstriction, and vasodilation was evidence of similarity and served as the basic foundation of this study.…”

“…All other existing noninvasive methods attempt to find a surrogate parameter that could replace CBF monitoring so that the related CA index can be calculated [25]. Among several noninvasive methods, the transcranial Doppler (TCD) method for assessing CA noninvasively is primarily used.…”

“…These are referred to as the cerebral oximetry (Cox or Tox) index [26,27] and the hemoglobin volume index (HVx), which are monitored with a moving linear correlation of blood pressure to cerebral blood volume near-infrared spectroscopy [28]. The local dependency is a limitation of these noninvasive methods [25].…”

“…A novel noninvasive technology (Certification (CE) marked device) was developed by the Health Telematics Science Institute at the Kaunas University of Technology (Kaunas, Lithuania). ICP(t) slow waves were replaced by IBV(t) slow waves to estimate CA status, which was included in the calculation of the noninvasive volumetric reactivity index VRx(t) as a moving correlation coefficient between the slow IBV(t) and ABP(t) waves [25]. Clinical applicability of the VRx has been proven by several clinical studies conducted by the Health Telematics Science Institute at the Kaunas University of Technology (Kaunas, Lithuania), such as the noninvasive ultrasonic VRx based on time-of-flight measurements with the invasive PRx on 61 patients with brain injuries and showed excellent coincidence to reflect autoregulation [25].…”

“…ICP(t) slow waves were replaced by IBV(t) slow waves to estimate CA status, which was included in the calculation of the noninvasive volumetric reactivity index VRx(t) as a moving correlation coefficient between the slow IBV(t) and ABP(t) waves [25]. Clinical applicability of the VRx has been proven by several clinical studies conducted by the Health Telematics Science Institute at the Kaunas University of Technology (Kaunas, Lithuania), such as the noninvasive ultrasonic VRx based on time-of-flight measurements with the invasive PRx on 61 patients with brain injuries and showed excellent coincidence to reflect autoregulation [25]. Another comparative study with 11 patients with brain injuries revealed a significant relationship associated with VRx and PRx outcomes [29], which indicated that VRx reflects autoregulation the same as PRx.…”