To the Editor: A 51-year-old woman who had recently come from sea level presented with cough and congestion at our emergency room in Frisco, Colorado (altitude, 9300 ft [3200 m]). She described a “swishing sound” in her breasts. She had had saline breast implants for 20 years and had noted this unusual sound on previous travel to high altitudes. She said that the sound in her breasts would disappear on her return to sea level or resolve slowly during a prolonged stay at high altitude. A chest film revealed crescent-shaped air-fluid levels in both implants (Figure 1). Trapped air in . . .