Peripheral edema is a common clinical sign along with weight gain, dyspnea, jugular distention, and elevated brain natriuretic peptides (BNP) of cardiac insufficiency associated with impending decompensation and hospitalization. Pitting edema is used in the clinical setting to classify edema severity. And patients occasionally use various subjective measures such as visibility of foot tendons, depth of sandal strap depression, and watch band tension to assess the degree of fluid retention. A better method is needed. A continuous, reliable, quantitative measurement of peripheral edema in the patient setting provides the early recognition necessary for diagnosis and treatment of the underlying causes of decompensation required to prevent the unnecessary cycle of crisis hospitalization.
Continuous monitoring of ankle circumference will establish a normal baseline and allow detection of “ankle swelling” (peripheral edema) associated with fluid retention. We hypothesize that fluid retention presents as deviations from a normal baseline or “dry state” and can be characterized to distinguish between compensated events and decompensation trends.
A method of continuously measuring ankle circumference with 1 mm accuracy in the patient setting was employed, allowing us to test the feasibility of detecting changes in ankle swelling (peripheral edema) associated with fluid retention. An open pilot study was performed which collected ankle circumference and orientation data from both healthy normal and heart failure subjects. This data was enhanced using Subject Information Logs which tracked medication adherence, activity, salt intake, and daily weight. Continuous monitoring of the Daily Swelling Profile (DSP) allows definition of a Normal Baseline for each subject. Changes in fluid retention is identified as the difference between the Ankle Circumference Daily Rolling Average (DRA) compared to the Normal Baseline. Events from the Subject Information Logs were mapped to the Ankle Circumference Data.
The following results were documented. Well-managed heart failure subjects present a DSP and Normal Baseline substantially equivalent to healthy normal subjects. Each subject’s DSP represented as the change in ankle circumference from a horizontal position (sleeping) to standing or sitting throughout the day is 5-8 mm. Fluid retention or loss presents as a shift in the Ankle Circumference DRA. Compensated fluid retention such as missed medication or isolated high salt intake are observed as an increase in the Ankle Circumference DRA and return to normal after the subject corrects the anomalous behavior. Decompensated fluid retention is observed as an increasing trend in Ankle Circumference DRA and indicates a medical assessment and intervention may be needed.
A continuous, reliable, quantitative measurement of peripheral edema in the patient setting is a feasible method to recognize acute decompensation early in the window of intervention.