Validation of a new technique for the quantitation of edema in the experimental setting.
BACKGROUND: An inherent limitation to the study of in vivo animal models of lymphedema is the potential inaccuracy or unreliability of existing methods for the quantification of edema volume as a surrogate functional measure of lymphatic transport capacity. Circumference-based techniques have been proposed and validated as a suitable alternative to volume displacement measurements in human clinical studies; accordingly, we have elaborated a new application of this approach that can be applied to small animal studies. METHODS: Acute postsurgical lymphedema was created experimentally in the murine tail. Both normal and lymphedematous murine tails were examined. Tail volume was quantitated both by water displacement and by a digital photographic technique. In selected mice, after sacrificed on postsurgical day 7, a 6 cm segment was resected from the midportion of the tail and cauterized to create a closed space. Known incremental volumes of saline (20-100 microL) were injected for subsequent digital photographic volumetry. RESULTS: The coefficients of variation for volume assessment by water displacement and by digital imaging were 0.08+/-0.09 and 0.01+/-0.009, respectively. The two techniques were poorly correlated: while serial water displacement analysis yielded highly variable measurements within the same tail, concurrent digital imaging of the tail circumference was quite reproducible. Furthermore, after parenteral injection of known incremental volumes of saline, the correlation between the injectate volumes and the digitally measured increases in volume was high, both in the normal and the lymphedematous tail. CONCLUSION: In the murine tail, when compared to water displacement volumetry, digital photography yields highly reproducible data. We can conclude that the lack of correlation between the two methods, with the relatively flat slope of the linear regression relationship, reflects inherent inaccuracies of the water displacement method.