INSPIRATORY DYNAMIC OBSTRUCTION DETECTED BY FORCED OSCILLATION DURINGCPAP - A MODEL STUDY

Assessment of upper airway mechanics in patients with obstructive slee p apnea/hypopnea (OSA) can be carried out qualitatively from indirect signals (flow pattern, snoring, strain gauges, inductance plethysmogra phy) or quantitatively by means of invasive estimation of esophageal p ressure. The forced oscillation technique (FOT) is a noninvasive metho d of potential interest for quantitatively assessing airway obstructio n in the sleeping patient. The aim of this work was to ascertain in a model study whether FOT could provide an index of airway obstruction w hen applied at the conditions of total and partial occlusions similar to the ones found in patients with OSA. An airway analog closely mimic king upper airway collapsibility was constructed and mechanically char acterized by the relationship between its flow, upstream and downstrea m pressures as well as by means of FOT. We simulated total collapse (a pnea), different levels of partial collapse with flow limitation (hypo pnea), and release of airway obstruction when the collapsible analog w as used as an artificial upper airway in a spontaneously breathing sub ject submitted to continuous positive airway pressure (CPAP) up to 14 cm H2O . s/L. The results showed that the amplitude of airway impedanc e measured by FOT was a suitable index to detect obstruction in collap sible segments. We concluded from this realistic model study that FOT could be a valuable tool for quantitatively assessing airway obstructi on in patients with OSA treated with CPAP. This noninvasive technique is potentially useful both in studying upper airway mechanics in detai l and in automatically monitoring airway obstruction in routine studie s.