One of the contributing factors to upper airway collaps in obstructive sleep apnea (OSA) is reduced end expiratory lungvolume (EELV) (Kapur, V.H. et al. Respiratory Care 2010;55). There is evidence for correlation of apnea hypopnea index (AHI) with EELV in supine position during sleep (Owens, R.L. et al. J App Physiol 2010;108:445-51). In respiratory function testing however, EELV is routinely measured in sitting position and during wake (EELVsit).
Aims and objectives
To establish the relationship between EELVsit and OSA. We hypothesized that EELVsit may affect the severity of OSA.
In an observational study the relationship between EELVsit and OSA in 59 adult patients of Orbis Medical Centre, Sittard (The Netherlands) was assessed using a regression analysis. EELVsit was evaluated by helium dilution technique, and severity of OSA by apnea hypopnea index (AHI) based on polysomnography measurements. In addition EELVsit was compared to other predictors of OSA; Epworth sleepiness scale (ESS), Mallampati-score, body mass index (BMI), and neck- and abdominal circumference, by means of a multiple regression analysis.
EELVsit was a predictor of AHI, R=-0,392 (p=0,003). Multiple regression analysis demonstrated that abdominal circumference explained 15,5% of variance of AHI, and together with EELVsit 23,4% of the variance of AHI was explained. Other predictors were not significant.
EELVsit contributes to the severity of OSA and might therefore be useful to differentiate between high and low risk patients for OSA in screening and diagnostics settings. Abdominal circumference also appeared to predict severity of OSA and had even more impact on AHI compared to EELVsit.