Pressure-flow behavior of pulmonary interstitium.

Abstract

A method to measure the pressure-flow behavior of the interstitium around large pulmonary vessels is presented. Isolated rabbit lungs were degassed, and the air spaces and vasculature were inflated with a silicon rubber compound. After the rubber had hardened the caudal lobes were sliced into 1-cm-thick slabs. Two chambers were bonded to opposite sides of a slab enclosing a large blood vessel and were filled with saline containing 3 g/dl albumin. The flow through the interstitium surrounding the vessel was measured at a constant driving pressure of 5 cmH2O and at various mean interstitial pressures. Flow decreased with a reduction of mean interstitial pressure and reached a limiting minimum value at approximately -9 cmH2O. The pressure-flow behavior was analyzed under the assumptions that the interstitium is a porous material described by a single permeability constant that increases with hydration and that the expansion of the interstitium with interstitial pressure was due to the elastic response of the surrounding rubber compound. This resulted in an interstitial resistance (reciprocal of permeability constant) of 1.31 +/- 1.03 (SD) cmH2O.h.cm-2 and a ratio of interstitial cuff thickness to vessel radius of 0.022 +/- 0.007 (SD), n = 11. The phenomenon of flow limitation was demonstrated by holding the upstream pressure constant at 15 cmH2O and measuring the flow while the downstream pressure was reduced. The flow was limited at downstream pressures below -10 cmH2O.