Prevalence of Physical Disability in Patients with Chronic Obstructive Pulmonary Disease and Associated Risk Factors

Abstract

Introduction: To analyze the prevalence of disability among patients with COPD as compared to people without this lung disease and to identify sociodemographic and health factors associated with these physical limitations. Methods: We performed a cross-sectional study based on data taken from the European Health Interview Survey for Spain (EHISS) 2009. The survey included adults aged 40 to 79 years (n = 13624). We identified patients with COPD using a direct question from the survey. The main study variable was disability, including basic activities of daily living (ADLs), instrumental activities (IADLs), and mobility disability (MD). Independent variables analyzed included socio-demographic characteristics, self-perceived health status, presence of mental disease and co-morbid chronic conditions and lifestyles. Results: The overall prevalence of self-reported COPD was 7.2%. The total prevalence of ADL, IADL and MD was higher among men suffering COPD than among the population without this disease (16.39% vs. 4.91%; 27.70% vs. 12.45%; 48.94% vs. 17.46% respectively). These significant differences were also observed among women with equivalent figures of: 23.25% vs. 8.71%; 31.03% vs. 10.53%; 64.83% vs. 34.08%. Being older, having a self-perceived health status of “fair/poor/very poor” and suffering from mental disease (anxiety and/or depression) were factors associated with a higher probability of reporting any disability in both men and women suffering from COPD. Conclusions: Higher rates of disability were seen among COPD patients compared to the general population. Among COPD patients older age, depression, anxiety and worse self-rated health were associated with higher disability.

Keywords :

• Activities
• chronic obstructive pulmonary disease
• disability
• mobidity
• sociodemographic factors.

Introduction

Chronic obstructive pulmonary disease (COPD) is a serious pathology with important global prevalence, between 4% and 11% (1). In this moment is in the fourth position global causes of death but in the near future is expected to be the third. COPD also represents a social and economic burden in the world, causing significant morbidity and disability in the population. Represents about one third of permanent work disability and is estimated to increase this data in the coming decades (1,2). Disability is a loss of skill to develop activities needed for independent living and self-care. Difficulties performing for activities of daily living (ADLs), instrumental activities of daily livings (IADLs) and mobility disability (MD) are the first to appear and, the most strongly associated with poorer quality of life and death (3).

There are many publications on disability-related factors. These studies conclude that disability has increased in recent decades by the aging population, associated co-morbidities and physical inactivity (3,4). Also, other authors have shown the relationship between disability and some chronic diseases, like diabetes and arthritis (5,6).

Some analyses have shown individuals with COPD have greater levels of disability than general population (7) and compared to people with other respiratory conditions (8). It causes a worse quality of life in these patients (9).

Although disability is common among individuals with COPD, relatively little is known about what co-morbidities or disease-related factors may influence the course of disability (10). Some investigation shows the relationship between mental disorders in COPD, such as anxiety or depression, (7), current smoking, fatigue (8, 11) and a higher degree of disability.

Currently the profile of COPD patients with greater disability is not completely understood. We need more research to try to reduce the impact of this large and growing public health problem because COPD will play a large role in the upcoming decades (12).

Our theoretical perspective is that patients with COPD would have more disability that persons without this disease and that those variables related to a worse physical or mental health would be associated to more disability among COPD patients.

The objectives of the current study were: a) to describe the prevalence of disability in Activities of daily living (ADL), Instrumental Activities of daily living (IADL) and Mobility disability (MD) according to socio-demographic characteristics, self-rated health status, co-morbidity, and lifestyle-related habits among COPD sufferers and compared to non-sufferers and b), to determine factors associated with these reported disabilities among men and women suffering from COPD.

Methods

The present study is a cross-sectional study based on data obtained from the European Health Interview Survey for Spain (EHISS, 2009), that was proposed by the European Commission to the European Union (EU) Member States (13).

For study purposes, subjects aged 40 to 79 years were selected. We identified individuals suffering COPD (chronic bronchitis or emphysema) as those that answered “yes” to the question, “Has your doctor told you that you are currently suffering from chronic bronchitis or emphysema?”

Information regarding functional disability was obtained from questions about distinct physical tasks in three functional domains. The questions covered: 1) Activities of daily living (ADL): bathing or showering, dressing and undressing, feeding yourself, getting in and out of a bed or chair and using the toilet; 2) Instrumental Activities of daily living (IADL): preparing meals, taking care of finances and everyday administrative tasks, doing light housework, managing medication and using the telephone; and, 3) Mobility disability (MD): Can you walk 500 meters on a flat terrain without a stick or other walking aid or assistance?, Can you walk up and down a flight of stairs without a stick, other walking aid, assistance or using the banister?, Can you bend and kneel down without any aid or assistance?, Using your arms, can you carry a shopping bag weighing 5 kilos for at least 10 meters without any aid or assistance? The questions chosen have been previously validated and used in other studies (3,5).

Participants were defined as having functional impairment in a particular domain if they answered “Yes, some difficulty,” “Yes, a lot of difficulty” or “I can't achieve it by myself” when they were asked whether they could do one or more of the specific tasks in these three domains.

We also analyzed socio-demographic characteristics such as age (40–59 years, and 60–79 years), educational level (no study, primary education completed, secondary education completed or more), marital status (married or living as a couple, unmarried/widow/divorced) employment status (Working or Unemployed or Retired/inactive) and monthly income (< 850 €; 850–1400 € and > 1400 €).

Self-perceived health status was assessed with the following question: “How did you self-perceive your health status over the previous 12 months?” Subjects described their health status as very good, good, fair, poor, or very poor, which was dichotomized into very good/good or fair/poor/very poor self-perceived health status.

The presence of mental disease was assessed using the following questions: 1) “Has your doctor told you that you are currently suffering from depression?” and, “Has your doctor told you that you are currently suffering from anxiety?” Those who answered yes to questions 1 and/or 2 were classified as “mental disease sufferers.”

We also collected the number of medical doctor diagnoses of co-morbid chronic conditions including: diabetes, high blood pressure, asthma, heart disease, myocardial infarction, cancer, arthritis and stroke. We analyzed the number of co-morbid diseases in three categories, namely: “None,” “One” and “Two or more.”

The body mass index (BMI) was also calculated from the self-reported body weight and height. Within lifestyle habits, alcohol consumption was measured using the question, “Have you consumed any alcoholic drinks during the last two weeks?” Smoking status was distinguished between current and ex-smokers/non-smokers. “No physical exercise” was deemed to apply to cases where the individuals in question acknowledged doing no physical activity in their free time.

Statistical methods

In this study we analyzed the disability separately for men and women and we excluded respondents with missing data for any disability outcome. We firstly analyzed descriptive measures for all variables of interest by age-group. Second, we compared reported prevalence for each aspect of disability and age group according to COPD status. To perform bivariate comparisons, we used the two-sided independent t-tests for continuous variables and chi- square statistics for categorical variables. Third, for each aspect of disability, and only among those suffering COPD, we then fit logistic regression models for each sex to assess the relative odds ratio of each aspect of disability.

The multivariate logistic regression model was built using the “enter modelling” method. The process included 4 steps: (1) Bivariate analysis of each variable; (2) Selection of variables for the multivariate analysis. We included all variables whose bivariate test results were statistically significant and those we considered scientifically relevant according to the references reviewed; (3) In order to ensure the fit of the multivariate model, the importance of each variable included was verified by examining the Wald statistic and comparing each estimated coefficient with the coefficient from the bivariate model containing only that variable. Variables that did not contribute to the model based on these criteria were eliminated and a new model was fitted. The new model was compared with the old model using the log-rank test. This process of deleting, refitting, and verifying continued until all the important variables were included in the model; (4) Once the model was constructed, we looked more closely at the variables included (linearity) and checked for interactions. The results of the logistic models were shown as adjusted odds ratios (ORs) with 95% confidence intervals.

The estimates were made using the “svy” (survey command) functions of the STATA program (version 11), which allowed us to incorporate the study design and weights in all our statistical calculations. Statistical significance was established at p < 0.05 (two-tailed p-values).

As this investigation was conducted using de-identified public-use databases, it was not necessary to have the approval of an ethics committee, as per Spanish legislation.

Results

The total number of subjects aged 40–79 years included in the study was 13,624 (7,512 woman and 6,112 men). The overall prevalence of self-reported COPD was 7.20% (95% CI 6.7 to7.74). The prevalence among those aged 40–59 was 4.8% (95% CI 4.23 to 5.41) and 11.1% (95% CI 10.2 to 12.11) among those aged 60–79 (p < 0.001).

Tables 1 and 2 show the distribution by socio-demographic features and health related variables among men and women included in the study population and also divided by age group and according COPD status. The prevalence of COPD among men was 7.4% (95% CI 6.4–8.2) and among women 7% (95% CI 6.1–7.8) (p = 0.468).

Table 1.  Descriptive statistics for men by age group and according to presence of COPD

		Age Group
		40–59 years				60–79 years
		COPD				COPD
		Yes		No		Yes		No
Variables	Categories^#	N	%	N	%	N	%	N	%
Educational level *α	Primary education completed	59	33.8	838	25,9	112	34.3	793	33.8
	Seconary education completed or more	88	53.8	2405	67.9	64	21.4	757	38.0
Marital status *	Married or living with couple	103	72.6	2463	77.3	225	81.3	1606	83.1
Employment status *	Unemployed	30	14.4	424	12.8	11	3.4	79	4.1
	Retired or inactive	41	23.0	538	16.0	253	79.2	1702	75.3
Monthly income (Euros) α	850–1400	37	20.8	643	21.3	89	32.7	600	34.3
	> 1400	81	68.6	1925	70.1	89	36.4	746	47.4
Self-rated health * α	Fair/poor/very poor	84	48.0	787	23.1	230	76.6	921	41.8
Mental disease * α	Yes	12	6.2	116	3.3	24	9.4	101	4.0
No. of chronicconditions* α	1	56	29.1	739	21.2	95	29.9	760	34.3
	≥2	37	25.6	194	5.5	144	50.4	550	25.5
BMI * α	≥30	45	28.8	664	20.4	84	30.1	440	21.5
Alcohol consumption *	Yes	84	55.9	1551	45.8	131	45.5	1044	49.6
Smoking habits *α	Current smokers	83	49.7	1351	38.9	77	22.1	428	18.3
Physical exercise α	Yes	71	48.3	1586	47.2	76	25.2	804	39.0

*Significant differences between those with and without COPD aged 40–59 years.

^αSignificant differences between those with and without COPD aged 60–79 years.

^#Reference category for study variables (not shown): No Studies; Unmarried/widow/divorced; Working; <850; Very good/good; No; None; < 30; No; Non or ex-smokers; No

Table 2.  Descriptive statistics by age group for women according to presence of COPD

		Age Group
		40-59 years				60-79 years
		COPD				COPD
		Yes		No		Yes		No
Variables	Categories^#	N	%	N	%	N	%	N	%
Educational level *α	Primary education completed	52	24.8	914	23.7	100	27.1	1186	35.9
	Seconary education completed or more	109	57.1	2665	69.0	63	19.5	699	24.2
Marital status	Married or living with couple	117	67.4	2565	74.1	165	57.7	1550	61.6
Employment status *	Unemployed	35	16.0	435	12.1	11	4.6	109	4.7
	Retired or inactive	51	26.7	752	20.0	301	83.4	2590	78.8
Monthly income (Euros)* α	850-1400	55	37.0	759	23.6	84	26.5	810	33.5
	> 1400	75	47.8	1945	66.2	90	36.4	897	40.5
Self-rated health * α	Fair/poor/very poor	117	59.6	1122	28.8	282	82.5	1795	57.7
Mental disease *α	Yes	48	22.3	359	8.6	87	22.5	493	14.4
No. of chronicconditions *α	1	74	38.2	737	19.6	118	29.6	1203	39.8
	≥2	38	21.0	165	4.2	165	50.0	744	22.5
BMI *α	≥30	49	22.1	505	14.7	107	38.8	638	23.7
Alcohol consumption	Yes	26	15.2	707	18.4	43	11.6	466	16.2
Smoking habits	Current smokers	73	34.6	1180	30.1	20	6.0	189	6.7
Physical exercise α	Yes	101	52.2	1949	55.0	120	34.4	1292	45.0

* Significant differences between those with and without COPD aged 40–59 years.

^α Significant differences between those with and without COPD aged 60–79 years.

^# Reference category for study variables (not shown): No Studies; Unmarried/widow/divorced; Working; <850; Very good/good; No; None; < 30; No; Non or ex-smokers; No

Among men and women, and in both age groups analyzed, those suffering from COPD had a significantly lower educational level, worse self-rated health status and a higher prevalence of mental disorder, chronic conditions and obesity. Among men current tobacco use was also higher among COPD sufferers. In the 60–79-year age group both men and women suffering COPD reported engaging in physical exercise significantly less that those without the disease.

The prevalence of each aspect of disability by age-group and sex according to COPD status are summarized in Table 3. Overall, women showed a higher prevalence of both ADL and MD disability compared to men regardless of COPD status. The differences in IADL prevalence were significant only for those patients suffering from COPD. For both sexes, and among those with and without COPD, the prevalence of all disabilities was significantly higher among the older age group.

Table 3.  Prevalence of basic activities of daily living disability (ADL), instrumental activities of daily living disability (IADL) and mobility disability (MD) by sex and age group according to COPD status

			COPD
			Yes		No
	Disability	Age group	n	%	n	%	p-value
Men	ADL *α	40-59	13	8.2	83	2.6	< 0.001
	60-79	66	21.8	206	9.5	< 0.001
	Total	79	16.4	289	4.9	< 0.001
	IADL *	40-59	24	12.7	262	8.3	0.010
	60-79	116	37.5	464	20.6	< 0.001
	Total	140	27.7	726	12.5	< 0.001
	MD *α	40-59	44	25.7	357	9.8	< 0.001
	60-79	192	64.2	724	32.3	< 0.001
	Total	236	48.9	1081	17.5	< 0.001
Women	ADL	40-59	24	11.6	149	3.5	< 0.001
	60-79	109	31.9	520	17.0	< 0.001
	Total	133	23.3	669	8.7	< 0.001
	IADL	40-59	36	16.9	175	4.5	< 0.001
	60-79	142	41.5	607	20.0	< 0.001
	Total	178	31.0	782	10.5	< 0.001
	MD	40-59	90	41.8	712	17.9	< 0.001
	60-79	279	81.9	1874	59.6	< 0.001
	Total	369	64.8	2586	34.1	<0.001

p-values for comparison of the prevalence of disabilities between those with and without COPD.

*Significant difference when comparing the age adjusted prevalence of disabilities between men and women with COPD.

^αSignificant difference when comparing the age adjusted prevalence of disabilities between men and women without COPD.

The total prevalence of ADL, IADL and MD were higher among men suffering from COPD than among those without this disease (16.4% vs. 4.9%; 27.7% vs. 12.45%; 49% vs. 17.5% respectively). These significant differences are also observed among women with equivalent figures of: 23.3% vs. 8.7%; 31% vs. 10.5%; 64.8% vs. 34.1% (Table 3).

The results of the multivariate analysis carried out to estimate factors associated with disability among men and women suffering from COPD are shown in Tables 4 and 5. There are three variables that are associated with a higher probability of reporting ADL disability, IADL disability and MD in both men and women. These factors are: being older (for ADL disability, OR 1.4 −95% CI 0.6 to 3.2- in men and 2.9 −95% CI 1.6 to 5.1- in women; for IADL disability, OR 2.3 −95% CI 1.1 to 4.6- in men and 1.3 –95% CI 0.6 to 2.6- in women; for MD, OR 2.3 −95% CI 1.4 to 2.6- in men and 5.4 −95% CI 3.0 to 9.7- in women); having a self-perceived health status of “fair/poor/very poor” (for ADL disability, OR 17.0 −95% CI 5.4 to 53.7- in men and 25.4 −95% CI 7.1 to 90.8- in women; for IADL disability, OR 4.9 −95% CI 2.5 to 9.3- in men and 9.2 −95% CI 3.7 to 22.6- in women; for MD, OR 7.7 −95% CI 3.9 to 15.5- in men and 8.0 −95% CI 4.2 to 15.2- in women); and suffering from a mental disease (for ADL disability, OR 3.0 −95% CI 1.2 to 7.6- in men and 2.2 −95% CI 1.3 to 3.8- in women; for IADL disability, OR 4.0 −95% CI 1.6 to 9.9- in men and 2.4 −95% CI 1.4 to 4.3- in women; for MD, OR 5.3 −95% CI 1.6 to 17.7- in men and 2.8 −95% CI 1.3 to 6.3- in women).

Table 4.  Results of Logistic Regression Models for Disabilities (ADL, IADL and MD) among men suffering COPD

		Men
		ADL	IADL	MD
Variable	Categories*	OR (95% CI)	OR (95% CI)	OR (95% CI)
Age	60–79 years	1.4(0.6–3.2)	2.3(1.1–4.6)	2.3(1.2–4.6)
Educational level	Primary education completed	0.5(0.3–1.0)	0.8(0.4–1.6)	0.3(0.1–1.3)
	Secondary education completed or more	0.3(0.1–0.7)	0.5(0.2–1.2)	0.2(0.1–1.1)
Employment status	Unemployed	0.4(0.1–2.2)	0.2(0.1–0,9)	1.2(0.5–3.2)
	Retired or inactive	0.8(0.3–2.0)	1.5(0.8–3.1)	2.19(1.1–4.2)
Self-rated health	Fair/poor/very poor	17.0(5.4–53.7)	4.9(2.5–9.3)	7.7(3.9–15.5)
Mental disease	Yes	3.0(1.2–7.6)	4.0(1.6–9.9)	5.3(1.6–17.7)
No. of chronicconditions	1	0.5(0.2–1.4)	2.1(0.9–4.3)	1.2(0.6–2.3)
	≥2	0.8(0.4-2.1)	1.9(0.9-4.6)	2.2(1.0–4.6)
Physical exercise	No	0.7(0.3–1.5)	1.2(0.6–2.0)	2.3(1.3–4.2)

Variable included in the model are those shown in the table.

*Reference category not shown: 40–59 years; No studies; Working; Very good/good; No; None; Yes.

Table 5.  Results of Logistic Regression Models for Disabilities (ADL, IADL and MD) among women suffering COPD

		Women
		ADL	IADL	MD
Variable	Categories*	OR (95% CI)	OR (95% CI)	OR(95% CI)
Age	60–79 years	2.9(1.6–5.1)	1.3(0.6–2.6)	5.4(3.0–9.7)
Marital status	Married or living with couple	1.0(0.6–1.7)	1.1(0.6–1.9)	1.9(1.1–3.4)
Employment status	Unemployed	1.2(0.3–4.4)	2.1(0.6–6.8)	1.1(0.3–3.5)
	Retired or inactive	1.9(0.8–4.5)	3.2(1.5–6.9)	0.9(0.4–1.9)
Self-rated health	Fair/poor/very poor	25.4(7.1–90.8)	9.2(3.7–22.6)	8(4.2–15.2)
Mental disease	Yes	2.2(1.3–3.8)	2.4(1.4–4.3)	2.8(1.3–6.3)
No. of chronicconditions	1	1.5(0.6–3.5)	2.3(0.9–5.4)	1.6(0.8–3.4)
	≥2	1.6(0.7–3.5)	3.3(1.4–7.5)	1.7(0.8–3.9)
BMI	≥30	0.8(0.4–1.7)	1.3(0.8–2.3)	3.5(1.9–6.4)
Physical exercise	No	1.6(0.5–5.8)	4.8(2.7–8.6)	1.2(0.7–2.3)

Variables included in the model are those shown in the table.

* Reference category: 40–59 years; Unmarried/widow/divorced; Working; Very good/good; No; None; < 30;Yes.

In addition to the three variables described above, ADL disability was independently and significantly associated with a lower educational level among men suffering from COPD (Table 4). IADL disability was also associated with employment status, the highest odds ratio was associated with those patients who were retired or inactive. Finally, the factors that increased the probability of MD included: being retired or inactive, having a higher number of associated chronic conditions and not engaging in physical exercise.

Among women suffering COPD the factors associated with ADL only included the three variables mentioned above. Being retired or inactive, having a higher number of associated chronic conditions and not engaging in physical exercise were significant factors in IADL. Mobility disability among women was associated with being Married or living as a couple and having a BMI > 30.

Discussion

We have found a higher prevalence of disability among COPD patients when compared to non-sufferers, as reported in previous studies (7, 8, 15, 16, 17). The main strength of this study is the use of a representative sample, 13,624 individuals, on a national level.

A relationship between socio-demographic factors and COPD has been shown. It has previously been proven that age has a synergistic effect on the diagnosis of COPD (10). Also, a past multicenter study showed patients with greater disability (the “weakest”) were older (17). In our study, we found a higher prevalence of COPD in patients over 60 years and we showed that this age increased the risk of disability in COPD. It increased mobility disability 5 times in women and twice in men.

Although COPD has been described most frequently in men (18, 20), in our study there were no differences in sex. This may be a response to the increase in smoking by women (19, 20). No previous studies had found sex differences; however, a new finding of our investigation was that women with COPD had higher levels of disability than men with this disease.

Other socio-demographic factors are associated with disability with this pathology. Some studies have shown the association between lower socioeconomic status and greater disability (17). In our study we did not find a relationship between socioeconomic status and disability. However, we observed that retired or inactive men and women had a greater prevalence of disability. This finding could be explained by the fact that these patients are more sedentary than working people.

Also, we found people suffering from COPD had a significantly lower educational level (18). This could be due to the fact that smoking is more common among people with a lower socioeconomic status (17). However, there was no relationship between disability in COPD and level of education.

An association between co-morbidity and disability in COPD has been shown in previous studies (17, 20). In a past multicenter study (EIME), investigators showed that about 70% of COPD patients with a disability had at least one other chronic disease. In our investigation, patients with one or more chronic disease had a greater prevalence of disability.

Prevalence estimates for anxiety and depression among COPD patients vary widely but are generally higher than those reported in some other advanced chronic diseases (7,21,22). In this investigation anxiety and depression were associated with greater disability in our COPD patients. These mental disorders increased mobility disability 5 times in men with COPD.

In this study, the factor most strongly associated with disability in COPD was poor self-assessed health. It increased the prevalence of disability 25 times in women. This could be explained by the high prevalence of depression among women. It is known that patients suffering from COPD have a higher prevalence of worse self-rated health (23), but the association with disability seen in our study is a new finding.

Most studies show that disability in COPD affects mandatory activities. However, in our study, mobility disability was the most affected. This fact could be explained by COPD patients having low levels of physical activity, especially patients aged over 60.

This study has potential limitations. It is a cross-sectional study, so the study does not answer the question of whether COPD causes physical disability or whether the perception of somatic symptoms could be worsened by previous physical disability. Nonetheless, a series of variables independently associated with the existence of disability in adults with COPD have been identified. Another limitation is that COPD diagnosis and co-morbidities were based on self-reporting and it was not collected the treatment (pharmacological, use of respirators, oxygen therapy.) of the disease. Thus, some individuals may have been classified into the wrong disorder group. However, it is probably that such misclassification would tend to attenuate differences among the groups, biasing our results toward null findings. Anyway, it has been shown that self-report-based surveys are an appropriate way to study respiratory diseases in healthcare professionals (24). Furthermore, many studies of COPD and associated co-morbidities have used self-reports (25–27).

Finally, the initial response rate for the EHISS was 64% so the existence of a non-response bias must be considered. Published data showed that the non-response was higher for both men and women on the age group of less than 40 years, and among immigrants. Since that time, we have collected in our study subjects 40–79 years and immigrants are also a young population in Spain, so we would expect that the possible impact of the non-response bias would be small. (28)

In conclusion, this study demonstrates that patients with COPD have a higher prevalence of disability compared to the general population. The factors associated with worse disability scores among COPD sufferers are: age over 60 years, suffering anxiety or depression and a poor self-rated health status.

Declaration of Interests Statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.