SignificanceA shortcoming of the routine clinical use of diffuse optics (DO) in the injured head has been that the results from commercial near-infrared spectroscopy-based devices are not reproducible, often give physiologically invalid values, and differ among systems. Besides the limitations due to the physics of continuous-wave light sources, one culprit is the head heterogeneity and the underlying morphological and functional abnormalities of the probed tissue.AimThe aim is to investigate the effect that different tissue alterations in the damaged head have on DO signals and provide guidelines to avoid data misinterpretation.ApproachDO measurements and computed tomography scans were acquired on brain-injured patients. The relationship between the signals and the underlying tissue types was classified on a case-by-case basis.ResultsExamples and suggestions to establish quality control routines were provided. The findings suggested guidelines for carrying out DO measurements and speculations toward improved devices.ConclusionsWe advocate for the standardization of the DO measurements to secure a role for DO in neurocritical care. We suggest that blind measurements are unacceptably problematic due to confounding effects and care using a priori and a posteriori quality control routines that go beyond an assessment of the signal-to-noise ratio that is typically utilized.
SignificanceThe optical measurement of cerebral oxygen metabolism was evaluated.AimCompare optically derived cerebral signals to the electroencephalographic bispectral index (BIS) sensors to monitor propofol-induced anesthesia during surgery.ApproachRelative cerebral metabolic rate of oxygen (rCMRO2) and blood flow (rCBF) were measured by time-resolved and diffuse correlation spectroscopies. Changes were tested against the relative BIS (rBIS) ones. The synchronism in the changes was also assessed by the R-Pearson correlation.ResultsIn 23 measurements, optically derived signals showed significant changes in agreement with rBIS: during propofol induction, rBIS decreased by 67% [interquartile ranges (IQR) 62% to 71%], rCMRO2 by 33% (IQR 18% to 46%), and rCBF by 28% (IQR 10% to 37%). During recovery, a significant increase was observed for rBIS (48%, IQR 38% to 55%), rCMRO2 (29%, IQR 17% to 39%), and rCBF (30%, IQR 10% to 44%). The significance and direction of the changes subject-by-subject were tested: the coupling between the rBIS, rCMRO2, and rCBF was witnessed in the majority of the cases (14/18 and 12/18 for rCBF and 19/21 and 13/18 for rCMRO2 in the initial and final part, respectively). These changes were also correlated in time (R > 0.69 to R = 1, p-values < 0.05).ConclusionsOptics can reliably monitor rCMRO2 in such conditions.
SignificanceBenign external hydrocephalus (BEH) is considered a self-limiting pathology with a good prognosis. However, some children present a pathological intracranial pressure (ICP) characterized by quantitative and qualitative alterations (the so-called B-waves) that can lead to neurological sequelae.AimOur purpose was to evaluate whether there were cerebral hemodynamic changes associated with ICP B-waves that could be evaluated with noninvasive neuromonitoring.ApproachWe recruited eleven patients (median age 16 months, range 7 to 55 months) with BEH and an unfavorable evolution requiring ICP monitoring. Bedside, nocturnal monitoring using near-infrared time-resolved and diffuse correlation spectroscopies synchronized to the clinical monitoring was performed.ResultsBy focusing on the timing of different ICP patterns that were identified manually by clinicians, we detected significant tissue oxygen saturation (StO2) changes (p = 0.002) and blood flow index (BFI) variability (p = 0.005) between regular and high-amplitude B-wave patterns. A blinded analysis looking for analogs of ICP patterns in BFI time traces achieved 90% sensitivity in identifying B-waves and 76% specificity in detecting the regular patterns.ConclusionsWe revealed the presence of StO2 and BFI variations—detectable with optical techniques—during ICP B-waves in BEH children. Finally, the feasibility of detecting ICP B-waves in hemodynamic time traces obtained noninvasively was shown.
One sedative drug to induce anesthesia during surgery is propofol. It diminishes the cerebral metabolic rate of oxygen (CMRO2), preventing memory formation and is coupled with a decrease in the cerebral blood flow (CBF). Anesthesia depth is commonly monitored by the bispectral index (BIS) to avoid awareness. Optical hybrid near-infrared spectroscopies have the potential to assess CMRO2 and other physiological signals (i.e. CBF). Optical signals acquired alongside BIS in surgeries were compared to it and provided additional information. Overall, agreement was found at different levels (group analysis, single subject analysis and simultaneity in time of changes).
Intracranial pressure (ICP) is a critical biomarker measured invasively with the risk of complications. There is a need for non-invasive methods to estimate ICP. Diffuse correlation spectroscopy (DCS) allows the non-invasive measurement of pulsatile, microvascular cerebral blood flow which contains information about ICP. Recently, our proof-of-concept study used machine-learning to deduce ICP from DCS signals to estimate ICP resulting in excellent linearity and a reasonable accuracy (±4 mmHg). Here, we extend to a multi-center (three centers) data set of adults with acute brain injury (N=34). We will present the results from the complete data set as new data flows in.
In a pilot study on acute ischemic stroke (AIS) patients, unexpected periodic fluctuations in microvascular cerebral blood flow (CBF) had been observed. Motivated by the relative lack of information about the impact of the emergence of breathing disorders in association with stroke on cerebral hemodynamics, we hypothesized that these fluctuations are due to apneic and hypopneic events. A total of 28 patients were screened within the first week after stroke with a pulse oximeter. Five (18%) showed fluctuations of arterial blood oxygen saturation (≥3 % ) and were included in the study. Near-infrared diffuse correlation spectroscopy (DCS) was utilized bilaterally to measure the frontal lobe CBF alongside respiratory polygraphy. Biphasic CBF fluctuations were observed with a bilateral increase of 27.1 % ± 17.7 % and 29.0 % ± 17.4 % for the ipsilesional and contralesional hemispheres, respectively, and a decrease of −19.3 % ± 9.1 % and −21.0 % ± 8.9 % for the ipsilesional and contralesional hemispheres, respectively. The polygraph revealed that, in general, the fluctuations were associated with apneic and hypopneic events. This study motivates us to investigate whether the impact of altered respiratory patterns on cerebral hemodynamics can be detrimental in AIS patients.
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