V. La hora de las psicoterapias 1 Delimitación conceptual
3. Eficacia de los tratamientos Psicoterapéuticos
Despite extensive research into the mechanisms of freeze-thaw damage at the cellular level, there are few publications that describe the gross changes that occur due to freezing. Two papers describe changes interpreted as freeze artefact: dark red fluid found in the body cavities of a frozen human infant (Tabata et al 2000), and blood- tinged discharge from the nares of a frozen rat (Micozzi 1986). Both of these changes were also present in frozen fur seals in this trial, along with several other changes resembling traumatic lesions. While the small sample size means that for some of these changes the association with freezing did not reach statistical significance, the results of this experiment indicate that accumulations of intra-abdominal fluid resembling unclotted blood, pseudo-bruising of subcutaneous tissues, apparent haemorrhage into the renal capsule and brain pseudocontusions are artefacts created during the freezing and thawing process.
Freezing damages cells by a combination of fluid shifts and mechanical damage to cytoplasmic membranes (Mazur 1970; Pegg and Diaper 1988; Ishiguro and Rubinsky 1994; Scott et al 2005). As tissue temperatures decrease, extracellular water begins to freeze, increasing the solute concentration of the unfrozen fraction of extracellular fluid and resulting in osmotically-induced cellular dehydration as intracellular fluid moves out of cells. On thawing, net flow of fluid back into cells can cause membrane rupture, as can direct membrane damage inflicted by ice crystals. The overall effect of these processes is cell shrinkage, tissue fragmentation, accumulation of extracellular fluid, and cell lysis (Baraibar and Schoning 1985, 1986; Schafer and Kaufmann 1999). The dark red fluid in the body cavities of thawed fur seals, therefore, is likely to be partly composed of accumulated extracellular fluid tinged with haemoglobin from lysed red blood cells.
The role of autolysis in development of freeze-thaw artefact also warrants consideration. While the aim of freezing a body before post mortem is to limit the effects of autolysis,
several authors have noted that autolysis is actually accelerated in the external tissues
of frozen bodies (Micozzi 1986; Zugibe and Costello 1993). Autolysis could have occurred in the frozen fur seals in the current study at several stages: during their time in the net after drowning; on board the fishing vessel post-capture; during transit (2-5 days); in the time taken to reach freezing point; and during thawing (3-5 days). Recognised autolytic changes include haemoglobin staining of tissues, which begins within 2-3 days of death (Saukko and Knight 2004), and would contribute to the red discolouration of soft tissues that was observed in the blubber, renal capsule and in the brain. The autolysed control fur seal in this trial, which had a death-to-post mortem interval of seven days, also had blubber discolouration and staining of the renal capsule, providing additional support for the theory that autolysis contributes to some freeze- thaw artefacts.
Post mortem autolytic changes have been extensively studied in human forensic medicine. Passive accumulation of blood under the effect of gravity (hypostasis or post mortem lividity) causes reddening of soft tissues that can be misinterpreted as bruising (Saukko and Knight 2004). In theory, microscopic examination of an ante-mortem bruise should demonstrate the presence of extravasated erythrocytes outside blood vessels, whereas in hypostasis erythrocytes should be contained within congested vessels (Saukko and Knight 2004; Pollanen et al 2009). The distinction is not always so clear-cut in practice, as extravasation of blood has also been shown to occur after death, i.e. pseudo-bruises, particularly within areas of hypostasis (Vanezis 2001; Saukko and Knight 2004; Bockholdt et al 2005; Pollanen et al 2009). In a study using human cadavers,
Pollanen et. al. (2009) were able to induce pseudo-bruises that were indistinguishable from true bruises on microscopic examination. The authors concluded that lesions resembling soft tissue injury can occur after death, and that these probably develop as a result of leakage of red blood cells from autolysing congested venous plexuses as hypostatic pressure progressively increases. They proposed that these changes would be particularly likely to occur in tissues with an extensive system of thin-walled
vascular channels that are surrounded by loose connective tissue (Pollanen et al 2009). Blood leaking from autolysed vessels would contribute to the fluid accumulations in body cavities, including the tunica vaginalis and the anterior ocular chamber.
Hypostatic congestion and autolysis, along with haemoglobin staining, may also explain the staining of the renal capsule in frozen NZ fur seals. This capsule comprises an outer, well vascularised layer of loose connective tissue and fat and an inner layer closely adherent to the cortical parenchyma (Stewardson et al 1999). Thawing would cause the fluid volume within intracapsular veins to expand, increasing intravascular pressure and forcing red cells out through the autolysing blood vessel walls. The loose connective tissue present in the renal capsule and the potential space between capsule layers create a site in which extravasated red cells and haemoglobin-stained extracellular fluid can accumulate, with more fluid accumulating around the dependent kidney. A similar process could have caused the changes resembling brain contusions in three
frozen fur seals. Macroscopic examination of the superficial vasculature in the brains of two non-frozen fur seals showed marked asymmetrical congestion of meningeal vessels over the cerebellum and the caudal occipital lobes, likely reflecting hypostatic congestion that developed during transit of the bodies. In an animal that was then frozen and thawed, autolytic damage of the vessel walls and escape of erythrocytes, coupled with haemoglobin staining around these congested vessels, would explain the development of unilateral pseudo-contusions. The specific location of these focal lesions would depend on the position of the body in the early hours after death. The pattern of subcutaneous pseudo-bruising that was consistently present in the ventrum, axillae and shoulders of the frozen fur seals in this trial is more difficult to explain. Since no attempt was made to standardise body position during transport and freezing it is unlikely that the ventral aspects of the body were consistently in a dependent position. Although the dermis and hypodermis of fur seals has been shown to contain numerous thin-walled arteriovenous anastomoses (Bryden and Molyneux
1978), all five fur seals were thawed in dorsal recumbency, making it improbable that there was a gradual, gravity-dependent increase in the intravascular pressure of ventral subcutaneous vessels during thawing.
The severe bruising and muscle damage present in the neck of one frozen fur seal was interpreted as a true ante mortem lesion. The cause of this damage was not established, but the involvement of significant damage to muscle, in conjunction with haemorrhage in affected muscle, overlying blubber and skin made this lesion distinct from the pseudo-bruising seen in the ventrum, axillae and shoulder regions of other frozen animals.
With respect to freezing NZ sea lion pups for later thawing and post mortem examination, there are several modifications of the protocol used for the adult fur seals that could decrease artefact formation. Firstly, careful and consistent positioning of pup bodies during freezing and thawing might decrease the creation of asymmetrical artefacts, although it seems likely that some pseudo-contusions may still have occurred. These could both be difficult to definitively distinguish from true contusions, and could also obscure true lesions such as a small subarachnoid haemorrhages or contusions. Secondly, autolytic changes may be less prominent than in sea lion pups as compared with the fur seals in this trial, since transport of the pup bodies would not be required and the smaller body size of the pups means that they would freeze and thaw more rapidly, which in turn would reduce autolysis.
Despite these considerations it is unlikely that all artefacts could be prevented, and accurate diagnosis of traumatic lesions was integral to this study of traumatic brain injury. Examination of tissues using histological techniques can help distinguish between lesions and artefacts in some circumstances. In human forensic medicine the presence of inflammation or haemosiderin in haemorrhagic tissue confirms that bruising occurred before death (Grellner and Madea 2007). Studies in animals indicate that there is considerable variation in tissue responses between species; aging using histological
criteria is not possible in very recent bruising (Thornton and Jolly 1986; Vanezis 2001). Hence these criteria cannot differentiate between peri-mortem bruising and post- mortem freeze artefact. In addition, although microscopy can identify haemoglobin staining as a cause of putrefactive discolouration or hypostatic congestion, evaluation of pseudo-bruises in non-frozen human cases shows extravasation of erythrocytes in a manner indistinguishable from true bruising (Prinsloo and Gordon 1951; Pollanen et al 2009), making routine histochemistry of little use in differentiating these from ante- mortem bruises. Similar findings were noted on examination of bruise-like changes in NZ fur seal brains, renal capsules and subcutaneous tissues.
Tabata and Morita (1997) used immunohistochemistry to demonstrate that glycophorin A, an erythrocyte membrane marker, was present outside blood vessels in ante- mortem bleeding, indicating haemorrhage rather than haemoglobin staining as a cause of discolouration in autolysed human tissues. In pseudo-bruises, where red cells escape from autolysed blood vessels, this technique will not add anything to routine histochemical evaluations. More recently, immunohistochemical detection of adhesion molecules and cytokines has shown promise in evaluation of peracute lesions (Grellner and Madea 2007), but these techniques are not yet validated for non-human species, and their utility in frozen tissues is uncertain.
In summary, freezing and thawing of NZ sea lion pup bodies would be likely to create artefacts that would be difficult or impossible to distinguish from true traumatic lesions. This study thus shows conclusively that storage of frozen bodies on site at Enderby Island for later examination by an experienced veterinary pathologist was not justified.