Lung volume and its correlation to nocturnal apnoea and desaturation

The cross-sectional area of the upper airway is known to be lung volume dep endent. If, and to what extent, lung volume variables correlate to nocturna l obstructive apnoeas and oxygen desaturations independently of other facto rs known to affect lung volumes and sleep disordered breathing is still unc lear. A total of 92 subjects were examined by ambulatory recording of nocturnal o bstructive apnoeas and desaturations. Sixty-nine of the subjects had a hist ory of snoring and 23 were healthy subjects without complaints of snoring a nd daytime sleepiness. All subjects performed static and dynamic spirometry for measurements of lung volumes. To evaluate the correlation between lung volume variables and apnoea index (AI) and oxygen desaturation index (ODI) , simple and multiple regression analysis was performed. Expiratory reserve volume (ERV) was found to be lower in subjects with snor ing and apnoeas (ERV = 1.01) than in non-snoring subjects (ERV = 1.71), (P< 0.001). Forced expiratory volume in 1 sec (FEV1)/vital capacity (VC) was sl ightly, but significantly (P=0.031), lower in subjects with snoring and noc turnal apnoeas and desaturations. In the multiple regression analysis ERV w as found to be independently correlated to both AI (R-2 = 0.13; P = 0.001) and ODI (R-2 = 0.11; P = 0.002). Multiple regression analysis also revealed that ERV, body mass index (BMI) and habitual smoking together accounted fo r 43% of the variation in AI and 48% of the variation in ODI. We find a significant independent association between ERV and nocturnal obs tructive apnoea and oxygen desaturation frequency. Our results indicate tha t ERV is correlated to these events to a similar extent, as is obesity.