The present study is a large data set furnishing information regarding the prevalence of obstructive sleep apnoea in patients with hypertension in India. The target population was identified on the basis of physician detected hypertension and the patient data was collected by a standardized protocol on snoring, daytime sleepiness, BP, and other features associated with OSA.
Our study demonstrates that OSA is widely prevalent in patients with hypertension. Based on the standard Berlin questionnaire, 24% of the test population was found to be at high risk for OSA (i.e., 1 in every 4 hypertensive individuals). Our study is in accordance with studies by Peppard and colleagues who identified 24-28% prevalence of OSA in hypertension (Peppard et al., 2013).
The prevalence of daytime sleepiness in this sample was 62·5% by the Epworth scale result above 10 points. This prevalence in our sample is in agreement with the prevalence identified in a previous report of patients with hypertension (Ngahane et al., 2015). In that study, the authors identified the prevalence of excessive daytime sleepiness to be 62·78% (95% CI 58·08 to 67·47).
The overall mean age of the high risk for OSA respondents was 53·4 ± 9·02 years. The prevalence of OSA was highest between 51-60 years of age and this risk increased exponentially from 0·8% at ≤ 30 years of age to 41·7% at 51-60 years of age (p˂0·001) (Figure 2). This finding is in agreement with the previous studies demonstrating the effect of age on OSA status (Deng et al., 2014; Ip et al., 1999).
The seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure recognizes both the independent role of OSA in the development of hypertension and OSA in association with obesity (Chobanian, 2003). In our study, patients with high-risk of OSA had significantly higher BMI, WC, WHR, and NC values statistically as compared to the patients with low-risk of OSA (Figure 3). All of the anthropometric indices (NC, WC, and BMI) were significantly correlated with the risk of OSA. These results are similar to those of previous studies. Kang et al. reported that NC [95% CI; p<0·001], WC (95% CI; p<0·001), and BMI (95% CI; p<0·001) were significantly associated with the presence of OSA (Kang et al., 2014). Hiestand and colleagues reported that among obese subjects (BMI ≥30kg/m2), 59% of subjects were at high risk of OSA (Hiestand et al., 2006). In our study, only 37·5% of subjects were at high risk of OSA among obese patients (BMI ≥30 kg/m2).
In a study by Endeshaw and colleagues the mean BP values among older adults with sleep-disordered breathing were 133±16 and 71±8 mm Hg for systolic and diastolic BP, respectively (p < 0·001) (Endeshaw et al., 2009). In our study, the average systolic and diastolic BP was 133·52 ± 17·503 and 84·37 ± 7·425 mm Hg (Figure 4).
In our study, OSA was found to be strongly associated with resistant hypertension. Though our sample size was not large enough to justify a meaningful conclusion on this, another case-control study by Gonçalves et al. reported that OSA is a strong independent risk factor for resistant hypertension (Gonçalves et al., 2007). This study represents an advanced approach in the understanding of the risk factors of hypertension and gives an insight into the prevalence of high-risk of OSA in patients with hypertension. The Berlin Questionnaire, used in our study, is a validated method that has been used widely to identify individuals who are at risk for OSA (Gus et al., 2008). Our assessment of excessive daytime sleepiness was based on the ESS score, which is a well-tested international tool for the evaluation of daytime sleepiness (Boyes et al., 2017). With the increasing problem of hypertension, the impact of undetected or under-diagnosed OSA as a healthcare burden cannot be undermined. Therefore, this study can help reduce CV outcomes and healthcare costs of a rigorous anti-hypertensive regimen by treating the underlying cause.
There are a few limitations in our study that need to be considered. Firstly, the collection of data has been from a single tertiary care hospital for a limited period of time yielding a small size of the patient population. Secondly, the Berlin Questionnaire was used to identify high risk for OSA instead of polysomnography which is the gold-standard test for the diagnosis of OSA in clinical settings (Pang et al., 2006). However, it is complex, expensive, time-consuming, and is not available for the general population in India. The Berlin Questionnaire is a reliable tool and has been found to generate comparable results to that of polysomnography, yet there is a possibility of variation in the precision of results (Amra et al., 2018). We believe further studies using overnight polysomnography are warranted to exhaustively elucidate the bidirectional association between OSA and hypertension from different healthcare facilities of the state.