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Background Although widely used in the evaluation of the diseased, normal intracranial pressure and lumbar cerebrospinal fluid pressure remain sparsely documented. Intracranial pressure is different from lumbar cerebrospinal fluid pressure. In addition, intracranial pressure differs considerably according to the body position of the patient. Despite this, the current reference values do not distinguish between intracranial and lumbar cerebrospinal fluid pressures, and body position-dependent reference values do not exist. In this study, we aim to establish these reference values. Method A systematic search was conducted in MEDLINE, EMBASE, CENTRAL, and Web of Sciences. Methodological quality was assessed using an amended version of the Joanna Briggs Quality Appraisal Checklist. Intracranial pressure and lumbar cerebrospinal fluid pressure were independently evaluated and subdivided into body positions. Quantitative data were presented with mean ± SD, and 90% reference intervals. Results Thirty-six studies were included. Nine studies reported values for intracranial pressure, while 27 reported values for the lumbar cerebrospinal fluid pressure. Reference values for intracranial pressure were −  5.9 to 8.3 mmHg in the upright position and 0.9 to 16.3 mmHg in the supine position. Reference values for lumbar cerebrospinal fluid pressure were 7.2 to 16.8 mmHg and 5.7 to 15.5 mmHg in the lateral recumbent position and supine position, respectively. Conclusions This systematic review is the first to provide position-dependent reference values for intracranial pressure and lumbar cerebrospinal fluid pressure. Clinically applicable reference values for normal lumbar cerebrospinal fluid pressure were established, and are in accordance with previously used reference values. For intracranial pressure, this study strongly emphasizes the scarcity of normal pressure measures, and highlights the need for further research on the matter.

The mean flow index—usually referred to as Mx—has been used for assessing dynamic cerebral autoregulation (dCA) for almost 30 years. However, concerns have arisen regarding methodological consistency, construct and criterion validity, and test–retest reliability. Methodological nuances, such as choice of input (cerebral perfusion pressure, invasive or non‐invasive arterial pressure), pre‐processing approach and artefact handling, significantly influence mean flow index values, and previous studies correlating mean flow index with other established dCA metrics are confounded by inherent methodological flaws like heteroscedasticity, while the mean flow index also fails to discriminate individuals with presumed intact versus impaired dCA (discriminatory validity), and its prognostic performance (predictive validity) across various conditions remains inconsistent. The test–retest reliability, both within and between days, is generally poor. At present, no single approach for data collection or pre‐processing has proven superior for obtaining the mean flow index, and caution is advised in the further use of mean flow index‐based measures for assessing dCA, as current evidence does not support their clinical application. What is the topic of this review? The validity and reliability of mean flow index‐based measures for assessing dynamic cerebral autoregulation (dCA) in humans. What advances does it highlight? Current evidence does not support the clinical application of mean flow index‐based measures, warranting caution in their further use for dCA assessment.

Background It is crucial to maintain the intracranial pressure (ICP) within the physiological range to ensure proper brain function. The ICP may fluctuate during the light-dark phase cycle, complicating diagnosis and treatment choice in patients with pressure-related disorders. Such ICP fluctuations may originate in circadian or sleep-wake cycle-mediated modulation of cerebrospinal fluid (CSF) flow dynamics, which in addition could support diurnal regulation of brain waste clearance. Methods ICP was monitored continuously in patients who underwent placement of an external ventricular drain (EVD) and by telemetric monitoring in experimental rats. CSF was collected via the EVD in patients and the rodent CSF secretion rate determined by in vivo experimentation. Rodent choroid plexus transporter transcripts were quantified with RNAseq and transport activity with ex vivo isotope transport assays. Results We demonstrated that ICP increases by 30% in the dark phase in both species, independently of vascular parameters. This increase aligns with elevated CSF collection in patients (12%) and CSF production rate in rats (20%), the latter obtained with the ventriculo-cisternal perfusion assay. The dark-phase increase in CSF secretion in rats was, in part, assigned to increased transport activity of the choroid plexus Na + ,K + ,2Cl - cotransporter (NKCC1), which is implicated in CSF secretion by this tissue. Conclusion CSF secretion, and thus ICP, increases in the dark phase in humans and rats, irrespective of their diurnal/nocturnal activity preference, in part due to altered choroid plexus transport activity in the rat. Our findings suggest that CSF dynamics are modulated by the circadian rhythm, rather than merely sleep itself.

Introduction Posthemorrhagic hydrocephalus (PHH) often develops following hemorrhagic events such as intraventricular hemorrhage (IVH) and subarachnoid hemorrhage (SAH). Treatment is limited to surgical diversion of the cerebrospinal fluid (CSF) since no efficient pharmacological therapies are available. This limitation follows from our incomplete knowledge of the molecular mechanisms underlying the ventriculomegaly characteristic of PHH. Here, we aimed to elucidate the molecular coupling between a hemorrhagic event and the subsequent PHH development, and reveal the inflammatory profile of the PHH pathogenesis. Methods CSF obtained from patients with SAH was analyzed for inflammatory markers using the proximity extension assay (PEA) technique. We employed an in vivo rat model of IVH to determine ventricular size, brain water content, intracranial pressure, and CSF secretion rate, as well as for transcriptomic analysis. Ex vivo radio-isotope assays of choroid plexus transport were employed to determine the direct effect of choroidal exposure to blood and inflammatory markers, both with acutely isolated choroid plexus and after prolonged exposure obtained with viable choroid plexus kept in tissue culture conditions. Results The rat model of IVH demonstrated PHH and associated CSF hypersecretion. The Na + /K + -ATPase activity was enhanced in choroid plexus isolated from IVH rats, but not directly stimulated by blood components. Inflammatory markers that were elevated in SAH patient CSF acted on immune receptors upregulated in IVH rat choroid plexus and caused Na + /K + /2Cl - cotransporter 1 (NKCC1) hyperactivity in ex vivo experimental conditions. Conclusions CSF hypersecretion may contribute to PHH development, likely due to hyperactivity of choroid plexus transporters. The hemorrhage-induced inflammation detected in CSF and in the choroid plexus tissue may represent the underlying pathology. Therapeutic targeting of such pathways may be employed in future treatment strategies towards PHH patients.

Background A range of neurological pathologies may lead to secondary hydrocephalus. Treatment has largely been limited to surgical cerebrospinal fluid (CSF) diversion, as specific and efficient pharmacological options are lacking, partly due to the elusive molecular nature of the CSF secretion apparatus and its regulatory properties in physiology and pathophysiology. Methods CSF obtained from patients with subarachnoid hemorrhage (SAH) and rats with experimentally inflicted intraventricular hemorrhage (IVH) was analyzed for lysophosphatidic acid (LPA) by alpha-LISA. We employed the in vivo rat model to determine the effect of LPA on ventricular size and brain water content, and to reveal the effect of activation and inhibition of the transient receptor potential vanilloid 4 (TRPV4) ion channel on intracranial pressure and CSF secretion rate. LPA-mediated modulation of TRPV4 was determined with electrophysiology and an ex vivo radio-isotope assay was employed to determine the effect of these modulators on choroid plexus transport. Results Elevated levels of LPA were observed in CSF obtained from patients with subarachnoid hemorrhage (SAH) and from rats with experimentally-inflicted intraventricular hemorrhage (IVH). Intraventricular administration of LPA caused elevated brain water content and ventriculomegaly in experimental rats, via its action as an agonist of the choroidal transient receptor potential vanilloid 4 (TRPV4) channel. TRPV4 was revealed as a novel regulator of ICP in experimental rats via its ability to modulate the CSF secretion rate through its direct activation of the Na + /K + /2Cl − cotransporter (NKCC1) implicated in CSF secretion. Conclusions Together, our data reveal that a serum lipid present in brain pathologies with hemorrhagic events promotes CSF hypersecretion and ensuing brain water accumulation via its direct action on TRPV4 and its downstream regulation of NKCC1. TRPV4 may therefore be a promising future pharmacological target for pathologies involving brain water accumulation.

Background Missing outcome data can pose a serious threat to the validity of randomised clinical trial results. We aimed to study the extent of missing outcome data in randomised clinical trials of psychological interventions. Methods We performed a retrospective study of randomised clinical trial reports of psychological interventions published in World Psychiatry, JAMA Psychiatry, Lancet Psychiatry, American Journal of Psychiatry, British Journal of Psychiatry, or Psychotherapy and Psychosomatics from 2017 to 2022. We assessed the proportion of missing outcome data, whether missing data patterns differed between types of outcomes, participants, intervention lengths, and psychological intervention types, how missing outcome data were handled in the statistical analyses, and whether trialists discussed missing outcome data in the discussion section of the manuscript. Results We identified 182 randomised clinical trials (233 primary outcomes), of which 206 outcomes (88.4%) were assessed at high risk of bias due to missing data. The overall mean percentage of missing outcome data was 18.3% (95% confidence interval (CI): 16.7–20%) for all outcomes. The percentages of missing data were 18.9% (95% CI: 17.1–20.6%; 180 outcomes) for symptom severity scales and 1.8% (95% CI: 2.3–3.3%; 6 outcomes) for ‘hard’ binary outcomes. Trials including participants with borderline personality disorder had the highest percentage of missing outcome data (33.1%; 95% CI: 22.3–43.9%) compared with other psychiatric disorders. Fisher’s exact test showed that intervention lengths and psychological intervention types were associated with the proportion of missing outcome data ( p  < 0.001), but there were no clear patterns. Conclusion Missing outcome data is a considerable problem in randomised clinical trials of psychological interventions, and trialists should consider the corresponding methodological limitations in the design and analysis to reduce the risk of bias due to missing outcome data. Clinical trial registration number Not applicable.

Purpose Understanding the adverse effects of an intervention is important for evaluating its overall effect. Clinical trials mainly focus on the benefits of interventions with a risk of overlooking potential harms. Additionally, patients with severe acute brain injury frequently experience adverse events from other causes, which complicates the recording of harms in trials involving such participants. In this study, we developed a standardized registration form for recording adverse events in trial participants with severe acute brain injury using a structured Delphi process. Methods After developing the tool, we employed a Delphi process comprising two rounds of feedback from clinical experts in Nordic countries. In the first round, the Delphi panel received a questionnaire with a preliminary registration form, consisting of a list of 25 suggested definitions for adverse events relevant in the context of intensive care and severe acute brain injury. Based on feedback from the Delphi panel, we revised the tool and sent the revised registration form as a questionnaire in the second Delphi round. Results The Delphi panel consisted of 10 specialist physicians with experience in intensive care, neurosurgery or neurology. Consensus on the definition of an adverse event (defined as ≥ 70% agreement) was achieved for 27 out of the resulting 28 adverse events; for one adverse event, delirium, the level of agreement did not reach consensus in the second Delphi round; however, following revision, it was retained in the registration tool. The final version of the registration tool consisted of 28 adverse events for patients with severe acute brain injury. Conclusion A new tool for registration of adverse events and reactions in trial participants with severe acute brain injury was reviewed and refined by a Delphi panel of 10 Nordic neurocritical-care experts. The intention is to enhance the transparency, accuracy and consistency of reporting harms in clinical trials. Through thorough and standardized recording, the tool has the potential to improve the overall quality of clinical trials.

The Difficulties in Emotion Regulation Scale (DERS) is widely used in both clinical and non-clinical research to assess emotional regulation difficulties. To guide interpretation of scores, establishing thresholds for normative DERS scores is informative. However, despite its widespread use, to date no study has provided such threshold for youths. This literature review aimed to fill this gap by examining the 90% reference interval for the DERS in youths aged 11-19 years. We conducted a systematic search on PubMed (MEDLINE) on 12 March 2024, to identify studies reporting DERS-36 total scores (DERS-T) in youths aged 11-19 years from either community-based populations or healthy volunteers. A total of 34 studies were included; 20 studies included community-based participants (n = 6,960), while the remaining 14 studies included healthy volunteers (n = 766), resulting in a total of 7,726 participants. The 90% reference interval for DERS-T from all included participants had a threshold of 121.8 normative emotion regulation in youths. This threshold is considerably higher than DERS-T scores reported in most clinical studies and a substantial variation in reference intervals across studies is observed. We identify five main methodological factors related to the DERS-36 and discuss their potential impact on the validity, reliability, and generalizability of findings. Given the DERS-T range of 36-180, we conclude that the 90% reference interval derived from our review is not sufficiently robust to guide clinical or scientific interpretations. Our work is not exhaustive, and further research is needed to validate and test the reliability of this reference interval.