Absence of intravascular bubble nucleation in dead rats.

Bubble formation in the inferior vena cavae (IVC) of dead rats was investigated after 6-15-h exposures to air at 123 atm abs (12.5 MPa) and decompression to 1 atm abs at 13.6 atm/min (1.4 MPa/min). The maximum estimated air-supersaturation attained in the IVCs after decompression was 6.1-18.3 atm (0.6-1.8 MPa). Bubbles were detected by light microscopy, buoyancy, and underwater dissection. No bubbles formed in 42 blood-filled IVCs that were isolated from the circulation by ligatures, but bubbles were always observed in unisolated IVCs (P < 0.000005). Other isolated IVCs were filled with tap water, water and bubbles, or water and iron filings. Bubbles formed in 13% of the IVCs filled with tap water, in 16% of the IVCs containing water with preexisting bubbles, and in 80% of the IVCs containing water with iron filings. Results indicate that at the air supersaturations attained in the isolated IVCs a) blood is resistant to de novo bubble formation; b) preexisting bubbles are dissolved by compression; c) bubbles in water originate from preexisting gas nuclei; and d) iron filings harbor gas nuclei that are able to survive 122 atm (12.4 MPa) overpressures and form bubbles on subsequent decompression.