Analysis of Transcranial Doppler Ultrasound Waveform Morphology for the Assessment of Cerebrovascular Hemodynamics

The use of transcranial Doppler (TCD) ultrasound for the assessment of cerebral blood flow velocity (CBFV) provides an indication of cerebral blood flow assuming the diameter of the insonated vessel remains constant. Studies using TCD have traditionally described cerebrovascular hemodynamics with respect to CBFV and cerebrovascular resistance (CVRi); however, a more complete assessment of the cerebral circulation can be gleaned from the analysis of within beat characteristic of the TCD velocity waveform for the determination of cerebrovascular tone. Therefore, the general purpose of the presented studies was to assess CBFV responses and within beat characteristic for the description of cerebrovascular hemodynamics after long duration spaceflight, with sustained orthostasis, in response to changes in the partial pressure of end tidal carbon dioxide (PETCO2), and with NG stimulation. After long duration spaceflight, cerebrovascular autoregulation was found to be impaired along with a reduction in cerebrovascular CO2 reactivity (Study 1). Additionally, critical closing pressure (CrCP) was found to be increased suggesting potential remodelling of the cerebrovasculature contributing to an increase in cerebrovascular tone (Study 2). With sustained orthostasis, CBFV was found to progressively decrease and to be related to reductions in PETCO2 and increases in CrCP suggesting the contribution of changes in cerebrovascular tone leading to the development of syncope (Study 4). The CBFV reduction with the progression towards syncope was also associated with changes in waveform morphology such that the dicrotic notch point was less than the end diastolic value (Study 3). Mathematical modelling (RCKL) was used to further assess changes in cerebrovascular hemodynamics for physiological interpretation of changes in CBFV waveform morphology and found that the amplitude of the dicrotic notch and the calculation of the augmentation index were both significantly related to vascular compliance before and after stimulation with NG (Study 5). The use of quantitative assessments of common carotid artery (CCA) blood flow as an indicator of cerebral blood flow suggested the dilation of the middle cerebral artery (MCA) with NG (Study 5 and 6) and changes in MCA diameter with acute alterations in PETCO2 (Study 6). CCA and MCA velocity wave morphology were assessed showing that with changes in PETCO2, changes in CBFV velocity wave were not reflected in the CCA trace (Study 7). In addition, further assessment of the CBFV velocity trace and the calculation of CrCP and the augmentation index suggested that with changes in PETCO2 cerebrovascular compliance and cerebrovascular tension, both thought to be components of cerebrovascular tone, change independently (Study 7). Combined, the results of the presented studies suggest that changes in cerebrovascular hemodynamics can be determined from alterations in the CBFV velocity waveform morphology. However, further work is required to determine how these variations relate to specific components of cerebrovascular tone, including alterations in cerebrovascular compliance and vascular tension, and how these variables change with acute and chronic alterations in cerebrovascular hemodynamics

The role of intolerance of uncertainty in classical threat conditioning::Recent developments and directions for future research

Intolerance of uncertainty (IU), the tendency to find uncertainty aversive, is an important transdiagnostic dimension in mental health disorders. Over the last decade, there has been a surge of research on the role of IU in classical threat conditioning procedures, which serve as analogues to the development, treatment, and relapse of anxiety, obsessive-compulsive, and trauma- and stressor-related disorders. This review provides an overview of the existing literature on IU in classical threat conditioning procedures. The review integrates findings based on the shared or discrete parameters of uncertainty embedded within classical threat conditioning procedures. Under periods of unexpected uncertainty, where threat and safety contingencies change, high IU, over other self-reported measures of anxiety, is specifically associated with poorer threat extinction learning and retention, as well as overgeneralisation. Under periods of estimation and expected uncertainty, where the parameters of uncertainty are being learned or have been learned, such as threat acquisition training and avoidance learning, the findings are mixed for IU. These findings provide evidence that individual differences in IU play a significant role in maintaining learned fear and anxiety, particularly under volatile environments. Recommendations for future research are outlined, with discussion focusing on how parameters of uncertainty can be better defined to capture how IU is involved in the maintenance of learned fear and anxiety. Such work will be crucial for understanding the role of IU in neurobiological models of uncertainty-based maintenance of fear and anxiety and inform translational work aiming to improve the diagnosis and treatment of relevant psychopathology.</p

Renewal of threat expectancy in an online contextual avoidance paradigm

Extinction of fear and avoidance is not permanent and can return following contextual changes (termed renewal). The aim of the current study was to investigate the renewal of avoidance, threat expectancy, and fear ratings in an online avoidance task administered during the COVID-19 pandemic. One-hundred and two participants completed a task consisting of habituation, threat conditioning, avoidance conditioning, extinction with response prevention, and renewal. Tests for renewal occurred either in the original conditioning context (ABA, n = 52) or the extinction context (ABB, n = 50). Images of a quiet and a busy street served as relevant contexts. Renewal was evident whereby the ABA group showed a significant increase in threat expectancy when tested in the conditioning context, which had not been extinguished. This effect was not found for avoidance or fear ratings, nor for the ABB group who underwent the renewal test in the extinction context. The current study demonstrated differential renewal of threat expectancy in an online contextual avoidance paradigm

Determining arterial blood velocity using MAUI software from recorded doppler ultrasound videos

Objectives: The purpose of this study was to investigate the repeatability and reproducibility of a new software, developed to provide measurements of arterial blood velocity from recorded Doppler ultrasound videos. Methods: The “Measurements from Arterial Ultrasound Imaging” (MAUI) software (Hedgehog Medical Inc.), developed for the measurement of arterial dimensions, has been expanded to measure the blood velocity from ultrasound videos. MAUI uses an adaptive based segmentation and intelligent outlier removal image analysis method to determine the instantaneous peak velocity in the positive and negative directions and the intensity weighted mean of the signal. Three recorded videos of popliteal arterial velocity were used to evaluate the reproducibility and repeatability of MAUI. For this assessment, two investigators (E1 and E2) each performed 10 measurements of the three test videos using MAUI. Results: MAUI provided blood velocity measurements (cm/s) for each frame of each video. The ten measurements made by E1 and E2 were averaged and are listed below (mean ± SD).Video # Velocity Measure E1 E21 Positive Envelope 27.84 ± 0.15 27.31 ± 0.28 Negative Envelope -13.99 ± 0.28 -13.68 ± 0.19 Mean Signal 13.80 ± 0.24 13.81 ± 0.102 Positive Envelope 42.30 ± 0.13 42.34 ± 0.33 Negative Envelope -11.51 ± 0.28 -11.53 ± 0.24 Mean Signal 29.69 ± 0.02 29.08 ± 0.363 Positive Envelope 53.48 ± 0.11 53.54 ± 0.20 Negative Envelope -13.66 ± 0.10 -13.40 ± 0.21 Mean Signal 38.60 ± 0.12 38.47 ± 0.17Conclusion: Preliminary assessments suggest that MAUI is a viable method for the measurement of blood velocity from recorded Doppler ultrasound video with high repeatability and low interrater variability. In future, measurements of velocity may be combined with existing continuous measurements of arterial diameter for the calculation of blood flow and assessments of vascular health and disease.<br/

Cigarette cravings impair mock jurors' recall of trial evidence

Prior research has demonstrated that cravings for substances, such as cigarettes and food, impair performance on basic cognitive tasks. This experiment examined whether these effects translate to impaired cognition on an important task in an applied setting: jury duty. Forty-six smokers were randomly allocated to a high-craving or control condition of an in vivo procedure designed to invoke cigarette cravings. Participants were then asked to act as mock jurors and read a written legal transcript based on evidence presented in an actual civil case. Later, participants were tested on their recall and recognition of information from the transcript. Participants in the high-craving condition recalled fewer correct facts from the transcript than participants in the control condition, but cravings did not significantly affect the recognition of trial information. These results are consistent with cognitive models of cravings, highlight the importance of providing jurors with sufficient breaks, and suggest that cravings may impair cognition in a variety of important applied settings

Greater sleep disturbance and longer sleep onset latency facilitate SCR-specific fear reinstatement in PTSD

Fear reinstatement is one of several paradigms designed to measure fear return following extinction, as a laboratory model for the relapse of Posttraumatic Stress Disorder (PTSD) symptoms. Sleep is a key factor in emotional memory consolidation, and here we examined the relationship between sleep quality and fear reinstatement in PTSD, relative to trauma-exposed and non-exposed controls. The Pittsburgh Sleep Quality Index (PSQI) was used as a subjective measure of sleep quality, and skin conductance responses (SCR) and unconditioned stimulus (US)-expectancy ratings were used to index threat responses during a differential fear conditioning, extinction, and reinstatement paradigm. There were no significant between-group differences in the reinstatement of conditioned responding. Sleep disturbance and sleep onset latency were significant moderators between reinstatement of fear and PTSD symptom severity, such that there was a positive relationship between PTSD symptoms and fear reinstatement for higher levels - but not lower levels - of sleep disturbance and sleep onset latency. To our knowledge, this is the first study to investigate PTSD-specific reinstatement patterns and sleep as a boundary condition of reinstatement. Future research using polysomnographic measures of sleep-wave architecture may further clarify the relationship between fear reinstatement and sleep quality in clinical samples with PTSD relative to controls