QUANTIFICATION OF RATE AND DEPTH OF PITTING IN HUMAN EDEMA USING AN ELECTRONIC TONOMETER

An instrument (tonometer) was developed to measure objectively the rat e as well as depth of pitting of edematous limbs under a sudden local load. Displacement versus time curves were obtained in vivo in postmas tectomy edema arms and also in vitro (compression of sponges) and were analyzed in terms of spring and dashpot constants. There was no signi ficant difference between the quasi-instantaneous indentation of tissu e in the edematous and normal arms (median 2.9mm), and the two correla ted strongly (r=0.91, p<0.0001). Art exponentially slowing indentation followed. The mean difference between initial and final deformation ( X(infinity)-X(0)) was greater in the swollen arms (5.7mm) than in the normal arms (1.3mm, p<0.01). The time constant of indentation (tau) wa s significantly greater in the swollen arms (227s) than in the normal arms (71s). There was no correlation between the duration of the edema and any of the pitting characteristics. There was a significant negat ive correlation between glycosaminoglycan concentration of interstitia l fluid and rate constant 1/tau(r=-0.9, p<0.01). The tonometer thus pr ovides an objective way of quantifying the rate and depth of pitting e dema.