Distribution of Internal Pressure around Bony Prominences: Implications to Deep Tissue Injury and Effectiveness of Intermittent Electrical Stimulation

Abstract

The overall goal of this project is to develop interventions for the prevention of deep tissue injury (DTI), a form of pressure ulcers that originates in deep tissue around bony prominences. The present study focused on: (1) obtaining detailed measures of the distribution of pressure experienced by tissue around the ischial tuberosities, and (2) investigating the effectiveness of intermittent electrical stimulation (IES), a novel strategy for the prevention of DTI, in alleviating pressure in regions at risk of breakdown due to sustained loading. The experiments were conducted in adult pigs. Five animals had intact spinal cords and healthy muscles and one had a spinal cord injury that led to substantial muscle atrophy at the time of the experiment. A force-controlled servomotor was used to load the region of the buttocks to levels corresponding to 25%, 50% or 75% of each animal's body weight. A pressure transducer embedded in a catheter was advanced into the tissue to measure pressure along a three dimensional grid around the ischial tuberosity of one hind leg. For all levels of external loading in intact animals, average peak internal pressure was 2.01 ± 0.08 times larger than the maximal interfacial pressure measured at the level of the skin. In the animal with spinal cord injury, similar absolute values of internal pressure as that in intact animals were recorded, but the substantial muscle atrophy produced larger maximal interfacial pressures. Average peak internal pressure in this animal was 1.43 ± 0.055 times larger than the maximal interfacial pressure. Peak internal pressure was localized within a ±2 cm region medio-laterally and dorso-ventrally from the bone in intact animals and ±1 cm in the animal with spinal cord injury. IES significantly redistributed internal pressure, shifting the peak values away from the bone in spinally intact and injured animals. These findings provide critical information regarding the relationship between internal and interfacial pressure around the ischial tuberosities during loading levels equivalent to those experienced while sitting. The information could guide future computer models investigating the etiology of DTI, as well as inform the design and prescription of seating cushions for people with reduced mobility. The findings also suggest that IES may be an effective strategy for the prevention of DTI.

Distribution of Internal Strains Around Bony Prominences in Pigs

“…In comparison, in the pigs with SCI (n = 3, one not used in this study) muscle volume in the paralyzed limb was 127.26 ± 41.61 cm 3 , indicating a reduction of 50.94% in muscle volume due to atrophy. 65 During the month that elapsed between surgery and the terminal experiment none of the pigs with SCI recuperated voluntary control of the ipsilateral hind-limb.…”

“…The lesion caused paralysis of the ipsilateral hind-limb but retained voluntary bladder and bowel function. Detailed descriptions of the surgical procedure and palliative care are provided in Solis et al 65 During the 1 month period between surgery and the terminal experiment, noticeable atrophy occurred in the paralyzed hind-limb. A quantification of muscle atrophy due to the spinal hemisection was obtained from MR images, in which the volume of muscles around the ischial tuberosity in the affected hind-limb in the pigs with SCI was compared to the muscle volume in the intact pigs on the day of the terminal experiment.…”

Modelling of pressure ulcer (PU) risk prediction system

“…Due to this loading, the blood flow and the oxygen supply become poor to the soft tissues [5], [1] and that leads to tissue necrosis [1], [2]. Studies suggest a pressure higher than 32 mmHg [1], [2], [8] Table I. To prevent ulceration in the human body, risk assessment scales are widely used in hospitals.…”

“…Mostly people with mobility impairments, spinal cord injury, head trauma or multiple sclerosis develop pressure ulcer [1], [2]. Also, people in coma or people in long surgical procedure develop pressure ulcer [3], which is also known as bedsore, ischemia, and decubitus ulcer.…”

Effect of interpolation on parameters extracted from seating interface pressure arrays

“…Feature extraction from pressure maps is a common practice, e.g., pursuant to some estimation of pressure ulcer risk [13][14][15][16]. Indeed, these variables have thorough representation in the literature, including studies invoking both the linear [17][18][19] and cubic [20][21][22] interpolation. Furthermore, data can be interpolated to any degree: once (e.g., 16-31 data points per row), twice (e.g., to 61 data points), or three times (e.g., 121 × 121 data points) are all typical.…”