Effect of diameter on force generation and responsiveness of bronchial segments and rings

Abstract

In this study, isovolumic bronchial segments and bronchial rings were used to investigate the influence of airway diameter on smooth muscle force generation and acetylcholine responsiveness.Segments with internal diameters ranging from 1.0-6.0 mm were obtained from the mainstem bronchus of eight pigs. Responses to increasing acetylcholine concentrations were quantified in segments by intralumenal pressure (cmH 2 O), and in rings by tension (g·cm -1 ). The negative log of the concentration producing half the maximal effect (EC50) (i.e. pD 2 ) to acetylcholine was calculated for each segment and ring. Ring tension was used to calculate a theoretical lumen pressure for each ring, and this, along with the pD 2 , was compared with values obtained from segments of the same diameter.Intermediate-sized segments produced significantly greater intralumenal pressures than did large or small segments. Small segments were 160 times more sensitive to acetylcholine than large segments. In contrast to the segments, bronchial rings showed no effect of size on acetylcholine sensitivity. Theoretical ring lumen pressures matched those measured for large and intermediate segments, but not for small segments.The different behaviour of bronchial segments and rings obtained from the same sized airway suggests that the three-dimensional architecture of the airway is an important factor in determining behaviour, particularly in small airways.

Physiological responses of the airway wall and lung in hyperresponsive pigs

“…The segment adventitia was bathed in Kreb9s solution and the lumen filled with Kreb9s from a separate reservoir. Stopcocks at either end of the segment allowed the airway lumen to be sealed so that intralumenal pressure could be monitored using a calibrated pressure transducer [10]. Segments were checked for pressure leaks throughout each experiment.…”

“…Cumulative CRCs to ACh (1610 -1610 -1 M) was obtained by adding ACh to the fluid bathing the segment lumen [10,13]. Bronchial responsiveness in vitro was quantified as the maximum pressure developed in response to ACh (Emax) and the negative log of the ACh concentration that produced half the maximum pressure (pD2).…”

“…The parenchyma was removed, side branches were ligated and a 25 mm-long segment was mounted in an organ bath, as previously described [7,13]. These segments were classified as small/medium sized based on internal diameter (2-3 mm), location (spanning generations [9][10][11][12][13][14], and the presence of cartilage [14]. The segment adventitia was bathed in Kreb9s solution and the lumen filled with Kreb9s from a separate reservoir.…”

“…In contrast, physiological responses described in intact bronchial airways isolated from asthmatics or animals models are scarce and the contributions that the bronchial wall may make to AHR in vivo remains controversial. A porcine model of AHR is presented in this study, which because of its size and ready availability allows the functional properties of different size bronchi to be investigated [9,10]. Early allergen-induced responses have previously been reported in the pig [7,11].…”

Delayed and persistent suppression of bronchoconstriction by trypsin in the airway lumen

“…A stem bronchus was dissected from the left and right lung, the parenchyma was removed by gentle dissection and the side branches were ligated [16]. An airway segment some 25 mm in length and 2-3 mm internal diameter was removed.…”