Continuous Sub-bandage Pressure Monitoring Identifies Dynamic Metrics to Characterize the Efficacy of Compression Therapy

Compression therapy for the treatment of venous leg ulcers (VLUs) is often inconsistent due to practitioner competencies, patient pain tolerance and anatomy, and material properties of the compression products used.  A multi-point wireless pressure sensor that continuously monitors sub-bandage pressure can provide real-time feedback that facilitates interventions to improve delivery of compression therapy. We sought to utilize this technology to identify potential physiologic indicators of compression bandage efficacy when used in a clinical setting.

Methods:

A two-layer compression system was applied to healthy volunteers (n=5) with a wireless pressure sensor (WPS) comprised of a thin, flexible sensing arm with three evenly spaced sensors. Two WPS devices were positioned beneath the bandage on each patient; one on the medial and one on the lateral calf with sensor regions aligned to the B, B1, and C positions (Figure 1a). Bandages were applied with and without live digital guidance to achieve target pressures of 40, 40 and 30 mmHg at each sensor position, respectively. Bandages were worn for 4 hours to monitor static pressure loss over time and pressure was recorded continuously during supervised walking and isolated plantar/dorsiflexion. Dynamic metrics were calculated and compared between activities at each sensor level. For comparison of proportions of successful target applications achieved, Fisher’s exact test was used. All other pairwise comparisons used a Student’s t-test (two-tailed).

Results: Using digital guidance with the WPS, the target pressure was achieved more frequently than when applied per the manufacturer guidelines at the B(93%vs29%), B1(79%vs43%) and C(85%vs21%) positions (p >0.05 for all). There was a gradual loss of pressure when static measurements in standing position were recorded over time, which plateaued by 4 hours. Continuous pressure tracings revealed cyclical pressure changes with gastrocnemius muscle activation. The magnitude of change in sub-bandage pressure and the rate of pressure fluctuations are potential indicators of bandage performance as it pertains to the augmentation of calf muscle function.  Therefore, we identified a novel dynamic metric (DM) based on the amplitude, and frequency of sub-bandage pressure oscillations (Figure 1b-c) during both walking and sedentary ankle plantar/dorsiflexion. The DM represents a quantifiable measurement that incorporates bandage performance and patient behavior over a wear period. There was no statistical difference in DM between activity types at any sensor position, suggesting that movements other than walking can lead to similar performance of the calf muscle pump.  

Conclusions:

Multi-point continuous sub-bandage pressure monitoring can improve the application of compression therapy. With this previously inaccessible data, new metrics can be identified which characterize the ability of a compression garment to aid calf muscle pump function.