The detection of gas bubbles in guinea-pigs after decompression from air saturation dives using ultrasonic imaging

1. Bubble formation in the hind limb of anaesthetized guinea-pigs, after decompression from two different saturation exposures to air, 0.69 and 0.83 MPa gauge, has been studied using an ultrasonic pulse--echo imaging technique. 2. A qualitative analysis of the bubble formation, observed over a 30 min period after decompression, showed that profuse, largely stationary bubble formation occurred within 3 min of the decompression from 0.83 MPa gauge but that extensive stationary bubble formation was not observed until 17 min after decompression from 0.69 MPa gauge. Electrocardiogram changes appeared coincidently with the appearance of major bubble formation after the 0.83 MPa decompression but after the 0.69 MPa decompression changes were not observed until the end of the 30 min surveillance period, considerably later than the occurrence of a large number of bubbles. 3. A quantitative analysis of the echo patterns recorded during the 60 sec decompression and for 60 sec after the decompression demonstrated that the increase in severity of the decompression corresponded to an increase of 152% in the number of bubbles observed. The echoes observed during this period have been identified as either transient or persistent and their distribution of size, location and times of appearance and duration have been described. 4. From the quantitative analysis approximate estimates of the contribution by mobile, intravascular gas bubbles to the elimination of the excess gas have been made. These estimates range from 0.01 to 0.9% after the 0.69 MPa decompression and from 0.06 to 6% after the 0.83 MPa decompression. 5. It is concluded that the pulse--echo ultrasonic imaging technique provides a powerful means of analysing the distributions of bubble formation, both qualitatively and quantitatively, after decompression; it has the important attribute of being able to monitor both moving and stationary bubbles simultaneously in a variety of tissue types.