Vytautas Petkus

Implementation of non-invasive brain physiological monitoring concepts.

The paper presents innovative methods and technology for non-invasive intracranial hemodynamics monitoring based on the measurement of brain parenchyma acoustic properties. The clinical investigation of new technology shows the similarity between the invasively recorded intracranial pressure (ICP) and non-invasively recorded intracranial blood volume (IBV) pulse waves, slow waves and slow trends under intensive care unit (ICU) conditions. Also, the applicability of the non-invasive IBV slow wave monitoring technique for cerebrovascular autoregulation non-invasive long-term monitoring is demonstrated by theoretical and experimental studies.

Investigation of intracranial media ultrasonic monitoring model.

The objectives are to investigate the peculiarities of the ultrasound pulse propagation through human extra/intracranial media by mathematical simulation and to confirm the simulation results experimentally by proving the suitability of the ultrasonic time-of-flight measurement method for human intracranial media (IM) physiological non-invasive monitoring. The mathematical model of ultrasound pulse propagation through the human extra/intracranial media is described. The simulation of various physiological phenomena were performed to determine the relationship between the characteristics of the transmitted ultrasound pulse through the human head and the acoustic properties of the IM. It is shown that non-invasive monitoring of the IM acoustic properties is possible by measuring the changes of the ultrasonic signal time-of-flight and the oscillation period. The influence made by variations in acoustic parameters of the external tissue/skull bones on the non-invasive measurement data is investigated and methods of compensation of that influence are presented. The models were applied for developing of a new non-invasive sonographic intracranial pressure (ICP) monitor (Vittamed). Comparative studies of this monitor with the invasive ICP monitor (Camino) have shown the possibility of achieving clinically acceptable accuracy of the long term non-invasive ICP monitoring of head injured patients in intensive care units.

Novel Technology of Non-invasive Cerebrovascular Autoregulation Monitoring

A novel technology for non - invasive cerebrovascular auto regulation (CA) status monitoring is presented. This fully non-invasive CA monitor is based on ultrasonic time-of-flight (TOF) measurement of cerebral blood volume pulsations within the brain parenchyma, processing of volumetric waves, and calculation of CA estimation indexes without using any additional arterial blood pressure (ABP) measurements. The CA status is estimated by extracting informative and reference slow waves from non-invasively measured TOF signals and by calculating Pearsons correlation coefficient between these waves as a CA index. The analysis of the signal extracted from the envelope of non-invasively measured pulse waves showed good agreement between this signal and ABP waves (r=0.68). Consequently, it shows that this signal might be used instead of ABP waves as a reference signal for calculation of the CA estimation indexes. Comparative invasive versus non-invasive CA monitoring study of 11 traumatic brain injury patients showed that correlation between invasively measured CA index and fully non-invasively measured CA index (no arterial line) was r=0.75. The proposed innovative CA real-time monitoring method gives us new possibilities to perform estimation of the CA status from intracranial waves only as well as to exclude the ABP lines errors and artifacts from the measurement results.

Clinical study of craniospinal compliance non-invasive monitoring method

BACKGROUND The ability to quantify non-invasively the effect of posture on intracranial physiology by using cine phase-contrast MRI may lead to the development of new diagnostic tests to evaluate such functions as regulation of CBF and ICP, and the effect of pathologies on these functions. METHODS Results similar to MRI technology can be obtained using non-invasive ultrasonic method (Vittamed) for intracranial blood volume pulse wave (IBVPW) measurement and intracraniospinal compliance (ICC) monitoring. FINDINGS IBVPW have been investigated in supine and upright positions of healthy volunteers using Vittamed technology. A group of 13 healthy volunteers (nine females, four males, mean age 25.1 +/- 3.4) was studied. More than 3,000 IBVPW were analysed in order to show the difference of shape and amplitude in supine and upright positions. Averaged shape of ten IBVPW waves was presented in the normalized window with dimensions 1.0 x 1.0. CONCLUSIONS The results show significant difference between averaged IBVPW shapes in upright (highest intracraniospinal compliance) and supine (lower intracraniospinal compliance) body positions. Body posture caused IBVPW subwave P2 and P3 changes deltaP2 = 18% and deltaP3 = 11%. Amplitude of IBVPW in upright body position was significantly higher than in the supine one. The value of IBVPW amplitudes ratio in supine and upright positions was 1.55 +/- 0.61.

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

BackgroundThis prospective study of an innovative non-invasive ultrasonic cerebrovascular autoregulation (CA) monitoring method is based on real-time measurements of intracranial blood volume (IBV) reactions following changes in arterial blood pressure. In this study, we aimed to determine the clinical applicability of a non-invasive CA monitoring method by performing a prospective comparative clinical study of simultaneous invasive and non-invasive CA monitoring on intensive care patients.MethodsCA was monitored in 61 patients with severe traumatic brain injuries invasively by calculating the pressure reactivity index (PRx) and non-invasively by calculating the volumetric reactivity index (VRx) simultaneously. The PRx was calculated as a moving correlation coefficient between intracranial pressure and arterial blood pressure slow waves. The VRx was calculated as a moving correlation coefficient between arterial blood pressure and non-invasively-measured IBV slow waves.ResultsA linear regression between VRx and PRx averaged per patients’ monitoring session showed a significant correlation (r = 0.843, p < 0.001; 95% confidence interval 0.751 – 0.903). The standard deviation of the difference between VRx and PRx was 0.192; bias was − 0.065.ConclusionsThis 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.

Response to Dr. Frederick Adam Zeiler

Dear Editor, We are very thankful to Dr. Frederick Adam Zeiler for his comments and interest in our article (Petkus V, Preiksaitis A, Krakauskaite S, Bartusis L, Chomskis R, Hamarat Y, et al. Non-invasive Cerebrovascular Autoregulation Assessment Using the Volumetric Reactivity Index: Prospective Study. Neurocrit Care. 2018 June 27; Epub Ahead of Print). We fully agree that the model of association between VRx and PRx is generally nonlinear [1]. On the other hand, we are using arterial blood pressure (ABP), intracranial blood volume, and intracranial pressure (ICP) slow waves for real-time monitoring of VRx(t) and PRx(t). Amplitudes of all slow waves are much smaller comparing with an interval of mean ABP and mean ICP changes observed during severe traumatic brain injury (TBI) patients’ treatment in neurosurgical intensive care units. Slow waves are almost always observed in a linear part of mean ICP versus mean intracranial volume curve. We appreciate the proposal of Dr. Frederick Adam Zeiler to use more sophisticated statistical analysis in order to evaluate the association between VRx and PRx [1]. We intend to do that and to publish more extended analysis results from our prospectively collected data base of VRx and PRx clinical data. We do not believe that VRx will replace PRx in the near future. Our intent is to apply VRx in clinical fields where invasive PRx monitoring technology is not applicable [2, 3]. We appreciate the excellent idea to validate noninvasive VRx on the Lassen curve [4]. We see the lower limit of cerebrovascular autoregulation according to the Lassen curve in our clinical studies of VRx(t) monitoring data during cardiac surgery with cardiopulmonary bypass and during intensive care of severe TBI patients. We intend to publish an additional article on this aspect of our prospective VRx monitoring studies.

Innovative Computerized Non-invasive Intracranial Pressure Measurement Technology and Its Clinical Validation

An innovative non-invasive absolute intracranial pressure (aICP) measurement method has been validated by multicenter comparative clinical studies. The method is based on two-depth transcranial Doppler technology and employs intracranial and extra cranial segments of the ophthalmic artery as a pressure sensor. The ophthalmic artery is used as a natural pair of scales which compares aICP with controlled pressure aPe which is externally applied to the orbit. In the case of scales balance, aICP=aPe. A two-depth transcranial Doppler device is used as a pressure balance indicator. The proposed method is the only non-invasive aICP measurement method which does not need patient-specific calibration.