International orienteering experts' consensus on the definition, development, cause, impact and methods to reduce mental fatigue in orienteering: A Delphi study.

Orienteering is an outdoor activity wherein participants use a map and compass to locate control points and choose the quickest path to the next control point in a natural environment. Attentional focus, rapid decision-making, and high aerobic fitness may influence orienteering performance. Therefore, this research aimed to seek international orienteering expert consensus regarding the definition, development, causes, influences and methods to reduce mental fatigue (MF) in orienteering based on practical experience. Following ethical approval, a three-round Delphi survey was conducted online with twenty-four orienteering coaches and athletes (or former athletes) from 10 different countries with international orienteering competition experience. The threshold of consensus was ≥ 70% agreement among respondents. The experts agreed that MF exists in daily life and orienteering with a substantial negative effect on their conscious decision-making performance and psychological responses. The experts disagreed that the form of MF that athletes experienced in orienteering training are similar to the competition. However, there was no agreement that MF would impact endurance and high-speed running performance during orienteering. This research refines the definition of MF and summarises the distinctions in what causes MF in orienteering training and competition, implying that MF should be addressed separately.

A Concussion Education Programme for Motorsport Drivers: A Field-Based Exploratory Pilot Study.

OBJECTIVE: Concussion education strategies that improve knowledge and attitudes long term are needed. This exploratory study piloted an interactive concussion education program, adopting concepts from the learning sciences and attitude change literature, for the underserved and high-risk population of motorsports. METHOD: Forty UK motorsport drivers (ages 16-20 years) participated. The workshop group received a two-phased workshop-based program. The comparison group received a concussion leaflet. Participants completed an adapted version of the Rosenbaum Concussion Knowledge and Attitudes Survey (RoCKAS-ST) at pre-, post- and 2-month follow-up. Within-group analysis for the workshop group explored the differential effect of the individual difference variable, Need for Cognition (NfC), and effectiveness was explored through post-workshop questionnaires and interviews. RESULTS: Unlike the comparison group, the workshop group showed a significant improvement in knowledge over time (F(2,58) = 45.49, p < .001, η2p = .61). Qualitative data indicated workshop-program participants developed safer attitudes toward concussion following programming. Preliminary evidence suggested individuals' responses to concussion education aligned with differences in NfC. CONCLUSION: This study piloted the first concussion education program for motorsport drivers and explored whether aligning educational provision with the NfC construct may help to improve program effectiveness. Findings are relevant to addressing the public health issue of concussion through educational approaches.

Exploring the use of high and low demand simulation for human performance assessment during multiorgan retrieval with the joint scrub practitioner.

Introduction: The National Organ Retrieval Service (NORS) 2015 review recommended a Joint Scrub Practitioner for abdominal and cardiac teams during combined organ retrieval. To evaluate the feasibility of this role, and to understand the functional implications, this study explores the use of simulation and provides a novel and comprehensive approach to assess individual and team performance in simulated multiorgan retrievals. Methods: Two high-fidelity simulations were conducted in an operating theatre with porcine organs, en bloc, placed in a mannequin. For donation after brainstem death (DBD) simulation, an anaesthetic machine provided simulated physiological output. Retrievals following donation after circulatory death (DCD) began with rapid arrival in theatre of the mannequin. Cardiothoracic (lead surgeon) and abdominal (lead and assistant surgeons; joint scrub practitioner, n=9) teams combined for the retrievals. Data collected before, during and after simulations used self-report and expert observers to assess: attitudinal expectations, mental readiness, mental effort, non-technical skills, teamwork, task workload and social validation perceptions. Results: Attitudinal changes regarding feasibility of a joint scrub practitioner for DBD and DCD are displayed in the main body. There were no significant differences in mental readiness prior to simulations nor in mental effort indicated afterwards; however, variance was noted between simulations for individual team members. Non-technical skills were slightly lower in DCD than in DBD. Global ratings of teamwork were significantly (p<0.05) lower in DCD than in DBD. Measures of attitude indicated less support for the proposed joint scrub practitioner role for DCD than for DBD. Discussion: The paper posits that the joint scrub practitioner role in DCD multiorgan retrieval may bring serious and unanticipated challenges. Further work to determine the feasibility of the NORS recommendation is required. Measures of team performance and individual psychological response can inform organ retrieval feasibility considerations nationally and internationally.

The Vanguard Study: Human Performance Evaluation of UK National Organ Retrieval Service Teams Utilizing a Single Scrub Practitioner in Multiorgan Retrieval.

BACKGROUND: The National Organ Retrieval Service (NORS) 2015 review recommended a single scrub practitioner provide support simultaneously to abdominal and cardiothoracic teams in UK multiorgan retrieval. Previously, this model had been used only by the combined abdominal and cardiac team in Scotland. This study reports the impact on performance as part of the Vanguard project, which utilized the single scrub practitioner role with 5 NORS teams, to determine applicability United Kingdom wide. METHODS: Participants comprised members of abdominal (n = 56) and cardiothoracic (n = 54) teams attending UK thoraco-abdominal retrievals. Data were collected by validated psychometric scales to assess individual workload, anxiety, confidence, demands/coping resources, and teamwork. Additional data were collected through open comments and quantitative data describing context and outcome of retrieval. RESULTS: Abdominal and cardiothoracic teams showed different responses when using single (Vanguard) or dual scrub practitioners (Standard). Vanguard configuration was associated with significantly higher anxiety for abdominal but not cardiothoracic teams. Perceived workload increased for abdominal teams during Vanguard but decreased for cardiothoracic teams. Scrub practitioners reported elevated anxiety and decreased confidence in retrievals using Vanguard configuration. CONCLUSIONS: This is the first large study examining human performance during organ retrieval in the United Kingdom. Despite previous regional success, this study showed a significant negative impact of the single scrub practitioner when extrapolated widely to UK teams. As a result of this study, NORS declined to implement the single scrub model. These data support the use of human performance analysis as an essential part of successful development in organ retrieval practice.

Concussion in Motorsport? Experience, Knowledge, Attitudes, and Priorities of Medical Personnel and Drivers.

OBJECTIVE: To assess concussion experiences, knowledge, and attitudes of motorsport medical personnel and drivers and to determine priority areas regarding concussion within the sport. DESIGN: Sequential mixed-method design. Part 1: stakeholder interviews; part 2: cross-sectional online survey. SETTING: United Kingdom. PARTICIPANTS: Part 1: key motorsport stakeholders (N = 8); part 2: motorsport medical personnel and drivers (N = 209) representing amateur and/or professional 4-wheeled motorsport. MAIN OUTCOME MEASURES: Concussion experience, knowledge, attitudes, and perceived priority areas. RESULTS: Thirty-one percent of surveyed drivers (age = 37.91 ± 13.49 years: 89% male) reported suffering from concussion in motorsport. Eighty-seven percent of surveyed medical personnel (age = 48.60 ± 10.68 years: 74% male) reported experience with concussed drivers, and 34% reported feeling pressured to clear a driver with concussion. Gaps in knowledge and misperceptions about concussion were reported in both groups, and disparity between concussion attitudes emerged between drivers and medical personnel. Application of assessment and management procedures varied between medical personnel and there was evidence motorsport policy and concussion guidelines may not be directly followed. According to both medical personnel (77%) and drivers (85%), "education and training" is the top priority area for the sport. CONCLUSIONS: There is clear evidence of concussions in motorsport, but accurate knowledge about this injury is missing. Concussion education and training for all drivers and medical personnel is required. Additional investigations into concussion attitudes are advised to complement and advance simple educational initiatives. Further investigation is also required to determine how to best support motorsport medical personnel, and general practitioners, who hold significant responsibility in guiding drivers from diagnosis to return to racing, and to support the effective implementation of policy.

Current epidemiology of cerebrospinal fluid shunt surgery in the UK and Ireland (2004-2013).

OBJECTIVES: To determine current epidemiology and clinical characteristics of cerebrospinal fluid (CSF) shunt surgery, including revisions. METHODS: A retrospective, multicentre, registry-based study was conducted based on 10 years' data from the UK Shunt Registry, including primary and revision shunting procedures reported between 2004 and 2013. Incidence rates of primary shunts, descriptive statistics and shunt revision rates were calculated stratified by age group, geographical region and year of operation. RESULTS: 41 036 procedures in 26 545 patients were submitted during the study period, including 3002 infants, 4389 children and 18 668 adults. Procedures included 20 947 (51.0%) primary shunt insertions in 20 947 patients, and 20 089 (49.0%) revision procedures. Incidence rates of primary shunt insertions for infants, children and adults were 39.5, 2.4 and 3.5 shunts per 100 000 person-years, respectively. These varied by geographical subregion and year of operation. The most common underlying diagnoses were perinatal intraventricular haemorrhage (35.3%) and malformations (33.9%) in infants, tumours (40.5%) and malformations (16.3%) in children, and tumours (24.6%), post-haemorrhagic hydrocephalus (16.2%) and idiopathic normal pressure hydrocephalus (14.2%) in adults. Ninety-day revision rates were 21.9%, 18.6% and 12.8% among infants, children and adults, respectively, while first-year revision rates were 31.0%, 25.2% and 17.4%. The main reasons for revision were underdrainage and infection, but overdrainage and mechanical failure continue to pose problems. CONCLUSIONS: Our report informs patients, carers, clinicians, providers and commissioners of healthcare, researchers and industry of the current epidemiology of shunting for CSF disorders, including the potential risks of complications and frequency of revision.

A Multidisciplinary Investigation of the Effects of Competitive State Anxiety on Serve Kinematics in Table Tennis.

Displays of anxiety in table tennis were assessed through subjective (a self-report questionnaire), physiological (heart-rate variability) and kinematic variables. Using a within-group crossover design, 9 university-level table tennis players completed a series of serves under low- and high-anxiety conditions. Anxiety manipulation was achieved through the introduction of a national standard table tennis player, known to the participants, to receive serves in the high-anxiety condition, whilst serves were received by no opponent in the low-anxiety condition. Automated motion capture systems consisting of high-speed 3D motion cameras and analytical software (QUALISYS) determined the subject's movement kinematics: bat face angle (degrees) and serve routine duration (s). Self-reported state anxiety (MRF-Likert) and heart rate measurements were collected to examine changes between conditions. Contrary to the hypothesis, bat face angles did not change significantly between anxiety conditions (F (1.8) = 2.791, p = 0.133) and movement times were faster in the high-anxiety condition. In light of these findings, research into other facets of movement behaviour must be analysed to gain further understanding of the effects of anxiety on performance, which remain unclear.

Doppler Non-invasive Monitoring of ICP in an Animal Model of Acute Intracranial Hypertension.

BACKGROUND: In many neurological diseases, intracranial pressure (ICP) is elevated and needs to be actively managed. ICP is typically measured with an invasive transducer, which carries risks. Non-invasive techniques for monitoring ICP (nICP) have been developed. The aim of this study was to compare three different methods of transcranial Doppler (TCD) assessment of nICP in an animal model of acute intracranial hypertension. METHODS: In 28 rabbits, ICP was increased to 70-80 mmHg by infusion of Hartmann's solution into the lumbar subarachnoid space. Doppler flow velocity in the basilar artery was recorded. nICP was assessed through three different methods: Gosling's pulsatility index PI (gPI), Aaslid's method (AaICP), and a method based on diastolic blood flow velocity (FVdICP). RESULTS: We found a significant correlation between nICP and ICP when all infusion experiments were combined (FVdICP: r = 0.77, AaICP: r = 0.53, gPI: r = 0.54). The ability to distinguish between raised and 'normal' values of ICP was greatest for FVdICP (AUC 0.90 at ICP >40 mmHg). When infusion experiments were considered independently, FVdICP demonstrated again the strongest correlation between changes in ICP and changes in nICP (mean r = 0.85). CONCLUSIONS: TCD-based methods of nICP monitoring are better at detecting changes of ICP occurring in time, rather than absolute prediction of ICP as a number. Of the studied methods of nICP, the method based on FVd is best to discriminate between raised and 'normal' ICP and to monitor relative changes of ICP.

Physiological and selective attention demands during an international rally motor sport event.

PURPOSE: To monitor physiological and attention responses of drivers and codrivers during a World Rally Championship (WRC) event. METHODS: Observational data were collected from ten male drivers/codrivers on heart rate (HR), core body (T core) and skin temperature (T sk), hydration status (urine osmolality), fluid intake (self-report), and visual and auditory selective attention (performance tests). Measures were taken pre-, mid-, and postcompetition day and also during the precompetition reconnaissance. RESULTS: In ambient temperatures of 20.1°C (in-car peak 33.9°C) mean (SD) peak HR and T core were significantly elevated (P < 0.05) during rally compared to reconnaissance (166 (17) versus 111 (16) beats · min(-1) and 38.5 (0.4) versus 37.6 (0.2)°C, resp.). Values during competitive stages were substantially higher in drivers. High urine osmolality was indicated in some drivers within competition. Attention was maintained during the event but was significantly lower prerally, though with considerable individual variation. CONCLUSIONS: Environmental and physical demands during rally competition produced significant physiological responses. Challenges to thermoregulation, hydration status, and cognitive function need to be addressed to minimise potentially negative effects on performance and safety.

Hydrocephalus shunt technology: 20 years of experience from the Cambridge Shunt Evaluation Laboratory.

OBJECT: The Cambridge Shunt Evaluation Laboratory was established 20 years ago. This paper summarizes the findings of that laboratory for the clinician. METHODS: Twenty-six models of valves have been tested long-term in the shunt laboratory according to the expanded International Organization for Standardization 7197 standard protocol. RESULTS: The majority of the valves had a nonphysiologically low hydrodynamic resistance (from 1.5 to 3 mm Hg/[ml/min]), which may result in overdrainage related to posture and during nocturnal cerebral vasogenic waves. A long distal catheter increases the resistance of these valves by 100%-200%. Drainage through valves without a siphon-preventing mechanism is very sensitive to body posture, which may result in grossly negative intracranial pressure. Siphon-preventing accessories offer a reasonable resistance to negative outlet pressure; however, accessories with membrane devices may be blocked by raised subcutaneous pressure. In adjustable valves, the settings may be changed by external magnetic fields of intensity above 40 mT (exceptions: ProGAV, Polaris, and Certas). Most of the magnetically adjustable valves produce large distortions on MRI studies. CONCLUSIONS: The behavior of a valve revealed during testing is of relevance to the surgeon and may not be adequately described in the manufacturer's product information. The results of shunt testing are helpful in many circumstances, such as the initial choice of shunt and the evaluation of the shunt when its dysfunction is suspected.

Cessation of diastolic cerebral blood flow velocity: the role of critical closing pressure.

BACKGROUND: Reducing cerebral perfusion pressure (CPP) below the lower limit of autoregulation (LLA) causes cerebral blood flow (CBF) to become pressure passive. Further reductions in CPP can cause cessation of CBF during diastole. We hypothesized that zero diastolic flow velocity (FV) occurs when diastolic blood pressure becomes less than the critical closing pressure (CrCP). METHODS: We retrospectively analyzed studies of 34 rabbits with CPP below the LLA, induced with pharmacologic sympathectomy (N = 23) or cerebrospinal fluid infusion (N = 11). Basilar artery blood FV and cortical Laser Doppler Flow (LDF) were monitored. CrCP was trended using a model of cerebrovascular impedance. The diastolic closing margin (DCM) was monitored as the difference between diastolic blood pressure and CrCP. LDF was recorded for DCM values greater than and less than zero. RESULTS: Arterial hypotension caused a reduction of CrCP (p < 0.001), consistent with decreased wall tension (p < 0.001) and a drop in intracranial pressure (ICP; p = 0.004). Cerebrospinal infusion caused an increase of CrCP (p = 0.002) accounted for by increasing ICP (p < 0.001). The DCM was compromised by either arterial hypotension or intracranial hypertension (p < 0.001 for both). When the DCM reached zero, diastolic FV ceased for a short period during each heart cycle (R = 0.426, p < 0.001). CBF pressure passivity accelerated when DCM decreased below zero (from 1.51 ± 0.51 to 2.17 ± 1.17 % ΔLDF/ΔmmHg; mean ± SD; p = 0.010). CONCLUSIONS: The disappearance of diastolic CBF below LLA can be explained by DCM reaching zero or negative values. Below this point the decrease in CBF accelerates with further decrements of CPP.

Critical closing pressure determined with a model of cerebrovascular impedance.

Critical closing pressure (CCP) is the arterial blood pressure (ABP) at which brain vessels collapse and cerebral blood flow (CBF) ceases. Using the concept of impedance to CBF, CCP can be expressed with brain-monitoring parameters: cerebral perfusion pressure (CPP), ABP, blood flow velocity (FV), and heart rate. The novel multiparameter method (CCPm) was compared with traditional transcranial Doppler (TCD) calculations of CCP (CCP1). Digital recordings of ABP, intracranial pressure (ICP), and TCD-based FV from previously published studies of 29 New Zealand White rabbits were reanalyzed. Overall, CCP1 and CCPm showed correlation across wide ranges of ABP, ICP, and PaCO2 (R=0.93, P<0.001). Three physiological perturbations were studied: increase in ICP (n=29) causing both CCP1 and CCPm to increase (P<0.001 for both); reduction of ABP (n=10) resulting in decrease of CCP1 (P=0.006) and CCPm (P=0.002); and controlled increase of PaCO2 (n=8) to hypercapnic levels, which decreased CCP1 and CCPm, albeit insignificantly (P=0.123 and P=0.306 respectively), caused by a spontaneous significant increase in ABP (P=0.025). Multiparameter mathematical model of critical closing pressure explains the relationship of CCP on brain-monitoring variables, allowing the estimation of CCP during cases such as hypercapnia-induced hyperemia, where traditional calculations, like CCP1, often reach negative non-physiological values.

The SILVER (Silver Impregnated Line Versus EVD Randomized trial): a double-blind, prospective, randomized, controlled trial of an intervention to reduce the rate of external ventricular drain infection.

BACKGROUND: Cerebrospinal fluid (CSF) infections associated with external ventricular drain (EVD) placement attract major consequences. Silver impregnation of catheters attempts to reduce infection. OBJECTIVE: To assess the efficacy of silver catheters against CSF infection. METHODS: We performed a randomized, controlled trial involving 2 neurosurgical centers (June 2005 to September 2009). A total of 356 patients requiring an EVD were assessed for eligibility; 325 patients were enrolled and randomized (167 plain, 158 silver); 278 patients were analyzed (140 plain, 138 silver). The primary outcome measure was CSF infection as defined by organisms seen on Gram stain or isolated by culture. Secondary outcome measures included ventriculoperitoneal (VP) shunting. RESULTS: There was a significant difference in infection risk between the 2 study arms: 21.4% (30/140) for plain catheters vs 12.3% (17/138) for silver catheters (P = .0427; 95% confidence interval [CI]: 1.015-3.713). Patients who had an EVD infection had more than double the risk of requiring a VP shunt compared with patients without an EVD infection (45.7% [21/46] vs 19.7% [45/229], respectively, P = .0002; 95% CI: 1.766-6.682). There was also a significant difference in VP shunt risk with infection: plain (55.2%; 16/29) vs the silver arm (29.4%; 5/17); P = .0244 (95% CI: 1.144-11.695). A multivariate analysis demonstrated that infection risk was increased by duration of EVD placement (odds ratio: 1.160), spontaneous intracranial hemorrhage (odds ratio 4.958) and decreased by silver catheters (odds ratio: 0.423). CONCLUSION: The study provides Class I evidence that silver-impregnated catheters reduce CSF infection.

Dynamic in vivo imaging of receptors in small animals using positron emission tomography.

Positron emission tomography (PET) is a functional imaging technique with the potential to image and quantify receptors in vivo with high sensitivity. PET has been used extensively to study major neurotransmitters such as dopamine, serotonin, and benzodiazepine in humans as well as proving to be a very powerful tool to accelerate development and assessment of existing and novel drugs. With the recent development of dedicated PET scanners for small animals, such as the microPET, it is now possible to perform functional imaging in small animals such as rodents at high resolution. This will allow the study of animal models of disease and longitudinal studies in these models to monitor disease progression or effect of treatment in the same animal. Furthermore, the complete pharmacokinetics of a drug as well as pharmacodynamic information can be obtained in a single animal. Thus, small animal imaging will significantly reduce the number of animals needed for this type of experiment as well as reducing the effect of inter-animal variation. Experimental protocols in small animal imaging potentially can be very labor intensive. In this chapter, we discuss methods and practical aspects related to this type of experiment using the microPET system.

Preventing flow-metabolism uncoupling acutely reduces axonal injury after traumatic brain injury.

We have previously presented evidence that the development of secondary traumatic axonal injury is related to the degree of local cerebral blood flow (LCBF) and flow-metabolism uncoupling. We have now tested the hypothesis that augmenting LCBF in the acute stages after brain injury prevents further axonal injury. Data were acquired from rats with or without acetazolamide (ACZ) that was administered immediately following controlled cortical impact injury to increase cortical LCBF. Local cerebral metabolic rate for glucose (LCMRglc) and LCBF measurements were obtained 3 h post-trauma in the same rat via ¹8F-fluorodeoxyglucose and ¹4C-iodoantipyrine co-registered autoradiographic images, and compared to the density of damaged axonal profiles in adjacent sections, and in additional groups at 24 h used to assess different populations of injured axons stereologically. ACZ treatment significantly and globally elevated LCBF twofold above untreated-injured rats at 3 h (p<0.05), but did not significantly affect LCMRglc. As a result, ipsilateral LCMRglc:LCBF ratios were reduced by twofold to sham-control levels, and the density of ß-APP-stained axons at 24 h was significantly reduced in most brain regions compared to the untreated-injured group (p<0.01). Furthermore, early LCBF augmentation prevented the injury-associated increase in the number of stained axons from 3-24 h. Additional robust stereological analysis of impaired axonal transport and neurofilament compaction in the corpus callosum and cingulum underlying the injury core confirmed the amelioration of ß-APP axon density, and showed a trend, but no significant effect, on RMO14-positive axons. These data underline the importance of maintaining flow-metabolism coupling immediately after injury in order to prevent further axonal injury, in at least one population of injured axons.

Psychological distress does not compromise outcome in spinal surgery.

SUMMARY OF BACKGROUND DATA: Physical outcomes following surgery for degenerative spine disease have been well studied whereas the importance of psychological factors has only recently been acknowledged. Previous studies suggest that pre-operative psychological distress predicts poor outcome from spinal surgery. In the drive to identify patients who will not benefit, these patients risk being denied surgery. STUDY DESIGN: This is a prospective series from a spinal surgical register. AIM: The study examines the relationship between the physical symptoms, pre-operative psychological distress and outcome following surgery. METHODS: The Short Form 36 (SF36) Health Survey Questionnaire and the Hospital Anxiety and Depression Scale (HADS) were administered to patients undergoing elective surgery for degenerative spine disease pre-operatively and at 3 and 12 months post-operatively. Levels of physical disability (SF-36 physical functioning (SF36PF) and bodily pain (SF36BP) scores) and psychological distress (HADS-anxiety and HADS-depression scores) before and after surgery were compared. RESULTS: A total of 302 patients were included (169 men, 133 women, mean age 55 years). Pre-operatively patients had worse physical scores than age-matched controls (SF36PF normative mean (S.D.) 80.97 (12.69) vs. pre-op 33.31 (24.7) P < 0.05). Of the 302 patients, 117 (39%) had significant anxiety or depression. Increased levels of anxiety or depression pre-operatively correlated with worse physical (SF-36PF and SF-36BP) scores pre-operatively (Spearman's r P < 0.05). Levels of anxiety and depression were reduced post-operatively and physical outcomes improved post-operatively. Physical function remained worse in those groups who had high levels of anxiety and depression pre-operatively but when matched for pre-operative physical function, psychological distress did not have any additional effect on outcome. CONCLUSIONS: Poor physical function pre-operatively correlates with psychological distress. Both physical and psychological symptoms improve after surgery. Physical outcome after surgery is strongly influenced by pre-operative physical functioning but not independently by psychological distress. Anxious and depressed patients should continue to be offered surgery if clinically indicated.

Cerebrovascular time constant: dependence on cerebral perfusion pressure and end-tidal carbon dioxide concentration.

OBJECTIVE: The cerebrovascular time constant (τ) describes the time to establish a change in cerebral blood volume after a step transient in arterial blood pressure (ABP). We studied the relationship between τ, ABP, intracranial pressure (ICP), and end-tidal carbon dioxide concentration (EtCO2). METHOD: Recordings from 46 anaesthetized, paralysed and ventilated New Zealand rabbits were analysed retrospectively. ABP was directly monitored in the femoral artery, transcranial Doppler (TCD) cerebral blood flow velocity (CBFV) from the basilar artery, and ICP using an intraparenchymal sensor. In nine animals end-tidal CO2 (EtCO2) was monitored continuously. ABP was decreased with injection of trimetophan (n = 11) or haemorrhage (n = 6) and increased by boluses of dopamine (n = 11). ICP was increased by infusion of normal saline into the lumbar cerebrospinal fluid space (n = 9). Changes in cerebral compliance (C(a)) were estimated as a ratio of the pulse amplitude of the cerebral arterial blood volume (CBV) and the pulse amplitude of ABP. Changes in cerebrovascular resistance (CVR) were expressed as mean ABP or cerebral perfusion pressure (CPP) divided by mean CBFV. Time constant τ was calculated as the product of CVR and C(a). RESULTS: The time constant changed inversely to the direction of the change in ABP (during arterial hypo- and hypertension) and CPP (during intracranial hypertension). C(a) increased with decreasing CPP, while CVR decreased. During a decrease in CPP, changes in C(a) exceeded changes in CVR. In contrast, during hypercapnia, the decrease in CVR was more pronounced than the increase in C(a), resulting in a decrease in τ. CONCLUSION: Cerebrovascular time constant τ is modulated by ABP, ICP, and EtCO2.

Assessing quality of life after traumatic brain injury: examination of the short form 36 health survey.

Measuring health-related quality of life (HRQoL) has an important role in the comprehensive assessment of patient recovery following traumatic brain injury (TBI). We examined the validity of domain and summary scores derived from the Medical Outcomes Survey 36-Item Short Form Health Questionnaire (SF-36) as outcome measures for TBI in a prospective study of 514 patients with a range of functional impairment (Glasgow Outcome Scale-Extended [GOSE] scores 3-8). Item scaling criteria for the eight domain scores were tested and principal component analysis was used to examine if physical and mental component summary scores were valid. External validity was assessed by comparison with GOSE. Mean response, variance, and distribution of the items were largely equivalent, and item-own scale correlations corrected for overlap all exceeded the threshold for equivalent contribution to domain scores and convergent validity. All corrected item-own scale correlations were greater than the respective item-other correlations indicating no scaling failures, and reliability coefficients for the domain scores were high and substantially more than the inter-domain correlations. Overall, criteria for summing items into domain scores were satisfied, and there was a significant relationship of increasing score with more favorable GOSE class across all domains. However, there were floor and/or ceiling effects in four of the eight domains, and principal component analysis of the domain scores demonstrated only a unidimensional structure to the data. We conclude that individual SF-36 domain scores are valid measures of HRQoL in TBI patients, but that the physical and mental component summaries should be interpreted with caution.

Positron emission tomography of [18F]-big endothelin-1 reveals renal excretion but tissue-specific conversion to [18F]-endothelin-1 in lung and liver.

BACKGROUND AND PURPOSE: Big endothelin-1 (ET-1) circulates in plasma but does not bind to ET receptors until converted to ET-1 by smooth muscle converting enzymes. We hypothesized that tissue-specific conversion of [(18)F]-big ET-1 to [(18)F]-ET-1 could be imaged dynamically in vivo within target organs as binding to ET receptors. METHODS: [(18)F]-big ET-1 conversion imaged in vivo following infusion into rats using positron emission tomography (PET). KEY RESULTS: [(18)F]-big ET-1 was rapidly cleared from the circulation (t(1/2)= 2.9 +/- 0.1 min). Whole body microPET images showed highest uptake of radioactivity in three major organs. In lungs and liver, time activity curves peaked within 2.5 min, then plateaued reaching equilibrium after 10 min, with no further decrease after 120 min. Phosphoramidon did not alter half life of [(18)F]-big ET-1 but uptake was reduced in lung (42%) and liver (45%) after 120 min, consistent with inhibition of enzyme conversion and reduction of ET-1 receptor binding. The ET(A) antagonist, FR139317 did not alter half-life of [(18)F]-big ET-1 (t(1/2)= 2.5 min) but radioactivity was reduced in all tissues except for kidney consistent with reduction in binding to ET(A) receptors. In kidney, however, the peak in radioactivity was higher but time to maximum accumulation was slower ( approximately 30 min), which was increased by phosphoramidon, reflecting renal excretion with low conversion and binding to ET receptors. CONCLUSIONS AND IMPLICATIONS: A major site for conversion was within the vasculature of the lung and liver, whereas uptake in kidney was more complex, reflecting excretion of [(18)F]-big ET-1 without conversion to ET-1.

Hypertonic saline in patients with poor-grade subarachnoid hemorrhage improves cerebral blood flow, brain tissue oxygen, and pH.

BACKGROUND AND PURPOSE: Delayed cerebral ischemia and infarction due to reduced CBF remains the leading cause of poor outcome after aneurysmal subarachnoid hemorrhage. Hypertonic saline (HS) is associated with an increase in CBF. This study explores whether CBF enhancement with HS in patients with poor-grade subarachnoid hemorrhage is associated with improved cerebral tissue oxygenation. METHODS: Continuous monitoring of arterial blood pressure, intracranial pressure, cerebral perfusion pressure, brain tissue oxygen, carbon dioxide, pH, and middle cerebral artery flow velocity was performed in 44 patients. Patients were given an infusion (2 mL/kg) of 23.5% HS. In 16 patients, xenon CT scanning was also performed. CBF in a region surrounding the tissue oxygen sensor was calculated. Data are mean+/-SD. RESULTS: Thirty minutes postinfusion, a significant increase in arterial blood pressure, cerebral perfusion pressure, flow velocity, brain tissue pH, and brain tissue oxygen was seen together with a decrease in intracranial pressure (P<0.05). Intracranial pressure remained reduced for >300 minutes and flow velocity elevated for >240 minutes. A significant increase in brain tissue oxygen persisted for 240 minutes. Average baseline regional CBF was 33.9+/-13.5 mL/100 g/min, rising by 20.3%+/-37.4% (P<0.05) after HS. Patients with favorable outcome responded better to HS in terms of increased CBF, brain tissue oxygen, and pH and reduced intracranial pressure compared with those with an unfavorable outcome. A sustained increase in brain tissue oxygen (beyond 210 minutes) was associated with favorable outcome (P<0.023). CONCLUSIONS: HS augments CBF in patients with poor-grade subarachnoid hemorrhage and significantly improves cerebral oxygenation for 4 hours postinfusion. Favorable outcome is associated with an improvement in brain tissue oxygen beyond 210 minutes.