Acoustic and vibration isolation for a gravity gradiometer.

Vibration in the audio frequency band affects the performance of rotating gravity gradiometers used for airborne mineral exploration. This is probably due to translation to rotation coupling inside the gradiometer platform. It was found that the DC gravity gradient signal was proportional to the square of the third time derivative of position, or jerk squared. The demanding airborne environment for such instrumentation demands a light weight broadband acoustic shield and vibration isolator. This paper presents the design principles for such an isolator, based on vibration isolated spherical shell structures. Performance data are presented as well as flight test data that demonstrated a 14% gravity gradient noise reduction compared with an unshielded instrument.

Six degrees of freedom vibration isolation with Euler springs.

A novel design allows column springs in Euler buckling mode to be laterally stable and thus provides vibration isolation in six degrees of freedom. Analytical models of the stiffness were used to develop a design with a vertical resonance of 1.13 Hz, a horizontal resonance of 1.68 Hz, and a roll resonance of 2.58 Hz. A prototype vibration isolator reduces vertical vibration by a factor of 2 at 2 Hz. Vertical, horizontal, and roll vibrations are reduced by a factor of 100 at frequencies above 20 Hz.

Rotational isolation with neutrally buoyant suspension.

Rotational vibration isolation is of critical importance for many airborne instrumentation applications. Such isolators require very low frequency isolation for the rotational degrees of freedom combined with translational rigidity and negligible translation to rotation coupling. This paper describes a vibration isolator using neutrally buoyant flotation to provide high translation rigidity combined with very low rotational rigidity. The isolator reduces the rotational vibration at all frequencies above its resonance (0.18 ± 0.01 Hz) and has a large dynamic range (±30°) suitable for airborne surveying. Viscous, inviscid, and mechanical coupling inside the isolator have been analyzed. A recent fixed wing flight test shows the isolator reducing the rotational vibration by more than a factor of 1000 at frequencies above 10 Hz.

Phased introduction of a universal childhood influenza vaccination programme in England: population-level factors predicting variation in national uptake during the first year, 2013/14.

INTRODUCTION: Through a phased rollout, the UK is implementing annual influenza vaccination for all healthy children aged 2-16 years old. In the first year of the programme in England in 2013/14, all 2-3 year olds were offered influenza vaccine through primary care and a primary school age programme was piloted, mainly through schools, in geographically distinct areas. Equitable delivery is a key aim of the programme; it is unclear if concerns by some religious groups over influenza vaccine content have impacted on uptake. METHODS: At the end of the 2013/14 season, variations in uptake for 2-3 year olds and 4-11 year olds were assessed and stratified by population-level predictors: deprivation, ethnicity, religious beliefs and rurality. GP practice or school level uptake was linearly regressed against these variables to determine potential predictors and changes in uptake, adjusting for significant factors. RESULTS: Uptake varied considerably by geographic locality for both 2-3 year olds and 4-11 year olds. Lower uptake was seen in increasingly deprived areas, with an adjusted uptake in the most deprived quintile 12% and 8% lower than the least deprived areas by age-group respectively. By ethnicity, the highest non-white population quartile had an adjusted uptake 9% and 14% lower than the lowest non-white quartile by age-group respectively. Uptake also varied according to religious beliefs, with adjusted uptake in 4-11 year olds in the highest Muslim population tertile 8% lower than the lowest Muslim population tertile. CONCLUSION: In the first season of the childhood influenza vaccination programme, uptake was not uniform across the country, with deprivation and ethnicity both predictors of low uptake in pre-school and primary school age children, and religious beliefs also an important factor, particularly the latter group. With the continued rollout of the programme, these population-level factors should be addressed to achieve sustained successful uptake, along with assessment of contribution of individual and household-level factors.

Impact of influenza vaccination on respiratory illness rates in children attending private boarding schools in England, 2013-2014: a cohort study.

Several private boarding schools in England have established universal influenza vaccination programmes for their pupils. We evaluated the impact of these programmes on the burden of respiratory illnesses in boarders. Between November 2013 and May 2014, age-specific respiratory disease incidence rates in boarders were compared between schools offering and not offering influenza vaccine to healthy boarders. We adjusted for age, sex, school size and week using negative binomial regression. Forty-three schools comprising 14 776 boarders participated. Almost all boarders (99%) were aged 11-17 years. Nineteen (44%) schools vaccinated healthy boarders against influenza, with a mean uptake of 48·5% (range 14·2-88·5%). Over the study period, 1468 respiratory illnesses were reported in boarders (5·66/1000 boarder-weeks); of these, 33 were influenza-like illnesses (ILIs, 0·26/1000 boarder-weeks) in vaccinating schools and 95 were ILIs (0·74/1000 boarder-weeks) in non-vaccinating schools. The impact of vaccinating healthy boarders was a 54% reduction in ILI in all boarders [rate ratio (RR) 0·46, 95% confidence interval (CI) 0·28-0·76]. Disease rates were also reduced for upper respiratory tract infections (RR 0·72, 95% CI 0·61-0·85) and chest infections (RR 0·18, 95% CI 0·09-0·36). These findings demonstrate a significant impact of influenza vaccination on ILI and other clinical endpoints in secondary-school boarders. Additional research is needed to investigate the impact of influenza vaccination in non-boarding secondary-school settings.

Uptake and impact of a new live attenuated influenza vaccine programme in England: early results of a pilot in primary school-age children, 2013/14 influenza season.

As part of the introduction and roll-out of a universal childhood live-attenuated influenza vaccination programme, 4­11 year-olds were vaccinated in seven pilot areas in England in the 2013/14 influenza season. This paper presents the uptake and impact of the programme for a range of disease indicators. End-of-season uptake was defined as the number of children in the target population who received at least one dose of influenza vaccine. Between week 40 2013 and week 15 2014, cumulative disease incidence per 100,000 population (general practitioner consultations for influenza-like illness and laboratory-confirmed influenza hospitalisations), cumulative influenza swab positivity in primary and secondary care and cumulative proportion of emergency department respiratory attendances were calculated. Indicators were compared overall and by age group between pilot and non-pilot areas. Direct impact was defined as reduction in cumulative incidence based on residence in pilot relative to non-pilot areas in 4­11 year-olds. Indirect impact was reduction between pilot and non-pilot areas in <4 year-olds and >11 year-olds. Overall vaccine uptake of 52.5% (104,792/199,475) was achieved. Although influenza activity was low, a consistent, though not statistically significant, decrease in cumulative disease incidence and influenza positivity across different indicators was seen in pilot relative to non-pilot areas in both targeted and non-targeted age groups, except in older age groups, where no difference was observed for secondary care indicators.

Amphetamine increases blood pressure and heart rate but has no effect on motor recovery or cerebral haemodynamics in ischaemic stroke: a randomized controlled trial (ISRCTN 36285333).

Amphetamine enhances recovery after experimental ischaemia and has shown promise in small clinical trials when combined with motor or sensory stimulation. Amphetamine, a sympathomimetic, might have haemodynamic effects in stroke patients, although limited data have been published. Subjects were recruited 3-30 days post-ischaemic stroke into a phase II randomized (1:1), double-blind, placebo-controlled trial. Subjects received dexamphetamine (5 mg initially, then 10 mg for 10 subsequent doses with 3- or 4-day separations) or placebo in addition to inpatient physiotherapy. Recovery was assessed by motor scales (Fugl-Meyer (FM)), and functional scales (Barthel index (BI) and modified Rankin score (mRS)). Peripheral blood pressure (BP), central haemodynamics and middle cerebral artery blood flow velocity were assessed before, and 90 min after, the first two doses. Thirty-three subjects were recruited, aged 33-88 (mean 71) years, males 52%, 4-30 (median 15) days post stroke to inclusion. Sixteen patients were randomized to placebo and seventeen to amphetamine. Amphetamine did not improve motor function at 90 days; mean (s.d.) FM 37.6 (27.6) vs control 35.2 (27.8) (P=0.81). Functional outcome (BI, mRS) did not differ between treatment groups. Peripheral and central systolic BP, and heart rate (HR), were 11.2 mm Hg (P=0.03), 9.5 mm Hg (P=0.04) and 7 beats per minute (P=0.02) higher, respectively, with amphetamine, compared with control. A nonsignificant reduction in myocardial perfusion (BUI) was seen with amphetamine. Other cardiac and cerebral haemodynamics were unaffected. Amphetamine did not improve motor impairment or function after ischaemic stroke but did significantly increase BP and HR without altering cerebral haemodynamics.

Cognitive effects of head-movements in stray fields generated by a 7 Tesla whole-body MRI magnet.

The study investigates the impact of exposure to the stray magnetic field of a whole-body 7 T MRI scanner on neurobehavioral performance and cognition. Twenty seven volunteers completed four sessions, which exposed them to approximately 1600 mT (twice), 800 mT and negligible static field exposure. The order of exposure was assigned at random and was masked by placing volunteers in a tent to hide their position relative to the magnet bore. Volunteers completed a test battery assessing auditory working memory, eye-hand co-ordination, and visual perception. During three sessions the volunteers were instructed to complete a series of standardized head movements to generate additional time-varying fields ( approximately 300 and approximately 150 mT.s(-1) r.m.s.). In one session, volunteers were instructed to keep their heads as stable as possible. Performance on a visual tracking task was negatively influenced (P<.01) by 1.3% per 100 mT exposure. Furthermore, there was a trend for performance on two cognitive-motor tests to be decreased (P<.10). No effects were observed on working memory. Taken together with results of earlier studies, these results suggest that there are effects on visual perception and hand-eye co-ordination, but these are weak and variable between studies. The magnitude of these effects may depend on the magnitude of time-varying fields and not so much on the static field. While this study did not include exposure above 1.6 T, it suggests that use of strong magnetic fields is not a significant confounder in fMRI studies of cognitive function. Future work should further assess whether ultra-high field may impair performance of employees working in the vicinity of these magnets.

The impact of cognitive impairment on upper body dressing difficulties after stroke: a video analysis of patterns of recovery.

OBJECTIVE: to study the underlying cognitive deficits influencing a stroke patient's ability to relearn to dress. The aim was to investigate how recovery had occurred and whether the nature of cognitive impairment was the reason for persistent dressing problems. METHODS: the dressing performance of 30 stroke patients was compared at the sub-acute stage and three months later. Standardised cognitive and physical tests were carried out, together with a video analysis of patients putting on a polo shirt. RESULTS: thirteen patients with preserved power in the upper limb used both arms to put on the shirt. Despite visuospatial impairment or apraxia in some cases, all were successful given sufficient time. Out of 17 patients with arm paresis, 12 were dependent putting on the shirt. Amongst the five who were independent, significantly fewer cases of cognitive impairment were seen on tests for apraxia (p<0.05) and visuospatial perception (p<0.05). Video analysis confirmed the importance of cognitive problems such as neglect or apraxia. Three patients who failed shirt dressing showed neglect or apraxia at follow up and had persistent arm paresis. Test failures also occurred amongst those who were independent. DISCUSSION: cognitive impairment affected patients attempting to relearn to dress with one hand, but did not affect patients who used both hands. The three patients who remained impaired on cognitive tests at follow up were unable to adapt or learn any compensatory strategies. The influence of cognition on a person's ability to learn compensatory strategies has implications for the design of rehabilitation therapies.

A pilot study of event-related functional magnetic resonance imaging of monitored wrist movements in patients with partial recovery.

BACKGROUND AND PURPOSE: Previous functional imaging studies of motor recovery after stroke have investigated cerebral activation during periods of repetitive, often complex, movement. This article reports the use of an event-related approach to study activation associated with isolated simple movements (wrist extension). This allows investigation of the pattern of the motor response and corresponding brain activation on a trial-by-trial basis. Patients with partial recovery can be assessed, and allowance can be made for abnormalities in the shape of hemodynamic responses. METHODS: Functional MRI at 3 T was performed during a series of isolated, near-isometric wrist extension movements. A visual tracking procedure was used to elicit forces of 10% and 20% of maximum voluntary contraction. Force output from both wrists was monitored continuously. A voxel-wise procedure was used to fit the optimum hemodynamic response functions in each case. RESULTS: Three chronic stage patients with partial recovery were successfully scanned and compared with 8 healthy controls. The patients showed well-lateralized motor responses but inaccurate control of force. During movement of the paretic wrist, we observed excessive activation of the ipsilateral primary motor cortex and increased relative activation of the supplementary motor area compared with movement of the nonparetic side. In the primary motor area, hemodynamic responses peaked more quickly on the ipsilateral side in 2 patients for movements of the paretic hand, whereas controls showed the opposite trend. CONCLUSIONS: An event-related approach can be used to study the relationship between motor responses and cerebral activation in patients with partial recovery. These preliminary findings suggest that excessive activation in ipsilateral motor cortex and secondary motor areas remains evident under these tightly controlled conditions and cannot be ascribed to mirror movements or abnormalities in the timing of the blood oxygen level-dependent (BOLD) response. However, close monitoring of motor responses also makes evident continuing impairment in motor skill, which makes comparison with activation in normal controls difficult.

Cerebral activation during a simple force production task: changes in the time course of the haemodynamic response.

An event-related paradigm was used to investigate the fMRI signal from the primary motor cortex (M1) and the supplementary motor area (SMA) during isolated isometric wrist extension at five different force levels. There was only a weak trend towards increased area of activation with increased force output, but there was a force-related increase in percentage change of signal within voxels in M1 (Kendall Tc = 0.48, p < 0.01), which may indicate control of force output by variation of neural firing rate. In SMA there was a correlation between peak force output and time-to-peak of the haemodynamic response in SMA (Kendall Tc = 0.74, p < 0.0001). This unexpected finding of a task-related change in the shape of the haemodynamic response within a single brain area requires further investigation. It may indicate a slower rise time at lower perfusion rates, or may be the result of inhibitory processes in motor control.

Ideomotor apraxia, visuomotor control and the explicit representation of posture.

Ideomotor apraxia is normally viewed as a disorder of the representation or execution of action. However, the evidence from gesture imitation is that apraxic patients are unable to reproduce the final posture of a gesture but may not show abnormality in movement kinematics. This supports a hypothesis that impaired gesture imitation is due to a deficit in a conceptual representation of body posture rather than indicating a disorder specific to action control. The present study evaluated whether other aspects of apraxic behaviour might also be most consistent with a deficit in the representation of posture. Patients with left hemisphere damage and apraxia on gesture imitation had difficulty in reproducing a series of actions due to failure to adopt the required configuration of the hand whereas there was no consistent reduction in speed of response once the actions had been learned. They also tended to use an abnormal, clumsy grasp when using a spoon but this dissociated from accurate performance on other tests of manual dexterity where there was less scope for variation in configuration of the hand. These data suggest that the most common deficit in ideomotor apraxia is impaired ability to perform tasks where the goal is to reproduce or adopt complex hand configurations and that impaired execution of some types of action is secondary to this problem. This is consistent with a role for the human left parietal lobe in providing an explicit representation of posture which is used to guide some actions and to supplement a more primitive system of direct visuomotor control.

Recovery of ipsilateral dexterity after stroke.

UNLABELLED: BACKGROUND AND PURPOSE; Previous work indicated that patients within 1 month of parietal or posterior frontal damage are often abnormally slow or clumsy when using the ipsilateral hand for dexterity tasks. This article reports a 6-month follow-up study to assess recovery and the impact on functional outcome. METHODS: Twenty-four patients (80%) were available for follow-up. They used the ipsilateral hand on a dexterity test that simulated everyday hand function. Weakness and ideomotor apraxia were also assessed. Performance was compared with that of healthy age-matched control subjects using the same hand. Rating scales for self-care and dexterity in everyday life were completed by patients and carers. RESULTS: Significant recovery had occurred on all measures, but patients with left hemisphere damage remained impaired on the dexterity test, with 7 patients (58%) scoring below the normal range. Five of these were apraxic. Reports of everyday functioning did not reflect this impairment, but there were inconsistencies in these reports, which raised doubts as to their accuracy. CONCLUSIONS: Ipsilateral dexterity shows recovery during the first 6 months, but there may be persistent impairment related to apraxia after left hemisphere stroke. It appears that the impact of this on functional outcome is typically small compared with the large effect of severity of contralateral paresis. It may be a significant factor in some cases, however, and direct observation of everyday functioning would be needed to clarify more subtle effects on outcome.

Impaired dexterity of the ipsilateral hand after stroke and the relationship to cognitive deficit.

BACKGROUND AND PURPOSE: Previous research has reported impaired hand function on the "unaffected" side after stroke, but its incidence, origins, and impact on rehabilitation remain unclear. This study investigated whether impairment of ipsilateral dexterity is common early after middle cerebral artery stroke and explored the relationship to cognitive deficit. METHODS: Thirty patients within 1 month of an infarct involving the parietal or posterior frontal lobe (15 left and 15 right hemisphere) used the ipsilateral hand in tests that simulated everyday hand functions. Performance was compared with that of healthy age-matched controls using the same hand. Standardized tests were used to assess apraxia, visuospatial ability, and aphasia. RESULTS: All patients were able to complete the dexterity tests, but video analysis showed that performance was slow and clumsy compared with that of controls (P<0.001). Impairment was most severe after left hemisphere damage, and apraxia was a strong correlate of increased dexterity errors (P<0.01), whereas reduced ipsilateral grip strength correlated with slowing (P<0.05). The pattern of performance was different for patients with right hemisphere damage. Here there was no correlation between grip strength and slowing, while dexterity errors appeared to be due to visuospatial problems. CONCLUSIONS: Subtle impairments in dexterity of the ipsilateral hand are common within 1 month of stroke. Ipsilateral sensorimotor losses may contribute to these impairments, but the major factor appears to be the presence of cognitive deficits affecting perception and control of action. The nature of these deficits varies with side of brain damage. The effect of impaired dexterity on functional outcome is not yet known.

The nature and prevalence of memory disorder late after stroke.

This study aimed to investigate the incidence and nature of memory impairment late after stroke. Out of 193 patients between 12 to 36 months post-cerebrovascular accident contacted in a postal survey, 113 replied that they had experienced memory impairment following the stroke. Seventy of these patients were assessed on an adapted version of the Rivermead Behavioural Memory Test, Warrington's Recognition Memory Test for words and faces, and an every day memory questionnaire. The Token Test and the Benton Facial Recognition Test were also administered as measures of language and visuoperceptual processing. Thirty-five of the patients were impaired on one or more of the memory measures. Of these, 16 showed no evidence of dysphasia or visuoperceptual impairment. The 16 cases of selective memory impairment typically had mild to moderate deficits, and only three were impaired across all three tests. The results suggest that memory impairment following stroke does not necessarily involve general memory impairment. The evidence for material-specific memory deficits was much weaker.

Adaptation to cognitive deficit? An exploration of apparent dissociations between everyday memory and test performance late after stroke.

It is widely believed that spontaneous improvements in functioning late after brain damage are due to processes of adaptation to permanent cognitive deficits. Reports of everyday memory and the pattern of performance on memory tests were investigated in 70 patients more than a year after a stroke. Contrary to the adaptation hypothesis, performance on simulations of everyday tasks (Rivermead Behavioural Memory Test) correlated strongly with performance on a test where there was little scope for compensatory strategies (forced-choice recognition memory for words). In 12 cases, initial assessment with the EMQ20 questionnaire suggested few cognitive failures in everyday life despite poor test performance. However, where further investigation was possible, it seemed that unreliability of measures or subtle everyday effects of non-verbal memory impairment could explain the apparent discrepancies. In addition, patients who did poorly on tests were not reported to make frequent use of memory aids. Adaptation to deficit does not therefore appear to be a major influence on everyday memory performance late after stroke, but it may have subtle effects or may be important in other areas of functioning. Implications for clinical memory assessment are discussed.

Differences in recovery from constructional apraxia after right and left hemisphere stroke?

Previous comparisons of constructional apraxia after right and left hemisphere damage have not investigated the influence of time since onset. This paper reports some preliminary findings from stroke patients in a physical rehabilitation trial. Fifty-five patients with right hemisphere damage and 65 with left hemisphere damage were assessed on the WAIS-R Block Design test at 1 month and 6 months post stroke. The groups were similar at 1 month but the left hemisphere group showed better average recovery by 6 months. There was great variability in amount of recovery within the left hemisphere group, suggesting individual differences in initial reasons for failing Block Design, and corresponding differences in the recovery process. Compensation by the right hemisphere is discussed as one possible process. Future detailed longitudinal studies may be useful in contrasting the cognitive deficits which underlie constructional apraxia after right-sided and left-sided lesions, and would provide evidence on mechanisms of recovery and adaptation.

Enhanced physical therapy for arm function after stroke: a one year follow up study.

Ninety seven patients with stroke who had participated in a randomised trial of conventional physical therapy nu an enhanced therapy for arm function were followed up at one year. Despite the emphasis of the enhanced therapy approach on continued use of the arm in everyday life, the advantage seen for some patients with enhanced therapy at six months after stroke had diminished to a non-significant trend by one year. This was due to some late improvement in the conventional therapy group whereas the enhanced therapy group remained static or fell back slightly. It is recommended that trials should be conducted comparing very intensive therapy for the arm with controls without treatment. This would provide a model of the effects of therapy on intrinsic neural recovery that would be relevant to all areas of neurological rehabilitation.

Enhanced physical therapy improves recovery of arm function after stroke. A randomised controlled trial.

Previous research on stroke rehabilitation has not established whether increase in physical therapy lead to better intrinsic recovery from hemiplegia. A detailed study was carried out of recovery of arm function after acute stroke, and compares orthodox physiotherapy with an enhanced therapy regime which increased the amount of treatment as well as using behavioural methods to encourage motor learning. In a single-blind randomised trial, 132 consecutive stroke patients were assigned to orthodox or enhanced therapy groups. At six months after stroke the enhanced therapy group showed a small but statistically significant advantage in recovery of strength, range and speed of movement. This effect seemed concentrated amongst those who had a milder initial impairment. More work is needed to discover the reasons for this improved recovery, and whether further development of this therapeutic approach might offer clinically significant gains for some patients.