The sites of obstruction in OSA, identified by continuous measurements of airway pressure and flow during sleep: ambulatory versus in-hospital recordings.

Polysomnography provides information about the severity of obstructive sleep apnoea (OSA), but is less satisfactory in predicting the effect of uvulopalatopharyngoplasty (UVPP). Another possible investigation in patients with suspected OSA is to determine the sites of pharyngeal obstruction or collapse by an overnight recording of airflow and upper airway pressures at several levels during sleep. Before these measurements can be established as a routine investigation, reproducibility studies have to be carried out. In 11 men with suspected OSA, we recorded airway pressure and airflow during sleep for 2 nights, the first in hospital and the second at home (ambulatory). The recording conditions were deliberately different in order to set up a 'worst case' comparison. Transpalatal (upper) or subpalatal (lower) obstructive predominance remained constant in 9 patients despite considerable changes in the absolute number of obstructive events. Only one patient had exclusively upper or lower obstructive events during the initial recording and this suggests that the level diagnosis after an overnight study using pressure and airflow may be more accurately described as percentage upper obstructive events of total. We conclude that the relationship between upper and lower obstructive events is reproducible between ambulatory and hospital recording, but recommend that level diagnosis should be interpreted with caution in patients with low recorded apnoea hypopnoea index (AHI).