Measuring mobility in older hospital patients with cognitive impairment using the de Morton Mobility Index

Background Mobility is a key outcome in older patients with cognitive impairment. The de Morton Mobility Index (DEMMI) is an established measure of older people’s mobility that is promising for use in older patients with cognitive impairment. The aim of this study was to examine the DEMMI’s psychometric properties in older patients with dementia, delirium or other cognitive impairment. Methods This cross-sectional study was performed in a geriatric hospital and includes older acute medical patients with cognitive impairment indicated by a Mini Mental State Examination (MMSE) score ≤ 24 points. A Rasch analysis was performed to check the DEMMI’s unidimensionality. Construct validity was assessed by testing 13 hypotheses about expected correlations between the DEMMI and outcome measures of similar or related constructs, and about expected differences of DEMMI scores between groups differing in mobility related characteristics. Administration times were recorded. Results A sample of 153 patients with mild (MMSE 19–24 points; 63%) and moderate (MMSE: 10–18 points; 37%) cognitive impairment was included (age range: 65–99 years; mean MMSE: 19 ± 4, range: 8–24 points; diagnosis of dementia and delirium: 40% and 18%, respectively). Rasch analysis indicated unidimensionality with an overall fit to the model (P = 0.107). Internal consistency reliability was excellent (Cronbach’s alpha = 0.92). Eleven out of 13 (85%) hypotheses on construct validity were confirmed. The DEMMI showed good feasibility, and no adverse events occurred. The mean administration time of 5 min (range: 1–10) was not influenced by the level of cognitive impairment. In contrast to some other comparator instruments, no floor or ceiling effects were evident for the DEMMI. Conclusions Results indicate sufficient psychometric properties of the DEMMI in older patients with cognitive impairment. Trial registration German Clinical Trials Register (DRKS00005591). Registered February 2, 2015. Electronic supplementary material The online version of this article (10.1186/s12877-018-0780-9) contains supplementary material, which is available to authorized users.

with dementia but adequate predictive validity as well as excellent concurrent validity and reliability have been reported for patients with stroke [8].
The 2-minute walk test (2minWT) can be used to quantify walking endurance and functionalexercise capacity [9]. By measuring similar constructs, the 2minWT seems to be better tolerated by geriatric inpatients than the 6 minute walk test [10]. Subjects were asked to walk as far as possible within two minutes on the hospital corridor. Only one trial was performed to avoid fatigue effects.
The psychometric properties in people with Alzheimer's dementia have not been established for the 2minWT but for the 6 minute walk test, which seems quite comparable and shows sufficient reproducibility [11][12][13].
The Short Physical Performance Battery (SPPB) is a measure of mobility and physical functioning. It includes three objective tests of lower body functions: a hierarchical test of standing balance, a four meter walk test (4mWT) and five times chair rise test (5xCRT) [14]. The SPPB has a scoring from 0 (unable) to 4 points for every sub-test, with a maximum of 12 points in total (ordinal scaled).
Sufficient validity and reliability of the SPPB have been described for older people with and without dementia [14][15][16].
Habitual gait speed in m/s over a distance of four meter was assessed as part of the SPPB. Timing was started when the participant began walking. The shorter time of two trials was used for analysis [17]. Walking speed is an objective and reliable physical performance test to evaluate functional capacity of the lower limbs and mobility with well-documented predictive value for major healthrelated outcomes in older people with and without dementia [11,12,16,18,19].
For the 5 times chair rise test (5xCRT), participants were asked to stand up and sit down from a chair as fast as possible for five times, with the hands being crossed in front of the chest. Shorter times indicate higher mobility. The 5xCRT seems to be a reproducible assessment in people with dementia [11,20,21].

The Timed Up and Go test (TUG) is a performance based test that assesses basic mobility functions.
The patient is asked to stand up from a chair, walk 3 meter, turn around, walk back and return to the chair [22]. In the present study, chair height was 46 cm, the participant was placed with the trunk leant backwards, the arms rested on the armrest and a cone had to be encircled. Participants chose the turning side. A familiarization trial was followed by two counted trials, of which the mean (in sec) was the final TUG score. At least one counted trial must have been valid to be included in the analysis. Shorter times indicate higher mobility. There is conflicting evidence for the TUG to be a sufficiently reliable test in people with dementia [11,12,20,21,23], the construct validity has not been examined properly and feasibility limitations have been reported due to significant floor effects [23].
The Barthel Index [24] (BI; 0-100 points) is a performance based measure of functioning and independence in the activities of daily living (ADL). Higher scores indicate better functioning. The Barthel Index has been reported to be the most widely used measure of ADL function [25]. In this study, the BI was applied by the nursing staff as part of routine care within the first 7 days after admission. Since most of these scores were recorded in a considerable time frame from the DEMMI scores, the BI score was only used to describe the sample. For the psychometric analysis, we reassessed the 3 mobility items #transfer (0 to 15 points), #walking (0 to 15 points) and #climbing stairs (0 to 10 points) [26] in the study assessment session. We summed these items to a Barthel Index mobility subscale (0 to 40 points). This subscale has sufficient face validity and the reliability of these 3 single BI items has been reported to be fair to excellent in various studies including individuals with stroke [27] and older people with and without cognitive impairment [28]. [29] is an 11-item assessment of cognitive function that assesses orientation, registration, attention or calculation (serial sevens or spelling), recall, naming, repetition, comprehension (verbal and written), writing, and construction. Scores can range from 1 to 30. By convention, scores <24 points indicate increasing cognitive impairment [30,31]. The cognitive impairment can be judged as severe (≤9 points), moderate (10-18 points) or mild (19)(20)(21)(22)(23) points) according to the MMSE score, although other cut-off points have been suggested due to the wide spectrum in the severity of disease that people with dementia have [32,33].

The Mini Mental State Examination Test (MMSE)
The Clock Drawing Test (CDT) [34] is one of the most widely used cognitive screening tools to measure a variety of cognitive functions, including selective and sustained attention, auditory comprehension, verbal working memory, numerical knowledge, visual memory and reconstruction, visuospatial abilities and executive function. There are multiple CDT administration and scoring systems [35]. The study hospital used a 6-point scoring system, with higher scores reflecting a higher number of errors and more cognitive impairment [36]. Scores ≥3 points are considered indicative of cognitive dysfunction.