Decompressive Pathology in Cetaceans Based on an Experimental Pathological Model

Abstract

Decompression sickness (DCS) is a widely known clinical syndrome in human medicine, mainly in divers, related to the formation of intravascular and extravascular gas bubbles. Gas embolism and decompression-like sickness have also been described in wild animals, such as cetaceans. It was hypothesized that adaptations to the marine environment protected them from DCS, but in 2003, decompression-like sickness was described for the first time in beaked whales, challenging this dogma. Since then, several episodes of mass strandings of beaked whales coincidental in time and space with naval maneuvers have been recorded and diagnosed with DCS. The diagnosis of human DCS is based on the presence of clinical symptoms and the detection of gas embolism by ultrasound, but in cetaceans, the diagnosis is limited to forensic investigations. For this reason, it is necessary to resort to experimental animal models to support the pathological diagnosis of DCS in cetaceans. The objective of this study is to validate the pathological results of cetaceans through an experimental rabbit model wherein a complete and detailed histopathological analysis was performed. Gross and histopathological results were very similar in the experimental animal model compared to stranded cetaceans with DCS, with the presence of gas embolism systemically distributed as well as emphysema and hemorrhages as primary lesions in different organs. The experimental data reinforces the pathological findings found in cetaceans with DCS as well as the hypothesis that individuality plays an essential role in DCS, as it has previously been proposed in animal models and human diving medicine.

Establishment of a fish model to study gas-bubble lesions

“…8 ). Overall, pathological findings were the same as those described in small mammals for the study of gas-bubbles lesions in explosive DCS by hyperbaric chamber 14 , 16 , 18 , 20 , validating the translational usefulness of this model from a pathological standpoint.…”

“…In some of these models, mainly developed in rats and rabbits, compressions were performed for a variable period (6–8 absolute atmospheres, 40–90 min) followed by rapid decompression (3–5 min), aiming to induce severe DCS 14 – 19 . These models have allowed comparison with marine mammals affected by DCS, showing very similar pathology findings 20 .…”

Biomarkers related to gas embolism: Gas score, pathology, and gene expression in a gas bubble disease model

“…The gas score index was validated as a method to evaluate the presence of gas bubbles postmortem by correlating this index with the amount of gas bubbles seen by ultrasound in vivo in the right heart of rabbits [ 57 ]. The gas score has been used as a diagnostic tool for gas embolism [ 26 , 55 , 58 ], with the affected animals showing high total gas scores, in agreement with the present study.…”

Microscopic Findings in the Cardiac Muscle of Stranded Extreme Deep-Diving Cuvier's Beaked Whales (Ziphius cavirostris)

“…Since then, many other cases have been diagnosed in cetaceans and other species, such as turtles (Fernández et al, 2005b(Fernández et al, , 2017García-Párraga et al, 2014). More recently, the decompressive pathology in cetaceans has been studied through an experimental pathological model, where the presence of not only gas bubbles but also other gross and histological lesions, such as vascular changes (e.g., interstitial edema, hemorrhages) and/or acute degenerative changes (e.g., contraction band necrosis, wavy fibers, hypereosinophilia, intracytoplasmic vacuolization), was described (Velázquez-Wallraf et al, 2021). Although these changes have been reported in previous investigations, it is essential to remark that in our study, there was no apparent difference and/or relationship between the extension and severity of the acute degenerative lesions and the atypical mass stranding involving beaked whales with gas embolism when compared with the corresponding findings related to other causes of death, such as live stranding or ship collision, with a stress component associated in both deepand shallow-diving cetaceans.…”

“…The formation of intravascular and extravascular gas bubbles (7/20–35.00%) are the main findings of forensic investigations related to a widely known clinical syndrome in human medicine, mainly occurring in divers, called Decompression Sickness (Vann et al, 2011; Velázquez-Wallraf et al, 2021). Gas embolism and decompression-like sickness have also been described in wild animals, first in cetaceans, more specifically with mass strandings of beaked whales, which occurred in 2003 and were coincidental in time and space with naval maneuvres (Jepson et al, 2003).…”