Significance of delayed symptom onset and bubble growth in altitude decompression sickness

Three characteristics of altitude induced decompression sickness (DCS) are: 1) symptoms occur some time after arrival at altitude; 2) symptoms seldom occur below 18,000 ft, even though bubbles are frequently detected at that low altitude; 3) symptoms seldom occur after 4 h at altitude. These observations could be explained if it were postulated that bubbles must reach a threshold size before symptoms of DCS occur. In vitro techniques were used in this study to measure bubble growth at various altitudes. The results indicate that although the growth rate of bubbles depends strongly on the altitude where they form, bubble growth requires time. This helps explain the first observation above. We found that bubbles stop growing early at a small size below 18,000 ft. This helps explain the second observation above. Finally, we found that bubbles stop growing when the fluid immediately surrounding the bubble is cleared of supersaturated gas regardless of the fluid composition a few centimeters from the bubble. This helps explain the last observation above.