Present cross-sectional study was carried out from 1^st October 2017 to 31^st March 2019 (18 Months) at the Department of Respiratory Medicine in collaboration of Department of Pathology at Institute of Medical Sciences, Banaras Hindu University, after getting approval from the ethical committee (IEC- Dean/2017/EC/204).

Patients willing and able to participate in the study, adult patients above 18 years of age, and suffering from OSA or had history suggestive of OSA were included in the study.

Unstable medical or psychiatric conditions that would interfere in performing the study. Chronic respiratory failure or insufficiency, recent myocardial infarction, exacerbation of obstructive airway diseases, Patients having a history of upper airway surgery, disorders of a craniofacial abnormality like Marfan’s syndrome, Down’s syndrome, Pierre-Robin syndrome.

Detailed history and physical examination with special attention to risk factors of OSA was done. Patients’ height, weight, neck circumference, neck length, abdominal and waist circumference were measured. Body Mass Index (BMI)- BMI >30 kg/m² was considered as obese. Neck Circumference (NC) >37 cm in men and >34 cm in women was set as the upper limit of overweight/obesity. Neck Length (NL) or Mentohyoid distance of less than 3 finger-width was considered as a strong association with OSA. Abdominal Circumference (AC) and Waist Circumference (WC): AC in Men: >102 cm; in Women: >88 cm taken as central obesity. WC Men: ≥90 cm; women: ≥80 cm and Waist Height Ratio (WHtR) 0.5 was taken as a cut-off for central obesity. Blood tests- Haematocrit, Glucose Fasting and Post-prandial, Lipid Profile- cholesterol, triglycerides, DHL, LDL, VLDL Thyrotropin (TSH), ELISA for IL-6 Normal range of haematocrit - 45% to 52% for men and 37% to 48% for women. Patients with blood glucose ≥110 mg/dL were considered diabetic. Patients with normal sugar values on medication were taken as a diabetic patient. Patients with triglycerides ≥150 mg/dL and HDL cholesterol <40 mg/dL in men and <50 mg/dL in ladies were delegated patient of dyslipidaemia. Diagnosis of metabolic syndrome was made in the presence of at least 3 of the 5 significant clinical signs i.e., Obesity, Hypertension, Diabetes mellitus, Hypertriglyceridaemia, Hypercholesterolaemia. IL-6 was measured by ELISA kit (Immunoshop India Pvt., Ltd.,) and immunoassay equipment. PSG study was done which included sleep stages, Heart rhythm monitoring, Leg movements recording, Breathing monitoring. Obstructive apnea was taken as cessation of airflow for at least 10 seconds with persistent respiratory effort. Following parameter were noted- AHI - Categorised as Mild OSAS: 5<AHI<15, Moderate OSAS: 15<AHI<30 and Severe OSAS: AHI >30.

Data collected for the sample was analysed using Microsoft Excel 2016. In present study, we used descriptive statistical methods such as computing percentage, mean, standard deviation, pivot tables, and correlation. SPSS Inc. (233 South Wacker Drive, 11^th Floor Chicago, IL 60606-6412) software was used and appropriate tests were employed for categorical, parametric or non-parametric data. Wherever necessary, the results of the study are depicted in the form of charts, tables, graphs and percentages.

A total number of 46 patients with OSA were evaluated, out of which 21 (46%) were females and 25 (54%) were males. Maximum number of male 7 (15%) and female 10 (22%) patients belonged to age group 50-59 and 60-69 years, respectively [Table/Fig-1]. The study showed that the average age of female and male patients was almost similar (58.8 yrs. Vs. 58 yrs.). In the study, 24% of males were smokers followed by the history of alcohol intake and tobacco chewing in 8% each. No female patient was having a history of smoking or tobacco chewing but 38% of females was exposed to biomass/kerosene fuel smoke at home. The severity of OSA was divided into Mild, Moderate and Severe AHI according to the number of apnoea episodes/hr. on Polysomnography (PSG) study. Mild, Moderate and Severe AHI is shown in [Table/Fig-2]. Due to financial issue, ELISA for IL-6 (Inflammatory Biomarker) was done in 41 patients only. The value ranged from 20.92 to 4145.23 pg/mL with SD±1769.32 pg/mL and Mean of 1427.94 pg/mL [Table/Fig-3,4]. Average values of biomarker IL-6 was estimated 675.26 pg/mL in mild OSA, 1261.19 pg/mL in Moderate ODA and 1658.58 pg/mL in severe OSA. There was a Positive correlation between AHI severity and IL-6 with Correlation Value (CV) of +0.369867430051592, means if the severity of OSA increases the IL-6 value will also increase and vice versa. It is also represented in [Table/Fig-5].

[Table/Fig-4]:

Shows IL-6 value in 41 patients with OSA (AHI value scaled by 100).

[Table/Fig-5]:

Shows positive correlation value between AHI and IL-6.

(*IL-6 values shown are multiplied by 100)

OSA is characterised by a recurrent partial or complete collapse of upper airways during sleep. In a survey from northern part of India, the prevalence of OSA Syndrome is estimated as 3.6% and separately for males and females it was 4.9% and 2.1%, respectively [14]. In this study, we included 21 (46%) female and 25 (54%) male patients who clinically had symptoms suggestive of OSA and underwent PSG to access severity of AHI. Present study showed that the average age of female and male patients was almost similar (58.8 yrs vs. 58 yrs), which was higher as compared to other study. The sex distribution of the patients was similar in the both studies [15].

Patients with OSAS are always exposed to intermittent hypoxia and re-oxygenation from the cycles of apnoea/arousals. It is suggested that sustained hypoxia leads to oxidative stress and activation of a systemic inflammatory response with increase in general blood antioxidant activity and in production of pro-inflammatory cytokines, including Tumour Necrosis Factor TNF-α and interleukin-6 [16]. In the present study, we had selected IL-6 as a biomarker to evaluate its levels in 41 patients with OSA. We correlated IL-6 levels with AHI. The average value of IL-6 was 1427.94 pg/mL, ranging from 20.9292 to 4145.235 pg/mL. Average values of IL-6 were estimated by Immunoassay (ELISA) as 675.26 pg/mL in mild OSA, 1261.19 pg/ml in Moderate OSA and 1658.58 pg/mL in severe OSA. A study was conducted by Podkówka R et al., to estimate IL-6 levels in 29 healthy young adults (27.0±4.2 years) and 30 healthy elderly (71.1±5.5 years). The level of interleukin-6 was five times higher in the patient’s who belonged to the older age group, but it was not statistically significant [17]. The findings in present study are also in support of some other studies [18-22]. PSG is a poor predictor of OSA-associated morbidities. Two patients with similar OSA severity may behave with markedly different clinical phenotypes. That’s why such studies have importance to enable incorporation of morbidity biomarkers into well-defined and validated clinical guidelines or algorithms [23].

The searching out of an important biomarker for OSA associated morbidity has the potential to provide knowledge related to prognosis and response to therapy. Blood-based biomarkers were accounted in the majority of the studies, and most of the explored approaches did not identify definitive biomarkers of OSA morbidity. Studies showed that interleukin-6 can be considered as a biomarker to differentiate the patients with OSA with different co-morbidities [24]. Furthermore, in the present study, the average value of IL-6 was significantly higher than general young and elderly population thus, we can presume that high levels were because of OSA but, cannot confirm that these levels were because of OSA or associated comorbidities, or both.

First limitation is a small sample size, and the second is that we did not rely on a control group, comprising individuals without OSA, to establish correlation with the associated morbidities.

Blood-based biomarkers accounted for the majority of the studies, but most of the studies did not identify a reliable biomarker of OSA morbidity.

In present study IL-6 levels have shown positive correlation with AHI. However, more large scale studies are required to establish a definitive correlation between OSA and IL-6. These findings warrant further research with case-control studies and standard statistical analyses to have a better understanding of interrelationships of these cytokines.