The micro-plethysmograph: a new device to measure small volume displacements by isolated human airway segments

For the study of airway responsiveness in vitro, airway segments have important advances over strip or spiral preparations. The method to study isobaric contraction of segments is not well established. The aim of this work was to develop a model to assess the smooth muscle responses in isolated airway segments under isobaric conditions. We developed a microplethysmograph with a volume measurement range of 10 to 700 microL, a resolution of 0.02-0.4 microL, and a drift of 2.6-0.7% of measurement range min(-1) for its most and least sensitive setting, respectively. The plethysmograph is able to compensate for the pressure changes induced by the volume changes, enabling for true isobaric measurements. We show examples of the isobaric contraction and relaxation of isolated human airway segments after stimulation of an airway segment by methacholine, isoprenaline, or electrical field stimulation. Apart from studying airway responses, the micro-plethysmograph is potentially useful to study the contractile properties of watertight and hollow structures like blood vessels, gut, and ureter. In addition, this device can be used to measure leak or diffusion at any transmural pressure.