Impact of obstructive sleep apnea on aortic elastic properties and left ventricular functions in hypertensive and normotensive patients: correlation with brain natriuretic peptide levels

Abstract

Background: Obstructive Sleep Apnea Syndrome (OSAS) has been linked to Cardiovascular (CVS) complications. Diagnosis of effects of sleep apnea on heart may be difficult before apparent examination findings. Although mechanisms underlying association between OSAS & CVS disease are not known,CVS effects of OSAS have a multifactorial pathogenesis. Objectives: To evaluate aortic elastic properties & Left Ventricular (LV) functions in patients with OSAS with & without systemic Hypertension (HTN) & correlate findings with Brain Natriuretic Peptide (BNP) levels. Patients and methods: The study comprised 133 patients & 30 healthy volunteers as a control group (Group I). Patients were divided according to presence of OSAS & HTN into 3 groups; Group II with HTN,Group III with OSAS and Group IV with both HTN & OSAS. All subjects underwent polysomnography & echocardiography. Assessment of LV functions,aortic strain (AS),distensibility (AD) & aortic wall systolic velocity (AWSV) was done using conventional echocardiography & Doppler tissue imaging (DTI). BNP levels were measured by rapid immunoassay. Results: Comparing control group to patients groups, AWSV (8.5±1.5 cm/sec vs. 6.04±2.4 cm/sec, 6.1±1.9 cm/sec,5.01±1.5 cm/sec p <0.001),AS (17.2±9% vs. 11.7±4%, 8.7±5%,8.7±4%,p <0.001 for each) & AD (10±5 cm2/dyn/103 vs. 6±2 cm2/dyn/103, 7±1 cm2/dyn/103, 4±2 cm2/dyn/103, p<0.01) were significantly lower in all patients groups than controls. Long axis LV systolic function & LV diastolic function parameters were significantly impaired in all patients groups compared to controls, whereas LV Tei index & BNP levels were significantly higher in patients in comparison to controls.AWSV,AD& AS have strong positive correlations with mitral annular plane systolic excursion (MAPSE) (r=0.61, r=0.55, r=0.41 respectively, p<0.01), Systolic mitral annular velocity (Sm) (r=0.64, r=0.48, r=0.47 respectively, p<0.001), mitral inflow E/A ratio (r=0.49, r=0.41, r=0.39 respectively, p<0.05) & DTI-derived mitral annular Em/Am ratio (r=0.60, r=0.45, r=0.42 respectively, p<0.01) while correlation was negative with Tei index (r= -0.61, r= -0.5, r= -0.45 respectively, p<0.01) & BNP levels (r= -0.67, r= -0.59, r= -0.5 respectively, p<0.001). In multivariate analysis, age, HTN, OSAS & LV mass index are independent predictors for impaired aortic elasticity. Conclusion: Aortic elasticity parameters (AWSV, AS & AD), Long axis LV systolic function, LV diastolic function parameters, Tei Index and BNP levels are all impaired in patients with OSAS, HTN or both. Accordingly subtle subclinical cardiac dysfunction is present in patients with OSAS independent from HTN.