Effects of dual task training on attention and executive functioning in hemodialysis patients: a preliminary study

Abstract

[Purpose] This study aimed to investigate the effects of aerobic exercise and dual-task training on the attention and executive functions of hemodialysis patients using the Trail Making Test B and to make recommendations for clinical practice. [Participants and Methods] Patients were randomly assigned to one of three groups, with 10 individuals in each group. The first group, designated the dual-task group, performed both motor and cognitive tasks in addition to regular dialysis treatment. The second group, designated the exercise group, performed only motor tasks in addition to regular dialysis treatment. The third group served as the control group and underwent regular dialysis. The performance on the Trail Making Test B was compared among the dual-task, exercise, and control groups. [Results] The dual-task group exhibited a significantly shorter completion time for the Trail Making Test B after the intervention period than at the pre-intervention baseline. However, no significant differences were observed between the exercise and control groups. [Conclusion] The findings of this study indicate that dual tasks may facilitate improvements in attention and executive function in hemodialysis patients. We conclude that dual-task training is effective in enhancing the attention and executive functions of hemodialysis patients.

INTRODUCTION

A survey conducted by the Ministry of Health, Labour and Welfare¹⁾ in 2022 revealed that dementia will be the primary cause of nursing care in Japan, and chronic kidney disease (CKD) is a risk factor of neurological disease development. A survey conducted by Murray et al.²⁾ revealed that 87.3% of 338 dialysis patients exhibited mild-to-severe cognitive impairment, with the prevalence of cognitive impairment increasing in patients with advanced CKD. A substantial body of epidemiological evidence demonstrates an association between CKD and cognitive decline. A meta-analysis by Tang et al.³⁾ also reported that worsening renal function was associated with cognitive decline. In Japan, the number of patients with CKD is unparalleled globally, with a considerable proportion of patients undergoing hemodialysis for over 30 years. These patients frequently present with complications associated with prolonged dialysis⁴⁾. Furthermore, the aging of dialysis patients in Japan is occurring at an accelerated rate, and dementia is a significant challenge associated with this process.

Once dialysis is initiated in patients with CKD, it becomes a lifelong treatment. The introduction of dialysis necessitates the implementation of various self-care measures, including shunt management; dietary management emphasizing the restriction of salt, phosphorus, and potassium; fluid management; medication management; and blood pressure management. For instance, in the context of shunt management, patients must be made aware of the potential for shunt blockage and infection as well as importance of avoiding overloading the shunt limb and exerting undue pressure on the shunt area during routine activities. Furthermore, based on the findings of periodic blood tests, dietary management, including alterations in the composition of meals, implementation of specific cooking techniques, and modification of intake levels, is essential. For hemodialysis patients to adequately engage in self-care and maintain stable dialysis therapy, their cognitive functions, particularly attention and executive functions, must be sustained. Patients with CKD frequently present with memory impairment, decreased attention and concentration, and communication difficulties⁵⁾.

Prior research on these functions indicates that 10 min of aerobic exercise at 60% of maximum oxygen intake in healthy adults increases the flow of oxygenated hemoglobin to the prefrontal cortex⁶⁾. Additionally, 6 months of aerobic exercise significantly enhances executive function in healthy older adults aged ≥65 years⁷⁾. Moreover, dual-task (DT) training, which combines motor and cognitive tasks, enhances attention and executive functions in healthy older adults and those with mild cognitive impairment⁸⁾. To date, few studies have focused on attention and executive functions in patients undergoing hemodialysis. Bogataj et al.⁹⁾ investigated the impact of a cognitive and physical training program on the functional capacity of hemodialysis patients. Participants were divided into two groups, an exercise group and a control group. The exercise group conducted cognitive tasks after aerobic exercise for 12 weeks. The results showed that cognitive function and mobility significantly improved in the exercise group⁹⁾. While a systematic review by Bogataj et al. suggests that physical exercise may improve, or at least not worsen, cognitive performance in HD patients, they report that the effects of cognitive training have not yet been adequately studied¹⁰⁾.

However, to our knowledge, no studies have been conducted on hemodialysis patients that focus on maintaining and improving attention and executive function by performing motor and cognitive tasks simultaneously during hemodialysis therapy. For hemodialysis patients to continue dialysis therapy, it is important to maintain independence in self-care activities that require attention and executive function, such as long-term shunt management and medication management. To prevent shunt occlusion and infection, excessive force on the shunt limb should be avoided during operation. It is necessary to maintain the distributive caution function by paying attention to loads and shocks to the shunt limb. In addition, the Trail Making Test B (TMT-B) is more appropriate than the Trail Making Test A for assessing advanced information processing (working memory) skills such as divided attention. Because dual-task training requires working memory, we designed the study with the following hypothesis: the group that received dual-task training would also reduce the time required for the TMT-B test. Therefore, for this TMT evaluation, we selected TMT-B, which can evaluate distributive attention function.

Considering the above points, this study aimed to investigate the effects of DT during aerobic exercise on the attention and executive functions of hemodialysis patients using the TMT-B along with make recommendations for clinical practice.

PARTICIPANTS AND METHODS

Thirty outpatient hemodialysis patients attending a dialysis clinic provided verbal and written consent to participate in this study. This study was approved by the Ethics Committee of the Zenjinkai Group (approval number: 2021-0017). The inclusion criteria entailed the following: the patient had to be ≥50 years, be on dialysis for ≥3 months, and have difficulty completing tasks due to cognitive impairment. Individuals with upper limb motor disorders, visual impairments, or cerebrovascular disorders were excluded from the study.

The patients were randomly assigned to one of the three groups, with 10 individuals in each group. Randomization assignments were carried out using computer-generated random numbers. The first group, designated the DT group, performed both motor and cognitive tasks in addition to regular dialysis treatment. The second group, designated the exercise group, performed only motor tasks in addition to regular dialysis treatment. The third group served as the control and received regular dialysis.

The exercise tasks for the DT and exercise groups were aerobic exercises (ergometer), and participants were required to engage in a warm-up (calisthenics) and cool-down (stretching) pre- and post-exercise. In accordance with the guidelines¹¹⁾, exercise intensity was set individually to 12–13 on the Borg scale, which is an index of the rate of perceived exertion, and exercise time was set to 20–60 min per session. The exercise frequency was twice weekly and intervention period was 12 weeks.

The cognitive task for the DT group was a calculation task (subtraction), performed concurrently with a motor task. The calculation task required the utilization of both short- and long-term memories, with the former employed for the manipulation of numerical data and latter for the execution of subtraction operations. The prefrontal cortex is instrumental in this process, making the task susceptible to fluctuations in attentional allocation and capacity. The specific method of the subtraction task was as follows: The patient was required to answer the number obtained by subtracting the single-digit numbers from 100, with the difficulty level gradually increasing until the patient could subtract the double-digit numbers.

Attention and executive function were assessed using the TMT-B, a test whose reliability and validity have been established through rigorous scientific inquiry¹²⁾. The TMT-B requires participants to alternate between two series of numbers from “1” to “13” and hiragana characters from “a” to “shi”, drawing lines between each series without making any errors, beginning with the smallest. The time required to complete the series was recorded using a stopwatch. A shorter completion time indicated superior attention and executive functioning. Cognitive functions such as information processing are susceptible to decline with age¹³⁾.

Each group was evaluated at the beginning of the intervention and again after 12 weeks of treatment. We calculated the rate of change using the formula shown below and compared the rate of change pre and post intervention. The timing of the assessment was set to coincide with the commencement of the final dialysis session of the week, allowing for fluctuations in bodily fluid volume and fatigue during each dialysis session.

Rate of change = (time required for TMT-B pre intervention − time required for TMT-B post intervention) / time required for TMT-B pre intervention × 100

Five patients who died, were hospitalized, or transferred to another hospital during the intervention period were excluded from the analysis, leaving nine patients in the DT group and eight each of the exercise and control groups (Fig. 1). After confirming the normality of the data using the Shapiro–Wilk test, pre- and post-intervention comparisons in each group were performed using a paired t-test or Wilcoxon signed rank test. One-way analysis of variance was selected as the most appropriate method to test for differences in age, dialysis history, and time required for TMT-B at baseline among the DT, exercise, and control groups. Furthermore, the χ² test was used to examine discrepancies in sex and diabetes prevalence ratios. Moreover, to facilitate a comparison of the rates of change among the three groups, one-way analysis of variance was conducted, with Tukey’s test employed as a post-hoc test. For all analyses, a p-value of <0.05 was considered statistically significant. All analyses were conducted using the SPSS software (version 25.0; SPSS Inc., Chicago, IL, USA).

Fig. 1.

Selection of participants.

RESULTS

No significant differences were observed in the baseline basic attributes among the three groups (Table 1). The DT group exhibited a significantly shorter completion time for the TMT-B following the post-intervention period (155.1 ± 74.4 s) than at pre-intervention (207.1 ± 118.1 s). The rates of change in the time required for completing the TMT-B by the three groups were −20.7 ± 16.5%, −8.9 ± 17.5%, and 7.7 ± 18.4%, respectively, a significant difference was observed between the DT group and the control group (p=0.008; Table 2).

Table 1. Basic characteristics of participants.

	Control group (n=8)	DT group (n=9)	Exercise group (n=8)
Age, years	64.0 ± 10.2	69.2 ± 12.2	70.8 ± 10.4
Sex, male/female	6/2	6/3	6/2
Dialysis history, years	11.0 ± 12.4	9.3 ± 12.4	11.1 ± 7.1
Diabetes mellitus, Diabetes/Non diabetes	3/5	2/7	3/5
TMT-B, sec	178.7 ± 144.1	207.1 ± 118.1	196.5 ± 174.3

Values are means ± SD of each period. DT: dual task; TMT-B: Trail Making Test B.

Table 2. Time required and rate of change in TMT-B in each group.

Group intervention	Control (n=8)		DT (n=9)		Exercise (n=8)
	Pre	Post	Pre	Post	Pre	Post
TMT-B time (s)	178.7 ± 144.1	189.9 ± 165.0	207.1 ± 118.1	155.1 ± 74.4*	196.5 ± 174.3	161.6 ± 108.6
Rate of change (%)		7.7 ± 18.4		−20.7 ± 16.5**		−8.9 ± 17.5

Mean ± standard deviation.

Comparison of the rates of change among the three groups: one-way analysis of variance, Tukey’s test.

Comparison of the rates of change among the three groups: one-way analysis of variance, Tukey’s test.

DT: dual task; TMT-B: Trail Making Test B.

DISCUSSION

This study examined the intervention effects of DT during aerobic exercise on the attention and executive function of hemodialysis patients using the TMT-B. The TMT-B performance was compared among the DT, exercise, and control groups. The DT group exhibited a significantly shorter completion time for the TMT-B following the intervention period than at the pre-intervention. However, no significant differences were observed between the exercise and control groups. The findings of this study indicate that DT may facilitate improvements in the attention and executive functions of hemodialysis patients.

The DT intervention involved the concurrent performance of two tasks: pedaling an ergometer at a specified speed and subtracting numbers. Therefore, in addition to executive function, the participants needed to allocate appropriate attention per task to ensure optimal performance. The use of functional magnetic resonance imaging to examine changes in brain activity during DT demonstrated that the dorsolateral frontal association cortex was activate¹⁴⁾. This study has several limitations, precluding the examination of the effects on the frontal association cortex or neural mechanisms involved in DT information processing. However, it can be inferred that DT affects information processing in the frontal lobe, attention, and executive function.

Furthermore, while no statistically significant difference was observed in the exercise group, the time required for the TMT-B post-intervention was shorter than pre-intervention. Exercise enhances cerebral blood flow and improves oxygen transport capacity, however, cerebral blood flow decreases during hemodialysis, with a particularly pronounced reduction in older hemodialysis patients^{15, 16)}. Nevertheless, the shortened time required for the TMT-B post-intervention in both the DT and exercise groups indicates that interventions such as DT and aerobic exercise may affect cerebral blood flow in hemodialysis patients. A study of patients with conservative CKD demonstrated that exercise intervention significantly improves memory function¹⁷⁾. Future research should aim to elucidate the differential effectiveness of exercise therapy alone and DT with the addition of attention tasks to exercise therapy.

The present study is not without limitations. Firstly, it was conducted at a single site, and the number of participants was small, so it is possible that sampling bias influenced the results. Additionally, because the study was limited to comparisons of TMT-B data, it was not possible to make comparisons using data from other cognitive function tests. Furthermore, despite the relatively brief period of 12 weeks, the time required for the TMT-B post-intervention in the control group was longer than pre-intervention. This study could not elucidate whether the observed increase was due to age-related changes or specific to hemodialysis patients.

Despite the study’s limitations, the rate of change in TMT-B was higher in the DT group, suggesting that DT training may enhance attention and executive function in hemodialysis patients. This finding lends support to our hypothesis. To gain further insights, it would be beneficial to establish a comparative control group of local residents or others, conduct a longitudinal survey, and clarify the characteristics of attention and executive function in hemodialysis patients. A collaborative study involving other facilities, with an increased number of participants and alterations in the intervention frequency, exercise intensity, and exercise time would yield more robust results.

Conflict of interest

The authors declare no conflicts of interest.