Intracardial gas bubbles of altitude after negative pressure breathing.

The influence of negative pressure breathing on the appearance of intracardial gas bubbles at a subsequent decompression to altitude was investigated in five subjects using the precordial Doppler ultrasound technique. Every subject was tested for a suitable exposition that, after 30 min oxygen breathing at surface, caused both intracardial bubbles and decompression sickness. An identical exposition followed a week later, except that oxygen breathing at the surface now included negative pressure breathing. In all cases, negative pressure breathing caused a delay of the onset of both intracardial bubbles and bends and, in some cases, neither bubbles nor bends appeared at all. The total amount of bubbles was always less after negative pressure breathing. Thus, negative pressure breathing in connection with decompression may reduce the amount of intracardial bubbles and the risk of decompression sickness. This may be of importance in diving procedures and in the construction of diving devices.