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 impor tant advances over strip or spiral preparations. The method to study isobar ic contraction of segments is not well established. The aim of this work wa s to develop a model to assess the smooth muscle responses in isolated airw ay segments under isobaric conditions. We developed a microplethysmograph w ith a volume measurement range of 10 to 700 mu L, a resolution of 0.02-0.4 mu L, 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 compe nsate for the pressure changes induced by the volume changes, enabling for true isobaric measurements. We show examples of the isobaric contraction an d relaxation of isolated human airway segments after stimulation of an airw ay segment by methacholine, isoprenaline, or electrical field stimulation. Apart from studying airway responses, the micro-plethysmograph is potential ly useful to study the contractile properties of watertight and hollow stru ctures like blood vessels, gut, and ureter. In addition, this device can be used to measure leak or diffusion at any transmural pressure. (C) 1999 Els evier Science Inc.