An observational cross-sectional study was conducted between November 2015 and April 2016. Male and female subjects aged 18 to 60 years presenting with chronic respiratory symptoms like cough, wheeze and SOB for more than three months duration were included in the study. All patients were Bengali speaking and belonged to urban areas of North 24–Parganas district, West Bengal, India. They were referred from different outpatient departments of a tertiary hospital, Kolkata for routine spirometric screening at the spirometry laboratory in Department of Physiology.

Asymptomatic patients coming for pre-anaesthetic checkup, Paediatric and Geriatric patients, patients suffering from acute illness and debilitation of any origin, patients with third trimester pregnancy, active haemoptysis, tuberculosis, sub diaphragmatic and known cardiovascular diseases associated with SOB were summarily excluded from the present study. On an average in our department we perform routine spirometry in 160 patients per month. In six months from about 950 patients we selected 550 patients maintaining appropriate inclusion and exclusion criteria. The sampling technique was complete enumeration. Ethical permission was obtained from Institutional Ethics Committee, prior to study and written consent was taken from each of the subject prior to examination.

At first all patients were asked to respond to a standardized respiratory symptoms questionnaire (ATS/DLD-78 A questionnaire) [9]. After obtaining detailed clinical profile, patients with respiratory symptoms were divided in two groups: subjects suffering from clinical symptoms suggestive of respiratory allergy (n=260) like nasal catarrh, nasal stuffiness and sneezing all together as written on OPD card and subjects with no symptoms suggestive of respiratory allergy (n=290).

We did not perform any laboratory test for allergy as clinical symptomatology is established as the most reliable factor in detection of allergy [10,11]. Smoking history was obtained and subjects were categorized as per US Centers for Disease Control and Prevention definition of “Never Smokers” – adults who have never smoked a cigarette or who smoked fewer than 100 cigarettes in their entire lifetime. Rest of the subjects was marked as smokers. All the patients had received one or more bronchodilators and anti-inflammatory agents for treatment of their respiratory symptoms.

As all the data was collected at a point of time (cross-sectional data) with no known confounding variable so unpaired t-test was applied to compare these two populations. After calibration, spirometry was carried out by using a non-heated spirometer (RMS HELIOS 702) following current guidelines of the American Thoracic Society [12]. The largest observed values of FEV₁ and FVC available from among at least three acceptable and reproducible tests were taken as the key parameters for interpretation. Then, the subject was asked to inhale short acting bronchodilator in the pre-prescribed doses. After ten minutes of taking the inhaler the subject was asked to perform the spirometry once again and thus the reversibility test done [12]. The highest values of FVC and FEV₁ were selected. Periodic calibrations were done as per protocol.

In absence of normative spirometric data of Indian population the data obtained was interpreted as per directions furnished in the user manual of RMS HELIOS 702 along with given ethnic correction [13]. As the study populace seemed to be ethnically homogenous predictive equation was not obtained.

We categorized all the patients as per pre-set criteria: i) Normal Spirometric Finding; ii) Small Airway Obstruction (SAO); iii) COPD; iv) Mixed Ventilatory Defect; & v) Restrictive Pattern [13].

Descriptive analyses were performed using Fisher’s-Exact Test (for categorical variables) and two-sided unpaired t-tests (for continuous variables). All spirometric variables were expressed in percent predicted (%) form. Statistical analyses was done by using Microsoft excel sheet and GraphPad Quickcalcs Software, California, USA. A p-value of <0.05 was considered significant.

Non allergic patients were significantly more likely to be older (mean age was 44 years), percentage of smokers were also higher in the older population. There was no significant difference regarding prevalence of respiratory symptoms like SOB, dry cough, wet cough between allergic and non-allergic populations except wheeze which was more significant finding in allergic population. Furthermore, bronchodilator reversibility (BDR) data had shown that mean values of FEV₁/FVC, FEF_25-75 and PEFR were significantly lower in non-allergic subjects as compared to allergic group [Table/Fig-1].

Occurrence of COPD in BDR analysis was significantly more in non-allergic group rather than allergic population [Table/Fig-2].

Non allergic patients with spirometry diagnosed COPD were significantly more likely to be older (mean age was 52 years). More than half of the non-allergic patients had smoking history. Non-allergic patients had a lesser mean body weight. Persistence of lower respiratory symptom like wet cough was more in the non-allergic population compared to allergic population. Furthermore mean values of FEV₁& FEV₁/FVC were significantly less in non allergic COPD population compared to allergic patients [Table/Fig-3].

In the present study, we divided the whole population based only on prior clinical diagnosis and allergy testing was not performed. As drug/treatment history of patients was not supposed to alter our study outcome so we had not included drug history as a study variable. As the present study was of observational and cross-sectional nature so no confounding variable like age and smoking could be ascertained. However, these were important variables which influenced the overall outcome. Therefore, we categorized the study subjects based on these parameters and compared the different groups to deduce the study results.

In the present study, we did not categorize patients based on grade of SOB as all of the patients fell in NYHA grade I or grade II. This is most probably because spirometry is very difficult or rather impracticable in the management of NYHA grade III or grade IV SOB.

In this study we found that respiratory allergic group was significantly younger and had lesser percentage of smokers compared to nonallergic group. This finding was in accordance with the study result of Eder W et al., [14]. They also documented that allergic hypersensitivity due to plant pollens was more commonly found in younger age group and in older people, the cause was almost always hypersensitivity to nonallergenic types of irritants in the air, such as irritants in smog.

The present study had shown that post BDR parameters were significantly lower in non allergic patients compared to allergic patients and smokers were at a significantly higher number in non allergic group. Detection of COPD by spirometry screening was much higher in the same group. Similarly Sichletidis L et al., found that prevalence of COPD was not significantly high among individuals having respiratory allergy [11]. As smoking causes COPD which showed poor BDR response in this study, the hypothesis that can be drawn from the constellation of these findings was that presence of respiratory allergy might refrain the affected subjects from smoking. This was in accordance with the findings of Shargorodsky J et al., that the relationship between tobacco smoke exposure and sinonasal pathology in adults might be independent of allergic sensitization [15]. Therefore, smoking may cause symptoms of respiratory allergy. Our study further indicates that smoking was probably a stronger causative factor for development of COPD than allergy. This was in accordance with the findings of Sichletidis et al., who had shown that prevalence of COPD was not significantly high among allergic subjects [11].

The mean age was significantly higher with greater percentage of smokers and more persistence of wet cough in non-allergic COPD population compared with allergic COPD patients. This was in accordance with the findings of Eisner et al., Jarad et al., & Smith et al., [16-18]. This further asserts that smoking was much stronger aetiological factor for COPD than respiratory allergy.

There were no significant differences in BMI, chronic respiratory symptoms like SOB, dry and wet cough and also FEV₁ reversibility between these two populations again most possibly because smokers were present in both in allergic and non-allergic patients with COPD and as because of stronger aetiopathogenic effect of smoking on COPD effect of allergy on symptoms was blurred.

All the subjects were residents of urban downtown areas. High degree of air pollution might also contribute to higher prevalence of symptoms in COPD besides smoking in non-allergic populace as shown by Ko FW et al., [19].

Due to cross-sectional nature of this study, it was difficult to establish causal association between impaired lung function and the chronic respiratory symptoms. Furthermore air pollution as a contributing factor cannot be quantified. These might act as important confounding variables influencing the study result.

This present study concludes that COPD may coexist with respiratory allergy but overall occurrence of COPD was significantly much more in non-allergic population presenting with chronic respiratory symptoms. However to establish this finding large scale follow up investigations should be performed in future.