Airways dilate to simulated inspiratory but not expiratory manoeuvres.

In a healthy human, deep inspirations produce bronchodilation of contracted airways, which probably occurs due to the transient distension of the airway smooth muscle (ASM). We hypothesised that deep expiratory manoeuvres also produce bronchodilation due to transient airway wall and ASM compression. We used porcine bronchial segments to assess the effects of deep inspirations, and maximal and partial expiration (submaximal) on airway calibre. Respiratory manoeuvres were simulated by varying transmural pressure using a hydrostatic pressure column: deep inspiration 5 to 30 cmH(2)O, maximal expiration 30 to -15 cmH(2)O, partial expiration 10 to -15 cmH(2)O; amidst a background of tidal oscillations, 5 to 10 cmH(2)O at 0.25 Hz. Changes in luminal cross-sectional area in carbachol-contracted airways were measured using video endoscopy. Deep inspirations produce an immediate bronchodilation (∼40-60%, p=0.0076) that lasts for up to 1 min (p=0.0479). In comparison, after maximal expiration there was no immediate change in airway calibre; however, a delayed bronchodilatory response was observed from 4 s after the manoeuvre (p=0.0059) and persisted for up to 3 min (p=0.0182). Partial expiration had little or no effect or airway calibre. The results observed demonstrate that the airway wall dilates to deep inspiration manoeuvres but is unresponsive to deep expiratory manoeuvres.