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Feasibility of the Divided Attention Steering Simulator (DASS) for the Assessment of Vigilance in Stroke Patients

Christine Roffe MD¹
Mohamed Halim MSc¹
Kathryn Wilde PhD¹
Peter Crome PhD¹

1Department of Geriatric Medicine, Keele University, Staffordshire, UK.

The research for this project was performed in the Department of Geriatric Medicine of Keele University, UK.

Acknowledgements

We are grateful for the support of the Novartis Foundation for Gerontological Research who contributed to the salary of one of the researchers. We are also grateful to Dr JO Davis of Stowood Scientific Instruments, Oxford for technical support. We thank all the patients and controls for their contribution to the study and the ward staff for their support of the project.

Funding

This study was supported by the Novartis Foundation for Gerontological Research.

Key words
Attention, vigilance, wakefulness, tiredness, cerebrovascular accident

Abstract

Background and purpose: Fatigue is a common complication of stroke, but difficult to assess objectively, since only few stroke patients can perform conventional vigilance tests because of dysphasia, hemianopia or hemi-inattention. The purpose of this study was to test the feasibility and acceptability of the Divided Attention Steering Simulator (DASS), a computer simulated driving task for the assessment of vigilance, in an unselected group of stroke patients.

Methods: Patients undergoing rehabilitation from an acute stroke and age and sex matched controls without stroke were recruited. Subjects were placed in front of a computer and given an adapted steering wheel with bilateral button controls. They were instructed verbally and by demonstration to keep the car on the road and to press a button whenever the target number '2' appeared.

Results: Thirty-three stroke patients (age 74±8 years (mean±SD), previous driving experience 82%, hemiparesis 91%, hemianopia 41%, tactile hemi-inattention 42%, dysphasia 18%) and 24 controls were recruited. All were able to follow the instructions to 'drive' the car, 76% patients and 83% controls completed the test, 85% patients and 88% controls enjoyed the test. DASS results (median [95% Confidence Interval]) were: off-road events 834 [693-881] and 338 [274-484], reaction time 8.8 [7.4-8.9] s and 3.4 [3.1-4.5] s, standard deviation from the road 2.4 [2.0-2.5] and 1.2 [0.9-1.4], and target signals identified 21 [21-44] % and 96 [82-97]% for stroke patients and controls respectively.

Conclusion: The DASS could be performed by the majority of stroke patients, including subjects with dysphasia and hemianopia/hemi-inattention. Tiredness or fatigue is a common and disabling problem in patients recovering from a stroke. Ingles et al reported a prevalence of self-reported fatigue of 68% 3-13 months after the stroke in community dwelling individuals. In 40% fatigue was rated as the worst or one of their worst symptoms after the stroke ⁽¹⁾. Its causes are likely to be multifactorial, and include the size and location of the brain lesion, cerebral blood flow, metabolic and environmental factors ^(2-5). Tiredness impairs attention, mood and mental flexibility ⁽⁶⁾ and can make rehabilitation difficult or even impossible. There is an association between the ability to maintain sustained attention early after stroke and functional status at 2 years ⁽⁷⁾.

Tiredness, and its effect on performance, can be assessed by vigilance tests. These assess the ability of the individual to sustain and focus attention. Typically stimuli (strings of letters, shapes or numbers) are presented over a period of time with instructions to the subject to indicate when the target stimulus is perceived ⁽⁸⁾. The Test of Everyday Attention ⁽⁹⁾ includes a five minute tone counting test (The Elevator Counting test), an auditory vigilance task (the Lottery test) and a visual search task (Telephone Search) ⁽⁹⁾. Perhaps the simplest vigilance test is the Osler test ⁽¹⁰⁾ which requires the subject to press a button each time a light flashes. All of these tests, however, require at least basic language skills to understand the instructions, and thus dysphasic subjects are usually excluded from clinical studies ^(7,11). The only data on vigilance after stroke are thus derived from relatively unimpaired patient population. With currently available tests it is not possible to assess vigilance reliably in unselected stroke patients.

The Divided Attention Steering Simulator (DASS) is a vigilance test commonly used in the assessment of sleep apnoea and narcolepsy ^(12-15). In a computer simulated driving situation subjects are instructed to steer a vehicle using a remote steering wheel with button controls down a winding road shown on the computer monitor. This test has the potential to be used in a wide range of patients with stroke. The driving situation is obvious, and dysphasic patients may be able to 'have a go' using non-verbal instructions. Patients with hemianopia or hemi-inattention may be able to use the road margin in the unaffected visual field to track the position of the vehicle ⁽¹⁶⁾. For patients with hemiparesis the steering wheel was adapted to have bilateral controls, so that it could be handled using the unaffected hand only.

The aim of this study is to assess the feasibility and acceptability of the adapted DASS in patients recovering from a stroke.

Methods

The protocol was approved by the North Staffordshire Research Ethics Committee. Written informed consent obtained from all competent and non-dysphasic participants. Assent from the next of kin was accepted for dysphasic non-competent patients.

Subjects

Patients were recruited from the stroke rehabilitation ward of the North Staffordshire Hospital, a large District General Hospital. Individuals were admitted to this ward if they had had a recent stroke, were medically stable and had potential for improvement with therapy. Patients over the age of 60 were admitted preferentially, but there was no fixed age limit. All patients resident on the ward during a period of two months were approached. Patients with acute medical problems and those refusing consent were excluded from the study. Patients were examined neurologically and classified into total anterior circulation syndrome (TAC), partial anterior circulation syndrome (PAC), lacunar syndrome (LAC) and posterior circulation syndrome (POC) using the Oxfordshire Community Project Classification ⁽¹⁷⁾. CT head scan results were classified into cerebral infarcts or intracerebral haemorrhages.

Controls

Age matched controls from a similar social background to the stroke group were recruited from the patients' spouses and visitors.

The Divided Attention Steering Simulator test

The Divided Attention Steering Simulator (DASS) test was performed using a computer generated driving simulation (Stowood Scientific Instruments, Oxford) installed on a personal computer with a 20 inch monitor and linked up to a steering wheel mounted on the computer table (figure 1). The program produces a computer-generated image of the moving edges of a road that winds pseudo-randomly into the horizon. A representation of the bonnet of the car is visible at the bottom of the screen and indicates the driver's position on the road. Medium speed and 'all view' screen settings were chosen for the driving simulator. Task 1 for the subject is to keep the car on the road (tracking). Task 2 is to identify the target number (target recognition) and press a button each time it occurs. Single digits (0-9) are displayed in 4 positions at the edge of the computer screen (figure 1) and change at random intervals in random order. While steering, the subject has to keep an eye on the numbers and to press a button on the right side of the steering wheel for any '2' in the right visual field and a button on the left for any '2' on the left side of the visual field. The steering wheel was adapted by adding a second button with a different colour and texture to both sides of the wheel. This enabled hemiparetic patients to use one side of the wheel only to indicate left and right targets (see figure 1). The target number is displayed 28 times for 10 s each over a standard 20 min driving test.

Test Protocol

The test was explained and demonstrated practically using verbal and visual cues. Instructions were:
1. Keep the car in the middle of the road by using the steering wheel.
2. Watch for the number '2', the target, appearing on the screen and press the right response button each time a '2' is displayed on the right side of the screen and the left response button for a '2' on the left side.
Each subject was given a 5 min practice session before starting the full 20 min test. If a car was off the road or if no steering input was detected for >15 s the test was terminated automatically. This event was interpreted as the driver falling asleep at the wheel and/or having an accident.

Assessments

Tracking accuracy was represented as the standard deviation of the centre of the car from the centre of the road and the number of off-road events. Visual attention was assessed by recording the number of appropriate responses to the targets and the reaction time. For missed targets a value of 10 s was entered as reaction time. All patients were asked whether they enjoyed the test. The time spent doing the test was recorded for patients who were unable to complete the full 20 min and the total number of off-road events was recalculated as events per hour to account for variations in test times. Similarly, the percentage of visual cues accurately recognised was calculated rather than the total number to allow for shorter tests with fewer targets.

Statistics

Descriptive data were generated in Excel for Office 2000. SPSS version 10 for Windows was used for statistical analysis. Correlations were assessed by calculation of a Pearson correlation co-efficient with an associated p-value. Categorical values were compared using the Chi-Square tests. Most results for the DASS test were skewed, and the data are therefore reported as medians 95% confidence intervals. Comparisons between groups were made using Mann-Whitney tests for two independent groups and Kruskal-Wallis tests for more than two groups.

Results

Baseline demographic data

Thirty-nine stroke patients were approached during the two months of recruitment. Of these 3 were excluded for medical reasons and 3 refused consent. Thirty-three patients were recruited. The mean age was 73.8 SD 7.6 years, 21 (64%) were males. The mean time from stroke onset was 8.9 SD 5.4 weeks. All had cerebral infarcts on CT head scan. Thirty (91%) had hemiparesis, 15 (45%) had hemianopia, 14 (42%) had tactile hemi-inattention and 6 (18%) were dysphasic. There were 11 (33%) total anterior circulation strokes (TACS), 14 (42%) partial anterior circulation strokes, 8 (24%) lacunar strokes (LACS) and 0 posterior circulation strokes (POCS). Twenty-seven (82%) had previous driving experience.

Twenty-four controls were recruited. They were well matched for age (mean age 72.5 SD 7.2 years), sex (52% males) and driving experience (80% were drivers). Twenty (83%) completed the full 20 minutes, one was timed out after 12 min and three abandoned the test prematurely.

Results of the DASS

All 33 stroke patients and all 24 controls were able to follow the instructions and to 'drive' the car. Twenty-four (75%) stroke patients and 20 controls (83%) completed the full 20 min, 2 (6%) strokes and 1 (4%) of control made a start, but were timed out
prematurely because of an off road event lasting >15 s, and 6 (18%) strokes and 3 (13%) controls abandoned the test prematurely. Twenty-eight (85%) strokes and 21 (88%) of controls enjoyed the test. There were no significant differences for any of the above parameters between the groups (Chi-square tests).

DASS results for all stroke patients and controls are described fully in table 1. Stroke patients performed significantly worse in all test categories than controls.

Within the stroke group test results were not related to age or time since stroke onset (correlation coefficients -0.16-0.24). Table 2 shows the effect of different patient characteristics on test performance. Six of the patients included in the study were dysphasic. Their results showed a trend towards a lower performance with the number of off road events per hour being significantly greater (p=0.05). Fifteen patients included in the study had hemianopia. These patients had a greater standard deviation from the road (p=0.02) and more off road events per hour (p=0.04) than patients without hemianopia. The 14 patients with tactile hemi-inattention had a greater standard deviation from the road (p=0.02) than those without. Patients with a lacunar syndrome had better test results than those with a partial or total anterior circulatory syndrome (p=0.03 for standard deviation from the road and p=0.04 for response time).

Discussion

Vigilance is an important factor for the success of rehabilitation. Fatigue is common after stroke, and may be worsened by drug treatment for stroke related problems such as incontinence, depression and insomnia. Vigilance testing is difficult in stroke patients because of weakness of the dominant hand, problems with understanding instructions in dysphasic patients and problems of perception in the affected visual field in patients with hemianopia or hemi-inattention. Thus, assessment of vigilance in stroke patients relies heavily on clinical observation, which is subjective and difficult to quantify. The results of this study show that the Divided Attention Steering Simulator test can be completed by the majority of unselected stroke patients resident on a rehabilitation ward, even by those who were dysphasic or had no prior experience of driving. Furthermore, most of the subjects tested found the experience enjoyable.

In this population of older individuals age and prior driving experience did not significantly affect test results. However, performance of both stroke patients and controls is worse than those of previously published normal control groups, which were taken from a much younger population (14).

As expected for a group of subjects with neurological problems, stroke patients performed worse than age and sex matched controls for all test parameters. Within group comparisons amongst the stroke patients showed that test performance in subjects with more extensive strokes (e.g. anterior circulation syndromes rather than lacunar syndromes), dysphasia, hemianopia, hemi-inattention, and dysphasia had slightly worse test results than those with less neurological deficits. While some of the comparisons yielded significant p-values, the differences within the stroke group were much less than the difference between stroke patients and controls.

Few targets were recognised by any of the patients (21%) and reaction time was slow (8.8 s). Most patients were unable successfully to divide their attention between tracking and cue recognition. The target recognition aspect of the test depends on the patients' ability to understand verbal instructions and to see the whole screen. This part of the test was, therefore, less useful in stroke patients, but still provided some baseline data which could be used to monitor changes over time within one individual.

The adapted version of the Divided Attention Steering Simulator test described here could be performed by most stroke patients, and the experience was enjoyable in the majority of subjects. It thus has the potential to become an important tool in the assessment of vigilance in this patient group. The 'Divided Attention' aspect of the test produces limited data in stroke patients. A simplified test, with an easier road, slower driving speed or concentrating on tracking alone should be explored in future studies.

References

November 2004
Volume 1,
Issue 2

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Editorial Ageing

Meet the team

Blood RNA concentration in Alzheimer disease and vascular dementia

Serum Zinc and Copper Concentration in Human-Age related cataract

The likelihood of being helped versus being harmed: useful in geriatric treatment dilemma's

Feasibility of the Divided Attention Steering Simulator (DASS) for the Assessment of Vigilance in Stroke Patients

The European Nursing Academy for Care of Older persons (ENACO)

Middle-East Academy for Medicine of Ageing, third session of the first course

Urogenital atrophy in climacteric women: Menopause or Geripause?

The diagnosis and management of Dementia

The length of hospital stay of Home Health Care patients at King Khalid National Guard Hospital, Jeddah, 1999.

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