obstructive sleep apnea ( osa ) is characterized by frequent episodes of termination of respiratory airflow caused by upper airway collapse during sleep , followed by oxyhemoglobin desaturation , persistent inspiratory attempts against the obstructed airway and arousals from sleep .
the inspiratory airflow can either decrease ( hypopnea ) or be completely absent ( apnea ) , and an apnea that lasts 10 seconds or longer , associated with ongoing ventilatory effort , characterizes a patient with osa .
the airflow limitation episodes are usually accompanied by decrease in hemoglobin level , which are usually terminated by quick micro - arousals as a result of excessive respiratory drive caused by the continuing hypoxemia [ 23 ] . to establish a definite diagnosis ,
the diagnosis of osa is confirmed when a person has an apnea / hypopnea index ( ahi : number of apneas and hypopneas per hour of sleep ) of more than five events per hour , associated with symptoms of excessive daytime sleepiness .
although known to be a benign disease , numerous studies have shown that osa is usually correlated with increased morbidity and mortality because of cvd such as systemic and/or pulmonary hypertension as its most common consequence , heart failure , myocardial infarction and stroke [ 69 ] .
oxyhemoglobin desaturation - resaturation , which is common in osa patients , results in free radical production , release of proinflammatory cytokines and prothrombotic mediators and endothelial dysfunction and leads to sympathetic nervous system activity and increased blood pressure , as well as impairment of cerebrovascular auto - regulation .
continuous positive airway pressure ( cpap ) has been shown to have cardio protective effects , decreasing mortality and morbidity among these patients [ 1214 ] .
numerous community - based studies have examined the relationship between osa and cvds [ 10 , 1821 ] .
based on these studies , age , gender , smoking status , bmi , ahi , total sleep time and day sleepiness were some of the clinically important predictors of cvd outcomes in osa patients .
we hypothesized that the ahi , currently used to determine the severity of osa , is not by itself enough to accurately predict cardiovascular outcomes in individuals with osa .
we also hypothesized that several factors such as patients demographic and clinical characteristics would have greater accuracy for predicting cvds . based on our electronic search ,
there is no published data about the prevalence of cvd among the iranian population with osa .
our study aimed to resolve conflicting evidence on the impact of severity of osa , gender , age , bmi , smoking status and socioeconomic status on the association between osa and development of cvds .
medical files of 385 patients ( from 2009 to 2011 ) with definite osa , confirmed by overnight polysomnography were selected in noor sleep clinic , tehran , iran .
participants were eligible if they only had osa ( not other types of sleep apnea such as central or mixed sleep apnea ) with ahi of equal or more than five events / hour .
demographic data were collected from patient files and included gender , age ( as reported by patients ) , smoking status and educational status ( last academic degree reported by patients ) .
three modes for smoking status were considered : never - smoker , ever - smoker and ex - smoker .
bmi ( weight in kilograms divided by the square of height in meters ) and ahi ( events per hour ) were derived from the polysomnography reports .
several questions were designed in a questionnaire to detect cvds such as presence of cvd , type of cvd and medications used .
if there was any controversy in the answers , the patients were questioned about their disease status to clarify their health / disease state .
the data were analyzed using single regression analysis followed by multiple regression analysis ( by backward method ) to identify variables that were independently associated with cvd .
the majority of patients were males ( 71.9% ) . among the studied individuals , 26.5% showed at least one sign / symptom of cvd and hypertension was the most commonly reported sign ( 74.5% ) .
demographic characteristics and polysomnographic data of patients in cvd positive and cvd negative groups ( values are presented as meansd ) of patients , 17.9% had hypertension , 2.6% had coronary artery disease , 0.5% had arrhythmia and 0.3% had stroke ; 2.3% of the patients had both hypertension and coronary artery disease , 0.3% had both hypertension and history of myocardial infarction and 0.3% had both hypertension and history of stroke ; 0.8% of patients had myocardial infarction and one of them had hypertension as well .
all variables had a significant association with cvd , except for smoking status ( p=0.77 ) .
we only selected variables with p - values less than 0.20 in simple regression analysis and entered them into the multiple logistic regression model .
multiple logistic regression analysis showed that the odds ratios for one grade increase in bmi and one year increase in age were 1.13 and 1.12 , respectively ( p<0.001 ) . in presence of these variables , severity of apnea ,
gender and level of education ( as a socioeconomic index ) had no significant correlation with cvd ( p=0.36 , p=0.83 and p=0.79 , respectively ) .
this study provided information on the association between osa and cvds . in our osa population ,
26.5% showed at least one sign / symptom of cvd , with hypertension being the most common sign ( 74.5% ) .
while ahi was found to predict cvd in simple regression analysis , no significant association was found in multiple model adjusted for potential confoundders .
multiple regression analysis showed that aging and obesity were significant predictors of the occurrence of cvd in osa patients .
lavie and lavie   in a case - control study on seventy of osa showed that severity of osa affected biochemical markers associated with cvds only in severe stage and not mild or moderate stage of osa .
shahar et al ,   in a cross sectional study also showed modest to moderate effects of sleep disordered breathing on various manifestations of cvds within a range of ahi values that were considered normal or only mildly upraised .
kendzerska et al ,   in a decade - long cohort study showed that osa - related factors other than ahi were important predictors of composite cardiovascular outcome .
our findings were in agreement with the afore - mentioned studies indicating that osa - related factors other than ahi ( bmi and aging ) are important predictors of cvds .
the mean of bmi in cvd+ group was calculated to be approximately 32 kg / m2 , which put them in obese group of bmi classification . in parallel with our study , dacal quintas
et al ,   found that the prevalence of osa in normal weight patients was lower than that in overweight and obese patients .
seetho et al ,   reported that patients with osa and severe obesity had increased arterial stiffness , which would possibly affect cardiovascular risk independently of metabolic abnormalities .
carlson et al ,   showed that age , sleep apnea and obesity represented both independent and additive risk factors for development of systemic hypertension .
similarly , lenfant   described the correlation among obesity , hypertension and osa as a triangular relationship ; osa and obesity have an interactive relation and both of them have increasing effect on incidence of hypertension .
our study showed that aging was another significant factor to explain the presence of cvd among osa patients .
pywaczewski et al ,   showed that the frequency of cardiovascular complications occurring in osa population increased with age .
evidence has been inconsistent on the effect of gender on the association between osa and cardiovascular events . in our study , women with osa were more susceptible to develop cvd than men .
drummond et al ,   and quintana - gallego et al ,   found that women with osa had hypertension more frequently than men .
faulx et al ,   found that ahi was inversely associated with flow - mediated dilation and peak blood flow in women .
in contrast , no relationship between ahi and flow - mediated dilation was found in men .
these results raise the possibility that women with sleep - disordered breathing are more vulnerable to related cvds than men .
on the other hand , mohsenin et al ,   showed that markedly obese men with osa may have a nearly two - fold greater risk for hypertension than women .
gaines et al ,   showed that although women have naturally higher levels of inflammatory and metabolic markers than men , men with sleep apnea appear to have a more severe inflammatory profile compared to women .
it is important to consider the role of bmi in this study and its conclusion : male sex is more susceptible for developing cvd only  at the highest quartile of bmi  . in a case - control study by lavie and lavie
, a comparison was made between smoker and non - smoker patients with osa and they showed a significant interaction effect between smoking and severity of apnea on ceruloplasmin and high - density lipoprotein ( hdl ) levels .
smokers with severe sleep apnea had the highest level of ceruloplasmin and the lowest level of hdl .
they concluded that smoking and sleep apnea had a synergistic effect on some of the biochemical cardiovascular risk markers .
patients with severe sleep apnea who smoked were at a greater risk for developing cvds than smokers with mild - moderate sleep apnea and patients who did not smoke .
in our study , no significant correlation was observed between smoking and cvds ( p=0.77 ) .
one probable reason may be that most ex - smokers stopped smoking before doing the sleep test according to the doctor s advice . some studies categorized ex - smokers in the non - smoker group [ 3536 ] .
based on the electronic search , the current study is the first to provide comprehensive information about the role of severity of osa as a cause of cvd and its relationship with other important risk factors in an iranian population .
we included patients with a wide range of osa severity and a relatively large number of females .
our findings are based on patients referred to a single center , which may reduce the generalizability of our findings .
our study showed that ahi was significantly associated with cvd in simple regression analysis ; however , this association was not significant after controlling for other predictors .
other osa - related predictors , such as bmi and age were significantly and independently correlated with increased risk of cvds , respectively . in presence of these variables , other phenotypic and socioeconomic factors like severity of apnea ,
thus , health care providers should implement bmi control strategies and improve the quality of care for the elderly patients .
 objectives : obstructive sleep apnea ( osa ) can lead to various cardiovascular disorders ( cvd ) such as hypertension . 
 there is no documented data about this relationship among the iranian population . 
 the aim of this study was to obtain comprehensive information about the severity of osa as a cause of cvd and its relationship with other important risk factors.materials and methods : in this cross sectional study , we studied patients with osa and apnea / hypopnea index of 5 or more . 
 the data were collected from the patients polysomnography report and medical files . 
 data analysis was done with spss version 18.results:the majority of patients were males ( 71.9% ) . among the studied individuals , 26.5% showed at least one sign of cvd , and hypertension was the most common condition ( 74.5% ) . 
 multiple regression analysis showed that the odds ratios for one unit increase in bmi and one year increase in age were 1.13 and 1.12 , respectively ( p<0.001).conclusions : in our study , bmi and age had the strongest relationship with cvd . 
 thus , public health care providers should implement weight control strategies and improve diagnostic and treatment procedures for the elderly patients . 