Introduction

Chronic obstructive pulmonary disease (COPD) is a common progressive pulmonary disease that is characterized by permanent airways obstruction that is caused partly either by chronic bronchitis or emphysema¹.

In clinical practice, COPD is usually underdiagnosed; many studies show that more than 25-50% of patients found to have this disease accidentally after doing spirometry screening with no previous diagnosis of COPD. The recent estimates for the disease suggest that about 80 million individuals across the world have moderate to severe COPD. In 2020, the disease accounts for the third most predominant reason for death around the world^2,3. The most prevalent risk factor for this disease is tobacco smoking, in addition to other risk factors can be involved like air pollution, airways genetic defects like alpha-1-antitrypsin deficiency, occupational dusts and chemicals, poor nutrition, respiratory tract infections that happen during childhood^4-7 as well as inflammation that had found to have a crucial role in COPD as confirmed in a recent study^8,9. Logically the early diagnosis for COPD is very important to prevent appearance of advanced symptoms and complications. The early diagnosis is also important in smokers who have no symptoms which may lead smoking cessation and this lastly gradually causes slowing down the loss of lung function¹⁰. Spirometric examination represents the gold standard for diagnosis of COPD and monitoring its progression. The confirmation of diagnosis occurs when the patient with airflow obstruction has a postbronchodilator FEV1 less than 0.70^11,12. In most patients, the diagnosis of COPD is performed by the combination of the clinical features and spirometric examination. Any case suspected to have COPD should be confirmed by using spirometric test¹³. The National Institute of Heart, Lung, and Blood recommends to use spirometry for all smoker subjects 45 years or older, especially those who have coughing, persistent sputum production, shortness of breath, or wheezing^14,15. The key features in spirometric examination of COPD are FEV1 and forced vital capacity (FVC)¹⁶. FEV1 is the volume of air can be forcefully expired in one second following a full inspiration¹⁷. The FVC is the maximum air volume can be exhaled after a full inspiration. COPD diagnosis is confirmed by finding a postbronchodilator FEV1/FVC ratio of less than 70% with FEV1 less than 80 percent of the predicted ^18-20. The classification of COPD severity based on spirometry findings was according to the guidelines of Global Initiative for COPD. The assessment of severity of the disease has a considerable importance in determining the suitable treatment for each patient^21,22. This study is aimed to early detect chronic obstructive pulmonary disease in asymptomatic male smokers and ex-smokers by spirometry.

Patients and Methods

This cross-sectional study was performed at respiratory outpatient clinic in Baghdad teaching hospital from September 2018 to July 2019, the study included 200 subjects participated in our study, 100 of them were current smokers and 100 were ex-smokers. Data about (age, residence, marital status, occupational state and smoking state which include number of cigarettes per day, duration of smoking, age of beginning smoking, pack per year and duration of quitting in ex- smokers) were collected from participants and as required.

Exclusion criteria:

1.If they stopped smoking for a period less than one year according to the definition of ex-smoker ³.

2.If they have bronchial asthma, COPD, or other chronic respiratory illness.

3.If they take bronchodilators, theophylline or montelukast.

4.If they have active respiratory symptoms.

Structured questionnaire consists of socio-demographic characteristics like: age groups, marital status, residence, occupational status and smoking state which include number of cigarettes per day, duration of smoking, age of starting smoking, pack per year and duration of quitting in ex-smokers. Oxygen (O.) saturation was measured by pulse oximeter (NINO Onyx 9500). By using a commercially available spirometer, spirometric study was done. Information was taken from each subject at the beginning of spirometry including name, age, gender, race, in addition to measurement of weight and height. The procedure was performed according to guidelines of American Thoracic Society (ATS)²³. Diagnosis of COPD depend on finding FEV1/FVC ratio less than 0.70 and FEV1% less than 80% with no change or trivial change after doing reversibility bronchodilator test. According to the result of spirometry and depending on classification of GOLD guidelines, the subjects were classified as the following ways:

·Stage (I): mild COPD - FEV1 80% predicted or more

·Stage (II): moderate COPD - FEV1 range from 50 to 79% predicted

·Stage (III): severe COPD - FEV1 range from 30 to 49% predicted

·Stage (IV): very severe COPD - FEV1 < 30% predicted or FEV 1 < 50% and chronic respiratory failure²⁴.

Statistical Analysis

The programme used to analyze the data was Statistical package for social sciences version 20 (SPSS 20). The means presented the continuous variables while discrete variables were presented as numbers and percentages. The difference in mean levels of two independent samples was analyzed by using T test. significance of associations between discrete variables was analyzed by using Chi-square test. Pearson's correlation coefficient was used to estimate the direction and degree of correlation between two continuous variables. Levels of significance was determined when P value <0.05.

Results

The mean age of the participants was (45.3±11.5) years old with an age range of (20-69) years old, 29% of them was aged (30-39) years old for current smokers and a mean age of (54.2±10.4) years old with an age range (35-69) years old, 38% of them were aged (60-69) years old for ex-smokers. All of the participants underwent spirometric screening.

1. Distribution of male smokers and ex-smokers according to age of starting smoking: Regarding current smokers 53% of them were started smoking at (20-29) years old of age while in ex-smokers 42% of them were started smoking at (10-19) years old of age.

2. Distribution of male smokers and ex-smokers according to smoking history: Regarding current smokers, the mean duration of smoking was (24.7±10.2) years and a range of (3-50) years. A large proportion (34%) of them had a range of (21-30) year’s duration of smoking. A large proportion of them (49%) smoked cigarettes at a range of (20-39) cigarettes per day (Figure 6). The mean pack years was (37.0±28.3) at a range of (2-150) pack years. A large proportion (35%) of them had a range of (21-40) pack years. While in ex-smokers, the mean duration of smoking was (25.3±9.2) years and a range of (10-46) years. A large proportion (38%) of them had a range of (11-20) year’s duration of smoking. A large proportion of them (48%) smoked cigarettes at a range of (40-59) cigarettes per day. The mean pack years was (45.0±26.1) at a range of (10-115) pack years. A large proportion (36%) of them had a range of (21-40) pack/year.

3. Mean differences of variables between current smokers and ex-smokers

Table (1) shows the mean value and range of age, age of beginning smoking, duration of smoking, number of cigarettes smoked per day, and pack/year. There was significant difference in mean value between current smokers and ex-smokers according to age, number of cigarettes per day and number of pack years (p value ≤0.05)

Table 1
Descriptive data for current smokers and ex-smokers

Table 1. Descriptive data for current smokers and ex-smokers
Variables		Total No.	Current Smoker	Ex- smoker	P value
Age (y)	Min -Max	20-69	20-69	35-69	---
	Mean ±SD	49.8±11.8	45.3±11.5	54.2±10.4	<0.001
Age at starting smoking (y)	Min -Max	8-43	11-33	8-43	---
	Mean ±SD	20.5±6.2	20.6±5.1	20.4±7.2	0.821
Duration of smoking (y)	Min -Max	3-50	3-50	10-46	---
	Mean ±SD	25.0±9.7	24.7±10.2	25.3±9.2	0.701
Cigarette/day	Min -Max	6-60	6-60	10-60	---
	Mean ±SD	31.5±14.4	27.9±13.9	35.1±14.0	<0.001
Pack/year	Min -Max	1.5-150	2-150	10-115	---
	Mean ±SD	41.0±27.5	37.0±28.3	45.0±26.1	0.040

4: Distribution of Participants according to the results of spirometry

Table (2) shows distribution of participants according to results of spirometric tests. In current smokers (49%) had obstructive pattern (FEV1/FVC ratio <70), from those (44.9%) had mild COPD (FEV. ≥80) and (55.1%) had moderate COPD (FEV. 79-50) according to GOLD staging, about 52% of ex- smokers had obstructive pattern, from those (25%) had mild COPD and (75%) had moderate disease according to GOLD staging.

Table 2.
Distribution of participants according to the results of pulmonary function tests

Table 2. Distribution of participants according to the results of pulmonary function tests
	FEV1/FVC for Current Smoker				FEV1/FVC for Ex-smoker
	< 70%		≥ 70%		< 70%		≥ 70%
FEV1%	N=100	100%	N=100	100%	N=100	100%	N=100	100%
≥ 80	22	44.9%	51	100.0%	13	25.0%	48	100.0%
79 – 50	27	55.1%	0	0.0%	39	75.0%	0	0.0%
< 50	0	0.0%	0	0.0%	0	0.0%	0	0.0%
P value	< 0.001*				< 0.001
*p value ≤ 0.05 is significant

5: Correlation of spirometric results with study variables

Table (3) shows the correlation of both FEV. % and FEV./FVC ratio with study variables (age, age of beginning smoking, duration of smoking, number of cigarettes per day, number of pack years and O. saturation). All of the variables were significantly inversely correlated to both FEV. % and FEV./FVC ratio except O. saturation which was directly correlated.

Table 3
Correlation of FEV1% and FEV1/FVC ratio with study variables

Table 3. Correlation of FEV1% and FEV1/FVC ratio with study variables
Variables	Total		Current Smokers		Ex-smokers
	r	P value	r	P-value	r	P value
A) Correlations of FEV1% with study variables
Age	-0.787*	< 0.001**	-0.832	< 0.001	-0.758	< 0.001
Age at starting smoking	-0.005	0.947	-0.151	0.134	0.087	0.390
Duration of smoking	-0.768	< 0.001	-0.865	< 0.001	-0.688	< 0.001
Cigarette/day	-0.794	< 0.001	-0.820	< 0.001	-0.758	< 0.001
Pack/year	-0.951	< 0.001	-0.944	< 0.001	-0.961	< 0.001
O2 Saturation	0.950	< 0.001	0.945	< 0.001	0.962	< 0.001
B) Correlations of FEV1/FVC ratio with study variables
Age	-0.760	< 0.001	-0.844	< 0.001	-0.734	< 0.001
Age at starting smoking	-0.074	0.299	-0.212	0.034	0.032	0.756
Duration of smoking	-0.736	< 0.001	-0.847	< 0.001	-0.595	< 0.001
Cigarette/day	-0.741	< 0.001	-0.749	< 0.001	-0.754	< 0.001
Pack/year	-0.853	< 0.001	-0.837	< 0.001	-0.875	< 0.001
O2 Saturation	0.932	< 0.001	0.944	< 0.001	0.923	< 0.001
r: Pearson’s correlation coefficient., negative sign means the correlation is invers, and p value ≤ 0.05 is significant

Figure )1 (illustrates the inverse correlation of FEV./FVC ratio with duration of smoking in the two study groups, so when duration of smoking increases, the ratio will decrease.

Figure 1
Correlation between FEV1/FVC ratio and duration of smoking according to each study group

Figure (2) shows the inverse correlation of FEV./FVC ratio and number of pack years in the two study groups, so when number of pack years increases, the ratio will decrease.

Figure 2.
Correlation of FEV1/FVC ratio and pack years

6. Mean differences of O. saturation, FEV. % and FEV./FVC ratio and between current smokers and ex-smokers

Table (4) shows the mean O. saturation was (96.3±1.8) in current smokers and was (96.3±1.8) in ex-smokers, with a range of (93-99) in both groups. The mean FEV.% was (82.2±6.6) in current smokers which is significantly higher than that of ex-smokers which was (79.9±7.2). The mean FEV./FVC ratio was (75.0±9.9) in current smokers and was (73.7±8.7) in ex-smokers.

Table 4.
Mean differences of O2 saturation, FEV1% and FEV1/FVC ratio between the two study groups

Table 4. Mean differences of O2 saturation, FEV1% and FEV1/FVC ratio between the two study groups
Variables		Total No	Current smokers	Ex- smokers	P-value
O2 saturation	Min -Max	93-99	93-99	93-99	---
	Mean ±SD	96.2±1.8	96.3±1.8	96.1±1.8	0.328
FEV1%	Min -Max	65-97	65-97	66-94	---
	Mean ±SD	81.0±7.0	82.2±6.6	79.9±7.2	0.018*
FEV1/FVC	Min -Max	55-97	59-97	55-93	---
	Mean ±SD	74.4±9.3	75.0±9.9	73.7±8.7	0.335
*p value ≤ 0.05 is significant

7. Association between spirometric diagnosis and number of pack years in both study groups

Table (5) and Table (6) shows significant association between results of spirometry and number of pack years in current smokers and ex-smokers respectively, participants in both groups with a range of (21-40) pack years show obstructive pattern in spirometry.

Table 5
Association between spirometric diagnosis and number of pack years in current smokers

Table 5. Association between spirometric diagnosis and number of pack years in current smokers
Characteristics	Spirometric diagnosis		P value
	Normal (%)	Obstructive (%)
Number of pack year			<0.001*
< 20 pack years	33 (100%)	0 (0.00%)
(21-40) pack years	19 (52.8%)	17 (47.2%)
(41-60) pack years	0 (0.00%)	15 (100%)
> 60 pack years	0 (0.00%)	16 (100%)
*P value ≤ 0.05 is significant

Table 6.
Association between spirometric diagnosis and number of pack years in ex-smokers

Table 6. Association between spirometric diagnosis and number of pack years in ex-smokers
Characteristics	Spirometric diagnosis		P value
	Normal (%)	Obstructive (%)
Number of pack year			<0.001*
< 20 pack years	20 (100%)	0 (0.00%)
(21-40) pack years	17 (47.2%)	19 (52.8%)
(41-60) pack years	0 (0.00%)	18 (100%)
> 60 pack years	0 (0.00%)	26 (100%)
*P value ≤ 0.05 is significant

Discusion

Chronic obstructive pulmonary disease is a highly prevalent disease that leads to high morbidity, early mortality and high expenditure for healthcare. The disease is commonly detected lately after failure of medical treatment to stop the disease progression, so, screening in order to early detect this disease is very important to for smoking cessation campaign and to reduce the bad sequel of COPD^1,2,24,25. In this study, we did evaluation for the results of spirometric examination of 200 asymptomatic male smokers and ex-smoker subjects. The age of study subjects was young and middle age group and this is important for the early screening of asymptomatic cases because the COPD will appear clear at elderly age group in addition to that the lung function will deteriorate gradually with increase in age, so the disease is more predominant in older age people although the highest percentage of the smoker subjects begin smoking at early period^26,27. Many studies that were done for early detection of COPD took the subjects who were above 30 years old. In our work, the prevalence of underdiagnosed airway obstruction was found in 50.5% in total sample (49.0% in current smokers and 52.0% in ex-smokers) and this was significantly related to the smoking duration and number of pack years. This finding illustrated the great importance of identifying asymptomatic smokers and ex-smokers with undetected airway obstruction. There was a significant reduction in prevalence of smokers after the national program for prevention and treatment of COPD in Finland in 2003 that led to early diagnosis for COPD in 1998 with aid of spirometry and this was followed by management in smoking cessation clinics. This gives a clue for the high benefit of the effects of early diagnosis on natural deleterious development of COPD²⁸. In a similar way, Giovino et al found that smoking cessation rate increased after early detection of airways limitation together with the increases in advice of smoking cessation²⁴. In this work, the higher percentage of airflow obstruction was because the study was performed on randomized samples that had high number of pack years in smokers and ex-smokers. Many previous studies had many various percentages and prevalence that depend on the features and criteria of the study subjects and on spirometer used in diagnosis. In a study done by Anto et al., they had found presence of airway obstruction in 18% of patients with only 4% among subjects without symptoms²⁸. In the epidemiologic study conducted by Churg et al for early detection of COPD by using spirometry, they found that airway limitation is present in about 23% of the subjects tested for detecting COPD²⁷. In a case finding study performed by Schane and colleagues in 1960 over 40 years of age using a questionnaire, physical examination and spirometry, they found that 9% of the involved subjects had airways limitation. mild obstruction was found in 63.3% of smokers who had smoking history more than 20 pack years. No airways obstruction detected in those who smoke less than 20 pack years²⁹.

Conclusion

From this study, we conclude that use of spirometry is very useful for early diagnosis of patients with COPD and this represents a great benefit for the patient and the community. The early COPD diagnosis will enhance smoking quitting and help in prevention of COPD exacerbations, limit the rapid decline in lung function, enhance life quality and reduce mortality.

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Notas de autor

samir.sawadi@gmail.com