Discomfort/Pain and Tissue Oxygenation at the Lower Limb During Circumferential Compression: Application to Soft Exoskeleton Design

Abstract

Objective To establish the relationship between circumferential compression on the lower limb during simulated ramp and staircase profile loading, and the resultant relationship with discomfort/pain and tissue oxygenation. Background Excessive mechanical loading by exoskeletons on the body can lead to pressure-related soft tissue injury. Potential tissue damage is associated with objective oxygen deprivation and accompanied by subjective perception of pain and discomfort. Method Three widths of pneumatic cuffs were inflated at the dominant thigh and calf of healthy participants using two inflation patterns (ramp and staircase), using a computer-controlled pneumatic rig. Participants rated discomfort on an electronic visual analog scale and deep tissue oxygenation was monitored using near infrared spectroscopy. Results Circumferential compression with pneumatic cuffs triggered discomfort and pain at lower pressures at the thigh, with wider cuffs, and with a ramp inflation pattern. Staircase profile compression caused an increase in deep tissue oxygenation, whereas the ramp profile compression decreased it. Conclusion Discomfort and pain during circumferential compression at the lower limb is related to the width of pneumatic cuffs, the inflation pattern, and the volume of soft tissue at the assessment site. The occurrence of pain is also possibly related to the decrease in deep tissue oxygenation during compression. Application Our findings can be used to inform safe and comfortable design of soft exoskeletons to avoid discomfort and possible soft tissue injury.

The effect of simulated circumferential soft exoskeleton compression at the knee on discomfort and pain

“…During standing, we found mean DDTs ranging from 12.0 to 32.2 kPa, and mean PDTs ranging from 35.8 to 61.2 kPa (Kermavnar et al, 2019). In both cases, compression was best tolerated during staircase inflation of the widest cuff at the calf, and worst during ramp inflation of the widest cuff at the thigh.…”

“…Separately, we conducted experiments in the context of circumferential compression at the thigh and calf using different sizes of pneumatic cuffs and inflation patterns for static (standing) and dynamic (walking) conditions (Kermavnar, 2019;Kermavnar, O'Sullivan, de Eyto, & O'Sullivan, 2019). Cuff inflation pressures that caused pre-pain discomfort (Discomfort Detection Threshold -DDT) and pain (Pain Detection Threshold -PDT) were assessed in addition to deep tissue oxygenation changes.…”

Reducing Migration of Knee Exoskeletons With Dynamic Waist Strap

“…Several categories of mechanisms have been proposed to address this issue. The high-tighten-able thigh cuffs, including the hook and loop straps [18]- [20], the pneumatic cuffs [6], [21] and the BOA straps [22] do not introduce additional constraints to human joints, but may not be effective under large external downward force, and will cause deformation of human thigh, leading to restraints of muscle activation [23], [24]. The articular ankle/hip joints [25]- [29] introduce extra support against downward migration, but may limit the motion of the corresponding human joint.…”

“…However, tightening the thigh cuff to decrease downward drift is not always effective, especially when the external downward force is large. And tightening the upper cuff could limit the activation of muscles in the human thigh, leading to discomfort or even pain [23], [24]. Other designs employ articular ankle/hip joints [25]- [29] to support the knee exoskeleton.…”

Introduction to the Human Factors Special Issue on User-Centered Design for Exoskeleton

“…Two studies investigated the biomechanical responses in the lower back when wearing exos (Alemi et al, 2020;Madinei et al, 2020). Three studies investigated the impact of lower extremity exos during various manual handling tasks (Bequette et al, 2020;Kermavnar et al, 2020;Pillai et al, 2020). Together, these studies provide some insight into the complex relationship between the exo and the human musculoskeletal system.…”