Pressure-volume and length-stress relationships in canine bronchi in vitro.

Intraparenchymal canine airway segments with branches tied off were mounted between two fluid-filled cannulas in an organ chamber. Airways were inflated to successive volumes ranging from 4 to 100% of the segment volume at 25 cmH2O. At each volume, pressure was monitored during isovolumetric contractions elicited by 10(-3) M acetylcholine. Small bronchi developed pressures greater than 30 cmH2O in response to acetylcholine at all volumes and were able to constrict to closure. Large bronchi developed pressures greater than 30 cmH2O only near maximal volumes and were able to constrict to only 30% of maximal volume. Maximal active pressures occurred at low volumes in small bronchi and at high volumes in large bronchi. However, maximal active circumferential tension and stress occurred at near-maximal volumes in both large and small bronchi. Circumferential length active-stress curves and maximal active-stress development for bronchi and trachealis muscle strips were similar. Similar length active-stress properties in different bronchi may produce significant differences in volume-pressure characteristics.