Snoring and risk for obstructive sleep apnea among nigerians with heart failure: Prevalence and clinical correlates.

BACKGROUND: Heart failure is an important cause of morbidity and mortality in developing nations like Nigeria. Sleep apnea and snoring has recently been recognized to be a cardiovascular risk factor. Sleep apnea is yet to be well studied among Africans with heart failure. We aimed to determine the prevalence of snoring and high risk for obstructive sleep apnea among Nigerians with stable heart failure.
MATERIALS AND METHODS: We studied 103 subjects that included 62 patients with heart failure and 41 control subjects. Demographic parameters and clinical examination were performed on the participants. The Berlin score and the Epworth Sleepiness Scale were administered for each participant. Echocardiography was done on all participants. Statistical analysis was done using Statistical Package for Social Sciences (SPSS) 17.0.
RESULTS: Snoring was reported in 48.4% of subjects with heart failure compared to 22.0% of control subjects ( P < 0.005). High risk for obstructive sleep apnea using the Berlin score was documented in 51.6% of heart failure subjects compared to 7.31% of controls. Excessive daytime somnolence occurred more in heart failure patients (51.6% vs. 9.8%, P < 0.05). Snorers tended to be older and were more likely to be obese than nonsnorers. Systolic blood pressure and fasting blood sugar were significantly higher among heart failure subjects with snoring than those without snoring (131.9 ± 19.2 vs. 119.2 ± 15.7 and 6.0 ± 0.8 vs. 5.4 ± 2.7, P < 0.005).
CONCLUSION: Heart failure seems to be associated with snoring and a high risk for obstructive sleep apnea among Africans with heart failure. Assessment for sleep disordered breathing should be incorporated into their routine clinical workup.

INTRODUCTION

Heart failure is becoming a major cause of morbidity and mortality even in the developing countries such as Nigeria. This is due to the increasing prevalence of etiological factors such as hypertension, cardiomyopathy, ischemic heart disease, rheumatic heart disease, and valvular heart disease.[1] Sleep disordered breathing (SDB) is common among normal population and those with heart failure. It can be obstructive sleep apnea (OSA) or central sleep apnea. Sleep apnea and heart failure are associated with significant morbidity and mortality among the general population.[12]

OSA is a potentially life-altering and life-threatening breathing disorder that occurs during sleep. It is due to recurrent occlusion of the upper airway due to pharyngeal collapse and retro positioning of the tongue. It is associated with fragmented sleep pattern, snoring, hypopnea, and apnea.[13] This sleep fragmentation may be manifested in excessive daytime sleepiness (EDS). Recent data have shown that OSA is an independent cardiovascular risk factor.[24] SDB includes snoring, apnea, and hypopnea. It is recognized to impact the cardiovascular system with significant influence on the morbidity and mortality pattern.[56] Studies have reported a high prevalence of snoring and sleep apnea among patients with severe heart failure in Caucasians.[7-9] Heart failure patients with sleep apnea have been shown to have poorer prognosis with a higher degree of left ventricular hypertrophy (LVH), systolic dysfunction, cardiac arrhythmias, poor quality of life, and myocardial ischemia than heart failure patients without sleep apnea.[47-9]

However, there is paucity of data on the burden of SDB, apnea, and snoring among Africans, both in the general population and in subjects with heart failure. Despite various advances in diagnostic and therapeutic modalities, mortalities in subject with heart failure still remain very high and heart failure has been compared with malignancies in term of the mortality.[10] Therefore, it is important to identify and treat comorbidities which may contribute to the progression in heart failure. Sleep apnea may contribute to cardiovascular morbidity in heart failure by several mechanisms including increased inflammatory activation, endothelial dysfunction, increased neurohormonal activation, and recurrent hypoxemia leading to myocardial ischemia.[11-13]

The aim of this study was to describe the prevalence of snoring and the risk for OSA using the Berlin score and the Epworth Sleepiness Scale (ESS) among Nigerian subjects with heart failure compared to normal controls.

MATERIALS AND METHODS

One hundred and three subjects were consecutively recruited for this study. They included 62 subjects with diagnosis of congestive heart failure (CHF). Diagnosis of heart failure was made using standard criteria.[14] Forty-one control subjects were also recruited. They were patients' relatives, hospital staffs, and willing adults who gave informed to participate in the study.

The study location was the cardiology clinic of Ladoke Akintola University of Technology Teaching Hospital, Osogbo, Nigeria. It was a cross-sectional study. Patients with clinical heart failure were on optimized medical therapy including, but not limited to, angiotensin converting enzyme inhibitors (ACE-I) or angiotensin receptor blockers (ARB), diuretics, aldosterone antagonist, and antiplatelets/anticoagulants. Clinical and demographic parameters including age, gender, body weight (in kilograms), height (in meters), waist circumference, and hip circumference of all participants were taken. Blood sample was taken after at least 8 h of overnight fasting to determine the fasting blood glucose using the glucose oxidase method. Informed consent was taken from each participant. Ethical approval was obtained from the Institutional Ethical Review Board.

The ESS was used to determine EDS. It is an eight-item self-administered questionnaire. Possible score ranged from 0 to 24. For this study, an ESS score of more than 11 was taken to mean EDS. The Berlin Questionnaire was used to identify the risk of having clinical OSA. The questionnaire consists of three categories related to the risk of having sleep apnea. Patients can be classified into high risk or low risk based on their responses to the individual items and their overall scores in the symptom categories. Subjects were categorized as high risk for having OSA if there were two or more categories where the scores were positive and low risk if there was only one or no categories where the score was positive.[15] The Berlin Questionnaire has been documented to be clinically sensitive and correlates significantly with the presence of OSA among various populations.[16] Clinically Suspected Obstructive Sleep Apneas (CSOSA) was defined in accordance with the 2001 International Classification of Sleep Disorders.[15]

Statistical analysis was done using the Statistical Package for Social Sciences (SPSS) 17.0 (Chicago, IL, USA). Numerical data were summarized using means and standard deviation, while categorical data were summarized using frequencies and percentages. Comparison between groups was done using t-test and Chi-square test. P < 0.05 was taken as statistically significant.

RESULTS

Table 1 shows the clinical and demographic characteristics of the study population. Subjects with heart failure were significantly older than control subjects. Mean waist circumference, body mass index, frequency of obesity, and diastolic blood pressure were not significantly different between the subjects with CHF and controls. Mean systolic blood pressure, mean ESS score, and fasting blood sugar were significantly higher among CHF subjects than controls as shown in Table 1. The prevalence of snoring among subjects with CHF was significantly higher than control subjects (48.4% vs. 22.0%, respectively, P < 0.05). High risk for OSA using the Berlin score was found in 51.6% and was significantly higher among the CHF subjects than controls (7.3%) ( P < 0.05). The frequency of high ESS score (ESS score > 11) was also significantly higher among CHF subjects than controls (51.6% vs. 9.8%, P < 0.05).

Table 1

Clinical and demographic characteristics of the study population

Table 2 shows that CHF-snorers were significantly older than CHF-nonsnorers. CHF-snorers had a significantly higher mean waist circumference, mean body mass index, systolic blood pressure, fasting blood sugar, and ESS than CHF-nonsnorers. Mean left ventricular mass and left ventricular mass index were significantly higher among CHF-snorers than CHF-nonsnorers. Although mean ejection fraction was lower among CHF-snorers than nonsnorers, it was not statistically significant.

Table 2

Clinical, demographic, and other parameters between heart failure subjects with snoring and those without snoring

DISCUSSION

This study showed that snoring is very common among subjects with heart failure. It also revealed that a significantly higher proportion of heart failure patients were recognized to be at high risk for having OSA and that heart failure may be a risk factor for SDB among Nigerians with heart failure. It therefore brings to light the relevance of screening for snoring and risk for sleep apnea among subjects with heart failure. This is in agreement with other studies that have documented a high frequency of sleep apnea and snoring among subjects with heart failure. These studies have documented the prevalence of SDB in heart failure subjects to be between 40% and 70%.[891718] Other authors have reported a prevalence of 11%-37% which is lower than that reported in this study.[1920] The prevalence of snoring reported in this study is more than what was reported by Adewole, et al.[21] among a heterogeneous population of Abuja residents where snoring was documented in 31% of the study participants. The lower prevalence in this study may be due to several reasons. It may be due to underreporting of snoring among our patients as there is a minimal form of social stigma associated with snoring in our environment. Secondly, our sample size was fairly small. Thirdly, we did not use polysomnography for evaluation and this might have underestimated the burden of SDB among the study participants. We depended on the assessment of risk for OSA using the Berlin Questionnaire.

While snoring may easily be identified by partners, OSA requires much more invasive studies for its diagnosis. The gold standard for evaluation of SDB is nocturnal polysomnography (NPSG) conducted in a sleep laboratory.[22] Polysomnography consists of electroencephalography (EEG), chin electromyelography (EMG), and electro-oculography to evaluate sleep duration, sleep latency, and sleep stages. Central or obstructive apneas and hypopneas are diagnosed through measurement of effort (chest and abdominal expansion), air flow or pressure, and oxygen saturation using pulse oximetry. Continuous electrocardiography (ECG) is also usually done to evaluate cardiac dysrhythmias and their association with respiration. Other physiological parameters such as periodic limb movement can be measured. EDS can be evaluated by self-report, using instruments such as the ESS or a Multiple Sleep Latency Test, an objective measure of EDS.[23]

Heart failure is associated with depressed and fatigued cardiovascular tolerance and reserve with many neurohormonal dysfunctions.[6] SDB is also associated with increased inflammatory activation, endothelial dysfunction,[1] increased neurohormonal activation, and recurrent hypoxemia leading to myocardial ischemia.[11-13] Therefore, it may be presupposed that heart failure subjects with SDB are likely to have more adverse cardiovascular risk than those without SDB. Mansfield, et al. showed that heart failure patients with SDB often have higher New York Heart Association classes and worse underlying heart functions than those without SDB.[24] This may therefore account for the result of this study showing that heart failure subjects with snoring had a significantly higher waist circumference, systolic blood pressure, left ventricular mass, left ventricular mass index, body mass index, and a higher degree of daytime excessive sleepiness using the ESS than heart failure subjects without snoring.

Increased left ventricular mass is a recognized major cardiovascular risk factor in many populations.[6] Obesity is also associated with increased cardiovascular morbidity. Adipocytes contribute to increased inflammation, endothelial dysfunction, and oxidative stress. The relationship of obesity to snoring has been recognized by several authors.[157] This may be the reason why CHF-snorers in this study had significantly higher mean body mass index and waist circumference than CHF-nonsnorers. The increased left ventricular mass index and the higher prevalence of left ventricular hypertrophy among CHF-snorers also further suggest an increased cardiovascular risk than among CHF-nonsnorers. EDS presents safety concerns, as it may have a negative impact on reaction time, decision making, and safe operation of machinery and motor vehicles. They are thereby prone to domestic and road traffic accidents, loss of concentration, and reduced productivity. Other factors may contribute to sleep abnormalities in patients with heart failure and these include medications (diuretics), nocturnal pain or dyspnea, poor sleep habits, environmental factors, and depression.

Although the mechanisms by which OSA and CHF are related are not completely understood, various potential mechanisms include the effect of hypoxia, hypercapnia, baroreceptors desensitization, and arousal responses which contribute to acute and chronic augmentation of the sympathetic nervous system.[5] The clinical features of SDB include sleep fragmentation and excessive daytime somnolence. This was manifested by the fact that the ESS score was significantly higher among heart failure subjects with SDB than those without SDB.

Treatment of OSA by continuous positive airway pressure (CPAP) in patients with normal ventricular function has been shown to reduce nocturnal and daytime sympathetic nervous system activity, augment heart rate variability, and may reduce oxidative stress, increase endothelially derived nitric oxide, and improve endothelially mediated vasodilatation.[2526] CPAP leads to improvement of left ventricular function and improvement in the sleep profile of heart failure patients.[11011]

In conclusion, snoring and high risk for sleep apnea are highly prevalent in CHF. Heart failure subjects with SDB seem to be associated with a higher cardiovascular risk than heart failure subjects without SDB. Further studies are suggested to document the pathogenetic association and the therapeutic modalities for reducing the CV risk in heart failure subjects with SDB. Giving the high prevalence of SDB in heart failure subjects, assessment for sleep disorders may be included in their clinical care in order to further reduce the cardiovascular risk.