Patent foramen ovale and hypobaric decompression.

Gas microbubbles were detected in the left ventricle of a supine subject being screened for an atrial septal defect as a participant of a hypobaric decompression study. This determination was made using the saline echocontrast procedure. We found provocation by a Valsalva maneuver not to be necessary in this individual for right-to-left passage of contrast microbubbles into the left heart and middle cerebral artery. When this same individual underwent hypobaric decompression to a simulated altitude of 21,000 ft, numerous gas microbubbles were detected in the right heart, but no gas bubbles were detected in either the left ventricular outflow tract or in the middle cerebral artery. This observation appears to be a novel finding, not previously reported.