A. Normal lung pattern on M-mode: the seashore sign. The motionless superficial layers generate horizontal lines (the waves). The deep artifacts follow the lung sliding, hence the sandy pattern. B. Exclusively horizontal lines are displayed, indicating complete absence of dynamics at the level of, and below, the pleural line, a pattern called the stratosphere sign. C. M-mode evaluation of the lung point: a sudden change from the seashore to the stratosphere sign is clearly visible (arrow). (Modified from Lichtenstein et al, 2000 ).