Liver Enlargement Predicts Obstructive Sleep Apnea-Hypopnea Syndrome in Morbidly Obese Women

Abstract

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is frequently present in patients with severe obesity, but its prevalence especially in women is not well defined. OSAHS and non-alcoholic fatty liver disease are common conditions, frequently associated in patients with central obesity and metabolic syndrome and are both the result of the accumulation of ectopic fat mass. Identifying predictors of risk of OSAHS may be useful to select the subjects requiring instrumental sleep evaluation. In this cross-sectional study, we have investigated the potential role of hepatic left lobe volume (HLLV) in predicting the presence of OSAHS. OSAHS was quantified by the apnea/hypopnea index (AHI) and oxygen desaturation index in a cardiorespiratory inpatient sleep study of 97 obese women [age: 47 ± 11 years body mass index (BMI): 50 ± 8 kg/m²]. OSAHS was diagnosed when AHI was ≥5. HLLV, subcutaneous and intra-abdominal fat were measured by ultrasound. After adjustment for age and BMI, both HLLV and neck circumference (NC) were independent predictors of AHI. OSAHS was found in 72% of patients; HLLV ≥ 370 cm³ was a predictor of OSAHS with a sensitivity of 66%, a specificity of 70%, a positive and negative predictive values of 85 and 44%, respectively (AUC = 0.67, p < 0.005). A multivariate logistic model was used including age, BMI, NC, and HLLV (the only independent predictors of AHI in a multiple linear regression analyses), and a cut off value for the predicted probability of OSAHS equal to 0.7 provided the best diagnostic results (AUC = 0.79, p < 0.005) in terms of sensitivity (76%), specificity (89%), negative and positive predictive values (59 and 95%, respectively). All patients with severe OSAHS were identified by this prediction model. In conclusion, HLLV, an established index of visceral adiposity, represents an anthropometric parameter closely associated with OSAHS in severely obese women.

Keywords: hepatic left volume; insulin resistance; metabolic syndrome; morbid obesity; non-alcoholic fatty liver disease; obstructive sleep apnea–hypopnea syndrome.

Figure 1

Correlations between anthropometric variables and respiratory paramenters in the cohort of 97 obese women. Relationships between the hepatic left lobe volume (HLLV) and the apnea/hypopnea index (AHI) (A) the mean percent oxygen saturation [SpO₂, (C)] and the oxygen desaturation index (ODI) (E). Relationship between neck circumference and AHI (B) mean percent oxygen saturation [SpO₂, (D)] and (ODI), (F). AHI and ODI values are reported on a logarithmic scale, i.e., LOG₁₀(1 + AHI) and LOG₁₀(1 + ODI) which can handle zero values. R: Pearson’s correlation coefficient (*p < 0.05).

Figure 2

Hepatic left lobe volume (HLLV) (A) and neck circumference (B) average values for each class of obstructive sleep apnea–hypopnea syndrome (OSAHS). OSAHS severity is defined as mild for apnea/hypopnea index (AHI) ≥ 5 and < 15; moderate for AHI ≥ 15 and ≤ 30; and severe for AHI > 30. Error bars represent the 95% confidence interval of the mean. The variances of HLLV (p = 0.08) and neck circumference (p = 0.38) were not significantly different among OSAHS categories by the Levene’s test. *: p < 0.05 for linear trend by ANOVA.

Figure 3

Cumulative effects of hepatic left lobe volume (HLLV) and neck circumference (NC) on the apnea/hypopnea index (AHI). Subjects were categorized in four subgroups according to the median values of HLLV (=408 cm³) and NC (=38 cm) in the whole cohort. The variances of AHI values were not significantly different among the four subgroups by the Levene’s test (p = 0.07). *p < 0.05 by ANOVA.

Figure 4

Receiver operating characteristic (ROC) curves for the diagnostic performance of hepatic left lobe volume (HLLV) (A) and neck circumference (NC) (B) to identify obstructive sleep apnea syndrome (OSAHS) in the cohort of 97 obese patients. Thin lines show 95% confidence intervals; arrows point at the optimal cutoff as defined by the Younden index for diagnostic sensitivity and specificity. AUC, area under the curve. *p < 0.05 by ROC curve analysis.