Measurement of human small airway smooth muscle function in vitro. Comparison of bronchiolar strips and segments

We have compared isotonic responses to methacholine of human bronchiolar segments and spiral strips. Both types of preparations contracted dose-dependently to methacholine and had a stable intrinsic contractile activity, which was significantly higher in segments (p less than 0.001). ANOVA indicated that the total variation in responses of both strips and segments was similar and was mainly due to a significant between-preparations/within-patients variation. There was a small but significant trend towards a decrease of sensitivity (EC50) in time for both segments and strips. Net contraction, i.e. the difference between resting length and the length at maximal contraction, did not change in time. Limited length-active shortening experiments indicated that 250 mg was a suitable load for both strips and segments. We concluded that, although human bronchiolar strips and segments are functionally comparable, bronchiolar segments are preferable because of their practical and theoretical advantages over bronchiolar strips.