The inflation of a balloon proceeds in a smooth manner. In contrast, a collapsed lung is much more difficult to inflate but the reasons for this have been unclear. In 20 June Nature, Adriano Alencar and colleagues at Boston University, Massachusetts, show that reinflation of the mammalian lung from a collapsed state proceeds through a sequence of gas avalanches and that the pressure inside the lung paradoxically decreases intermittently.

Alencar et al. inflated isolated rat lungs with a computer-controlled piston and observed that with increasing volume (V), the pressure (P) also increases, but showed intermittent decreases, causing the elastance E (E= dP/dV), to fluctuate between negative and positive values.

In addition, they observed that the newly opened airways increase the volume of the lung, which cause the pressure to decrease and terminate the propagation of the avalanche (a phenomenon termed an avalanche shock). The pressure then increases again...

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