Ratio of aldosterone to B-type Natriuretic Peptide is independently associated with severity of obstructive sleep apnea among middle-aged men

Abstract

Background: Recently, nocturnal rostral fluid shift from legs to neck has been proposed as one of a pathophysiological concept of obstructive sleep apnea (OSA). On the other hand, several reports have demonstrated that both aldosterone which acts fluid retention and B-type natriuretic peptide (BNP) which acts fluid diuresis on the contrary, are associated with severity of OSA and obesity. Therefore, we evaluated whether the imbalance of these neurohumoral factors is associated with OSA severity. Methods: 349 middle-aged men with severe OSA {apnea-hypopnea index (AHI)≥30/h} were enrolled in this study. Patients with taking beta blockers, aldosterone receptor blockers, diuretics, ACE-Is, and ARBs were excluded. All participants were measured plasma aldosterone and BNP early in the morning after polysomnogragy, and calculated the ratio of aldosterone to BNP (A/B). Furthermore, participants were divided into 3 groups according to tertiles of A/B. Multi-variate analysis was performed to determine whether A/B was the independent variables for AHI. Results: AHI and body mass index (BMI) increased significantly with higher tertiles of A/B (50.6±17.0, 53.4±16.2, 59.8±22.0/h, and 26.8±3.9, 27.7±4.6, 28.5±4.1kg/m2, P<0.05 for trend, respectively). AHI showed a positive correlation with A/B (r=0.20, P=0.0001), whereas no significant correlations were observed between AHI and plasma aldosterone or BNP. Aldosterone/renin ratio also did not have significant correlation with AHI. BNP showed significantly a negative correlation with BMI (r=-0.14, P=0.008). Multivariate analysis revealed that A/B, norepinephrine and BMI were significantly independent variables for AHI even after adjustments for age, waist circumference, blood pressure, fasting glucose level and medications for hypertension and diabetes (Beta=0.13, 0.18, and 0.42, P<0.05, respectively). Conclusions: These results show that the increase of A/B is independently associated with OSA severity among middle-aged men with severe OSA. Therefore, this imbalnce of neurohumoral factors which leads to excessive fluid retension might be an important pathophygiology which contibutes to rostral fluid shift.