Measuring and representing peripheral oedema and its alterations.

Correlation was very good between 1,500 simultaneous measurements of peripheral lymphoedema (arms and legs) by water displacement and by calculating volumes from circumferences, but in the legs "circumferences" gave only half the absolute amount of oedema when compared with "water displacement." For 150 arms, however, each method provided almost identical values for oedema. Arms when oedematous are fairly uniformly swollen; legs, on the other hand, are typically more oedematous distally. Circumference measurements accordingly include portions of nearly normal (i.e., minimally or nonoedematous) leg; water displacement by contrast measures only the oedematous, distal region. When only the circumferences of the lower legs were taken into consideration, the amount of oedema as measured by water displacement were almost identical. Nonetheless, measuring the proximal, more normal, or nonoedematous regions of the leg is critical for assessing treatment by physical methods (e.g., complex physical therapy). The various equations representing oedema can be greatly affected by errors in the initial, final or normal measured volumes. Relative errors differ as these variables alter. Many of the equations are non-linear, i.e., small alterations in one variable may produce widely differing results depending on the other variables. Problems in the use of an abnormal contralateral or "normal" limb as a reference point are discussed. The best equation to use in bilateral oedema is "Difference in Volume/Initial Volume"; in unilateral oedema the best equation is "Difference in Oedema/Normal". "Change in Oedema" i.e., "Difference in Oedema/Initial Oedema" is best derived from the Means of other equations.