Posted by John Walker on January 21, 2002 at 12:13:44:
From NAUI sources Jan/Feb 2002
Physical Issues
Patent Foramen Ovale (PFO)
During fetal development, blood flows through a small opening between the right and left upper chambers of the heart. The lungs are inoperative and the mother oxygenates blood. At birth, however, this opening is supposed to close, shunting blood to the now functioning lungs. While this “hole in the heart” usually seals by the third month of life, it does not always occur. Estimates of incomplete closures of varying size in older children and younger teens runs higher than 50 percent in certain groups. Whatever the exact figures, the research evidence suggests an increases incident of PFO as age decreases below 20.
Without complete closure, blood can flow from the right to left side of the heart without passing through the lungs. Increases in right chamber pressure that occurs with common equalization techniques like the Valsalva maneuver – squeezing your nose, closing your mouth, and blowing – can move blood through the hole and bypass the lungs. When this happen, nitrogen bubbles that can form in the bloodstream during decompression may pass directly into the arteries and not be filtered by the lungs. This of course can lead to an embolism or DCS.
Possible retardation of bone growth
Long bones, like the humerus and femur, mature from growth plates, the active ends of bones where increases I length occur. The last of the growth plates generally do not cease activity until the late teens or early twenties. As these growth plates depend upon nearby blood vessels for oxygen and nutrition, physicians have long been concerned that nitrogen bubbles in the bloodstream may result in damage to these critical tissues. In addition, the development of bone and connective tissues involves molecular oxygen, raising the possible adverse effect of the elevation of partial pressures occurring during diving.
Maybe someone can forward this to PADI.