Coherent spatial imaging of hemodynamics

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Methodology to rapidly map and quantify whole-brain microvasculature in 3d

The role of microvasculature in the development of cerebral disorders remains ambiguous despite recent implications in ~45% of dementia cases (including Alzheimer’s) and ~20% of strokes.1 Our goal is to develop 3D, high resolution, whole-brain maps of the cerebral microvasculature. This will address the knowledge gap surrounding vasculature changes during disease progression and ultimately support the development of innovative treatment paradigms. This effort is complementary to the BRAIN Initiative’s emphasis on comprehensive neuronal mapping. To better understand the role of vasculature in the onset of cerebral pathologies, we have developed a protocol for capture, conversion and comparison of vascular structure and key characteristics in the intact mouse brain with quotidian programs. We created a novel pipeline for 3D whole-brain modeling using techniques of perfusion for vascular labeling, amendment of the iDISCO+ organ clearing protocol, light sheet microscopy (LSM), data handling and image processing. Our protocol relies on vascular labeling via retro-orbital perfusion of fluorescent Lectin-Dylight 649 (Vector Labs), which we have observed to label vasculature in a more comprehensive fashion than other dyes (i.e., lectin-FITC, DiI). It takes up to two days to achieve whole-brain clearing; whereas the iDISCO+ protocol requires the use of secondary antibodies and a timeline of weeks. In lieu of expensive software packages, such as the Filament Tracer feature in Imaris, we trace the vasculature using freeware packages that can be used for 3D reconstruction and manipulation from most personal computers (Figure 1B). Current work involves integration of our data with the Allen Brain Atlas, to merge our vascular computational data sets to an averaged frame of reference map for use by other groups. We anticipate that this approach can be used to study the relationship between microvascular structure and function with cerebral pathology and to fit mathematical models of hypoxia predictive of ischemic conditions in the brain. Please click Additional Files below to see the full abstract

Dissociation of Cerebral Blood Flow and Femoral Artery Blood Pressure Pulsatility After Cardiac Arrest and Resuscitation in a Rodent Model: Implications for Neurological Recovery.

Background Impaired neurological function affects 85% to 90% of cardiac arrest (CA) survivors. Pulsatile blood flow may play an important role in neurological recovery after CA. Cerebral blood flow (CBF) pulsatility immediately, during, and after CA and resuscitation has not been investigated. We characterized the effects of asphyxial CA on short-term (<2 hours after CA) CBF and femoral arterial blood pressure (ABP) pulsatility and studied their relationship to cerebrovascular resistance (CVR) and short-term neuroelectrical recovery. Methods and Results Male rats underwent asphyxial CA followed by cardiopulmonary resuscitation. A multimodal platform combining laser speckle imaging, ABP, and electroencephalography to monitor CBF, peripheral blood pressure, and brain electrophysiology, respectively, was used. CBF and ABP pulsatility and CVR were assessed during baseline, CA, and multiple time points after resuscitation. Neuroelectrical recovery, a surrogate for neurological outcome, was assessed using quantitative electroencephalography 90 minutes after resuscitation. We found that CBF pulsatility differs significantly from baseline at all experimental time points with sustained deficits during the 2 hours of postresuscitation monitoring, whereas ABP pulsatility was relatively unaffected. Alterations in CBF pulsatility were inversely correlated with changes in CVR, but ABP pulsatility had no association to CVR. Interestingly, despite small changes in ABP pulsatility, higher ABP pulsatility was associated with worse neuroelectrical recovery, whereas CBF pulsatility had no association. Conclusions Our results reveal, for the first time, that CBF pulsatility and CVR are significantly altered in the short-term postresuscitation period after CA. Nevertheless, higher ABP pulsatility appears to be inversely associated with neuroelectrical recovery, possibly caused by impaired cerebral autoregulation and/or more severe global cerebral ischemia

Influence of bottom currents on the sedimentary processes at the western tip of the Gulf of Corinth, Greece

We investigated the sedimentary processes that were active during the Holocene in the Gulf of Corinth, using high-resolution seismic reflection profiles and gravity cores. Seismic reflection data clearly show the presence of shallow-water sediment drifts at the western end of the Gulf, close to the Rion Sill that links the gulf to the Ionian Sea. Short cores indicate that drifts are composed of homogenous bioturbated mud in their upper part. The drift deposits flank a wide central area where the sea floor is eroded and where pre-Holocene deposits locally outcrop. The sea floor morphology in this area is marked by furrows oriented in different directions and by a depression attributed to the action of bottom-currents. The magnetic fabric of sediment samples from the drift, shelves, sub-basins and from the basin floor show a significant anisotropy and a similar orientation of Kmax axes along core. The largest anisotropy (P = 1.043 ± 0.007) is observed in the drift and is interpreted as resulting from the action of bottom currents. The similar orientation of Kmax axes in the other cores, collected from areas East of the drifts, suggests that bottom currents also affect sediment deposition in the rest of the study area, even if seismic profiles and core analyses demonstrate that gravitational processes such as submarine landslides and turbidity currents exert the main control on sediment transport and deposition. Average Kmax axes for four cores were reoriented using the declination of the characteristic remanent magnetization. Kmax axes show variable orientations relatively to the slope of the sea floor, between along-slope and roughly parallel to the contour lines.SISCO

Speckleplethysmographic (SPG) estimation of heart rate variability

Heart rate variability (HRV), a class of metrics derived from variability in R-R intervals typically measured using electrocardiography (ECG), has implications for cardiovascular and neurological health1. Recently, HRV was used to track the recovery of athletes after exercise training due to its ability to noninvasively monitor the autonomic nervous system (ANS)2. Exercise training generally has a positive impact on the ANS by reducing resting heart rate and increasing cardiac vagal tone at rest3. However, overexertion from excessive workout sessions can counteract the benefits of regular exercise and reduce HRV4. Unfortunately, routine, remote ECG HRV monitoring is limited due to portability, cost, and loss of accuracy. Various groups have attempted to address the limitations of ECG monitored HRV by estimating HRV with simpler photoplethysmography (PPG) technology5. Transmittance PPG, the signal used in pulse oximetry, measures changes in intensity due to light absorption caused by the dilation and constriction of arteries and arterioles in the finger due to pulsatile blood flow. Alas, HRV approximated from PPG finger measurements loses accuracy due to significant peak time delays related to various factors such as arterial stiffness, vascular tone, and height6. Please click Additional Files below to see the full abstract

Spatiotemporal propagation of cerebral hemodynamics during and after resuscitation from cardiac arrest

Cardiac arrest (CA) affects over 500,000 people in the United States. Although resuscitation efforts have improved, poor neurological outcome is the leading cause of morbidity in CA survivors, and only 8.3% of out-of-hospital CA survivors have good neurological recovery. Therefore, a detailed understanding of the brain before, during, and after CA and resuscitation is critical. We have previously shown, in a preclinical model of asphyxial CA, that measurement of cerebral blood flow (CBF) is essential to better understand what happens to the brain during CA and resuscitation. We have shown that CBF data can be used to predict the time when brain electrical activity resumes. Moreover, we have described CBF characteristics after resuscitation, including the hyperemic peak and stabilized hypoperfusion. Overall, our previous work focused on the study of the temporal evolution of CBF dynamics. To provide a more complete picture of CBF dynamics associated with CA and resuscitation, we postulate that both the temporal and spatial evolution of CBF dynamics must be understood. To investigate spatiotemporal dynamics, we used laser speckle imaging (LSI) to image rats (n = 6) that underwent either 5- or 7-min asphyxial CA, followed by cardiopulmonary resuscitation (CPR) until return of spontaneous circulation (ROSC). During induction of global cerebral ischemia through CA, we have observed two periods during which a decrease in CBF propagates in space in a cranial window over the right hemisphere. The first period of time is during CA and the second is after the hyperemic peak, before stabilized hypoperfusion occurs post-ROSC. Figure 1 shows a representative rat blood flow maps of the spatial propagation during CA (top row) and after ROSC (bottom row). For each row, the leftmost image shows CBF at t = 0min, and each subsequent image to the right is the time after the initial image. The arrows on the images represent the propagation direction in which CBF decreases. In this example, during CA, the propagation direction is down and to the left (posterior-medial anatomically), while after ROSC it is down and to the right (posterior-laterally, anatomically). Please click Additional Files below to see the full abstract

Drilling Overdeepened Alpine Valleys (ICDP-DOVE): Quantifying the age, extent, and environmental impact of Alpine glaciations

The sedimentary infill of glacially overdeepened valleys (i.e., structures eroded below the fluvial base level) is an excellent but yet underexplored archive with regard to the age, extent, and nature of past glaciations. The ICDP project DOVE (Drilling Overdeepened Alpine Valleys) Phase 1 investigates a series of drill cores from glacially overdeepened troughs at several locations along the northern front of the Alps. All sites will be investigated with regard to several aspects of environmental dynamics during the Quaternary, with focus on the glaciation, vegetation, and landscape history. Geophysical methods (e.g., seismic surveys), for example, will explore the geometry of overdeepened structures to better understand the process of overdeepening. Sedimentological analyses combined with downhole logging, analysis of biological remains, and state-of-the-art geochronological methods, will enable us to reconstruct the erosion and sedimentation history of the overdeepened troughs. This approach is expected to yield significant novel data quantifying the extent and timing of Middle and Late Pleistocene glaciations of the Alps. In a first phase, two sites were drilled in late 2021 into filled overdeepenings below the paleolobe of the Rhine Glacier, and both recovered a trough filling composed of multiphase glacial sequences. Fully cored Hole 5068_1_C reached a depth of 165m and recovered 10m molasse bedrock at the base. This hole will be used together with two flush holes (5068_1_A, 5068_1_B) for further geophysical cross-well experiments. Site 5068_2 reached a depth of 255m and bottomed out near the soft rock-bedrock contact. These two sites are complemented by three legacy drill sites that previously recovered filled overdeepenings below the more eastern Alpine Isar-Loisach, Salzach, and Traun paleoglacier lobes (5068_3, 5068_4, 5068_5). All analysis and interpretations of this DOVE Phase 1 will eventually lay the ground for an upcoming Phase 2 that will complete the pan-Alpine approach. This follow-up phase will investigate overdeepenings formerly occupied by paleoglacier lobes from the western and southern Alpine margins through drilling sites in France, Italy, and Slovenia. Available geological information and infrastructure make the Alps an ideal area to study overdeepened structures; however, the expected results of this study will not be restricted to the Alps. Such features are also known from other formerly glaciated mountain ranges, which are less studied than the Alps and more problematic with regards to drilling logistics. The results of this study will serve as textbook concepts to understand a full range of geological processes relevant to formerly glaciated areas all over our planet

Earthworms mitigate pesticide effects on soil microbial activities

Earthworms act synergistically with microorganisms in soils. They are ecosystem engineers involved in soil organic matter degradation and nutrient cycling, leading to the modulation of resource availability for all soil organisms. Using a soil microcosm approach, we aimed to assess the influence of the earthworm Aporrectodea caliginosa on the response of soil microbial activities against two fungicides, i.e. Cuprafor micro® (copper oxychloride, a metal) and Swing® Gold (epoxiconazole and dimoxystrobin, synthetic organic compounds). The potential nitrification activity (PNA) and soil enzyme activities (glucosidase, phosphatase, arylamidase, and urease) involved in biogeochemical cycling were measured at the end of the incubation period, together with earthworm biomass. Two common indices of the soil biochemistry were used to aggregate the response of the soil microbial functioning: the geometric mean (Gmean) and the Soil Quality Index (SQI). At the end of the experiment, the earthworm biomass was not impacted by the fungicide treatments. Overall, in the earthworm-free soil microcosms, the two fungicides significantly increased several soil enzyme and nitrification activities, leading to a higher GMean Index as compared to the non-treated control soils. The microbial activity responses depended on the type of activity (nitrification was the most sensitive one), on the fungicide (Swing® Gold or Cuprafor micro®), and on the doses. The SQI indices revealed higher effects of both fungicides on the soil microbial activity in the absence of earthworms. The presence of earthworms enhanced all soil microbial activities in both the control and fungicide-contaminated soils. Moreover, the magnitude of the fungicide impact, integrated through the SQI index, was mitigated by the presence of earthworms, conferring a higher stability of microbial functional diversity. Our results highlight the importance of biotic interactions in the response of indicators of soil functioning (i.e., microbial activity) to pesticides

Using a multimodal platform to investigate the role of spreading depolarization and hemodynamics in neurological recovery

Acute brain injury, such as traumatic brain injury, stroke, and subarachnoid hemorrhage exhibit spreading depolarizations (SDs). SDs have been associated with worsening neuronal injury and are thought to contribute towards overall worse neurological outcome. SDs during global cerebral ischemia and its implications on neurological recovery following reperfusion are poorly understood. We investigated the role of SDs in a global cerebral ischemia model of cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). To induce SD, rats underwent asphyxial CA (ACA) for 5-, 7-, or 8-min, which was followed by CPR. Previous studies used electrocorticography (ECoG) to detect SDs. We used a multimodal platform of ECoG, laser speckle imaging (LSI), and spatial frequency domain imaging (SFDI) to continuously monitor rats during SD and recovery. We measured brain electrophysiology, cerebral blood flow (CBF), tissue scattering, and cerebral metabolic rate of oxygen (CMRO2). Neurological outcome was measured 90min post-CPR using quantitative ECoG (i.e. information quantity (IQ)) and 24h post-CPR using behavioral tests (i.e. Neurological Deficit Score; NDS). SDs were manually detected after applying a 1Hz low-pass filter on ECoG (Fig 1A, red number 2) and with tissue scattering from SFDI (Fig 1B, bottom, spatial increase in tissue scattering from right to left). SDs typically occurred within 2-3min after onset of asphyxia, during which vasoconstriction of cerebral vessels, waves of spreading ischemia and scattering, and abrupt changes in CMRO2 were visualized. Interestingly, rats with earlier SD showed better neurological recovery (NDS) (Fig 1C). In addition to earlier SD being associated with better neurological recovery, we also found that less total CBF prior to SD (Fig 1D) and a smaller change in tissue scattering (Fig 1E) during SD were associated with better neurological recovery (ECoG IQ). Although SDs have typically been perceived to be harmful and detrimental to neurological outcome, our data provides evidence that earlier SDs may have neuroprotective potential. These data provide support for the earliest known biomarker of neurological outcome post-CA. These findings may lead to novel therapies to modulate SDs during CA and acute brain injury that improve neurological outcome

In-vitro validation and quantitative measurements of graded burn wounds on a porcine model using handheld laser speckle imaging

Burn wound severity can be difficult to assess and the diagnosis is usually subjective. Optical techniques have emerged as alternative methods for providing objective, non-contact assessment of burn wound severity. One such technique is Laser Speckle Imaging (LSI), which quantifies superficial blood flow using coherent laser light. We have previously demonstrated that LSI can be used to accurately assess burn wounds. However, LSI is conventionally used in static designs, such as cart-based or tripod mounted configurations, due to the susceptibility of LSI to motion artifact. This can limit the portability and usability of the device in a clinical. Handheld LSI can potentially overcome these limitations. However, accounting for motion artifact associated with user movement must be addressed to obtain accurate and reliable blood flow measurements. Please click Additional Files below to see the full abstract