The variability of the apnoea-hypopnoea index

This study was designed to evaluate the variability of the apnoea-hypopnoea index (AHI) in 20 patients with obstructive sleep apnoea-hypopnoea syndrom e (OSAHS) and to determine possible relationships of this variability with other polysomnographic parameters. The subjects were recorded on four conse cutive nights. The mean AHI values were not significantly altered throughou t the four recording nights (P = 0.67). The intraclass correlation coeffici ent of the AHI on the four nights was 0.92. However, the Bland and Altman p lot showed that, individually, the AHI presented an important variability, which was not related to its initial value. In regard to the OSAHS severity , 50% of the patients changed the classification from the first to the subs equent nights. Thirteen of the 20 patients (65%) presented a variation in t he AHI value equal or higher than 10 events h(-1). When we evaluated the AH I mean values for a specific body position and sleep stage, no difference w as observed among the nights. In both supine and lateral-ventral decubitus, higher AHI was observed during Stages 1 and 2 than the other stages. Addit ionally, the AHI during Stages I and 2 and REM sleep was higher on the supi ne than on the lateral-ventral decubitus. The AHI in OSAHS patients present ed a good correlation among the four recording nights; however, a significa nt individual variability should be considered, especially when AHI is appl ied in OSAHS classification or as a criterion of therapeutic success.