Abstract
[Purpose] This study retrospectively examined the physical characteristics of patients with chronic obstructive pulmonary disease who experienced decreased physical activity due to low-frequency pulmonary rehabilitation. [Participants and Methods] Eighty outpatients with stable chronic obstructive pulmonary disease were included. Participants were categorized into two groups based on changes in physical activity after six months of low-frequency pulmonary rehabilitation. Those whose daily step count decreased by 600 steps or more were classified as the decreased group, while the others were classified as the non-decreased group. [Results] The decreased group had a lower predicted value of forced expiratory volume in one second compared to the non-decreased group. Additionally, a greater proportion of participants in the decreased group lived in hilly areas compared to those living in flat areas. [Conclusion] It may be important to consider appropriate intervention strategies at the initial assessment of low-frequency pulmonary rehabilitation, especially for individuals with reduced forced expiratory volume in one second and those living in hilly environments.
Keywords: Chronic obstructive pulmonary disease, Low-frequency pulmonary rehabilitation, Physical activity
INTRODUCTION
Physical activity in patients with chronic obstructive pulmonary disease (COPD) is a prognostic factor for survival and is widely recognized as an important indicator1). Therefore, increasing physical activity is a management goal for COPD2). Studies have reported that using pedometers3) and interventions combining exercise therapy with counseling4) effectively improves physical activity levels, whereas exercise therapy alone does not necessarily increase physical activity5). This is because physical activity consists of two elements6): “exercise” and “daily activities”, indicating the need for individualized approaches considering patients’ living backgrounds.
Conventional reports on pulmonary rehabilitation have mostly involved high-frequency interventions conducted two to three times per week7). However, in clinical practice, various challenges, such as severe dyspnea preventing outdoor activity, the need for family accompaniment, transportation issues, financial constraints, and weather conditions can make maintaining such a high frequency of interventions difficult. Furthermore, outpatient rehabilitation scheduling is often unpredictable owing to varying appointment times and additional examinations, leading to inefficiencies in clinical workflow.
In this context, our institution provides outpatient pulmonary rehabilitation at a lower frequency, generally aligned with patients’ scheduled medical appointments (one to two times per month), which is less frequent than the interventions reported in previous studies. However, few studies have been conducted on low-frequency pulmonary rehabilitation, and no definitive conclusions have been established. Prior research in Japan has shown that interventions performed one to three times per month can help maintain a 6-min walk distance and significantly improve knee extension strength and activities of daily living (ADL)8). Additionally, studies have reported that even a frequency of once per week can significantly increase step count and knee extension strength following pulmonary rehabilitation interventions9). These findings suggest that low-frequency pulmonary rehabilitation can yield favorable outcomes, making it a valuable approach in clinical settings.
Therefore, if we can identify the characteristics of patients whose physical activity levels decrease following low-frequency pulmonary rehabilitation, we can tailor the intervention frequency to each patient’s needs, thereby enhancing clinical effectiveness. Moreover, this approach may help address the various challenges associated with high-frequency interventions.
Therefore, this study’s objective was to retrospectively examine whether differences existed in other physical activity parameters, exercise tolerance, muscle strength, body composition, ADL, respiratory function, quality of life (QOL), and living background among outpatients with COPD whose step counts decreased after low-frequency pulmonary rehabilitation.
PARTICIPANTS AND METHODS
The participants in this study were stable outpatients with COPD who were admitted to our hospital. A total of 80 patients were included. The inclusion criteria were male patients with COPD who had received low-frequency pulmonary rehabilitation, regardless of disease stage, and who provided consent and cooperation. The exclusion criteria were individuals who walked fewer than 600 steps per day at the time of intervention, those with respiratory diseases other than COPD, those who had experienced an exacerbation within the past month, those with mobility impairments, those with severe internal complications, and those who had difficulty understanding the purpose and methods of the study, missing date (Fig. 1).
Fig. 1.
Flowchart of the analysis.
COPD: chronic obstructive pulmonary disease.
The basic attributes of the participants included age, body composition (body mass index [BMI] and body fat percentage), dyspnea (Modified Medical Research Council Dyspnea Scale), Global Initiative for Chronic Obstructive Lung Disease (GOLD) category, and GOLD stage. The explanatory measurement indicators included physical activity measured using a triaxial accelerometer (Active style Pro®, Omron Corporation, Kyoto, Japan), including step count (initial evaluation/after 6 months) and its change (Δ), weekly exercise (Ex) volume, daily Ex volume, activity below three metabolic equivalents (METs), and activity of three METs or more. Additionally, exercise tolerance was assessed using the Incremental Shuttle Walking Distance, muscle strength was assessed using maximal knee extension strength (μTas F-1®, Anima Corporation, Tokyo, Japan) and maximal grip strength (Digital Grip Strength Meter®, Takei Scientific Instruments Co., Ltd., Niigata, Japan), and body composition was assessed using the Skeletal Muscle Mass Index (SMI), lower limb skeletal muscle mass, and height-adjusted lower limb SMI measured with InBody270® (InBody Japan Corporation, Tokyo, Japan).
ADL were evaluated using the total score of the Nagasaki University Respiratory ADL Questionnaire, pulmonary function was assessed using forced expiratory volume in one second (FEV1), forced expiratory volume percentage in 1 s (FEV1%), and % predicted FEV1 (%FEV1). QOL was evaluated using the COPD Assessment Test. Lifestyle background factors included the presence of a spouse, employment status, use of home oxygen therapy (HOT), home environment, and whether the participant drove a car.
The step count and other physical activity metrics were measured by lending a triaxial accelerometer to the participants and collecting it after 1 month. The device was set such that physical activity data were not displayed on the monitor screen. The device was worn at the waist and removed only during bathing and sleeping, with verbal instructions to wear it at all other times. The collected step count data were analyzed using dedicated software, and average values over 1 month were calculated. Data with less than 360 min of daily wear time were excluded. The same procedure was used to analyze the other physical activity data.
Participants were categorized into two groups: those whose step count decreased by 600 steps or more per day after 6 months of low-frequency pulmonary rehabilitation were classified as the “decrease group”, whereas those who did not meet this criterion were classified as the “non-decrease group”. In previous studies, the minimal clinically important difference (MCID) in daily step count for COPD has been reported to be between 600 and 1,100 steps per day. In the present study, we used an increase of 600 steps per day—the lower limit of this range—as the threshold for a clinically meaningful change and applied it to group classification10). Low-frequency rehabilitation was defined as occurring once or twice per month.
The intervention method for low-frequency pulmonary rehabilitation included a 6-month intervention period, with a frequency of once or twice per month and a duration of 40 min per session. The intervention included bodyweight strength training and aerobic exercise through walking and cycling on an ergometer. Patients were also given an exercise pamphlet and instructed to continue exercising at home.
Comparisons of basic attributes between the decreased and non-decreased groups were conducted using an unpaired t-test or the χ2 independence test. Differences in physical activity, exercise tolerance, muscle strength, body composition, ADL, pulmonary function, and QOL between the decreased and non-decreased groups at the initial evaluation were analyzed using an unpaired t-test. Lifestyle background factors, including the presence of a spouse, employment status, use of HOT, home environment, and driving status, were analyzed using the χ2 independence test. A significant level of 5% was considered statistically significant. Adjusted residuals of +1.96 or higher in the χ2 independence test were considered “significantly high”, while those of −1.96 or lower were considered “significantly low”. SPSS version 30 (IBM Corp., Armonk, NY, USA) was used for statistical analysis.
Oral and written informed consent were obtained from all participants in our hospital’s outpatient pulmonary rehabilitation program. During this process, participants were informed of the potential publication of the data, and consent was obtained through their handwritten signatures. This study was approved by the hospital’s research ethics committee (Approval Number: 20190515-2).
RESULTS
Table 1 presents the baseline characteristics during the initial evaluation of low-frequency pulmonary rehabilitation. The total number of participants was 34. The mean age was 75.3 ± 7.5 years, and the BMI was 21.5 ± 2.8. The GOLD category distribution was as follows: A (12 patients), B (10 patients), and E (12 patients). The GOLD stage distribution was as follows: Stage I (eight patients), Stage II (five patients), Stage III (14 patients), and Stage IV (six patients). Cognitive function, assessed using the Mini-Mental State Examination, showed an average score of 28.3 points.
Table 1. baseline characteristics at the initial evaluation of low-frequency pulmonary rehabilitation.
| Total | Decrease group | Non-decrease group | Effect size | |
| n | 34 | 10 | 24 | - |
| Age (years) | 75.3 ± 7.5 | 76.1 ± 8.2 | 75.0 ± 7.3 | 0.14 |
| BMI (kg/m2) | 21.5 ± 2.8 | 21.0 ± 2.2 | 21.7 ± 3.1 | −0.26 |
| Body fat percentage (%) | 24.2 ± 7.6 | 22.5 ± 9.1 | 24.7 ± 7.2 | −0.28 |
| mMRC scale (grade 0/1/2/3/4) | 2/12/9/10/1 | 1/4/2/2/1 | 1/8/7/8/0 | 0.32 |
| GOLD category (A/B/E) | 12/10/12 | 4/3/3 | 8/7/9 | 0.08 |
| GOLD stage (I/II/III/IV) | 8/5/14/6 | 0/2/6/2 | 8/3/8/4 | 0.38 |
| MNA-SF (points) | 11.6 ± 2.2 | 11.0 ± 3.1 | 11.8 ± 1.8 | −0.36 |
| MMSE (points) | 28.3 ± 1.8 | 28.3 ± 1.8 | 28.3 ± 1.8 | <0.01 |
*p<0.05. The measurements are presented as mean ± standard deviation.
BMI: body mass index; mMRC: modified medical research council dyspnea scale; GOLD: global initiative for chronic obstructive pulmonary disease; MNA-SF: mini nutritional assessment short form; MMSE, mini-mental state examination.
Regarding classification into two groups, the decreased group consisted of 10 patients, while the non-decreased group included 24 patients. No significant differences existed in the basic attributes between the decreased and non-decreased groups.
Table 2 compares the measurement indices from the initial evaluation of low-frequency pulmonary rehabilitation between the decreased and non-decreased groups. The step count after 6 months of physical activity (p=0.04, d=−0.64) and the change in step count (Δ steps, p<0.01, d=−2.30) were significantly lower in the decreased group compared to the non-decreased group. Regarding pulmonary function, %FEV1 was significantly lower in the decreased group than in the non-decreased group (p=0.04, d=−0.66). No significant differences were observed in the other measurement indices.
Table 2. The measurement indices at the initial evaluation of low-frequency compared between the two groups.
| Total | Decrease group | Non-decrease group | Effect size | |
| (n=34) | (n=10) | (n=24) | ||
| Initial evaluation step count (step/day) | 3,005 ± 1,839 | 3,428 ± 1,986 | 2,829 ± 1,788 | 0.33 |
| After six months step count (step/day) | 2,905 ± 2,230 | 1,924 ± 1,390 | 3,314 ± 2,405* | −0.64 |
| Δ Step count (step/day) | −100.0 ± 1,264 | −1,505 ± 746 | 485 ± 927* | −2.30 |
| Weekly Ex volume (Ex/week) | 16.3 ± 10.8 | 16.4 ± 10.0 | 16.3 ± 11.3 | <0.01 |
| Daily Ex volume (Ex/day) | 2.3 ± 1.5 | 2.3 ± 1.4 | 2.3 ± 1.6 | <0.01 |
| Activity time below 3 METs (min/day) | 606.7 ± 118.5 | 579.3 ± 121.8 | 618.2 ± 117.8 | −0.33 |
| Activity time above 3 METs (min/day) | 38.5 ± 26.1 | 38.8 ± 22.8 | 38.4 ± 27.8 | 0.02 |
| ISWD (m) | 337.9 ± 160.9 | 346.0 ± 177.8 | 334.6 ± 157.3 | 0.01 |
| Knee extension strength (kgf) | 33.7 ± 10.6 | 31.1 ± 9.1 | 34.9 ± 11.2 | −0.36 |
| Grip strength (kg) | 33.1 ± 6.1 | 31.0 ± 9.1 | 34.0 ± 5.7 | −0.50 |
| SMI | 6.7 ± 0.7 | 6.7 ± 0.7 | 6.7 ± 0.7 | 0.01 |
| Lower limb skeletal muscle mass (kg) | 13.9 ± 1.7 | 14.2 ± 1.7 | 13.8 ± 1.8 | 0.21 |
| Lower limb SMI | 5.1 ± 0.4 | 5.1 ± 0.4 | 5.1 ± 0.4 | −0.08 |
| NRADL (points) | 77.8 ± 17.3 | 83.0 ± 13.5 | 75.6 ± 18.5 | 0.43 |
| FEV1 (L) | 1.5 ± 0.7 | 1.2 ± 0.5 | 1.6 ± 0.8 | −0.59 |
| FEV1% (%) | 53.6 ± 14.7 | 50.7 ± 13.3 | 54.8 ± 15.4 | −0.27 |
| %FEV1 (%) | 56.8 ± 26.3 | 45.1 ± 16.8 | 61.7 ± 28.3* | −0.66 |
| CAT (points) | 16.6 ± 8.1 | 20.4 ± 7.3 | 15.0 ± 8.0 | 0.70 |
*p<0.05. The measurements are presented as mean ± standard deviation.
Ex: exercise; METs: metabolic equivalents; ISWD: incremental shuttle walking distance; SMI: skeletal muscle mass index; NRADL: The Nagasaki University Respiratory activities of daily living (ADL) questionnaire; FEV1: forced expiratory volume in one second; FEV1%: forced expiratory volume % in one second; %FEV1, % forced expiratory volume in one second; CAT: chronic obstructive pulmonary disease (COPD) assessment test.
Additionally, concerning lifestyle background, the home environment showed a significant association with more hilly areas than flat areas (adjusted residual=± 2.04, χ2 value=4.16, p=0.046, φ=−0.35). No significant associations were found with the other lifestyle background items (Table 3).
Table 3. Association between the lifestyle characteristics of the two groups.
| Decrease group (n=10) | Non-decrease group (n=24) | χ2 value | Effect size | ||
| Spouse | Yes | 9 | 18 | 0.97 | −0.17 |
| Adjusted residuals | 0.99 | −0.99 | |||
| No | 1 | 6 | |||
| Adjusted residuals | −1 | 1 | |||
| Employment | Yes | 4 | 6 | 0.77 | −0.15 |
| Adjusted residuals | −0.87 | 0.87 | |||
| No | 6 | 18 | |||
| Adjusted residuals | 0.87 | −0.87 | |||
| HOT | Yes | 6 | 12 | 0.28 | −0.09 |
| Adjusted residuals | 0.53 | −0.53 | |||
| No | 4 | 12 | |||
| Adjusted residuals | −0.53 | 0.53 | |||
| Home environment | Hilly | 8 | 10 | 4.16* | −0.35 |
| Adjusted residuals | 2.04 | −2.04 | |||
| Flat | 2 | 14 | |||
| Adjusted residuals | −2.04 | 2.04 | |||
| Driving status | Yes | 6 | 18 | 0.77 | 0.15 |
| Adjusted residuals | −0.87 | 0.87 | |||
| No | 4 | 6 | |||
| Adjusted residuals | 0.87 | −0.87 | |||
*p<0.05. HOT: home oxygen therapy.
DISCUSSION
This study aimed to examine the characteristics of patients with COPD whose physical activity levels decreased after undergoing low-frequency pulmonary rehabilitation. Comparative analysis revealed that %FEV1 in the decreased group was significantly lower. Previous studies have reported that %FEV1 is associated with physical activity levels in patients with COPD11, 12). Additionally, a decline in %FEV1 reflects airflow limitation, which may lead to increased dyspnea and decreased exercise tolerance. These factors may have contributed to the inability to maintain or increase physical activity levels. Therefore, these findings suggest that patients with a low %FEV1 at the initial evaluation may not experience significant improvements in physical activity through low-frequency pulmonary rehabilitation.
A significant association was found between the differences in home environments, whether hilly or flat, across the two groups. Previous studies have reported no association between physical activity levels and the home environment in patients with COPD13). However, participants in these studies had higher physical activity levels than those in this study, which may have led to differences in the results. Patients undergoing HOT were excluded from the analysis. It has been reported that patients undergoing HOT have significantly lower physical activity levels than those not undergoing HOT14, 15), which may have contributed to the differences in findings. Based on these observations, it is possible that living in hilly areas makes going out and exercising more difficult, thereby restricting physical activity. Therefore, similar to %FEV1, living in a hilly environment may also limit the effectiveness of low-frequency pulmonary rehabilitation in improving physical activity levels.
This study had a few limitations. First, to eliminate the potential influence of gender differences on characteristics, we limited the study participants to male COPD patients. Therefore, it may be difficult to generalize the findings to other populations, such as females. Second, the small sample size and imbalance in group allocation may have introduced bias into the results. Third, some participants may have experienced exacerbations during the 6-month low-frequency pulmonary rehabilitation period. The possibility that reduced physical activity was due to exacerbations cannot be ruled out. Fourth, the home environment assessment was subjective and based on whether the area was hilly or flat, without a detailed evaluation of the slope’s degree or length. It was difficult to determine whether the slopes limited daily physical activity.
This study’s findings suggest that patients with COPD and a low %FEV1 at the initial evaluation or those living in hilly environments may require modifications to their pulmonary rehabilitation programs. Specifically, increasing the frequency of interventions and securing exercise opportunities through outpatient or home-visit rehabilitation services should be considered intervention strategies for those with access to care. Furthermore, it is considered necessary to establish walking routes that avoid slopes and to implement long-term follow-up to prevent a decline in physical activity. Additionally, it is important to evaluate physical activity, including daily living activities at home, and to provide exercise guidance based on that evaluation.
The results indicate that among outpatient individuals with COPD whose physical activity levels decreased after 6 months of low-frequency pulmonary rehabilitation, having a lower %FEV1 and living in a hilly environment may be relevant contributing factors. Therefore, careful consideration of intervention methods is essential for individuals exhibiting these characteristics during the initial evaluation of pulmonary rehabilitation.
Conflicts of interest
No conflicts of interest are disclosed regarding this study.
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