| Objective: Increasing collapsibility of pharyngeal airway, based on stenosis of upper-airway are known to cause obstructive sleep apnea(OSA). Researchers found that elevation of end-expiratory lung volume(EELV) above functional residual capacity(FRC), is accompanied by improvement in pharyngeal collapsibility and decrease in pharyngeal resistance, due to increases in the cross-sectional area of pharyngeal. Conversely, decreasing EELV below FRC, there are increases in pharyngeal collapsibility and reduces its size, manifest as markedly increases in upper-airway resistance. Therefor, changes in lung volume sizes are well known as involve in the pathogenesis of OSA. Obesity a common risk factors for OSA, studies in obesity have been found they usually decreased in FRC or EELV, due to increase of chest wall elastic loading or decreased in compliance. Some scholars, therefor, believe that the obesity susceptibility to OSA is associated with decreased in their FRC or EELV. However, not all obese persons present with OSA, especially women, who generally have less lung volume than men, but prevalence of OSA in women are low than man. In fact, the sizes of FRC or EELV was not only depends on a chest wall compliance(chest wall outward recoil forces), but also was determined by the compliance of the lungs(lung inward elastic recoil forces). Change of the mechanical properties of respiratory system and lung volume in obses man and women with and without OSA are required to study, this may provide new insights into the underlying pathophysiology of OSA. Thereby, 1.Firstly, a case-control study are required to conduct, and comparisons the difference of lung volume and the respiratory mechanical properties between obese and obese patients with OSA, and aims to explore the account of obese OSA patients respiration with low lung volume and change in the mechanical properties of respiratory in those patient. 2.In order to investigate the adverse effects of the upper-airway stenosis on the mechanical properties of respiratory system and lung volume in patients with OSA, a cross-sectional study are carry out in various severity of OSA patients. 3. To evaluate the ability of impulse oscillometry(IOS) parameters for predicting OSA in obese snorers, and to provide a reliable screening tool for diagnostic OSAS in clinical. 4. To evaluate the mechanical properties of respiratory, gastroesophageal acid reflux events, and serum pulmonary surfactant protein levels in patients with OSA and the correlationship between those factors were appraised, aims to discuss the cause of serum surfactant protein level decreased in OSA patient, and this may provide a new susceptibility locus for OSA in genetic studies in the future. Methods: 1.Subjects who were obese to various degrees with normal spirometric values underwent overnight polysomnography to determine the presence or absence of OSA and were labeled as cases or controls. Lung volume and respiratory mechanical properties were measured by plethysmograph and impulse oscillometry, respectively. 2. Consecutive subjects who were overweight and obese without a history of lung diseases, but troubled with snoring or suspicion of OSA were included in this cross-sectional study. According to polysomnography the subjects were distributed into OSA and non-OSA groups, and were further sub-grouped by gender, because of differences between males and females, in term of, lung volume size, airway resistance, and the prevalence of OSA among genders. Lung volume and respiratory mechanical properties at different-frequencies were evaluated by plethysmograph and an IOS, respectively. 3.Consecutive patients with normal spirometric values were included in study. Full laboratory polysomnography was performed and IOS measurements were determined in sitting and supine positions to obtain respiratory impedance(Zrs), resistance(Rrs), and reactance(Xrs) parameters. The respiratory resistance at zero-frequency(Rrs0) was extrapolated by linear regression analysis of Rrs versus low-oscillatory-frequencies and its inverse, respiratory conductance(Grs), was calculated. 4.Consecutive subjects who absence of lung diseases with suspicion of OSA were underwent nocturnal polysomnography to determine the presence or absence of OSAS, the mechanical properties of respiratory, gastroesophageal acid reflux and laryngopharyngeal reflux events, and serum pulmonary surfactant protein levels were measured by applying IOS, ambulatory 24-hour multichannel intraluminal impedance-p H monitoring and ELISA methods, respectively. Results: 1. A total of 76 men and 31 women were diagnosed with OSA(cases); 64 men and 33 women without OSA were confirmed as controls. Expiratory reserve volume(ERV) and FRC were significantly decreased in cases compared with controls. Respiratory impedance and resistance at 5 Hz were significantly higher in cases than in controls, although reactance at low frequencies was significantly lower in cases than in controls Reactance at 5 Hz(Xrs5) was found to be independently highly correlated with the severity of OSA as defined by the Apnea-Hypopnea Index and was significantly correlated with FRC. 2.FRC and ERV were significantly decreased in the OSA group compared to the non-OSA group among males and females. As weight and BMI in males in the OSA group were greater than in the non-OSA group(90±14.8vs.82±10.4kg, P<0.001; 30.5±4.2 kg/m2 vs.28.0±3.0 kg/m2, P<0.001), multiple regression analysis was required to adjust for BMI or weight and demonstrated that these lung volumes decreases were independent from BMI and associated with the severity of OSA. This result was further confirmed by the female cohort. Significant increases in total respiratory resistance and decreases in Grs were observed with increasing severity of OSA, as defined by the apnea-hypopnea index(AHI) in both genders. The specific Grs(s Grs) stayed relatively constant between the two groups in woman, and there was only a weak association between AHI and s Grs among man. Multiple stepwise regression showed that reactance at 5Hz(Xrs5) was highly correlated with AHI in males and females or hypopnea index in females, and also independently highly correlated with peripheral airway resistance and significantly associated with decreasing FRC. 3.In both the sitting and supine positions Rrs0, Zrs5, and Rrs at 5Hz and Grs, the reciprocal of Zrs5(Gz), and Xrs at 5 Hz(Xrs5) all had significant positive or negative correlations with OSAS severity as defined by AHI. The correlation coefficients between Rrs0, Zrs5, Rrs5, Grs0, Gz, Xrs5 and AHI were 0.424, 0.393, 0.377,-0.424,-0.393, and-0.514, respectively(all P<0.001). Both the ROC curves and a logistic regression predict model, we constructed based on parameters of respiratory mechanical properties measured by IOS showed that Xrs5 in the supine position was the best for predicting OSAS with a sensitivity of 73 % and specificity of 84% at the optimal cut-off point of-0.21 k Pa·s·L-1. A logistic predict model revealed that the Xrs5 combined with patient sex and lung volume yielded a specificity of 83.3 % with a sensitivity of 76.8 % for indicating OSAS.4. A total of 58 patients with OSA was diagnosed with polysomnography, according to the subjects AHI they were distributed into OSAS and non-OSAS groups; Compared with non-OSAS group, there were significantly decreased of FRC and ERV, and were significantly increased of the Zrs5, and all oscillatory frequencies of Rrs were found, although, Xrs was significantly lower in OSAS patients; total reflux episodes, proximal esophageal acid reflux episodes and De Meeste scores were significantly higher in OSAS patients comparison with non-OSAS group; serum SP-B levels significantly lower in OSAS patients than non-OSAS and was independently of BMI associated with OSA severity as defined by the AHI. Conclusions: 1. FRC is significantly decreased in overweight or obese patients with OSA compared with those without OSA, which may be attributed to an increase in lung elastic recoil. The stronger correlation between Xrs5 and OSA severity might indicate upper airway stenosis, and abnormally increased lung elastic recoil may contribute to OSA. 2.Total respiratory resistance and peripheral airway resistance significantly increase, and its inverse Grs decrease, in obese patients with OSA in comparison with those without OSA, and are independently associated with OSA severity. These results might be attributed to the abnormally increased lung elasticity recoil pressure on exhalation, due to increase in lung elasticity and decreased lung volume in obese OSA.3.Respiratory resistance and reactance measured by IOS are abnormal in obese OSAS patients, and these parameters are moderate to closely correlated with OSAS severity. IOS might be a useful screening tool for detecting OSAS in clinic based populations.4. Increase with severity of OSA, respiratory resistance increased and manifest as Zrs5 and all frequencies Rrs are rising; compliance of the lungs decreased manifest as Xrs5 is dropping; episodes of gastroesophageal and proximal esophageal acid reflux are increased with OSA severity as defined by AHI increasing, this also positively associated with respiratory resistance and inversely associated with respiratory reactance. Change of the mechanical properties of respiratory in OSAS patients appear to not significantly associated with lower levels of serum SP-B... |
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