Associations Between Cognitive Function, Balance, and Gait Speed in Community-Dwelling Older Adults with COPD : Journal of Geriatric Physical Therapy

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Associations Between Cognitive Function, Balance, and Gait Speed in Community-Dwelling Older Adults with COPD

Gore, Shweta PT, DPT, PhD1; Blackwood, Jennifer PT, PhD2; Ziccardi, Tyler SPT2

Author Information
Journal of Geriatric Physical Therapy 46(1):p 46-52, January/March 2023. | DOI: 10.1519/JPT.0000000000000323
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Abstract

CLINICAL HIGHLIGHTS

  • Is there a relationship between cognitive function, balance, and gait speed in older adults with COPD?
  • In older adults with COPD, 1 of 4 cognitive functions, delayed word recall, was associated with timed tandem standing balance. There was no association between any cognitive function score and gait speed.
  • Older adults with COPD should be screened for cognitive functioning using measures such as the Mini-Cog, which assesses both recall and executive function.

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a chronic progressive life-threatening condition affecting 251 million individuals globally, and more than 15 million people in the United States.1,2 Chronic obstructive pulmonary disease is the third leading cause of death in the United States and a major contributor of impaired mobility, disability, and decreased quality of life.3,4 People with in COPD have decreased strength, endurance, and balance, and changes in gait, which further contribute to the decreased quality of life.5–7

In addition to physical impairments, a notable proportion (57.6%) of individuals with COPD live with substantial deficits in cognitive function.8,9 Presence of COPD is also associated with an increased risk of cognitive decline over time, even in adults with mild COPD.8,10 Both global and domain-specific cognitive impairments are reported in adults with COPD, specifically in the areas of memory, learning, concentration, attention, planning, psychomotor speed, verbal memory, language abilities, and executive function. Specific components of executive function that have been reported include cognitive flexibility, planning, and working memory.11–13 Although both physical and cognitive impairments are found in individuals with COPD, it is not currently known whether the decline in cognitive abilities is associated with functional decline.

In older adults without reported COPD, a growing body of literature highlights the impact of cognitive function on physical mobility and increased risk of falls.14,15 Impairments in executive function are associated with changes in the quality of gait, decreased balance, fall incidence, and injury.16 In those with cognitive impairment, impaired executive function is significantly associated with decreased or slowed gait speeds.15 Results from a population-based epidemiological study reported a similar relationship between cognitive function, gait speed, and late-life disability in a large sample of older adults (n = 2481).5 However, specific relationships between cognitive function and balance or mobility have not been reported in the COPD population.

Increased age is the most notable determinant of cognitive decline. However, factors associated with the pathology of COPD including vascular-mediated brain pathology, increased oxidative burden, hypoxemia, and systemic inflammation may accelerate this process, and therefore may have a greater impact on function.13,17,18 We hypothesize that in older adults with COPD, cognitive function would play a more significant role in physical mobility and balance as compared with those without COPD.5 Due to the limited data in older adults with COPD on the relationships between cognitive function, mobility, and balance, we sought to describe these relationships with intent to identify potential areas for screening as a part of the management of fall risk in this population. This study aims to investigate the relationship between cognitive function, balance, and mobility in older adults with COPD.

METHODS

This cross-sectional study involved a secondary analysis of existing data from the 2010 wave of the Health and Retirement Study (HRS). The HRS is an ongoing national survey of Americans older than 50 years conducted face-to-face every 2 years since 1992.19 The survey focuses on 4 broad topics: income and wealth, use of health care services, cognition, and health, and includes physical measure data.20 This study was granted exempt status from the University of Michigan Institutional Review Board.

Data collected in the HRS between March 2010 and May 2011 were screened for selection criteria.20 The 2010 HRS wave consisted of a total of 22 034 respondents, of which 4051 reported having COPD, and 382 who met the inclusion/exclusion criteria for this study were assigned to the COPD group. The non-COPD group was a random age-matched comparison group of older adults (age ≥65 years) who did not have a chronic lung disease diagnosis but met the other inclusion/exclusion criteria. To have an equal comparison between groups, a random sample of 382 participants was drawn from the dataset for the non-COPD group. Selection criteria included respondents 65 years and older with a self-reported physician diagnosis of chronic lung disease (emphysema or bronchitis). Since other conditions such as stroke, Alzheimer disease, or dementia could directly impact cognition, data of participants with these specific conditions were excluded from analyses. Disease severity indicator data were not available in the 2010 dataset for analysis.

For this study, demographic information on age, gender, education, marital status; disease-specific information (COPD, comorbidities including hypertension, diabetes, depression, arthritis, cancer, and incontinence); anthropometric measures for calculation of body mass index (BMI, kg/m2); and cognitive and physical function information (grip strength, gait speed, balance performance, and oxygen use) were extracted. HRS participants who had complete data for the variables of interest were included in the sample. Fall information required respondents or their proxy to account for any falls that occurred in the 2 years prior to the survey interview. Information about falls-related injuries and number of falls in the 2 years prior to the survey are reported.

Cognition

Cognition was assessed in the HRS via multiple tests, which included immediate word recall (IWR), delayed word recall (DWR), orientation, and semantic verbal fluency. For IWR, participants were read a randomly selected list of 10 words from 4 possible lists by the survey interviewer, and immediately afterward, the participant was asked to recall as many words as possible. The number of correctly recalled words was recorded.19 After a timespan of roughly 5 minutes had passed, they were then asked to recall as many words from the same 10-word list for DWR. The number correctly recalled words was recorded for DWR.21,22 The 10-word recall tests have demonstrated construct validity23 and have internal consistency and stability from wave to wave after controlling for cohort effects and test-retest bias.23–25 Both immediate and delayed recall demonstrated acceptable sensitivity and specificity in differentiating mild cognitive impairment (IWR specificity 71.2%, DWR specificity 83.1%).26 Additionally, the DWR scores 4 or less (score range = 0-9) were 87% sensitive in predicting Alzheimer disease pathology.27

Orientation was assessed by asking the participant to tell the interviewer the testing date (month, day, year, and day of the week). As a common clinical screen for orientation, impaired performance has been associated with increased risk of cognitive impairment.28,29 One point was allocated for recall of each item, with scores ranging from “0” meaning not oriented to month, day, year, and day of the week to “4” indicating no deficits in orientation.21,22 Tests of orientation to time, place, and person have shown excellent test-retest reliability (r = 0.85-0.95)30 and excellent sensitivity for distinguishing mild cognitive impairment from normal controls (91.5%).26 Failure to correctly identify the year was highly sensitive and specific in determining cognitive impairment; failure to correctly identify both the year and month proved to be the best combination for both specificity and sensitivity.31

Executive function was measured in the HRS using the semantic verbal fluency test, which has established validity and test-retest reliability.32 The measure was performed by a request for participants to name as many animals they could within a 60-second time limit.21,22 The total number of animals named comprised the score for this measure. High test-retest reliability (r = 0.84) has been reported for semantic verbal fluency tests.33 The verbal fluency test is able to distinguish mild cognitive impairment from normal controls, with a sensitivity of 72.3%.26 Verbal fluency tests exhibit good sensitivity to various conditions affecting executive function.34,35

Physical Function

Physical function was assessed using multiple tests of balance and gait.14 Gait speed was measured via a timed walking test over an 8.2-ft distance (98.5 in).19 Participants were allowed to use an assistive device, were required to wear shoes during the test, and were told to walk at their normal pace from the starting line. The participant was told to “begin” walking and time was recorded between when the foot crossed the start line and was in full contact with the floor and when the same foot crossed the finish line at the 8.2-ft distance and was in contact with the floor. Gait speed was measured over 2 trials and the total time to complete the test in seconds was recorded. The average time for the trials was used and later converted to meters/second for analyses.22 Gait speed measurement has reported concurrent validity and both test-retest and inter-rater reliability in older adults with COPD.36,37

Balance was measured using tandem stance time. Directions for tandem stance in the HRS allowed one foot, of the participant's choice, to be placed fully in front of the other such that the heel of the front foot was touching the toe of the back foot or as close as the participant was able to get them.22 Participants were instructed to stand in that same position without assistance for as long as they were able, up to 60 seconds. Participants were allowed to have assistance to get into the position and the average time for completion was recorded in seconds. The time ended if the participant stepped out of place or grabbed hold of an assistive device. As a measure of balance, tandem stance time has established construct validity and inter-rater and test-retest reliability.38,39

Statistical Analyses

Demographic data were described by measures of central tendency (mean, standard deviation, and frequency) and comparisons between groups were completed using multivariate analysis of variance. To examine the associations between cognitive function and measures of gait speed or balance, multivariate linear regression modeling was completed via the forced entry method for both groups. Two regression models were performed for each group with gait speed as the outcome for one regression model and balance the outcome for the other model. The cognitive predictor variables included orientation, executive function measured via semantic verbal fluency, IWR, and DWR while the outcome variable was gait speed (model 1) and tandem stance (model 2). Associations between the outcomes and each independent variable were first examined. Demographic factors that were correlated at 0.25 or greater with any of the outcomes were considered for inclusion in the models. As a result, age, grip strength, and education variables were controlled for in regression models. All data were analyzed using SPSS 26.0 (IBM Inc, Armonk, New York) and a significance level was set at P < .05.

RESULTS

Characteristics of the Study Population

Three hundred and eighty-two community-dwelling individuals with COPD who met the inclusion criteria were selected for the study. Characteristics of the study population, by group, can be found in Table 1. In addition, 382 age-matched individuals who did not have COPD were randomly selected to serve as the comparison group. Groups did not differ in age with a mean age of 74.94 (SD = 6.75) years for COPD and 75.23 (SD = 6.92) years for the non-COPD group (P = .75). Overall, 55% were married, and 56.5% were female in the COPD group compared with 60.7% and 58.4% in the non-COPD group, respectively (P = .61 and P = .20, respectively). Education was not significantly different between groups (P = .21), with an average of 12.06 (SD = 3.31) years for the COPD group and 12.58 (SD = 2.67) years for the non-COPD group. Additionally, about 19% of individuals in the COPD group used supplemental oxygen.

Table 1. - Demographic, Physical, and Cognitive Data of the COPD (n = 382) and Non-COPD (n = 382) Groups
Variable COPD Group
n = 382
Non-COPD Group
n = 382
P-Value
Mean (SD) or Percentage Range Mean (SD) or Percentage Range
Age, y 74.94 (6.75) 65-94 75.23 (6.92) 65-92 .75
Education, y 12.06 (3.31) 0-17 12.58 (2.67) 0-17 .21
Gender, female, % 56.50 ... 58.40 ... .20
Marital status, married, % 55.00 ... 60.70 ... .61
History of falls in past 2 y, % 44.90 ... 34.00 ... .003a
Injury due to fall, % 20.50 ... 29.20 ... .17
Number times fallen 2.65 (2.52) 1-50 2.32 (1.99) 1-12 .28
Comorbidities
Hypertension, % 68.8 ... 64.7 ... .19
Diabetes, % 24.6 ... 22.8 ... .80
Cancer, % 24.1 ... 19.9 ... .49
Arthritis, % 81.7 ... 68.6 ... .02a
Depression, % 22.8 ... 12.3 ... .22
Incontinence, % 34.0 ... 26.4 ... .37
Medications for lung disease, yes, % 61.5 ... ... ... ...
Oxygen use, yes, % 18.8 ... ... ... ...
Physical activity
Mild level, >1/wk, % 38.7 ... 46.7 ... .01a
Moderate, >1/wk, % 30.9 ... 45.7 ... .27
Body mass index, kg/m2 29.94 (6.69) 15.59-55.44 30.39 (5.34) 16.68-48.69 .59
Grip strength, kg 26.34 (9.41) 3.25-56.00 25.45 (9.03) 9.50-55.25 .48
Gait speed, m/s 0.69 (0.22) 0.09-1.43 0.73 (0.19) 0.27-1.40 .24
Tandem stance time, s 24.63 (18.15) 0.1-60.00 26.50 (18.05) 0.59-60.00 .45
Immediate word recall 5.11 (1.68) 0-10 5.05 (1.65) 0-9 .80
Delayed word recall 3.88 (1.99) 0-9 4.16 (1.87) 0-9 .29
Orientation 3.69 (0.63) 0-4 3.80 (0.47) 1-4 .14
Executive function 15.70 (6.00) 0-36 15.49 (6.65) 0-39 .81
Abbreviation: COPD, chronic obstructive pulmonary disease.
aP < .05.

A greater percentage of individuals in the COPD group, 44.9%, reported falling as compared with individuals in the non-COPD group, 34% (P = .003). Average BMI was not significantly different between groups (P = .59). Grip strength was not significantly different between groups (P = .48). Neither gait speed (P = .24) nor tandem stance (P = .45) was significantly different between groups. With regard to performance on the measures of cognitive function, no significant differences were found for any of the measures. Full demographic, mobility, and cognitive data can be found in Table 1.

Associations of Cognitive Function With Gait Speed

COPD group

When relationships between cognitive function and gait speed were examined with linear regression modeling in the COPD group, none of the cognitive measures were significantly associated with gait speed after age, education, and strength were controlled for: IWR (β= 0.003, P = .75), DWR (β= 0.01, P = .10), orientation (β= 0.03, P = .12), executive function (β= 0.0034, P = .14); R2 = 0.24.

Non-COPD group

For the non-COPD group, the only cognitive function associated with gait speed was executive function, albeit a weak association (β= 0.004, P = .04, R2 = 0.15). All other cognitive variables were not significantly associated with gait speed.

Association of Cognitive Function With Balance

COPD group

When relationships between cognitive function and balance were examined in the COPD group with linear regression modeling, DWR (β= 1.42, P = .04, R2 = 0.30) was the only cognitive function significantly associated with tandem balance time after controlling for covariates. Executive function (β= 0.12, P = .43), orientation (β=−0.68, P = .64), and IWR (β=−0.39, P = .62) were not significantly associated with tandem balance.

Non-COPD group

For the non-COPD group, none of the cognitive measures were associated with tandem stance after controlling for covariates. Information from all regression models can be found in Table 2.

Table 2. - Relationship Between Cognitive Function and Balance and Gait Speed in Older Adults With COPD (n = 382) and Without COPD (n = 382) Expressed as Unstandardized Regression β-Coefficients (95% CI)a
Group Variable Immediate Word Recall Delayed Word Recall Orientation Executive Function
COPD group Gait Speed 0.003 (−0.02, 0.02) 0.01 (−0.003, 0.03) 0.03 (−0.01, 0.07) 0.003 (−0.001, 0.01)
Tandem stance −0.39 (−1.91, 1.14) 1.42 (0.10, 2.74)b −0.68 (−3.54, 2.19) 0.12 (−0.18, 0.43)
Non-COPD group Gait Speed −0.004 (−0.03, 0.02) 0.002 (−0.021, 0.02) 0.01 (−0.04, 0.05) 0.004 (0.00, 0.01)b
Tandem stance 0.39 (−1.15, 1.93) −0.13 (−1.40, 1.14) −0.52 (−3.51, 2.46) 0.14 (−0.12, 0.39)
Abbreviations: CI, confidence interval; COPD, chronic obstructive pulmonary disease.
aAdjusted for age, education, and grip strength.
bP < .05.

DISCUSSION

To our knowledge, this is the first population-based study that examined the association of cognitive function on functional mobility and balance in community-dwelling older adults with COPD as compared with those without the disease. The findings of this study confirmed part of our initial hypothesis that cognitive function was significantly associated with balance in individuals with COPD. However, we did not find an association between gait speed and cognition.

Despite the COPD group sharing similarities with the non-COPD group in age, BMI, and gait speed, the COPD group had a significantly greater percentage of individuals with a history of falls and depression. Additionally, the COPD group was relatively stable; all members were community-dwelling, and only 19% required supplemental oxygen (Table 1). The underlying respiratory impairments, particularly higher ventilatory demands and higher oxygen consumption, for any given workload may explain significant differences seen in depression and falls across older adults with and without COPD.40 Both groups showed no statistically significant baseline differences in cognitive function (Table 1).

In contrast to the non-COPD group, the COPD group demonstrated a significant association between balance and cognition. Balance requires a complex interaction of numerous cognitive, sensory, and neuromotor processes.41,42 The idea that cognition plays a role in balance control has been demonstrated in previous research in individuals with Alzheimer disease and mild cognitive impairments.43,44 However, the contribution of different domains of cognition on balance has been less explored, especially in COPD. A large body of research highlights executive function as the cognitive function most often associated with impaired balance.41 This study found contradictory results in that delayed recall demonstrated significant contributions to balance in individuals with COPD. Notably, DWR was the only cognitive function measured, which was significantly associated with static tandem balance time in individuals with COPD. This difference is likely due to the use of a global measure of cognition in the previous study as compared with more specific measures in this study. When working with individuals with COPD, clinicians should consider using cognitive screening measures such as the Mini-Cog, which assesses both recall and executive function.45 Given that the individuals in this sample had no reported sensorineural problems and that the peripheral muscle strength was similar between groups, the association between recall and static balance, even though small, cannot be ignored. The direct association in this study indicates that in individuals with COPD as delayed recall declines, then the ability to perform a balance tasks like tandem balance declines as well. Future studies in adults with COPD should consider using a measure of mobility/balance that incorporates a secondary cognitive task, like the Timed Up and Go-cognitive,46 to determine whether differences in balance are more pronounced when dual-task activities are performed.

Poor recall memory may be reflective of alteration in the neuronal structures from ischemic lesions that may be a direct effect of persistent hypoxemia commonly seen in COPD. Since DWR provides more information on the neuroplasticity and overall function of the brain,47 it may be plausible that good recall in those with COPD may be an indicator of greater cognitive reserve and better balance. No such associations were noted between executive function and balance in the COPD group. Although balance is a complex skill that requires both attention and executive function, the lack of associations between executive function and tandem balance could be due to the use of a static balance test. Since dynamic balance is more cognitively challenging than static balance, the role of executive function and planning may be more apparent with dynamic activities. Since participants were community-dwelling with relatively stable and less severe COPD evidenced by the minimal use of supplemental oxygen in the group, it is likely that standing, a low-level balance task, was not much affected by cognition.

The association of gait speed with functional cognitive domains such as executive function is widely reported in the older adult population.47,48 Consistent with previous literature, we found significant associations between executive function and gait speed in this study. However, surprisingly, these associations were only significant in the non-COPD group. Several explanations of this are possible. Previous research in COPD highlighted that gait speed declines were more noticeable when walking over longer distances such as during the 6-minute walk test as compared with short distances such as during a 4-m baropodometry.49 Since gait speed was measured over an 8.2-ft walk distance, which is shorter than the standard 10-m walk test distance, it is likely that it was not sufficient to elicit speed changes. Although gait speed has been measured over shorter distances in previous research with COPD and heart failure,50 and has excellent reliability, shorter walk tests lack concurrent validity with the standard 10-m walk test.51 Future studies, which compare gait speed changes across tests of short and longer distances, are warranted.

The lack of associations between cognition and gait speed in the COPD group suggests cognition in COPD, especially in less severe disease, is more strongly related to other determinants such as the severity of pulmonary limitations, use of supplemental oxygen, and presence of cardiovascular comorbidities. As the disease severity advances, the associations between mobility and cognition may become more apparent. Similar results were noted in a previous study with a smaller sample of people with moderate to severe COPD.50 The authors found a significant univariate relationship between gait speed and executive function.50 However, when a multivariate model was constructed, this relationship was no longer significant and other determinants like the 6-minute walk test, diffusing capacity of carbon monoxide percent, and dyspnea became more predominant predictors of gait speed.50 Since only 19% of the sample in this study used supplemental oxygen, the sample was too low to perform a sensitivity analysis for regression. Nevertheless, this study had a large nationally representative sample size, which increases the generalizability of these results. Future population-based studies are needed to examine the relationship between gait speed and cognition by comparing gait speed and cognition across disease severity as well as between individuals using and not using oxygen.

The authors recognize the limitations of this study. Since this was a population-based study with previously collected data, the authors had little control over the variables available. First, the diagnosis of COPD was gathered via self-report rather than actual lung function data. Although self-report of physician diagnosis has been previously validated against actual diagnosis in COPD,52 access to lung function values would have allowed us to determine disease severity indicators and comorbidity indices and differentiate the effect of disease severity and comorbidity on the relationship between cognition and mobility. Second, although 22.8% of the COPD group and 12.3% of the non-COPD group reported a diagnosis of depression at any point, correlations between depression and the dependent variables did not reach the cutoff score for inclusion in the regression models. Future studies are indicated to determine whether associations between physical and cognitive measure performance are influenced by depression in adults with COPD. Finally, the cross-sectional nature of our study does not allow for any causal inference. Future prospective studies are needed to examine causal relationships between cognition and balance within this population.

CONCLUSION

There has been a growing realization of cognitive impairment in individuals with COPD. Neuronal injury caused directly by the disease, chronic hypoxemia, lung function impairment, exacerbations, systemic inflammation, lack of physical activity, poor health status, depression, or other vascular comorbidities could all be factors linked with the development of cognitive impairment in COPD.17 The present study demonstrated that, in older adults with COPD, decline in cognitive function, specifically delayed recall was significantly associated with balance, but not gait speed after controlling for covariates. Therefore, assessment of cognitive function including DWR should be implemented as part of routine fall risk screening and assessment for all individuals with COPD, regardless of disease severity.

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Keywords:

chronic lung disease; executive function; gait speed; recall

© 2021 APTA Geriatrics, An Academy of the American Physical Therapy Association.