The evaluation of retinal and choroidal structural changes by optical coherence tomography in patients with chronic obstructive pulmonary disease

Retinal Nerve Fiber Layer Changes in Patients With Chronic Obstructive Pulmonary Disease Compared to Healthy Controls: A Meta-analysis

BACKGROUND AND OBJECTIVE

This study investigated changes in retinal nerve fiber layers (RNFL) in patients diagnosed with chronic obstructive pulmonary disease (COPD) compared to healthy control patients, using optical coherence tomography.

METHODS

PubMed, Cochrane Library, and Google Scholar databases were systematically searched for published articles comparing RNFL between patients with COPD and healthy controls. Standardized mean difference (SMD) with 95% confidence interval (CI) was computed to compare continuous variables.

RESULTS

Average RNFL thickness was significantly reduced in COPD patients compared to healthy controls (SMD = -0.31, 95% CI = -0.48 to -0.14, P = 0.0004, I2 = 0%). Average RNFL thickness did not differ significantly between patients with mild/moderate COPD and healthy controls (SMD = -0.17, 95% CI = -0.39 to 0.04, P = 0.12, I2 = 2%), while a statistically significant reduction in average RNFL thickness was noticed in patients with severe COPD compared to healthy controls (SMD = -0.72, 95% CI = -1.23 to -0.21, P = 0.006, I2 = 83%). Average RNFL thickness was significantly higher in patients with mild/moderate COPD compared to patients with severe COPD (SMD = 0.69, 95% CI = 0.29 to 1.09, P = 0.0008, I2 = 66%).

CONCLUSIONS

This meta-analysis showed that RNFL thickness was decreased in patients with COPD compared to healthy controls. Patients diagnosed with severe COPD seem to be more affected and have thinner RNFL. [Ophthalmic Surg Lasers Imaging Retina 2024;55:334-342.].

Phenome- and genome-wide analyses of retinal optical coherence tomography images identify links between ocular and systemic health

The human retina is a multilayered tissue that offers a unique window into systemic health. Optical coherence tomography (OCT) is widely used in eye care and allows the noninvasive, rapid capture of retinal anatomy in exquisite detail. We conducted genotypic and phenotypic analyses of retinal layer thicknesses using macular OCT images from 44,823 UK Biobank participants. We performed OCT layer cross-phenotype association analyses (OCT-XWAS), associating retinal thicknesses with 1866 incident conditions (median 10-year follow-up) and 88 quantitative traits and blood biomarkers. We performed genome-wide association studies (GWASs), identifying inherited genetic markers that influence retinal layer thicknesses and replicated our associations among the LIFE-Adult Study (N = 6313). Last, we performed a comparative analysis of phenome- and genome-wide associations to identify putative causal links between retinal layer thicknesses and both ocular and systemic conditions. Independent associations with incident mortality were detected for thinner photoreceptor segments (PSs) and, separately, ganglion cell complex layers. Phenotypic associations were detected between thinner retinal layers and ocular, neuropsychiatric, cardiometabolic, and pulmonary conditions. A GWAS of retinal layer thicknesses yielded 259 unique loci. Consistency between epidemiologic and genetic associations suggested links between a thinner retinal nerve fiber layer with glaucoma, thinner PS with age-related macular degeneration, and poor cardiometabolic and pulmonary function with a thinner PS. In conclusion, we identified multiple inherited genetic loci and acquired systemic cardio-metabolic-pulmonary conditions associated with thinner retinal layers and identify retinal layers wherein thinning is predictive of future ocular and systemic conditions.

Investigation of ocular microstructural changes according to disease severity in patients with chronic obstructive pulmonary disease

OBJECTIVE

To investigate retinal nerve fibre layer (RNFL) thickness and vascular density alterations in the retina and optic disc in patients with chronic obstructive pulmonary disease (COPD).

METHODS

A total of 66 COPD patients and 54 age- and sex-matched healthy individuals were enrolled in this prospective cross-sectional study. The COPD patients were divided into 3 subgroups (mild, moderate, and severe COPD) based on spirometric parameters as per the Global Initiative for Chronic Obstructive Lung Disease guideline. RNFL thickness, foveal avascular zone area, and vessel density in the superficial capillary plexus, deep capillary plexus, and radial peripapillary capillary plexus were measured by optical coherence angiography and compared among groups.

RESULTS

There was no significant difference between COPD patients and control individuals in terms of foveal avascular zone area or RNFL thickness (p = 0.891 and p = 0.896, respectively). Patients with severe COPD showed lower vessel density in the superficial capillary plexus compared with the other groups, but the difference was not significant (p > 0.05). In the deep capillary plexus, vessel density did not differ significantly among groups in the foveal region (p > 0.05) but was significantly lower in all parafoveal quadrants in the severe COPD group. Radial peripapillary capillary plexus vessel density also was lower in the severe COPD group, especially the peripapillary region (p = 0.044).

CONCLUSION

Although COPD is primarily a lung disease, the eye seems to be among the tissues affected in its natural course. The effects are more pronounced in patients with severe COPD and in the deep capillary plexus and radial peripapillary capillary plexus.

Association of retinal microvascular density and complexity with incident coronary heart disease

BACKGROUND AND AIMS

The high mortality rate and huge disease burden of coronary heart disease (CHD) highlight the importance of its early detection and timely intervention. Given the non-invasive nature of fundus photography and recent development in the quantification of retinal microvascular parameters with deep learning techniques, our study aims to investigate the association between incident CHD and retinal microvascular parameters.

METHODS

UK Biobanks participants with gradable fundus images and without a history of diagnosed CHD at recruitment were included for analysis. A fully automated artificial intelligence system was used to extract quantitative measurements that represent the density and complexity of the retinal microvasculature, including fractal dimension (Df), number of vascular segments (NS), vascular skeleton density (VSD) and vascular area density (VAD).

RESULTS

A total of 57,947 participants (mean age 55.6 ± 8.1 years; 56% female) without a history of diagnosed CHD were included. During a median follow-up of 11.0 (interquartile range, 10.88 to 11.19) years, 3211 incident CHD events occurred. In multivariable Cox proportional hazards models, we found decreasing Df (adjusted HR = 0.80, 95% CI, 0.65-0.98, p = 0.033), lower NS of arteries (adjusted HR = 0.69, 95% CI, 0.54-0.88, p = 0.002) and venules (adjusted HR = 0.77, 95% CI, 0.61-0.97, p = 0.024), and reduced arterial VSD (adjusted HR = 0.72, 95% CI, 0.57-0.91, p = 0.007) and venous VSD (adjusted HR = 0.78, 95% CI, 0.62-0.98, p = 0.034) were related to an increased risk of incident CHD.

CONCLUSIONS

Our study revealed a significant association between retinal microvascular parameters and incident CHD. As the lower complexity and density of the retinal vascular network may indicate an increased risk of incident CHD, this may empower its prediction with the quantitative measurements of retinal structure.

Alterations of Macular Structure in Non-Glaucomatous Subjects With Obstructive Pulmonary Function

Purpose

The purpose of this study was to identify possible associations between obstructive pulmonary function and macular structure parameters on optical coherence tomography (OCT) and angiography in subjects without glaucomatous optic neuropathy.

Methods

A total of 70 patients were prospectively enrolled from June to December 2021 as a part of All About Life Yongin-Pulmonary/Psychiatry, Rehabilitation, Eye (AALY PRE) cohort in Yongin Severance Hospital. Patients underwent intraocular pressure (IOP), visual acuity measurements, cirrus OCT, OCT angiography, and pulmonary function testing (PFT) on the same day. Subjects with glaucomatous optic nerve damage were excluded. Those whose first second of forced expiration (FEV1) to forced vital capacity (FVC) ratio was below 70% were diagnosed with obstructive pulmonary function. Vessel densities (VDs) of retinal superficial vascular plexus were compared.

Results

Patients with obstructive function (n = 30) were significantly older than those with normal pulmonary function (n = 40, P < 0.001). After adjusting for age, IOP, and average ganglion cell-inner plexiform layer (GCIPL) thickness, macular VD was significantly decreased in all sectors except for the nasal sector in subjects with obstructive pulmonary function in comparison to those with normal function (P = 0.006). Multivariate regression analysis demonstrated that macular VD was linearly associated with FEV1/FVC (β = 0.102, P = 0.031). In subjects with obstructive function, the severity of pulmonary obstruction, FEV1, was linearly associated with GCIPLT (β = 0.302, P = 0.017).

Conclusions

Obstructive pulmonary function is associated with reduced macular VD in subjects without glaucoma. Among subjects with obstructive pulmonary function, the severity of pulmonary obstruction is associated with GCIPL thickness in the macular region. Further studies are needed on the relationship between pulmonary function and macular disease.

Insights into human health from phenome- and genome-wide analyses of UK Biobank retinal optical coherence tomography phenotypes

The human retina is a complex multi-layered tissue which offers a unique window into systemic health and disease. Optical coherence tomography (OCT) is widely used in eye care and allows the non-invasive, rapid capture of retinal measurements in exquisite detail. We conducted genome- and phenome-wide analyses of retinal layer thicknesses using macular OCT images from 44,823 UK Biobank participants. We performed phenome-wide association analyses, associating retinal thicknesses with 1,866 incident ICD-based conditions (median 10-year follow-up) and 88 quantitative traits and blood biomarkers. We performed genome-wide association analyses, identifying inherited genetic markers which influence the retina, and replicated our associations among 6,313 individuals from the LIFE-Adult Study. And lastly, we performed comparative association of phenome- and genome- wide associations to identify putative causal links between systemic conditions, retinal layer thicknesses, and ocular disease. Independent associations with incident mortality were detected for photoreceptor thinning and ganglion cell complex thinning. Significant phenotypic associations were detected between retinal layer thinning and ocular, neuropsychiatric, cardiometabolic and pulmonary conditions. Genome-wide association of retinal layer thicknesses yielded 259 loci. Consistency between epidemiologic and genetic associations suggested putative causal links between thinning of the retinal nerve fiber layer with glaucoma, photoreceptor segment with AMD, as well as poor cardiometabolic and pulmonary function with PS thinning, among other findings. In conclusion, retinal layer thinning predicts risk of future ocular and systemic disease. Furthermore, systemic cardio-metabolic-pulmonary conditions promote retinal thinning. Retinal imaging biomarkers, integrated into electronic health records, may inform risk prediction and potential therapeutic strategies.

Evaluation of the impact of COPD severity grading and oxygen saturation on the retinal nerve fiber layer thickness and subfoveal choroidal thickness in COPD patients

Background

Retinal and choroidal blood vessels are involved in many systemic diseases because they are complex vascular systems. Chronic obstructive pulmonary disease is considered as an inflammatory disease that affects many systems and coexists with several co-morbidities. Systemic inflammation and hypoxia affect the macula, choroid, retinal nerve fiber layer (RNFL), and blood vessels. Ocular co-morbidities have been detected in COPD patients. These can be quantitatively and qualitatively evaluated by Spectral Domain Optical Coherence Tomography (SD-OCT). Enhanced depth imaging OCT (EDI-OCT) is a quite new technique that utilizes light with an extended wavelength. An apparent relation has been found between chronic pulmonary disease and low corneal endothelial cell density preoperatively. So this work aimed to assess the impact of COPD severity grading and oxygen saturation on retinal nerve fiber layer thickness and subfoveal choroidal thickness.

Results

This was a case-control study, recruited 50 COPD patients and another 50 healthy volunteers as a control group. Measuring the thickness of the RNFL (superior, inferior, nasal, and temporal) in the four quadrants as well as the subfoveal choroidal thickness was done to both groups. The RNFL thickness in all quadrants and the SFCT in the COPD group were statistically significantly thinner in comparison to the control group. The RNFL thickness (mean) was 79.16 ± 10.49 μm compared to 96.30 ± 4.66 μm in the control group (p value 0.001). The SFCT (mean) was 213.12 ± 25.61 μm compared to 354.62 ± 53.82 μm in the control group (p value 0.001). The degree of thinning of the RNFL (superior, inferior, and temporal) and the SCFT was related to COPD (GOLD) stages severity (p value 0.001). Nasal RNFL was thinned out in all stages of COPD (GOLD) but with no statistical significance (p value 0.264).

Conclusion

The choroid and retina seem to be of the affected tissues during the progressive inflammatory course of COPD. Ocular pathologies should be evaluated in patients with systemic hypoxia. The eye examination for COPD patients can be carried out via a non-invasive procedure such as the OCT and the changes in the RNFL and SFCT thickness could be used as indicators for the severity of COPD.

Retinal Vascular Changes in Patients with Chronic Obstructive Pulmonary Disease: An Optical Coherence Tomography Angiography Study

Objectives:

In the current study, we aimed to investigate retinal vascular density and blood flow changes in patients with chronic obstructive pulmonary disease (COPD) using optical coherence tomography angiography (OCTA) (AngioVue Avanti, Optovue).

Methods:

Thirty eyes of 30 patients with COPD and 30 eyes of 30 healthy controls were evaluated with OCTA. Foveal and parafoveal vessel density, inner retinal and choriocapillary flow area, and foveal avascular zone (FAZ) area were measured and compared between the groups.

Results:

No statistically significant differences were observed in the outer retinal flow area and choriocapillary flow area measurements between the groups (p=0.609 and p=0.162, respectively). There was no statistically significant difference in FAZ and FAZ perimeter values between the groups (p=0.725 and p=0.820, respectively). Vascular density measurements in the superficial foveal and parafoveal areas were not statistically significantly different between the groups (p>0.05, for all). Deep parafoveal vascular density values of the COPD group were statistically significantly lower than the control group in all investigated areas except the superior and inferior quadrants.

Conclusion:

The results of our study demonstrated for the first time that vascular density decreased in the parafoveal area due to COPD-related hypoxemia and endothelial dysfunction.

Retinochoroidal vascular plexuses in patients with iron deficiency anaemia

Clinical relevance: Optical coherence tomography angiography (OCT-A) may enable the identification of alteration in the retinochoroidal microvasculature in patients with iron deficiency anaemia.Background: To investigate the presence of macular microvascular alterations in females with IDA by using OCT-A.Methods: This is a cross-sectional comparative study. Forty patients with IDA and 35 age-matched healthy women underwent a complete ophthalmologic examination and OCT-A imaging. Foveal avascular zone parameters and the vessel density in the superficial (SCP) and deep capillary plexus (DCP) were calculated using automated software. All measurements were compared between groups. Correlations between the OCT-A metrics and haematological laboratory parameters were evaluated.Results: Compared to healthy subjects, IDA patients revealed significantly decreased vessel density of the SCP in all parafoveal quadrants (p < 0.05). In contrast, vessel density analysis in DCP has shown no statistically significant difference in all parafoveal quadrants (p > 0.05). Although foveal vessel density in both SCP and DCP were higher in the IDA group, only the foveal vessel density in DCP was significantly higher than controls (p = 0.001). The mean values of the foveal avascular zone area and perimeter and choriocapillaris flow area were significantly lower in the IDA group (p < 0.05). The parafoveal vessel density in SCP, foveal avascular zone area, and choriocapillaris flow area were positively correlated with haematological parameters including haemoglobin, haematocrit, mean corpuscular haemoglobin, and mean corpuscular volume (p < 0.01).Conclusion: Patients with IDA had decreased parafoveal vessel density in the SCP, but not the DCP. Foveal avascular zone metrics and choriocapillaris flow area measurements were significantly lower in IDA.

Peripapillary vascular density and retinal nerve fibre layer changes in patients with chronic obstructive pulmonary disease

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a systemic disease which may cause end organ damage.

OBJECTIVES

In this study, we aimed to investigate the radial peripapillary capillary (RPC) density and retinal nerve fibre layer (RNFL) thickness changes in patients with COPD.

METHODS

The right eyes of 35 patients with COPD and 35 healthy controls were evaluated with optical coherence tomography angiography (OCTA). RPC density values and RNFL thicknesses were measured and compared.

RESULTS

The mean inside disc vascular density and the mean peripapillary vascular density values were lower in the COPD group (p = 0.002, p < 0.001, respectively). When the peripapillary area was evaluated independently as eight different quadrants, the RPC density values were lower in the COPD group in all of the quadrants except superotemporal and temporal superior quadrants. RNFL was thinner in all quadrants in the COPD group compared to the control group. But this difference was significant only in the nasal superior and inferonasal quadrants (p = 0.03, p = 0.04, respectively). Although, there was no correlation between the mean RPC density and the mean peripapillary RNFL thickness of the patients, FEV1 values for all patients were found to be correlated with the mean peripapillary RPC density (r = 0.406, p = 0.015).

CONCLUSION

OCTA may have a potential to be used in the follow-up of COPD patients.

Retinal vascular tortuosity: Mechanisms and measurements

Retinal vessel tortuosity has been used in the diagnosis and management of different clinical situations. Notwithstanding, basic concepts, standards and tools of measurement, reliable normative data and clinical applications have many gaps or points of divergence. In this review we discuss triggering causes of retinal vessel tortuosity and resources used to assess and quantify it, as well as current limitations.

Digit ratio as a risk factor for muscle dysfunction and acute exacerbation in patients with chronic obstructive pulmonary disease

Objective

This study investigated the correlations of digit ratio (relative length of second and fourth fingers, 2D: 4D) and muscular strength with the progression of chronic obstructive pulmonary disease (COPD).

Methods

In total, 164 patients with COPD were enrolled in this prospective study. In all patients, the following parameters were measured: body compartments, pulmonary function, digit ratio (i.e., 2D: 4D), muscle function, and levels of partial pressure of oxygen and partial pressure of carbon dioxide in arterial blood.

Results

The right-hand digit ratio (R2D: 4D) was associated with dominant hand muscle dysfunction, non-dominant hand muscle dysfunction, and inspiratory muscle dysfunction. Logistic regression analysis showed that right-hand 2D: 4D (odds ratio [OR] = 0.01) and dominant hand muscle dysfunction (OR = 5.60) were significantly associated with past hospital admission. After adjustment for forced expiratory volume in 1 second, the following factors were associated with present acute exacerbations: right-hand 2D: 4D (OR = 0.01), dominant hand muscle dysfunction (OR = 3.83), expiratory muscle dysfunction (OR = 3.80), and inspiratory muscle dysfunction (OR = 3.61).

Conclusions

Lower digit ratio may be associated with higher prevalence of muscle dysfunction. This factor could be used to identify patients with COPD who are at higher risk of acute exacerbation.

Simple non-mydriatic retinal photography is feasible and demonstrates retinal microvascular dilation in Chronic Obstructive Pulmonary Disease (COPD)

BACKGROUND

Chronic Obstructive Pulmonary Disease (COPD) is associated with an increased risk of myocardial infarction and stroke but it remains unclear how to identify microvascular changes in this population.

OBJECTIVES

We hypothesized that simple non-mydriatic retinal photography is feasible and can be used to assess microvascular damage in COPD.

METHODS

Novel Vascular Manifestations of COPD was a prospective study comparing smokers with and without COPD, matched for age. Non-mydriatic, retinal fundus photographs were assessed using semi-automated software.

RESULTS

Retinal images from 24 COPD and 22 control participants were compared. Cases were of similar age to controls (65.2 vs. 63.1 years, p = 0.38), had significantly lower Forced Expiratory Volume in one second (FEV1) (53.4 vs 100.1% predicted; p < 0.001) and smoked more than controls (41.7 vs. 29.6 pack years; p = 0.04). COPD participants had wider mean arteriolar (155.6 ±15 uM vs. controls [142.2 ± 12 uM]; p = 0.002) and venular diameters (216.8 ±20.7 uM vs. [201.3± 19.1 uM]; p = 0.012). Differences in retinal vessel caliber were independent of confounders, odds ratios (OR) = 1.08 (95% confidence intervals [CI] = 1.02, 1.13; p = 0.007) and OR = 1.05 (CI = 1.01, 1.09; p = 0.011) per uM increase in arteriolar and venular diameter respectively. FEV1 remained significantly associated with retinal vessel dilatation r = -0.39 (p = 0.02).

CONCLUSIONS

Non-mydriatic retinal imaging is easily facilitated. We found significant arteriole and venous dilation in COPD compared to age-matched smokers without COPD associated with lung function independent of standard cardiovascular risk factors. Retinal microvascular changes are known to be strongly associated with future vascular events and retinal photography offers potential to identify this risk.

TRIAL REGISTRATION

clinicaltrials.gov NCT02060292.

To Evaluate the Effect of Chronic Obstructive Pulmonary Disease on Retinal and Choroidal Thicknesses Measured by Optical Coherence Tomography

Purpose

To evaluate the retinal and choroidal thicknesses in patients with chronic obstructive pulmonary disease using optical coherence tomography.

Methods

The study included 26 patients with chronic obstructive pulmonary disease (COPD) and 26 age-matched healthy control groups. Detailed ocular examinations were performed on all participants. Cirrus EDI-OCT (enhanced depth imaging-optical coherence tomography) was used for choroidal thickness measurements with frame enhancement software. The subfoveal area was used for choroidal thickness measurements.

Results

The patients with the chronic obstructive pulmonary disease had an average 239.13 ± 57.77 μm subfoveal choroidal thickness, and the control group had an average 285.02 ± 25 μm subfoveal choroidal thickness. The subfoveal choroidal thickness measurements revealed a statistically significant difference between patients and the control group (p < 0.05). There were no statistically significant differences between patients and control group regarding mean macular thickness, central macular thickness, and GCIPL (ganglion cell-inner plexiform layer) thickness. Also, there was no statistically significant difference between patients and control group regarding mean, superior, nasal, inferior, and temporal RNFL (retinal nerve fiber layer) thicknesses.

Conclusion

Chronic hypoxemia seems to cause decreased choroidal thickness in patients with chronic obstructive pulmonary disease.

Short-term variations of optic coherence tomography findings in mild and severe chronic obstructive pulmonary disease

OBJECTIVE

To evaluate the short-term changes in subfoveal choroidal thickness (SFCT), ganglion cell complex (GCC) analysis, and retinal nerve fiber length (RNFL) of patients with chronic obstructive pulmonary disease (COPD) in a 3-month follow-up.

MATERIALS AND METHODS

Forty-eight patients with COPD (96 eyes) and 40 control subjects (80 eyes) were enrolled in our study. COPD patients were grouped according to disease severity as Group 1 (mild-moderate) and Group 2 (advanced). GCC, RNFL, and SFCT analysis by Cirrus SD-OCT were obtained for all eyes, in two consecutive examinations with a 3-month interval.

RESULTS

SFCT in Group 2 was lower than Group 1 and control group in the initial and 3rd month examination (p < 0.001, respectively). Inferior RNFL in Group 2 were lower than control group in the initial and 3rd month examination (p = 0.002, p < 0.001, respectively) Temporal RNFL were lower in Group 2 than Group 1 in 3rd month examination (p = 0.009). Average, superior, superotemporal, inferior, and inferonasal GCC analyses of the Group 2 were lower than control group both in the initial and 3rd month examination (p = 0.001, p < 0.001, respectively) SFCT, average, and superior GCC of Group 2 were significantly reduced during the 3-month follow-up (p < 0.001).

CONCLUSION

Hypoxia is thought to be the underlying mechanism in COPD, which may influence retinal and choroidal OCT parameters. Decrease in blood flow of optic nerve head, increased vascular resistance, and reduced blood flow in choroid may affect the visual ability in these patients, which should be kept in mind during their follow-up.

Choroid and Retinal Nerve Fiber Layer Thickness in Patients with Chronic Obstructive Pulmonary Disease Exacerbation

PURPOSE

We aimed at measuring the choroid and retinal nerve fiber layer thickness with optic coherence tomography (OCT) in patients diagnosed with chronic obstructive pulmonary disease (COPD).

METHODS

A total of 60 patients with COPD and 23 healthy controls were evaluated in the scope of this prospective, observational study. COPD patients were divided into two groups as those that were stable and those with an exacerbation based on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification. Subfoveal choroid thickness (SFCT) of the patients and the control group was compared by measuring the choroid thickness at points 1000 µm nasal and temporal to the fovea and the mean retinal nerve fiber layer (RNFL) thickness.

RESULTS

The subfoveal choroid thickness of the COPD patients in both the exacerbation and stable groups was found to be statistically significantly thinner than the control group (p=0.047 and p=0.046, resp.). No statistically significant difference was found between the subfoveal choroid thickness of the patients that were stable and those that had an exacerbation (p=0.813). No statistically significant difference was found between the mean RNFL, 1000 µm nasal, or 1000 µm temporal choroid thicknesses of the COPD patients and the control group (p=0.263, p=0.455, and p=0.611, resp.).

CONCLUSION

Decreased subfoveal choroid thickness was found in the COPD patients both during an exacerbation and in the stable period, when compared to the control group. The mean RNFL thickness was similar in the exacerbation and stable period of the stable COPD patients when compared to the control group. This suggests that ocular findings might be important in terms of COPD morbidity. This trial is registered with www.chictr.org.cn/enIndex.aspx.