Sick and injured sea turtles presenting to rehabilitation facilities commonly exhibit positive buoyancy, which prevents normal diving behaviors.7 Positive buoyancy has been attributed to gastrointestinal (GI) disorders,1,2,6 lung pathology,5 gas-producing coelomic infections,7 and spinal cord injury4. While functional lung volume has been thought to play a role in buoyancy,3 there are no studies that objectively measure lung volumes in sea turtles. The aim of this study was to establish an index of lung volumes that constitute normal sea turtles (without apparent GI or lung disease) of neutral buoyancy. These results were compared to animals with lung pathology, GI disorders, and positive buoyancy that did or did not resolve with time. Computed tomography (CT) studies of 56 green sea turtles (Chelonia mydas) performed from 2007–2010 were collected from various rehabilitation facilities and a veterinary hospital. The animals were analyzed in groups that displayed lung pathology (n = 10), GI disorders (n = 10), or no apparent lung or GI disease (n = 36). Animals were also evaluated separately based on their buoyancy status: normal buoyancy with ability to dive (n = 44), positive buoyancy that resolved with time (n = 7), and positive buoyancy that did not resolve with time (n = 5). Using OsiriX, a software program for navigating multidimensional DICOM images, volumetric analysis was completed by selecting the Hounsfield unit (HU) of the lungs and computing lung volume. The areas of the lungs not involved with gas exchange (oropharynx, trachea, mainstem bronchi, and lobar bronchi) were manually erased from the total lung volume. This volume was compared to the total volume of the body (including the shell, and carapace, but excluding limbs) from the mid-eighth cervical vertebrae to the mid-seventh thoracic vertebrae, and results were reported as lung volume to body volume percentages (LV/BV). LV/BV of turtles without lung or GI pathology [mean ± 95% confidence interval (CI), 22.4% ± 1.6] had significantly larger lung volume percentage than turtles with gastrointestinal disease (mean ± 95%CI, 15.8% ± 4.2) but no significant difference compared to animals with lung pathology (mean ± 95%CI, 23.1 ± 3.5). Although there was no significant difference in LV/BV for individuals that remained positively buoyant (mean ± 95%CI, 20.7% ± 7.0) or those that resolved with time (mean ± 95%CI, 18.2% ± 5.1) compared to neutrally buoyant turtles (mean ± 95%CI, 22.1% ± 1.5), turtles with positive buoyancy had a very large range of lung volumes. This study established the first measurements of sea turtle lung volumes in normal and diseased animals. The findings indicate that positive buoyancy can be present with large, average, or small lung volumes, depending on the concurrent disease process. At this time, lung volume does not correlate with future resolution of positive buoyancy, but this topic requires further research to offer rehabilitation facilities prognosis and management strategies for floating sea turtles.
The authors wish to thank Dr. Daniel Vanderhart, Dr. Jorge Hernandez, Dr. Clifford Berry, and Dr. Shona Reese of the University of Florida - College of Veterinary Medicine for their assistance with this project. We also like to thank the Georgia Sea Turtle Center, the Clearwater Marine Aquarium, Adrienne Cardwell, and Patrick Thompson of the Aquatic Animal Health Program at the University of Florida for helping to gather records.
* Presenting author
+ Student presenter
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