The distribution of hypopnoeic events in relation to apnoeic events in patients with sleep-induced upper airway narrowing.

The purpose of this study was to investigate patients with sleep-induced upper airay narrowing to see if: (1) apnoeic and hypopnoeic events regularly coexist; (2) if sleep-induced upper airway narrowing usually involves more than one level; and (3) whether the distribution of hypopnoeic events reflects that of apnoeic events. A retrospective review of 50 patients with sleep-induced upper airway narrowing was conducted. Recordings were made with a solid-state microtransducer pressure-catheter and an external thermistor for assessment of the distribution and number of obstructive events. Ninety-four per cent of the patients had a mixture of apnoeic and hypopnoeic events. Both transpalatal and subpalatal obstructions were identified in 84% of patients. In 80% of the patients the level of apnoeic events, classified as either mainly (> 50% of total) transpalatal (upper) or subpalatal (lower) reflected that of hypopnoeic events. The percentage upper to total amount of hypopnoeic events correlated significantly with that of apnoeic events (R = 0.77, P < 0.001; Spearman rank correlation).