Beware of the toilet: The risk for a deep tissue injury during toilet sitting

The complex interplay between mechanical forces, tissue response and individual susceptibility to pressure ulcers

OBJECTIVE

The most recent edition of the International Clinical Practice Guideline for the Prevention and Treatment of Pressure Ulcers/Injuries was released in 2019. Shortly after, in 2020, the first edition of the SECURE Prevention expert panel report, focusing on device-related pressure ulcers/injuries, was published as a special issue in the Journal of Wound Care. A second edition followed in 2022. This article presents a comprehensive summary of the current understanding of the causes of pressure ulcers/injuries (PU/Is) as detailed in these globally recognised consensus documents.

METHOD

The literature reviewed in this summary specifically addresses the impact of prolonged soft tissue deformations on the viability of cells and tissues in the context of PU/Is related to bodyweight or medical devices.

RESULTS

Prolonged soft tissue deformations initially result in cell death and tissue damage on a microscopic scale, potentially leading to development of clinical PU/Is over time. That is, localised high tissue deformations or mechanical stress concentrations can cause microscopic damage within minutes, but it may take several hours of continued mechanical loading for this initial cell and tissue damage to become visible and clinically noticeable. Superficial tissue damage primarily stems from excessive shear loading on fragile or vulnerable skin. In contrast, deeper PU/Is, known as deep tissue injuries, typically arise from stress concentrations in soft tissues at body regions over sharp or curved bony prominences, or under stiff medical devices in prolonged contact with the skin.

CONCLUSION

This review promotes deeper understanding of the pathophysiology of PU/Is, indicating that their primary prevention should focus on alleviating the exposure of cells and tissues to stress concentrations. This goal can be achieved either by reducing the intensity of stress concentrations in soft tissues, or by decreasing the exposure time of soft tissues to such stress concentrations.

Comparative analysis of effects of various toilet seat cushions on buttock pressure during toileting in persons with spinal cord injury

OBJECTIVES

To measure buttock pressure during toilet seating in persons with spinal cord injury (SCI).

DESIGN

A case series study.

SETTING

Kibikogen Rehabilitation Center for Employment Injuries.

METHODS

The study included 41 persons with SCI. Buttock pressure was measured during toilet seating, with or without a toilet seat cushion (foam cushion, gel cushion, air cushion) on the toilet seat.

RESULTS

The subjects were classified into three groups according to the site of the maximum pressure [greater trochanter (GT) region, ischial tuberosities (IT), and sacral region (SR)] recorded on the pressure map of the non-cushioned toilet seat, into the GT, IT and SR groups, respectively. All three types of cushions altered the buttock pressure distribution during no-cushion toilet seating. In the GT group, all three cushions significantly reduced the peak pressure in the GT area, compared to the control (no-cushion). The foam cushion significantly increased the peak pressure in the IT area (Pisch) in the GT group, relative to the control. However, the foam cushion significantly increased while the gel cushion significantly reduced Pisch, relative to the control. In SR group, the air cushion significantly reduced the peak pressure in the SR, relative to the control.

CONCLUSION

We recommend the use of the gel cushion for the IT group and the air cushion in GT and SR group to reduce buttock pressure during toilet seating in persons with SCI.

Effect of mattress bedding layer structure on pressure relief performance and subjective lying comfort

Mattresses' pressure relief performance and comfort largely affect sleep quality. Mattress filling materials have been proven to affect the interface pressure distribution and comfort, but the effect of mattress structure is unclear. In this paper, the interface pressure distribution and subjective comfort of 10 subjects were assessed in the different bedding layer structures of mattresses, after mattress support performance was tested. The results show that the mattresses with bedding material hardness gradually increasing from the top layer to the bottom layer (BMH-ITTB) structure have a softer surface layer, a better support core layer, and higher fitness. This enables the mattress to achieve a better decompression effect. The low-pressure area (PAI_≤0.67kPa) increased, while the high-pressure area (PAI_≥2.67kPa and PAI_≥4.00kPa), maximum pressure (P₉₅), average pressure (P₅₀), and pressure index (PI) decreased. This also enables the mattress to achieve higher subjective comfort scores.

Reducing Test Anxiety by Device-Guided Breathing: A Pilot Study

Test anxiety remains a challenge for students and has considerable physiological and psychological impacts. The routine practice of slow, Device-Guided Breathing (DGB) is a major component of behavioral treatments for anxiety conditions. This paper addresses the effectiveness of using DGB as a self-treatment clinical tool for test anxiety reduction. This pilot study sample included 21 healthy men and women, all college students, between the ages of 20 and 30. Participants were randomly assigned to two groups: DGB practice (n = 10) and wait-list control (n = 11). At the beginning and the end of 3-weeks DGB training, participants underwent a stress test, followed by measures of blood pressure and reported anxiety. Anxiety reduction in the DGB group as compared to controls was not statistically significant, but showed a large effect size. Accordingly, the clinical outcomes suggested that daily practice of DGB may lead to reduced anxiety. We assume that such reduction may lead to improved test performance. Our results suggest an alternative treatment for test anxiety that may also be relevant for general anxiety, which is likely to increase due to the ongoing COVID-19 pandemic.

Computational studies of the biomechanical efficacy of a minimum tissue deformation mattress in protecting from sacral pressure ulcers in a supine position

Sustained soft tissue exposure to localised deformations is a trigger for the formation of pressure ulcers. Immersion and envelopment are critical benchmarks that determine comfort and the pressure ulcer risk mitigation, as they have considerable influence on tissue stress concentrations near bony prominences. In the present study, we developed a computer modelling framework for quantifying the extent by which optimal envelopment disperses tissue stress concentrations near the sacrum. To compare the risk of developing a sacral pressure ulcer while lying supine on a regular foam mattress with respect to lying on a specialised, minimum tissue deformation mattress (which closely conforms to the body contours), we used a three‐dimensional anatomically‐realistic model of the adult female buttocks. The strains and stresses in the subdermal soft tissues reached peak values of 65% and 2.4 kPa for the regular mattress, respectively, but always remained below 45% and 1.2 kPa for the minimum tissue deformation mattress, which indicates longer safe times for supine support on the latter mattress. Our work demonstrates that alleviation of localised, sustained stress concentrations through good immersion and envelopment of the support surface protects from pressure ulcers, and has the potential to relieve chronic pain which is associated with the pressure ulcer risk.

Our contemporary understanding of the aetiology of pressure ulcers/pressure injuries

In 2019, the third and updated edition of the Clinical Practice Guideline (CPG) on Prevention and Treatment of Pressure Ulcers/Injuries has been published. In addition to this most up‐to‐date evidence‐based guidance for clinicians, related topics such as pressure ulcers (PUs)/pressure injuries (PIs) aetiology, classification, and future research needs were considered by the teams of experts. To elaborate on these topics, this is the third paper of a series of the CPG articles, which summarises the latest understanding of the aetiology of PUs/PIs with a special focus on the effects of soft tissue deformation. Sustained deformations of soft tissues cause initial cell death and tissue damage that ultimately may result in the formation of PUs/PIs. High tissue deformations result in cell damage on a microscopic level within just a few minutes, although it may take hours of sustained loading for the damage to become clinically visible. Superficial skin damage seems to be primarily caused by excessive shear strain/stress exposures, deeper PUs/PIs predominantly result from high pressures in combination with shear at the surface over bony prominences, or under stiff medical devices. Therefore, primary PU/PI prevention should aim for minimising deformations by either reducing the peak strain/stress values in tissues or decreasing the exposure time.

Positron emission tomography study of effects of two pressure-relieving support surfaces on pressure ulcer development

OBJECTIVE

To study the pathophysiological cascade of pressure ulcer (PU) development consisting of tissue deformation, inflammation and hypoxia.

METHOD

In this crossover study, deformation was measured with computerised tomography (CT) linked with contact area reflecting immersion and envelopment. Inflammation and hypoxia were measured using subepidermal moisture (SEM), skin temperature and tissue perfusion with positron emission tomography. These variables were investigated under 90 minutes of pressure exposure caused by two functionally different support surfaces-a regular foam mattress and a minimum pressure air (MPA) mattress.

RESULTS

A total of eight healthy volunteers took part in the study. There was major tissue deformation when the participants lay on a foam mattress while the tissues retained their original shape on the MPA mattress (p<0.0001). During the pressure exposure, the skin temperature increased significantly on both support surfaces but the final temperature on the foam mattress was about 1oC higher than on the MPA mattress (p<0.0001). SEM increased on both support surfaces compared with an unexposed reference site, but the cause may be different between the two support surfaces. Tissue perfusion was lowest in the skin followed by subcutaneous tissues and highest in the muscles. The pressure exposure did not cause any substantial changes in perfusion. The results showed that tissue deformation was more pronounced, the support surface contact area (envelopment), was smaller and the skin temperature higher on the foam mattress than on the MPA mattress, without significant differences in tissue perfusion.

CONCLUSION

In this study, the MPA mattress support surface had mechanobiological properties that counteracted tissue deformation and thereby may prevent PUs.

Design and Analysis of an Intelligent Toilet Wheelchair Based on Planar 2DOF Parallel Mechanism with Coupling Branch Chains

Due to the fixed size of the structure or the possibility of only simple manual adjustment, the traditional toilet wheelchair cannot easily be adapted to the size of the user or the toilet. In this paper, a planar two-degree-of-freedom parallel mechanism with coupling branch chains is proposed to enable both seat height adjustment and body posture adjustment of a toilet chair, solving the problems of posture adaptability between the user and the machine, and height matching in the process of using the wheelchair-assisted toilet. The model of the parallel mechanism was designed after analyzing the general rules of posture transformation in the human body before and after the toilet process, and the dimensions of each linkage were then determined according to the constraint conditions. By analyzing the degree of freedom, kinematics, workspace, singularity and position of the center of gravity, the rationality of the design was ensured. The weighted average function was used to find the optimal fixed point of the horizontal moving slider, and the actual trajectory at the end of the single driving mode was close to the ideal trajectory. The experimental results show that the adjustable seat height range is 290~550 mm and the adjustable angle range is 0~90°, which can enable disabled people to use the toilet independently.

Assessment of blood distribution in response to post-surgical steal syndrome: A novel technique based on Thermo-Anatomical Segmentation

The distal ischemic steal syndrome (ISS) is a complication following the construction of an arteriovenous (A-V) access for hemodialysis. The ability to non-invasively monitor changes in skin microcirculation improves both the diagnosis and treatment of vascular diseases. In this study, we propose a novel technique for evaluating the palms' blood distribution following arteriovenous access, based on thermal imaging. Furthermore, we utilize the thermal images to identify typical recovery patterns of patients that underwent this surgery and show that thermal images taken post-surgery reflect the patient's follow-up status. Thermal photographs were taken by a portable thermal camera from both hands before and after the A-V access surgery, and one month following the surgery, from ten dialysis patients. A novel term "Thermo-Anatomical Segmentation", which enables a functional assessment of palm blood distribution was defined. Based on this segmentation it was shown that the greatest change after surgery was in the most distal region, the fingertips (p < 0.05). In addition, the changes in palm blood distribution in both hands were synchronized, which indicates a bilateral effect. An unsupervised machine learning model revealed two variables that determine the recovery pattern following the surgery: the palms' temperature difference pre- and post-surgery and the post-surgery difference between the treated and untreated hand. Our proposed framework provides a new technique for quantitative assessment of the palm's blood distribution. This technique may improve the clinical treatment of patients with vascular disease, particularly the patient-specific follow-up, in clinics as well as in homecare.

The microclimate under dressings applied to intact weight-bearing skin: Infrared thermography studies

BACKGROUND

When a patient is lying in a hospital bed (e.g. supine or prone), bodyweight forces distort soft tissues by compression, tension and shear, and may lead to the onset of pressure ulcers in those who are stationary and insensate, especially at their pelvic region. Altered localized microclimate conditions, particularly elevated skin temperatures leading to perspiration and resulting in skin moisture or wetness, are known to further increase the risk for pressure ulcers, which is already high in immobile patients.

METHODS

We have used infrared thermography to measure local skin temperatures at the buttocks of supine healthy subjects, to quantitatively determine, for the first time in the literature, how skin microclimate conditions associated with a weight-bearing Fowler's position are affected by application of dressings. Our present methodology has been applied to compare a polymeric membrane dressing versus placebo foam, with a no-dressing case used as reference.

FINDINGS

One hour of lying in a Fowler's position was already enough to cause considerable heat trapping (~3 °C rise) between the weight-bearing body and the support surface. Analyses of normalized local skin temperatures and entropy of the temperature distributions indicated that the polymeric membrane dressing material allowed better and more homogenous clearance of locally accumulated body-heat with respect to simple foam.

INTERPRETATION

Infrared thermography is suitable for characterizing skin microclimate conditions under different dressings, and, accordingly, is effective in developing and evaluating pressure ulcer prevention and treatment strategies - both of which require adequate skin microclimate.

Non-invasive thermal imaging of cardiac remodeling in mice

Thermal infrared imaging has been suggested as a non-invasive alternative to monitor physiological processes and disease. However, the use of this technique to image internal organs, such as the heart, has not yet been investigated. We sought to determine the ability of our novel thermal image-processing algorithm to detect structural and functional changes in a mouse model of hypertension and cardiac remodeling. Twelve mice were randomly assigned to receive either the pro-inflammatory, hypertensive hormone angiotensin-II (2 mg/kg/day, n = 6) or saline (n = 6) infusion for 28 days. We performed weekly blood pressure measurements, together with serial trans-thoracic echocardiography studies and histopathological evaluation of the hearts. Thermal images were captured with a commercially available thermal camera, and images were processed by our novel algorithm which analyzes relative spatial temperature variation across the animal's thorax. We assessed cardiac inflammation by measuring inflammatory cell infiltration through flow cytometry. Angiotensin infusion increased blood pressure together with cardiac hypertrophy and fibrosis. Thermal imaging at day 28 of the experiment detected an increase in the fraction of the skin heated by the heart in angiotensin-treated mice. Thermal image findings were significantly correlated to left ventricular volume and mass parameters seen on echocardiography (r = 0.8, p < 0.01 and r = 0.6, p = 0.07). We also identified distinct changes in the spatial heat profiles of all angiotensin-treated hearts, possibly reflecting remodeling processes in the hypertensive heart. Finally, a machine learning based model using thermal imaging parameters predicted intervention status in 10 out of 11 mice similar to a model using echocardiographic measurements. Our findings suggest, for the first time, that a new thermal image-processing algorithm successfully correlates surface thermography with cardiac structural changes in mice with hypertensive heart disease.

Sodium pyruvate pre-treatment prevents cell death due to localised, damaging mechanical strains in the context of pressure ulcers

We demonstrate sodium pyruvate (NaPy) pre-treatment as a successful approach for pressure ulcer (PU) prevention by averting their aetiological origin-cell-level damage and death by large, sustained mechanical loads. We evaluated the NaPy pre-treatment effect on permeability changes in the cell's plasma membrane (PM) following application of in vitro damaging-level strains. Fibroblasts or myoblasts, respectively, models for superficial or deep-tissue damage were grown in 0 or 1 mM NaPy, emulating typical physiological or cell culture conditions. Cells were pre-treated for 4 hours with 0 to 5 mM NaPy prior to 3-hour sustained, damaging-level loads (12% strain). PM permeability was quantified by the cell uptake of small (4 kDa), fluorescent dextran compared with unstrained control using fluorescence-activated cell sorting (FACS). Pre-treatment with 1 mM, and especially 5 mM, NaPy significantly reduces damage to PM integrity. Long-term NaPy pre-exposure can improve protective treatment, affecting fibroblasts and myoblasts differently. Pre-treating with NaPy, a natural cell metabolite, allows cells under damaging-level mechanical loads to maintain their PM integrity, that is, to avoid loss of homeostasis and inevitable, eventual cell death, by preventing initial, microscale stages of PU formation. This pre-treatment may be applied prior to planned periods of immobility, for example, planned surgery or transport, to prolong safe time in a position by preventing initial cell damage that can cascade and lead to PU formation.

Bioengineering considerations in the prevention of medical device-related pressure ulcers

BACKGROUND

In recent years, it has become increasingly apparent that medical device-related pressure ulcers represent a significant burden to both patients and healthcare providers. Medical devices can cause damage in a variety of patients from neonates to community based adults. To date, devices have typically incorporated generic designs with stiff polymer materials, which impinge on vulnerable soft tissues. As a result, medical devices that interact with the skin and underlying soft tissues can cause significant deformations due to high interface pressures caused by strapping or body weight.

METHODS

This review provides a detailed analysis of the latest bioengineering tools to assess device related skin and soft tissue damage and future perspectives on the prevention of these chronic wounds. This includes measurement at the device-skin interface, imaging deformed tissues, and the early detection of damage through biochemical and biophysical marker detection. In addition, we assess the potential of computational modelling to provide a means for device design optimisation and material selection.

INTERPRETATION

Future collaboration between academics, industrialists and clinicians should provide the basis to improve medical device design and prevent the formation of these potentially life altering wounds. Ensuring clinicians report devices that cause pressure ulcers to regulatory agencies will provide the opportunity to identify and improve devices, which are not fit for purpose.

Dressings cut to shape alleviate facial tissue loads while using an oxygen mask

Non-invasive ventilation (NIV) masks are commonly used for respiratory support where intubation or a surgical procedure can be avoided. However, prolonged use of NIV masks involves risk to facial tissues, which are subjected to sustained deformations caused by tightening of the mask and microclimate conditions. The risk of developing such medical device-related pressure ulcers can be reduced by providing additional cushioning at the mask-face interface. In this work, we determined differences in facial tissue stresses while using an NIV mask with versus without using dressing cuts (Mepilex Lite; Mölnlycke Health Care, Gothenburg, Sweden). First, we developed a force measurement system that was used to experimentally determine local forces applied to skin at the bridge of the nose, cheeks, and chin in a healthy sample group while using a NIV mask. We further demonstrated facial temperature distributions after use of the mask using infrared thermography. Next, using the finite element method, we delivered the measured compressive forces per site of the face in the model and compared maximal effective stresses in facial tissues with versus without the dressing cuts. The dressings have shown substantial biomechanical effectiveness in alleviating facial tissues deformations and stresses by providing localised cushioning to the tissues at risk.

The response of peripheral microcirculation to gravity-induced changes

BACKGROUND

The peripheral microcirculation supplies fresh blood to the small blood vessels, providing oxygen and nutrients to the tissues, removing waste, and maintaining normal homeostatic conditions. The goal of this study was to characterize the response of the peripheral microcirculation, in terms of blood flow and tissue oxygenation variables, to gravity-induced changes.

METHODS

The study included 20 healthy volunteers and the experiment involved monitoring central and peripheral variables with the right hand positioned at different heights. These positions correspond to various gravitational levels. Peripheral perfusion and oxygenation were monitored using a laser Doppler flowmeter, photoplethysmograph, and transcutaneous oxygen tension monitor. Local blood pressure and respiration rate were also measured.

FINDINGS

At the heart level, tissue oxygenation displayed a nadir, while capillary flow displayed a peak. Similar but weaker changes were observed at the control hand. In contrast, the photoplethysmograph's amplitude strongly decreased upon reducing the arm position below heart level. Both systolic and diastolic pressures decreased linearly between the highest to lowest arm position.

INTERPRETATION

The results may reflect peripheral compensation mechanisms, as well as an interaction between the central and peripheral cardiovascular systems, in response to local changes in blood pressure. The observed dependence of the oxygenation pattern on height could lead to important new insights for the diagnosis and treatment of problems in the regulation of tissue perfusion.

Deep tissue loads in the seated buttocks on an off-loading wheelchair cushion versus air-cell-based and foam cushions: finite element studies

For wheelchair users, a common injury is a sitting-acquired pressure ulcer (PU) which typically onsets near the interface between the ischial tuberosity (IT) and the overlying soft tissues. The risk of developing PUs can be reduced considerably if an adequate cushion is placed on the wheelchair in order to protect tissues from PUs by minimising interface mechanical loads between the body and cushion and also, exposure to internal soft tissue loads. In this work, we studied the biomechanical performances of an off-loading (OL) cushion with limited adjustability, in comparison to a standard foam cushion and a fully adjustable air-cell-based (ACB) cushion. These different cushion design approaches were methodologically and quantitatively analysed and compared here using a finite element (FE) modelling framework. We determined the internal mechanical deformations, strains and stresses in soft tissues of the seated buttocks during symmetric sitting, in a specific anatomy of a person with a spinal cord injury that was acquired during sitting in an open, magnetic resonance imaging configuration. Our results have shown that strains and stresses in muscle, fat and skin tissues are orders of magnitude lower for the ACB cushion with respect to the standard foam and OL cushions. The OL cushion design has taken the approach of protecting at-risk sites of the buttocks by transferring local internal tissue loads away from the ITs and towards the greater trochanters, at the price of increasing exposure to internal tissue loads at sites other than the ITs. The ACB cushion design, however, has taken a different approach, that is, immersion and envelopment of the entire buttocks structure, which is useful for minimising the exposure to internal tissue loads throughout the whole buttocks. Quantifying performances of wheelchair cushions using FE modelling provides insights into deep tissue loads, which is essential for informed decision-making in developing sitting solutions for individuals at risk, as well as for patient groups.

What makes a good head positioner for preventing occipital pressure ulcers

Patients who are stationary endure prolonged soft tissue distortions and deformations at contact areas between their body and the support surface, which may lead to the onset of pressure ulcers (PUs) over time. A novel technology for patient positioning employs innovation in materials science, specifically viscoelastic materials with shape memory properties that compose the Z-Flo™ head positioner (Mölnlycke Health Care, Gothenburg, Sweden). Head positioners are generally known to reduce the occurrence of PUs in scalp tissues and the ears, but quantitative assessments of their biomechanical efficacy are missing in the literature. To determine potential differences in mechanical loads formed in the soft tissues of the back of the head while in contact with 2 head positioner types, Z-Flo vs flat medical foam, we developed 2 comparable finite element model configurations, both including the same 3-dimensional adult head. For both model variants, stresses in skin and fat peaked at the occiput. The skin at the back of the resting head is subjected to greater stress values with respect to fat; however, the Z-Flo positioner reduced the exposure of both skin and fat tissues to elevated stresses considerably (by a factor of 3) compared to the medical foam support. We found the Z-Flo device effective in reducing tissue loads at the surface of the head as well as internally in scalp tissues, with a particular strength in reducing internal tissue shear. The Z-Flo device achieves this protective quality through highly effective immersion and envelopment of the back of the head, generated in the process of manual moulding of the device in preparation for use. Additional protection is achieved through the viscoelastic response of the filling material of this positioner, which relaxes promptly and considerably under the weight of the head (by more than 2-fold within approximately 1 s) as opposed to the elastic recoil of the foam that pushes back on scalp tissues.