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Abstract

The aim of this article is to investigate which global initiative for chronic obstructive lung disease (GOLD) classification (B-C-D or II-III-IV) better reflects the functionality of patients with moderate to very severe chronic obstructive pulmonary disease (COPD). Ninety patients with COPD were classified according to the GOLD B-C-D and II-III-IV classifications. Functionality was assessed by different outcomes: 6-min walk test (6MWT), activities of daily living (ADL) (London Chest ADL Scale), and daily life activity/inactivity variables assessed by activity monitoring (SenseWear armband, Pittsburgh, Pennsylvania, USA). The 6MWT was the only outcome significantly associated with both the GOLD classifications. Good functionality as assessed by the 6MWT was observed in 80%, 69%, and 43.5% (GOLD B, C, and D, respectively) and 81%, 59%, and 29% (GOLD II, III, and IV, respectively) of the patients. Association (V Cramer’s) and correlation (Spearman) coefficients of 6MWT with GOLD B-C-D and II-III-IV were V = 0.30, r = −0.35, and V = 0.37, r = −0.25, respectively. Neither GOLD classification showed V or r ≥ 0.30 with any other functionality outcome. Both the GOLD B-C-D and II-III-IV classifications do not reflect well COPD patients’ functionality. Despite low association and correlation coefficients in general, both GOLD classifications were better associated with functional exercise capacity (6MWT) than with subjectively assessed ADL and objectively assessed outcomes of physical activity/inactivity.

Keywords

Chronic obstructive pulmonary disease guideline pulmonary function

Introduction

Chronic obstructive pulmonary disease (COPD) is one of the major causes of morbidity and mortality in the world,¹ and there is increasing evidence showing that there is large heterogeneity within patients’ characteristics.^2
–4 Because of this marked COPD heterogeneity in terms of clinical outcomes, disease severity and progression, the 2011 update of the global initiative for chronic obstructive lung disease (GOLD)⁵ proposed a multidimensional clinical evaluation that classifies patients into one of four groups (A, B, C, and D) according to exacerbation history, level of symptoms, and severity of airflow obstruction. This was in contrast with the traditional unidimensional GOLD classification (I, II, III, and IV), which takes into account only the severity of airflow obstruction.⁶

The GOLD classification was developed to reflect disease severity, its impact on patient’s health status and the risk of future events (such as exacerbations, hospital admissions or death) in order to help guiding therapy of patients with COPD.⁷ A number of recent studies have investigated the association between the multidimensional GOLD A-B-C-D classification and health outcomes^8

–14 as well as compared the traditional GOLD classification with the new multidimensional GOLD classification concerning hospitalizations,¹¹ mortality,^11
–13 and health-related quality of life (HRQOL).¹⁴ These studies demonstrated that the unidimensional and multidimensional GOLD classifications do not differ significantly in terms of ability to predict hospitalization and mortality, except for HRQOL in which GOLD A-B-C-D is more closely associated with this outcome than GOLD I-II-III-IV due to the nature of the A-B-C-D classification involving a measure of HRQOL. Concerning the unidimensional GOLD classification, it is known that the forced expiratory volume in the first second, on which the classification is based, is not strongly associated with physical activity level.¹⁵ However, it remains unknown whether the multidimensional GOLD classification correlates with functionality indicators such as functional exercise capacity, activities of daily living (ADLs) (self-reported limitations during day-to-day activities) and physical ADL (quantification of the amount of activities performed). Taking this into account, it is expected that the functionality will be better associated with multidimensional index than the unidimensional index. For this reason, it is interesting to know whether these two GOLD classifications reflect differently the functionality of patients with COPD.

The objectives of this study were to investigate the association of different functionality outcomes with the new multidimensional GOLD B-C-D groups, and to identify which GOLD classification (II-III-IV or B-C-D) better reflects the functionality of patients with COPD.

Methods

Subjects

All patients taking part in this study were recruited from the initial assessment for admission to the Pulmonary Rehabilitation Program at the University Hospital of Londrina, Universidade Estadual de Londrina (Brazil). No patient had already started the rehabilitation program by the time of his/her data collection. Data were collected from July 2006 to February 2014. This study was approved by the ethics committee of Universidade Estadual de Londrina (Brazil) and all patients gave written informed consent.

The diagnosis of COPD was established according to the current GOLD criteria.¹⁶ In addition to the diagnosis, patients’ inclusion criteria were: clinical stability (i.e., no infection or exacerbation for at least the 12 previous weeks) and absence of severe or unstable heart disease or any other comorbidities that might influence the performance of the assessments. Participants were be excluded if they were unable to understand or perform any assessment procedure or if they wanted to leave the study for any reason.

Participants were classified according to the traditional unidimensional GOLD classification (based on the forced expiratory volume in the first second (FEV₁) in percentage of the predicted values) from moderate to very severe stage (GOLD II-III-IV) as well as according to the new multidimensional GOLD classification from group B to group D (GOLD B-C-D). The number of patients classified as GOLD I and GOLD A assessed during the data collection period was too small to include these patients in the statistical analysis. The study was approved by the institution’s Ethics in Research Committee and all patients gave their written informed consent to participate.

Assessments

Lung function

Pre and postbronchodilator spirometry was performed following the American Thoracic Society/European Respiratory Society guidelines¹⁷ by using the SpirobankG^® spirometer (MIR, Italy). Brazilian reference values were used.¹⁸

Symptoms and exacerbations

Symptoms and exacerbation history were assessed for the GOLD B-C-D classification. Dyspnea during daily life was assessed using the modified Medical Research Council (mMRC) scale that describes five grades of breathlessness ranging from 0 to 4. The low or high-symptom burden of the GOLD B-C-D was based only on the mMRC scores (<2 or ≥2, respectively)⁵ since the COPD assessment test (CAT) questionnaire was not applied in this sample of patients.

The history of exacerbations was retrospectively recorded from the year before inclusion in the study. Exacerbation was defined as an acute event characterized by a sustained worsening of the patient’s condition, from the stable state beyond normal day-to-day variations, and leading to change in regular medication.¹⁹ The individual patient’s history of two or more exacerbations in the preceding year indicated high risk, whereas less than two exacerbations indicated low risk.⁵

Functional exercise capacity

Functional exercise capacity was assessed by the 6-min walk test (6MWT), which was performed twice in a 30-m corridor, with a resting period between tests of at least 30 min, according to international standards.²⁰ Patients were instructed to walk as fast as they can during 6 min and the best of the two walks was used for analysis.

Moreover, for the classification of functionality, two groups were formed according to the walked distance in percentage of predicted values: ≥80% of the predicted was considered as better functionality and <80% of the predicted as worse functionality.²¹ The reference values used were those by Britto et al.²² for Brazilian subjects.

Activities of daily living

Self-reported limitations during ADL were assessed using the London Chest ADL (LCADL) scale, which is a short disease-specific scale with 15 items divided into four domains: self-care (four items), domestic (six items), physical (two items), and leisure (three items).^23,24 This scale is used to grade how intensely dyspnea (and consequently the disease) impairs the performance of various ADL in a Likert-type scale of 0–5 points per item. A total score ranging from 0 to 75 is calculated by summing the domains, with higher values indicating more marked limitation in ADL.

A LCADL total score higher than 22 was considered as indicative of a limited level of ADL performance according to Vilaro et al.²⁵ Therefore, in this study, a total score of ≤22 was considered as better functionality and >22 as worse functionality.

Physical (in)activity in daily life

Physical (in)activity in daily life (PADL) was assessed by wearing the SenseWear Armband monitor. All subjects were instructed to use the monitor for two consecutive week days,²⁶ during 12 h/day (from the moment the patient wakes up until 12 h after that), and the average of the 2 days was used for analysis.

Patients were classified as physically active (better functionality) or inactive (worse functionality) according to achieving or not more than 80 min/day of nonbouts moderate intensity activities as described by van Remoortel et al.²⁷ Moderate physical activity intensity was considered as activities above the threshold of three metabolic equivalents of task (MET).²⁸

In addition to physical activity, sedentary behavior (i.e., physical inactivity) was also analyzed in terms of time spent per day below a certain MET threshold criteria (<3 MET) that was denominated as inactive time per day in this study. To calculate the inactive time per day, we considered the total assessment time (12 h) minus the time spent on moderate, vigorous, and very vigorous activities. The median of inactive time per day was calculated in order to classify the patients into two functionality groups: better functionality (below the median) and worse functionality (above the median).

Statistical analysis

The softwares used for data analysis were Statistical Package for the Social Sciences Version 20.0 and GraphPad Prism Version 3.01. Normality in data distribution was checked with the Shapiro–Wilk test. Data were expressed as mean ± SD or median (interquartile range 25–75%).

To investigate the association between functionality variables and GOLD classifications, the Chi-square test and the Cramer’s V coefficient were used to identify the strength of association. The Cramer’s V ranges between 0 and 1, and in the context of this study, higher values are indicative of stronger relationship between functionality outcomes and GOLD classification, whereas lower values indicate weaker relationship. The Spearman correlation coefficient was also used to analyze the association between functionality outcomes and GOLD classifications. The level of significance was set at p < 0.05.

Results

Demographic and clinical characteristics of the 90 patients included in the study are shown in Table 1. According to the new GOLD B-C-D classification, the majority of patients was classified in group D (68%), whereas according to the traditional GOLD II-III-IV classification the majority of patients was classified as grade III (51%).

Table 1.

Clinical characteristics and demographics of the sample (n = 90).^a

Characteristics	n = 90
Age (years)	67 ± 8
Gender, male/female (%)	59/41
Smoking history (pack-years)	47 (17–70)
BMI (kg/m²)	26 ± 6
FEV₁/FVC	49 ± 14
FEV₁ (% pred)	39 ± 14
mMRC	2.7 ± 0.9
6MWT (m)	432 ± 90
GOLD II-III-IV classification, n (%)
II	16 (18)
III	46 (51)
IV	28 (31)
GOLD B-C-D classification, n (%)
B	15 (17)
C	13 (15)
D	62 (68)

BMI: body mass index; FEV₁: forced expiratory volume in the first second; FVC: forced vital capacity, mMRC: modified Medical Research Council dyspnea scale, 6MWT: 6-min walk test; GOLD: global initiative for chronic obstructive lung disease.

^aResults presented as mean ± SD, median (interquartile range), and number of patients (%).

Tables 2 and 3 show the distribution of patients’ functionality outcomes according to the multidimensional B-C-D and unidimensional II-III-IV GOLD classifications, respectively, as well as their association with functionality outcomes. Functional exercise capacity assessed by 6MWT (in percentage of the predicted values) was the only functionality outcome significantly associated with the multidimensional and unidimensional classifications. However, in general, the value of V Cramer’s coefficient was low (Tables 2 and 3), indicating weak associations between both GOLD classifications and 6MWT, and even weaker with the other functionality outcomes. Comparison of the 6MWT results among multidimensional GOLD groups showed shorter distances when comparing group D versus B and C, both for absolute values (p = 0.003) and for results in percentage of the predicted value (p = 0.005). Concerning the unidimensional GOLD, similar results were observed for group IV versus II and III in percentage of the predicted values, with a strong trend for results in absolute values as well (Figure 1).

Figure 1.

Comparison of 6MWT results in patients classified according to the GOLD multidimensional index (a and b) and the GOLD unidimensional index (c and d) (both in meters (left panels) and in percentage of the predicted values (right panels)). 6MWT: 6-min walk test; GOLD: global initiative for chronic obstructive lung disease. *p < 0.05.

Table 2.

Distribution of patients’ functionality outcomes and association with the new GOLD B-C-D classification.

Functionality outcomes	GOLD B (n = 15)	GOLD C (n = 13)	GOLD D (n = 62)	Cramer’s V	p value
6MWT, n (%)
≥80% of predicted	12 (80)	9 (69)	27 (43.5)	0.30	0.006
<80% of predicted	3 (20)	4 (31)	35 (56.5)
PADL (time > 3METs), n (%)
≥80 (min)	5 (33)	3 (23)	12 (19)	0.12	0.25
<80 (min)	10 (67)	10 (77)	50 (81)
Inactivity (time < 3 METs), n (%)
≤689 (min)	8 (53)	9 (69)	28 (45)	0.17	0.33
>689 (min)	7 (47)	4 (31)	34 (55)
LCADL, n (%)
Total score ≤ 22	9 (60)	10 (77)	25 (40)	0.27	0.06
Total score > 22	6 (40)	3 (23)	37 (60)

Results presented as number of patients (%).

6MWT: 6-min walk test; PADL: physical activity in daily life; MET: metabolic equivalent of task; LCADL: London Chest Activity of Daily Living scale; GOLD: global initiative for chronic obstructive lung disease.

Table 3.

Distribution of patients’ functionality outcomes and association with the GOLD II-III-IV classification.^a

Functionality outcomes	GOLD II (n = 16)	GOLD III (n = 46)	GOLD IV (n = 28)	Cramer’s V	p value
6MWT, n (%)
≥80% of predicted	13 (81)	27 (59)	8 (29)	0.37	<0.001
<80% of predicted	3 (19)	19 (41)	20 (71)
PADL (time > 3METs), n (%)
≥80 (min)	5 (31)	9 (20)	6 (21)	0.10	0.54
<80 (min)	11 (69)	37 (80)	22 (79)
Inactivity (time < 3 METs), n (%)
≤689 (min)	8 (50)	27 (59)	10 (36)	0.20	0.22
>689 (min)	8 (50)	19 (41)	18 (64)
LCADL, n (%)
Total score ≤ 22	10 (62.5)	18 (39)	16 (57)	0.20	0.90
Total score > 22	6 (37.5)	28 (61)	12 (43)

^aResults presented as: number of patients (%).

When comparing the median values of physical activity or inactivity outcomes among different patient groups (B vs. C vs. D and II vs. III vs. IV), there were no significant differences in active or inactive time (Table 4). A further analysis was performed with two MET as the threshold for inactivity instead of three MET, and results were similar.

Table 4.

Comparison of active or inactive time (in minutes) in patients with COPD classified according GOLD B-C-D and GOLD II-III-IV.

	GOLD B	GOLD C	GOLD D	p value
Active time (min)
>3 METs	42.5 (14–91.5)	55 (25.5–84)	26 (14.6–91)	0.13
>2 METs	218 (74–355)	235 (157–245)	147 (66–245)	0.09
Inactive time (min)
<3 METs	677 (628–706)	667 (640–697)	693 (651–713)	0.13
<2 METs	502 (365–646)	510 (362–579)	570 (474–641)	0.10

	GOLD II	GOLD III	GOLD IV	p value
Active time (min)
>3 METs	34.2 (15–91.4)	50.2 (15–75)	17 (6–42.6)	0.16
>2 METs	220 (168–241)	184 (92–291)	136 (90–207)	0.39
Inactive time (min)
<3 METs	686 (628–705)	670 (645–705)	703 (677–714)	0.15
<2 METs	500 (381–636)	536 (429–628)	583 (513–625)	0.30

COPD: chronic obstructive pulmonary disease; GOLD: global initiative for chronic obstructive lung disease; MET: metabolic equivalent of task.

Spearman coefficients showed that the B-C-D and II-III-IV GOLD classifications were weakly but significantly correlated with the 6MWT (r = −0.43 and −0.41, respectively; p < 0.001 for both). Furthermore, the LCADL total score showed a statistically significant but even weaker correlation only with the GOLD B-C-D classification (r = 0.26, p = 0.01) and no correlation with the GOLD II-III-IV classification (r = 0.04; p = 0.68). For the PADL activity and inactivity variables, no correlation was found with either GOLD classifications: for activity, r = −0.18 (p = 0.08) with both classifications; and for inactivity, r = 0.17 (p = 0.1) with the B-C-D classification and r = 0.19 (p = 0.07) with the II-III-IV classification.

Discussion

Regarding the functionality outcomes assessed in this sample of patients with COPD, only the 6MWT was associated with the new GOLD B-C-D classification as well as with the traditional GOLD II-III-IV classification. However, the association was weak suggesting that the combined assessment proposal (A-B-C-D) does not reflect well the functionality of patients with moderate to very severe COPD, similarly to the unidimensional assessment based only on the FEV₁. Additionally, we found differences in the 6MWT between the severe groups (D and IV) in comparison to the less severe classifications (B, C and II, III).

Dyspnea sensation, exacerbation frequency, and FEV₁ are well-known risk factors for poor prognosis in patients with COPD.²⁹ Despite this, some studies have shown that the combination of these three components that compose the multidimensional GOLD A-B-C-D classification is not different from the unidimensional classification to predict long-term COPD outcomes such as hospitalization¹¹ and mortality.^11
–13 The same was observed in this cross-sectional study concerning functionality of patients with COPD, the results of which are in agreement with these studies. It is interesting that even the new GOLD A-B-C-D classification, which considers aspects other than airflow limitation alone, does not reflect well COPD patients’ functionality. Therefore, according to the previous literature and the present results, the multidimensional GOLD index may be superior to the unidimensional GOLD classification for staging the disease and for guiding individualized management, but not for reflecting functionality. Hence, the usefulness of the multidimensional GOLD classification in clinical practice remains unclear in some points and more data with this proposed approach are needed.

It is known that the use of different tools to evaluate symptoms (mMRC versus health status with CAT or clinical COPD questionnaire) significantly influences the grading assignment in the multidimensional GOLD.³⁰ In this study, only the mMRC was used. The new GOLD strategy recommends that is it not necessary to use more than one of these self-reported tools for symptom evaluation. However, this is not supported by strong scientific evidence and it is still unclear whether they can be used interchangeably.

The only statistically significant association of both GOLD classifications with the functionality outcomes proposed in this study was with functional exercise capacity, and a weak one. Nishimura et al.³¹ found significant correlations between the new GOLD A-B-C-D classification with maximal exercise capacity evaluated by the peak volume of oxygen intake (VO₂), as well as with the modified BODE index. However, the authors did not present the correlation coefficient values and only highlighted that the peak VO₂ was stratified by the new GOLD classification, showing a severity gradient from GOLD A to GOLD D, although no difference between groups B and C was observed. In this study, when analyzing the functionality assessed by the median of 6MWT (expressed as percentage of predicted values) between groups B-C-D and grades II-III-IV, both classifications discriminated group D from B and C and grade 4 from 3 and 2, without significant differences among the other groups. A study which compared the two GOLD classifications concerning HRQOL and health costs concluded that the multidimensional GOLD classification had better discriminative capacity than the unidimensional GOLD classification¹⁴; on the other hand, this study concluded that this does not apply to patients’ functionality.

The absence of association between the new GOLD classification and PADL can possibly be related to the fact that daily physical activity involves a complex interaction affected not only by physical components but also by psychosocial, personal, and environmental factors^32,33 which are beyond the scope of the GOLD classification. Additionally, data from a systematic review showed that association between physical activity and clinical outcomes such as FEV₁ and dyspnea were lacking consistency and quality of evidence, which was rated as low to very low.³⁴ Therefore, the multidimensional GOLD A-B-C-D classification, as already demonstrated for the unidimensional I-II-III-IV classification,¹⁵ is not a proper way to reflect the level of PADL in patients with COPD, as well as functionality of these patients in a broader sense.

Scientific attention has also been recently given to sedentary behavior or physical inactivity,³⁵ and therefore inactive time per day was also included among the outcomes proposed to assess and classify functionality in this study. However, results of inactivity were similar to those found for activity, that is, no association between inactive time and both GOLD classifications, what does not suggest advantage of an inactivity outcome over an activity outcome in the context of this study.

The relationship between LCADL total score and the multidimensional GOLD classification was weak and its association with the unidimensional classification was even less evident. The study describing the original development of the LCADL found no association between the scale and the FEV₁,²³ whereas only a modest relationship between the two outcomes was observed in the validation study of the Portuguese LCADL version.²⁴ In addition, a study that investigated the association of different multidimensional indices with the LCADL showed that, among all multidimensional indices studied, only the SAFE index was an independent contributor to the self-reported limitations in ADL.³⁶ Although the LCADL is used to grade how intensely dyspnea impairs the performance of various ADL and the GOLD A-B-C-D classification involves the limitations due to dyspnea in daily life as assessed by mMRC scale, no association was found regarding the LCADL 22-points cut-off and a very weak association was found when considering the Spearman correlation coefficient (r = 0.26). Future studies can aim at investigating if the assessment of symptoms using the CAT questionnaire may find different results, since the CAT is an instrument which reflects more globally the health related quality of life of patients with COPD and can be considered as more comprehensive.

An interesting finding from this study is that the majority of patients had a 6MWD exceeding 80% of the predicted value, what appears to reflect a sample with well-preserved functional status. However, according to the previous literature, Brazilian patients with COPD present higher values of 6MWT when compared to European patients.³⁷ Furthermore, healthy Brazilian subjects present higher values of 6MWT when compared to patients from the United States and even from other countries in Latin America.³⁸ For this reason, we believe that this sample is indeed a reflection of the population studied.

As limitations of this study, the absence of patients in group A and grade 1 can be firstly mentioned. Because of the patient profile in our rehabilitation center, we did not have a reasonable number of patients in this group or grade, which made their analysis not feasible. Secondly, a previous study³⁹ showed that the choice of symptom assessment tool (mMRC or CAT) directly influences the category assignment in the GOLD A-B-C-D classification, suggesting that both tools could be applied and the higher value should be used to classify patients according to their level of symptoms. However, we did not collect data of the CAT in our sample, and therefore it is possible that we may have underestimated symptom severity for patients that were included in group C by using only mMRC scale. However, the ideal symptoms questionnaire and associated cut-points are still a matter of debate, and at this moment either of the two instruments can be used as recommended by the 2011 GOLD document.⁵ Daylight time can be considered as a confounder of physical activity assessment;²⁶ however, these data were not available and therefore could not be taken into consideration in this study. Nevertheless, we believe that this fact does not hinder our results since the region where this study was developed presents nonmarked variations of daylight time throughout the year. And finally, in this study the history of exacerbations was self-reported and this may have underestimated the risk in case patients were classified as GOLD B, since exacerbation self-report by patients with COPD to health care professionals may not be optimal.⁴⁰

In conclusion, both the GOLD B-C-D and II-III-IV classifications do not reflect well patients’ functionality in a broad sense. Despite low association and correlation coefficients in general, both GOLD classifications were better associated with functional exercise capacity (6MWT) than with subjectively assessed ADL and objectively assessed outcomes of physical activity/inactivity. Future longitudinal studies can be performed to identify the impact of improving functionality on the distribution of the GOLD A-B-C-D groups.

Footnotes

Author note

Joint first authorship: Both authors contributed equally to the study.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

References

Soriano

Lamprecht

. Chronic obstructive pulmonary disease: a worldwide problem. Med Clin North Am 2012; 96: 671–680.

Parr

. Patient phenotyping and early disease detection in chronic obstructive pulmonary disease. Proc Am Thorac Soc 2011; 8: 338–349.

Agusti

Calverley

Celli

. Characterisation of COPD heterogeneity in the ECLIPSE cohort. Respir Res 2010; 11: 122.

Vestbo

Agusti

Wouters

. Should we view chronic obstructive pulmonary disease differently after eclipse? A clinical perspective from the study team. Am J Respir Crit Care Med 2014; 189: 1022–1030.

Global Strategy for the Diagnosis, Management and Prevention of Chronic Obstructive Pulmonary Disease (GOLD), Revised 2011. Avaliable at: http://www.goldcopd.org (accessed 12 October 2014).

Rabe

Hurd

Anzueto

. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease: GOLD executive summary. Am J Respir Crit Care Med 2007; 176: 532–555.

Global Strategy for the Diagnosis, Management and Prevention of Chronic Obstructive Pulmonary Disease (GOLD), Updated 2013. Avaliable at: http://www.goldcopd.org (accessed 14 October 2014).

Lange

Marott

Vestbo

. Prediction of the clinical course of chronic obstructive pulmonary disease, using the new gold classification: a study of the general population. Am J Respir Crit Care Med 2012; 186: 975–981.

Han

Muellerova

Curran-Everett

. Gold 2011 disease severity classification in COPDGene: a prospective cohort study. Lancet Respir Med 2013; 1: 43–50.

10.

Agusti

Edwards

Celli

. Characteristics, stability and outcomes of the 2011 Gold copd groups in the eclipse cohort. Eur Respir J 2013; 42: 636–646.

11.

Johannessen

Nilsen

Storebo

. Comparison of 2011 and 2007 global initiative for chronic obstructive lung disease guidelines for predicting mortality and hospitalization. Am J Respir Crit Care Med 2013; 188: 51–59.

12.

Soriano

Alfageme

Almagro

. Distribution and prognostic validity of the new global initiative for chronic obstructive lung disease grading classification. Chest 2013; 143: 694–702.

13.

Leivseth

Brumpton

Nilsen

. GOLD classifications and mortality in chronic obstructive pulmonary disease: the hunt Study, Norway. Thorax 2013; 68: 914–921.

14.

Boland

Tsiachristas

Kruis

. Are gold abcd groups better associated with health status and costs than gold 1234 grades? A cross-sectional study. Prim Care Respir J 2014; 23: 30–37.

15.

Pitta

Takaki

Oliveira

. Relationship between pulmonary function and physical activity in daily life in patients with copd. Respir Med 2008; 102: 1203–1207.

16.

Vestbo

Hurd

Agusti

. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease: gold executive summary. Am J Respir Crit Care Med 2013; 187: 347–365.

17.

Miller

Hankinson

Brusasco

. Standardisation of spirometry. Eur Respir J 2005; 26: 319–338.

18.

Pereira

Sato

Rodrigues

. New reference values for forced spirometry in white adults in Brazil. J Bras Pneumol 2007; 33: 397–406.

19.

Rodriguez-Roisin

. Toward a consensus definition for COPD exacerbations. Chest 2000; 117: 398S–401S.

20.

ATS statement: guidelines for the six-minute walk test. Am J Respir Crit Care Med 2002; 166: 111–117.

21.

Troosters

Gosselink

Decramer

. Six minute walking distance in healthy elderly subjects. Eur Respir J 1999; 14: 270–274.

22.

Britto

Probst

de Andrade

. Reference equations for the six-minute walk distance based on a Brazilian multicenter study. Braz J Phys Ther 2013; 17: 556–563.

23.

Garrod

Bestall

Paul

. Development and validation of a standardized measure of activity of daily living in patients with severe copd: the London chest activity of daily living scale (LCADL). Respir Med 2000; 94: 589–596.

24.

Pitta

Probst

Kovelis

. Validation of the portuguese version of the london chest activity of daily living scale (LCADL) in chronic obstructive pulmonary disease patients. Rev Port Pneumol 2008; 14: 27–47.

25.

Vilaro

Gimeno

Sanchez Ferez

. Daily living activity in chronic obstructive pulmonary disease: validation of the Spanish version and comparative analysis of 2 questionnaires. Med Clin (Barc) 2007; 129: 326–332.

26.

Demeyer

Burtin

Van Remoortel

. Standardizing the analysis of physical activity in patients with COPD following a pulmonary rehabilitation program. Chest 2014; 146: 318–327.

27.

van Remoortel

Camillo

Langer

. Moderate intense physical activity depends on selected metabolic equivalent of task (MET) cut-off and type of data analysis. PLoS One 2013; 8: e84365.

28.

Garber

Blissmer

Deschenes

. American college of sports medicine position stand. quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc 2011; 43: 1334–1359.

29.

Dolan

Varkey

. Prognostic factors in chronic obstructive pulmonary disease. Curr Opin Pulm Med 2005; 11: 149–152.

30.

Casanova

Marin

Martinez-Gonzalez

. New gold classification: longitudinal data on group assignment. Respir Res 2014; 15: 1465–9921.

31.

Nishimura

Oga

Tsukino

. Reanalysis of the Japanese experience using the combined copd assessment of the 2011 gold classification. Respir Investig 2014; 52: 129–135.

32.

van Sluijs

Griffin

van Poppel

. A cross-sectional study of awareness of physical activity: associations with personal, behavioral and psychosocial factors. Int J Behav Nutr Phys Act 2007; 4: 53.

33.

Bauman

Reis

Sallis

. Correlates of physical activity: why are some people physically active and others not? Lancet 2012; 380: 258–271.

34.

Gimeno-Santos

Frei

Steurer-Stey

. Determinants and outcomes of physical activity in patients with COPD: a systematic review. Thorax 2014; 69 (8): 731–799.

35.

Troosters

. Physical inactivity in patients with copd: the next step is … action. Prim Care Respir J 2013; 22: 391–392.

36.

Garcia-Rio

Soriano

Miravitlles

. Frequency of multi-dimensional COPD indices and relation with disease activity markers. COPD 2013; 10: 436–443.

37.

Pitta

Breyer

Hernandes

. Comparison of daily physical activity between COPD patients from central europe and South America. Respir Med 2009; 103: 421–426.

38.

Casanova

Celli

Barria

. The 6-min walk distance in healthy subjects: reference standards from seven countries. Eur Respir J 2011; 37: 150–156.

39.

Kim

. Differences in classification of COPD group using COPD assessment test (CAT) or modified Medical Research Council (mMRC) dyspnea scores: a cross-sectional analyses. BMC Pulm Med 2013; 13: 35.

40.

Seemungal

Donaldson

Paul

. Effect of exacerbation on quality of life in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1998; 157: 1418–1422.

GOLD B-C-D groups or GOLD II-III-IV grades

Abstract

Keywords

Introduction

Methods

Subjects

Assessments

Lung function

Symptoms and exacerbations

Functional exercise capacity

Activities of daily living

Physical (in)activity in daily life

Statistical analysis

Results

Discussion

Footnotes

Author note

Funding

References