***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    ***EXAMPLES*** 
    Input: Background —The purpose of this study was to determine the role of obstructive sleep apnea syndrome ( OSAS ) as an independent risk factor for the development of left ventricular diastolic abnormalities . Moreover , we tested the hypothesis that nasal continuous positive airway pressure ( nCPAP ) improves such alterations in OSAS patients by eliminating apneic events . Methods and Results —In this prospect i ve , r and omized , placebo-controlled , double-blind crossover study , 27 consecutive newly diagnosed middle-aged OSAS men with neither controllable factors nor conditions affecting left ventricular diastolic function and 15 healthy control subjects were selected . OSAS patients were r and omized to 12 weeks on sham nCPAP and 12 weeks on effective nCPAP application .  Echocardiographic parameters , blood pressure recordings , and urinary catecholamine levels were obtained at baseline and after both treatment modalities . At baseline , an abnormal left ventricular filling pattern was present in 15 of the 27 OSAS patients and only in 3 of the 15 control subjects ( P=0.020 ) . Impaired relaxation was by far the most common abnormal pattern in both groups ( 11 and 3 patients , respectively ) . In OSAS patients , 12 weeks on effective nCPAP induced a significant increase in E/A ratio ( P<0.01 ) , as well as reductions in mitral deceleration ( P<0.01 ) and isovolumic relaxation ( P<0.05 ) times . Conclusions —OSAS can affect left ventricular diastolic function independently of other possible factors . Chronic application of nCPAP could avoid the progression of diastolic abnormalities , and indeed , it might reverse these alterations , at least in the initial stages before severe structural changes can be developed BACKGROUND Limited data have suggested that sleep-disordered breathing , a condition of repeated episodes of apnea and hypopnea during sleep , is prevalent among adults . Data from the Wisconsin Sleep Cohort Study , a longitudinal study of the natural history of cardiopulmonary disorders of sleep , were used to estimate the prevalence of undiagnosed sleep-disordered breathing among adults and address its importance to the public health . METHODS A r and om sample of 602 employed men and women 30 to 60 years old were studied by overnight polysomnography to determine the frequency of episodes of apnea and hypopnea per hour of sleep ( the apnea-hypopnea score ) . We measured the age- and sex-specific prevalence of sleep-disordered breathing in this group using three cutoff points for the apnea-hypopnea score ( > or = 5 , > or = 10 , and > or = 15 ) ; we used logistic regression to investigate risk factors . RESULTS The estimated prevalence of sleep-disordered breathing , defined as an apnea-hypopnea score of 5 or higher , was 9 percent for women and 24 percent for men . We estimated that 2 percent of women and 4 percent of men in the middle-aged work force meet the minimal diagnostic criteria for the sleep apnea syndrome ( an apnea-hypopnea score of 5 or higher and daytime hypersomnolence ) . Male sex and obesity were strongly associated with the presence of sleep-disordered breathing . Habitual snorers , both men and women , tended to have a higher prevalence of apnea-hypopnea scores of 15 or higher . CONCLUSIONS The prevalence of undiagnosed sleep-disordered breathing is high among men and is much higher than previously suspected among women . Undiagnosed sleep-disordered breathing is associated with daytime hypersomnolence Obstructive sleep apnoea ( OSA ) is primarily regarded as a male disorder , presenting with snoring , daytime sleepiness and cardiovascular disease . We aim ed to determine the frequency of sleep apnoea among females in the general population . We investigated 400 females from a population -based r and om sample of 10,000 females aged 20–70 yrs . They answered a question naire and performed overnight polysomnography .  OSA ( apnoea/hypopnoea index ( AHI ) ≥5 ) was found in 50 % ( 95 % CI 45–55 % ) of females aged 20–70 yrs . Sleep apnoea was related to age , obesity and hypertension , but not to daytime sleepiness . Severe sleep apnoea ( AHI ≥30 ) was present in 14 % ( 95 % CI 8.1–21 % ) of females aged 55–70 yrs and in 31 % ( 95 % CI 12–50 % ) of obese females with a body mass index of ≥30 kg·m−2 aged 55–70 yrs . Sleep apnoea with daytime sleepiness and sleep apnoea with hypertension were observed as two different phenotypes of OSA . OSA occurs in 50 % of females aged 20–70 yrs . 20 % of females have moderate and 6 % severe sleep apnoea . Sleep apnoea in females is related to age , obesity and hypertension , but not to daytime sleepiness . When search ing for sleep apnoea in females , females with hypertension or obesity should be investigated The relative contributions of hypoxia and hypercapnia in causing persistent sympathoexcitation after exposure to the combined stimuli were assessed in nine healthy human subjects during wakefulness . Subjects were exposed to 20 min of isocapnic hypoxia ( arterial O(2 ) saturation , 77 - 87 % ) and 20 min of normoxic hypercapnia ( end-tidal P(CO)(2 ) , + 5.3 - 8.6 Torr above eupnea ) in r and om order on 2 separate days . The intensities of the chemical stimuli were manipulated in such a way that the two exposures increased sympathetic burst frequency by the same amount ( hypoxia : 167 + /- 29 % of baseline ; hypercapnia : 171 + /- 23 % of baseline ) . Minute ventilation increased to the same extent during the first 5 min of the exposures ( hypoxia : + 4.4 + /- 1.5 l/min ; hypercapnia : + 5.8 + /- 1.7 l/min ) but declined with continued exposure to hypoxia and increased progressively during exposure to hypercapnia . Sympathetic activity returned to baseline soon after cessation of the hypercapnic stimulus . In contrast , sympathetic activity remained above baseline after withdrawal of the hypoxic stimulus , even though blood gases had normalized and ventilation returned to baseline levels . Consequently , during the recovery period , sympathetic burst frequency was higher in the hypoxia vs. the hypercapnia trial ( 166 + /- 21 vs. 104 + /- 15 % of baseline in the last 5 min of a 20-min recovery period ) . We conclude that both hypoxia and hypercapnia cause substantial increases in sympathetic outflow to skeletal muscle . Hypercapnia-evoked sympathetic activation is short-lived , whereas hypoxia-induced sympathetic activation outlasts the chemical stimulus Objective Unfavourable effects of sleep-disordered breathing ( SDB ) in heart failure ( HF ) are mainly mediated by impaired sympathetic activity . Few data are available on SDB and cardiac adrenergic impairment evaluated at myocardial level . The aim of the study was to assess the relationship between SDB , cardiac sympathetic innervation assessed by 123I-metaiodobenzylguanidine ( 123I-MIBG ) imaging and prognosis in HF . Methods Observational , prospect i ve study enrolling patients with HF and reduced systolic function . Patients underwent nocturnal cardiorespiratory monitoring to assess SDB presence by apnoea/hypopnoea index ( AHI ) , and 123I-MIBG imaging to calculate heart-to-mediastinum ( H/M ) ratios and washout rate . Patients were prospect ively followed for 29±18 months for the combined endpoint of cardiovascular death and HF hospitalisation . Results Ninety-four patients ( 66.1±9.8 years ; left ventricular ejection fraction 32±7 % ) were enrolled ; 72 ( 77 % ) showed SDB and , compared with non-SDB , significantly reduced early ( 1.67±0.22 vs 1.77±0.13 ; p=0.019 ) and late H/M ratios ( 1.50±0.22 vs 1.61±0.23 ; p=0.038 ) . Dividing patients into two groups according to SDB severity , patients with a moderate – severe disturbance ( AHI > 15 ; n=43 ) showed significantly worse survival for the composite study outcome ( log-rank test , p=0.001 ) with respect to patients with mild or no disorder ( AHI ≤15 ; n=51 ) . Adding SDB variables to the already known prognostic role of 123I-MIBG imaging , we observed a worse survival in patients with both SDB and H/M impairment . Conclusions Patients with systolic HF and SDB show more impaired cardiac adrenergic innervation assessed by 123I-MIBG imaging , and more adverse prognosis compared with HF patients without SDB Background : Obstructive sleep apnea ( OSA ) is characterized by repetitive upper airway obstructions during sleep , and it might cause cardiovascular complications such as heart failure , arrhythmias , myocardial infa rct ion , systemic and pulmonary hypertension . Objectives : To determine right ventricular diameters and myocardial performance index ( MPI ) reflecting ventricular global function in uncomplicated OSA patients . Methods : 49 subjects without hypertension , diabetes mellitus , or any cardiac or pulmonary disease referred for evaluation of OSA had overnight polysomnography and complete echocardiographic assessment .  According to the apnea-hypopnea index ( AHI ) , subjects were divided into three groups : group 1 : control subjects  ( AHI < 5 , n = 20 ) , group 2 : patients with mild OSA ( AHI : 5–14 , n = 11 ) , and group 3 : moderate-severe OSA  ( AHI ≧15 , n = 18 ) . Right ventricular free wall diameter was measured by M mode , and right ventricular MPI was calculated as ( isovolumic contraction time + isovolumic relaxation time)/pulmonary ejection time . Results : There were no differences of age , body mass index , heart rates , systolic and diastolic blood pressures among the groups ( p > 0.05 ) . Right ventricular end-diastolic and end-systolic diameters were not statistically different between the groups , and were within normal limits . Also , right ventricular free wall diameter was not significantly different between the groups of control , mild OSA and moderate-severe OSA ( 6.7 ± 0.9 , 6.9 ± 1.0 , 7.1 ± 1.1 mm , p > 0.05 ) . Right ventricular diastolic dysfunction was shown only in group 3 patients . Right ventricular MPI was statistically higher in group 3 ( 0.62 ± 0.18 ) than in group 2 patients ( 0.50 ± 0.10 ) , and group 1 patients ( 0.48 ± 0.08 , p < 0.001 ) . Conclusions : It wassuggested that patients with moderate-severe OSA had a right ventricular global dysfunction , in addition to the presence of a diastolic dysfunction BACKGROUND In patients with obstructive sleep apnea syndrome ( OSAS ) , repetitive hypoxia due to sleep-induced apnea adversely affects the interaction between myocardial oxygen dem and and supply , result ing in the development of sub clinical cardiac dysfunction . The purpose of the study was to analyze the different involvement of left and right heart myocardial function in patients with OSAS treated with noninvasive ventilation ( NIV ) .  METHODS Conventional Doppler echocardiography , Doppler myocardial imaging ( DMI ) , and two-dimensional speckle tracking echocardiography ( 2DSTE ) of left ( LV ) and right ventricular ( RV ) longitudinal and right atrial ( RA ) deformation were performed in 55 patients with OSAS undergoing NIV ( M/F 38/17 ; mean age 67.8 ± 11.2 years ) . LV and RV global longitudinal strain ( GLS ) was calculated by averaging local strain along the entire right and left ventricle , before and during NIV , and after 6 months of nocturnal NIV therapy . RESULTS LV morphology was comparable before and during NIV , whereas LV ejection fraction and LV DMI early diastolic peak velocity were significantly improved in patients with OSAS during NIV , as was LV regional peak myocardial strain ( P < 0.001 ) . RV diameters were slightly increased in patients with OSAS during ventilation , whereas pulmonary artery systolic pressure ( PASP ) , RV GLS , and regional peak myocardial RV strain were significantly reduced during ventilation ( P < 0.0001 ) . RA transverse diameters and RA area were also slightly increased during NIV , whereas RA lateral wall strain was reduced ( P < 0.001 ) . Acute RV myocardial impairment completely reversed at follow-up , with a decrease in PASP and subsequent increase in both RV and RA myocardial performance . CONCLUSIONS Conventional 2DSTE is a useful tool for assessing left and right heart morphology and myocardial deformation in patients with OSAS and for monitoring both acute and chronic effects of N 
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In addition , left ventricular ejection fraction ( LVEF ) significantly decreased in the OSAS group compared with the controls ( WMD , 95 % CIs : −1.82 [ −2.76 , −0.87 ] ; p < 0.001 ) , and the reduction in LVEF was consistent with the severity of OSAS .