Measuring the mechanical properties of the lung in vivo with spatial resolution at the acinar level

The alveolar capsule technique involves measuring subpleural alveolar pressure in the chamber of a plastic capsule glued to the perforated lung surface. However, measurements of alveolar pressure alone do not permit one to say whether the inhomogeneities that develop are due to changes in local lung resistance, elastance, or both. We have developed an extension of the alveolar capsule technique in which small broad-band oscillations in flow are applied through the capsule. At low oscillation frequencies the imposed flows travel all the way through the airway system, so the associated alveolar pressures then reflect the resistance of the pathway from a small local alveolar region out to the tracheal opening. At high frequencies flows propagate only a very short distance into the lung whereupon the dynamic relationship between flow and alveolar pressure gives a measure of local lung elastance. In this paper we show that considerations of canine lung anatomy suggest that the elastic and resistive quantities provided by the capsule oscillator technique pertain to a lung region of the order of a single acinus with its associated terminal bronchioles. This represents a greatly improved spatial resolution of lung mechanics over that which was possible before the development of the alveolar capsule oscillator technique.