title: Microbubbles are detected prior to larger bubbles following decompression.
abstract: Using dual-frequency ultrasound (DFU), microbubbles (<10 μm diameter) have been detected in tissue following decompression. It is not known if these microbubbles are the precursors for B-mode ultrasound-detectable venous gas emboli (bmdVGE). The purpose of this study was to determine if microbubbles could be detected intravascularly postdecompression and to investigate the temporal relationship between microbubbles and larger bmdVGE. Anesthetized swine (n = 15) were exposed to 4.0-4.5 ATA for 2 h, followed by decompression to 0.98 ATA. Microbubble presence and VGE grade were measured using DFU and B-mode ultrasound, respectively, before and for 1 h postdecompression, approximately every 4-5 min. Microbubbles appeared in the bloodstream postdecompression, both in the presence and absence of bmdVGE. In swine without bmdVGE, microbubbles remained elevated for the entire 60-min postdecompression period. In swine with bmdVGE, microbubble signals were detected initially but then returned to baseline. Microbubbles were not detected with the sham dive. Mean bmdVGE grade increased over the length of the postdecompression data collection period. Comparison of the two response curves revealed significant differences at 5 and 10 min postdecompression, indicating that microbubbles preceded bmdVGE. These findings indicate that decompression-induced microbubbles can 1) be detected intravascularly at multiple sites, 2) appear in the presence and absence of bmdVGE, and 3) occur before bmdVGE. This supports the hypothesis that microbubbles precede larger VGE bubbles. Microbubble presence may be an early marker of decompression stress. Since DFU is a low-power ultrasonic method, it may be useful for operational diving applications.
authors.affiliation: Geisel School of Medicine, Dartmouth University, Hanover, New Hampshire;
authors.forename: J G
authors.initials: JG
authors.lastname: Swan
authors.forename: J C
authors.initials: JC
authors.lastname: Wilbur
authors.forename: K L
authors.initials: KL
authors.lastname: Moodie
authors.forename: S A
authors.initials: SA
authors.lastname: Kane
authors.forename: D A
authors.initials: DA
authors.lastname: Knaus
authors.forename: S D
authors.initials: SD
authors.lastname: Phillips
authors.forename: T L
authors.initials: TL
authors.lastname: Beach
authors.forename: A M
authors.initials: AM
authors.lastname: Fellows
authors.forename: P J
authors.initials: PJ
authors.lastname: Magari
authors.forename: J C
authors.initials: JC
authors.lastname: Buckey
mesh_terms: D000818:Animals; D003287:Contrast Media; D003665:Decompression Sickness / Q000097:blood / Q000000981:diagnostic imaging*; D004195:Disease Models, Animal; D042241:Early Diagnosis; D004618:Embolism, Air / Q000097:blood / Q000000981:diagnostic imaging*; D005466:Fluorocarbons; D045423:Microbubbles; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013552:Swine; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D003287:Contrast Media; D005466:Fluorocarbons; C042852:perflutren
keywords: decompression sickness; dual-frequency ultrasound; ultrasound; venous gas emboli