Missing links in pressure ulcer research—An interdisciplinary overview

Effects of loading processes on contact forces when simulating static seating with a finite element human body model

Seat interface forces, particularly shear forces, play an essential role in predicting the risk of pressure ulcers and seating discomfort. When a finite element human body model (HBM) is used for static seating simulation, the most common loading method is to put the model in a position close to the desired final posture and then 'drop' it from just above the seat by applying the gravity (DROP). This does not represent how people sit in a seat. In addition, high coefficients of friction (COF) are often used to prevent sliding, which may lead to unrealistically high tangential forces. This study aims to investigate the effects of the loading process and the COF on seating simulations with a HBM. We propose a new loading approach called 'drop and rotate' (D&R) to better mimic people sitting on a seat. With the trunk more flexed than the desired posture, the model is dropped to establish the contact between the buttocks and thighs, and the seat pan first, and then between the back and the backrest by rotating the hip. Simulations were performed using a recently developed and validated adult male model in two different seat configurations. Results show that the proposed D&R method was less sensitive to COF and gave a better prediction of contact forces, especially on the seat pan. However, its computational time is higher than the DROP method. The study highlights the importance of the loading process when simulating static seating.

The effect of wheelchair cushion properties on the microclimate at the cushion-user interface: A systematic review and meta-analysis

INTRODUCTION

Pressure injuries are a preventable yet highly prevalent health concern. Wheelchair cushion prescription can have significant implications for wheelchair users' risk of pressure injury development, which can impact functional abilities and quality of life. The efficacy of a wheelchair cushion to redistribute pressure has been well-researched, but the efficacy to manage the microclimate is less clear, particularly in warm-hot environments. The aim of this study was to systematically review studies examining the effect of wheelchair cushions on temperature, moisture and thermal perception to determine which cushions are superior to improve these responses.

METHOD

A systematic review with meta-analyses of randomised cross-over and randomised control trials of wheelchair cushion interventions on measures of temperature, moisture, and thermal perception was conducted.

RESULTS

Eight studies were identified that met the eligibility criteria and six meta-analyses were conducted. Pooled analyses identified a significantly lower temperature on foam-gel cushions compared to air cushions (MD = 0.80, 95% CI: 0.31, 1.29; p = 0.002) and a significantly lower temperature on foam-gel cushions compared to foam cushions (SMD = 0.76, 95%CI; 0.45, 1.06; p < 0.00001). Pooled analyses also demonstrated significantly lower relative humidity (i.e., moisture) on foam cushions compared to foam-gel cushions (p = 0.02). Differences in thermal perception were inconclusive due to limited data found.

CONCLUSION

It is clear that not one cushion is ideal in managing all aspects of microclimate, as foam-gel cushions were the superior cushion to manage temperature and foam cushions were the superior cushion to manage moisture. This article provides occupational therapists and other health professionals with evidence-based information to assist with wheelchair cushion prescription that minimises the temperature and moisture accumulation, and associated risk of pressure injury for wheelchair users.

Review of assistive devices for the prevention of pressure ulcers: an engineering perspective

PURPOSE

Pressure ulcers (PUs) are prevalent among immobile bed or wheelchair-reliant individuals who experience prolonged sedentary positions. Pressure relief and frequent repositioning of body posture help to mitigate complications associated with PUs. Adherence with regular repositioning is difficult to maintain due to nursing labour shortages or constraints of in-home caregivers. Manual repositioning, transferring, and lifting of immobile patients are physically demanding tasks for caregivers. This review aimed to explore and categorize these devices, discuss the significant technical challenges that need addressing, and identify potential design opportunities.

MATERIALS AND METHODS

In this review, a literature search was conducted using PubMED, Science Direct, Google Scholar and IEEE Xplore databases including studies from 1995 until Feb 2023 with keywords such as pressure ulcer, assistive device, pressure relief, repositioning, transfer, etc. Both commercial and research-level devices were included in the search.

RESULTS

142 devices or technologies were identified and classified into four main categories that were further subcategorized. Within each category, the devices were investigated in terms of their mechanical design, actuation methods, control strategies, sensing technologies, and level of autonomy. Limitations of current technologies are design complexity, lack of patient comfort, and a lack of autonomy requiring caregivers frequent intervention.

CONCLUSIONS

Several devices have been developed to help with prevention and mitigation of PUs. There remain challenges that hinder the widespread accessibility and use of current technologies. Advancements in assistive technologies for pressure ulcer mitigation could lie at the intersection of robotics, sensors, perception, user-centered design, and autonomous systems.

Incidence and risk factors for pressure injuries in patients who have undergone vascular operations: a scoping review

BACKGROUND

Patients who have undergone vascular operations are thought to be at an increased risk for developing pressure injuries; however, the extent to which pressure injuries occur in this population is not clear. This scoping review sought to summarize what is known about the incidence of pressure injuries, and the risk factors for the development of pressure injuries in patients who have undergone vascular operations. MAIN: An initial search identified 2564 articles, and 9 English language studies were included. Results showed that due to study design limitations in the available literature preventing hospital-acquired and present on admission pressure injuries to be distinguished, it is difficult to ascertain the incidence rate of pressure injuries in this population.

CONCLUSION

Certain vascular procedures were found to be higher risk for the development of pressure injuries such as major amputations and lower extremity bypass surgery. In addition to procedural risk factors, patient factors were identified that may be associated with the development of pressure injuries in the vascular population, and these in the authors' view deserve further exploration. Overall, this scoping review identified an area ripe for future research, the results of which would have implications for wound care in healthcare institutions and at home.

Influence of car seat firmness on seat pressure profiles and perceived discomfort during prolonged simulated driving

During a driving task, the seat-driver interface is particularly influenced by the external environment and seat features. This study compares the effect of two different seats (S₁ - soft & S₂ - firm) and the effect of visual simulation of different road types (city, highway, mountain, country), on pressure distribution and perceived discomfort during prolonged driving. Twenty participants drove two 3-h sessions (one per seat) on a static simulator. Contact Pressure (CP), Contact Surface (CS), and Seat Pressure Distribution Percentage (SPD%) were analyzed throughout, using two pressure mats positioned on seat cushion and backrest. Whole-body and local discomfort for each body part were rated every 20 min. The softer seat, S₁, induced a greater contact surface on cushion and backrest and a lower SPD%, reflecting better pressure distribution. Pressure profiles were asymmetrical for both S₁ and S_2, with higher CP under left buttock (LBu) and right lower back (RLb) and greater CS under thighs and RLb. Pressure distribution was less homogeneous on mountain and city roads than on monotonous roads (highway and country). Despite the pressure differences between the seats, however, both led to similar increases in perceived whole-body discomfort throughout the driving session. Moreover, the highest discomfort scores were in the neck and the lower back areas, whatever the seat. These findings on pressure variables may have implications for the design of backrests and cushions to ensure more homogeneous pressure distribution, even though this is not shown to minimize perceived driver discomfort.

Brief intermittent pressure off-loading on skin microclimate in healthy adults - A descriptive-correlational pilot study

AIM

This study examined microclimate changes to the skin as a result of pressure over a 1 h period. The results were compared to skin parameter results following brief consecutive off-loading of pressure-prone areas.

DESIGN

A descriptive-correlational pilot study was undertaken.

METHOD

A convenience sample of 41 healthy adults aged 18-60 years was recruited. Participants engaged in four 1 h data collection sessions. The sessions were conducted in both semi-recumbent and supine positions. Measures of erythema, melanin, stratum corneum hydration, and skin temperature were taken at pressure-prone areas at baseline and after 1 h in an uninterrupted method (continuous pressure-loading) and every 10 min in an interrupted method (brief off-loading). The Corneometer and Mexameter (Courage + Khazaka Electronics GMbH, 2013) and Exergen DermaTemp DT-1001 RS Infrared Thermographic Scanner (Exergen Corporation, 2008) provided a digital appraisal of skin parameters. Intraclass correlation coefficients (ICC) were calculated to indicate test-retest reliability and absolute agreement of results between the two methods.

RESULTS

Strong agreement between the interrupted and uninterrupted method was observed with ICCs ranging from 0.72 to 0.99 (supine) and 0.62-0.99 (semi-recumbent). Endpoint measures tended to be higher compared to baseline measures for all skin parameters. Differences in skin parameters results by anatomical location were evident particularly for erythema and stratum corneum hydration; the elbows and heels yielded lower scores compared to the sacrum. Erythema had the most variation across methods. The supine and semi-recumbent positions had negligible effect on measured skin parameters.

CONCLUSIONS

Minimal variation between skin parameter results indicates that brief off-loading in the interrupted method did not significantly change the outcomes; minor shifts in positioning do not alter changes to the skin from pressure. Skin parameters varied by anatomical location and changed over a 1 h period of pressure-loading.

RELEVANCE TO CLINICAL PRACTICE

Biophysical techniques may be able to assist accurate assessment of skin microclimate and skin colour. As brief off-loading (interruptions) to enable skin parameter measurement does not alter skin readings, researchers can proceed with some confidence regarding the use of this protocol in future studies assessing skin parameters. This study data provides a library of cutaneous changes at pressure-prone areas of healthy adults and is expected to inform innovative approaches to pressure injury risk assessment.

A Case Study on the Effects of Foam and Seat Pan Inclination on the Deformation of Seated Buttocks Using MRI

OCCUPATIONAL APPLICATIONSWe investigated the effects of seat pan inclination and foam on the deformation of the seated buttocks using an upright MRI system. From observations among four healthy males, we found that soft tissue deformation under the ischial tuberosity (IT) could be reduced not only by using a soft cushion, but also by decreasing the shear force on the seat pan surface. These results suggest that soft tissue deformation could be used as an objective measure for assessing seating discomfort and injury risk, by accounting for the effects of both contact pressure and shear. We also confirmed that the gluteus maximus (GM) muscle displaced away from the IT once seated. As peak pressure and shear are most likely located below the IT, more realistic computational human body models in this region are needed that consider muscle sliding.

Effects of cycle periods and pressure amplitudes of alternating pressure on sacral skin blood flow responses

BACKGROUND

There are no guidelines on selecting alternating pressure (AP) configurations on increasing sacral skin blood flow (SBF).

AIM

The specific aims were to compare different cycle periods and pressure amplitudes of AP on sacral SBF responses in healthy people to establish the efficacy and safety of the protocols.

METHODS

Two studies were tested, including the cycle period study (8 2.5-min vs 4 5-min protocols) and the pressure amplitude study (75/5 vs 65/15 mmHg protocols). Sacral SBF was measured using laser Doppler flowmetry (LDF) in 20 participants. AP loads were randomly applied using an indenter through the rigid LDF probe. Each protocol included a 10-min baseline, 20-min AP and 10-min recovery periods. A 30-min washout period was provided. The SBF response was normalized to the baseline SBF of each condition of each participant.

RESULTS

For the cycle period study, the 4 5-min cycle protocol partially restored more SBF than the 8 2.5-min cycle protocol at the low-pressure phase (0.87 ± 0.04 vs 0.71 ± 0.03, p < 0.05) and at the high-pressure phase (0.25 ± 0.03 vs 0.19 ± 0.03, p < 0.05). For the pressure amplitude study, the 75/5 mmHg protocol partially restored more sacral SBF than the 65/15 mmHg protocol at the low-pressure phase (0.87 ± 0.1 vs 0.25 ± 0.03, p < 0.05) but not at the high-pressure phase (0.23 ± 0.02 vs 0.21 ± 0.02, non-significant).

CONCLUSION

This study demonstrated that 1) a cycle period of 5 min was better than 2.5 min and 2) a pressure amplitude of 75/5 mmHg was better than 65/15 mmHg. The finding provides insights for selecting the AP configurations for increasing SBF.

Lateral pressure equalisation as a principle for designing support surfaces to prevent deep tissue pressure ulcers

When immobile or neuropathic patients are supported by beds or chairs, their soft tissues undergo deformations that can cause pressure ulcers. Current support surfaces that redistribute under-body pressures at vulnerable body sites have not succeeded in reducing pressure ulcer prevalence. Here we show that adding a supporting lateral pressure can counter-act the deformations induced by under-body pressure, and that this 'pressure equalisation' approach is a more effective way to reduce ulcer-inducing deformations than current approaches based on redistributing under-body pressure. A finite element model of the seated pelvis predicts that applying a lateral pressure to the soft tissue reduces peak von Mises stress in the deep tissue by a factor of 2.4 relative to a standard cushion (from 113 kPa to 47 kPa)-a greater effect than that achieved by using a more conformable cushion, which reduced von Mises stress to 75 kPa. Combining both a conformable cushion and lateral pressure reduced peak von Mises stresses to 25 kPa. The ratio of peak lateral pressure to peak under-body pressure was shown to regulate deep tissue stress better than under-body pressure alone. By optimising the magnitude and position of lateral pressure, tissue deformations can be reduced to that induced when suspended in a fluid. Our results explain the lack of efficacy in current support surfaces and suggest a new approach to designing and evaluating support surfaces: ensuring sufficient lateral pressure is applied to counter-act under-body pressure.

Nonnegative matrix factorization for the identification of pressure ulcer risks from seating interface pressures in people with spinal cord injury

The purpose of this study was to predict and visualize pressure ulcer risks by using a novel approach of extracting computational features from seating interface pressures in people with spinal cord injury (SCI). In conventional clinical practice, seating interface pressure assessments rely on descriptive statistics of pressure magnitude. In this study, rank-2 nonnegative matrix factorization (NMF) was applied to the seating interface pressure maps during loading and pressure-relieving conditions in 16 people with SCI. The NMF basis images were used for visual interpretation and computational prediction of pressure ulcer risks. The two NMF basis images encapsulated pressure concentration and pressure dispersion, respectively. The first basis converged on the ischial tuberosity under both seating conditions, whereas the second basis converged anterior to the ischial tuberosity during loading and converged on the coccyx during unloading. The classification yielded 81.25% overall accuracy. In general, higher ulceration risk was associated with higher and lower activations of the first and second bases, respectively. The NMF pipeline yielded promising performance. Basis visualization affirmed the importance of lower ischial pressure and higher distribution dispersion while also revealing that clinical practice may currently be underestimating the importance of coccygeal pressure in response to pressure-relieving activities. Graphical abstract.

Wheelchair Tilt-in-Space and Recline Functions: Influence on Sitting Interface Pressure and Ischial Blood Flow in an Elderly Population

Pressure ulcers (PUs) result from localised injury to the skin and underlying tissue and usually occur over a bony prominence as a result of pressure, often in combination with shear forces. Both pressure magnitude and duration are thought to be key risk factors in the occurrence of PUs, thus exposing wheelchair-bound subjects to high risk of PU development. As a result, wheelchairs that incorporate tilt-in-space and recline functions are routinely prescribed to redistribute pressure away from their ischial tuberosities. The goal of this study was to analyse the role of full-body tilt and recline angles in governing sitting interface pressure and blood circulation parameters in elderly subjects and thereby investigate the efficacy of tilt-in-space wheelchairs for aiding pressure relief activity. Sitting interface pressure and ischial blood flow parameters were examined in 20 healthy elderly subjects while seated in a tilt-in-space and recline wheelchair. Five different angles of seat tilt (5°, 15°, 25°, 35°, and 45°) were assessed in combination with three different angles of backrest recline (5°, 15°, and 30°). The results of the study show that when compared to the upright reference posture, every position (except 15°T/5°R) resulted in a significant decrease in sitting interface pressure. Ischial blood flow also showed significant increases at four different positions (45°T/15°R, 15°T/30°R, 35°T/30°R, and 45°T/30°R) but only at larger tilt-in-space and recline angles. The results therefore suggest that small tilt-in-space and recline angles are indeed able to reduce sitting interface pressures, whereas changes in ischial blood flow only occur at larger angles. In the literature, cell deformation is thought to be dominant over tissue ischemia in the development of tissue necrosis and PUs. Therefore, together with our findings it can be concluded that frequently undertaking small adjustments in tilt-in-space and recline angle might be important for preventing cell deformation and any associated cell necrosis. Larger angles of tilt-in-space and recline seem to support blood flow returning to the tissues, which is likely to play a positive role in healing damaged tissue.

Using Multiscale Entropy to Assess the Efficacy of Local Cooling on Reactive Hyperemia in People with a Spinal Cord Injury

Pressure ulcers are one of the most common complications of a spinal cord injury (SCI). Prolonged unrelieved pressure is thought to be the primary causative factor resulting in tissue ischemia and eventually pressure ulcers. Previous studies suggested that local cooling reduces skin ischemia of the compressed soft tissues based on smaller hyperemic responses. However, the effect of local cooling on nonlinear properties of skin blood flow (SBF) during hyperemia is unknown. In this study, 10 wheelchair users with SCI and 10 able-bodied (AB) controls underwent three experimental protocols, each of which included a 10-min period as baseline, a 20-min intervention period, and a 20-min period for recovering SBF. SBF was measured using a laser Doppler flowmetry. During the intervention period, a pressure of 60 mmHg was applied to the sacral skin, while three skin temperature settings were tested, including no temperature change, a decrease by 10 °C, and an increase by 10 °C, respectively. A multiscale entropy (MSE) method was employed to quantify the degree of regularity of blood flow oscillations (BFO) associated with the SBF control mechanisms during baseline and reactive hyperemia. The results showed that under pressure with cooling, skin BFO both in people with SCI and AB controls were more regular at multiple time scales during hyperemia compared to baseline, whereas under pressure with no temperature change and particularly pressure with heating, BFO were more irregular during hyperemia compared to baseline. Moreover, the results of surrogate tests indicated that changes in the degree of regularity of BFO from baseline to hyperemia were only partially attributed to changes in relative amplitudes of endothelial, neurogenic, and myogenic components of BFO. These findings support the use of MSE to assess the efficacy of local cooling on reactive hyperemia and assess the degree of skin ischemia in people with SCI.

Dynamic changes in seating pressure gradient in wheelchair users with spinal cord injury

Pressure ulcer interventions are commonly assessed with measures of seating interface pressure, such as peak pressure gradients (PPGs). Decreases in PPG magnitudes may reduce pressure ulcer risk by decreasing tissue deformation and increasing tissue perfusion of at-risk weight-bearing tissues. Changes in PPG directions, which have previously been overlooked in the seating pressure literature, may provide a transient increase in blood flow to at-risk tissues, even if the PPG magnitude and location remain the same. The purpose of this study was to assess both PPG components in response to combinations of wheelchair tilt and recline angles. Thirteen power wheelchair users were recruited into the study. Six combinations of wheelchair tilt (15°, 25°, and 35°) and recline (10° and 30°) were tested in random order. Each combination was tested with 5-min upright sitting, 5-min tilt and recline, and 5-min maximal pressure relief recovery. Changes in PPG magnitudes and PPG directions under the left ischial tuberosity were computed for the six angle combinations. The findings in this study suggested that when combining wheelchair tilt and recline, the recline function may be particularly useful in reducing PPG magnitudes, while the tilt function may be particularly useful in manipulating PPG directions.

Comfort evaluation of a subject-specific seating interface formed by vibrating grains

Sitting is the most common posture for work in offices, and spinal cord injury (SCI) patients who are wheelchair dependent spend 10.6 h per day seated in wheelchairs. Thus, the comfort of subject-specific interfaces is increasingly important for the well-being of patients and office workers. This paper introduces a new method of forming a subject-specific interface, based on vibrating grains. Twenty subjects (10 females and 10 males) participated in the sitting test. Interface comfort was evaluated using the pressure distribution and subjective rating methods. Five seating interface types were compared. The results showed that compared with a flat interface, the interfaces formed by vibrating grains had a significantly reduced peak contact pressure (PeakCP) (by more than 58.03%), and that PeakCP was highly correlated with the comfort rating (R = -0.533) and discomfort rating(R = -0.603). This new method shows promise for guiding the future development of customized seating interfaces.

The effect of pressure and shear on tissue viability of human skin in relation to the development of pressure ulcers: a systematic review

Pressure ulcers are a significant problem in health care, due to high costs and large impact on patients' life. In general, pressure ulcers develop as tissue viability decreases due to prolonged mechanical loading. The relation between load and tissue viability is highly influenced by individual characteristics. It is proposed that measurements of skin blood flow regulation could provide good assessment of the risk for pressure ulcer development, as skin blood flow is essential for tissue viability. . Therefore, the aim of this systematic review is to gain insight in the relation between mechanical load and the response of the skin and underlying tissue to this loading measured in-vivo with non-invasive techniques. A systematic literature search was performed to identify articles analysing the relation between mechanical load (pressure and/or shear) and tissue viability measured in-vivo. Two independent reviewers scored the methodological quality of the 22 included studies. Methodological information as well as tissue viability parameters during load application and after load removal were extracted from the included articles and used in a meta-analysis. Pressure results in a decrease in skin blood flow parameters, compared to baseline; showing a larger decrease with higher magnitudes of load. The steepness of the decrease is mostly dependent on the anatomical location. After load removal the magnitude of the post-reactive hyperaemic peak is related to the magnitude of pressure. Lastly, shear in addition to pressure, shows an additional negative effect, but the effect is less apparent than pressure on skin viability.

Skin perfusion responses under normal and combined loadings: Comparisons between legs with venous stasis ulcers and healthy legs

BACKGROUND

Venous ulcers, also known as stasis ulcers, are skin wounds often found at the medial surface of the lower leg. These wounds are related to chronic venous insufficiencies and affect almost 2.5 million patients every year in the United States.

METHOD

Eighteen participants with venous stasis ulcers on at least one leg and twenty healthy participants were tested. Normal and combined normal and shear loadings were applied to each lower leg and local blood perfusion was monitored. Basal perfusion, post-occlusive reactive hyperemia as well as changes in perfusion due to different loadings were compared.

FINDINGS

Legs with existing venous stasis ulcers ("wounded legs") had the highest reactive hyperemia and basal perfusion values. Legs without ulcers but from participants with venous stasis ulcers ("non-wounded legs") had intermediate reactive hyperemia, and healthy legs exhibited the lowest values. Wounded legs also exhibited the largest decrease in blood perfusion under both normal and combined loadings. Non-wounded legs decreased perfusion similarly to healthy legs under normal loadings; however, non-wounded legs exhibited larger decreases in blood flow than healthy legs in response to shear and normal loading together.

INTERPRETATION

These results suggest that patients with venous stasis disease have abnormal responses to tissue loading and raise the possibility that this technique may have the potential to identify patients at risk for developing a venous stasis ulcer. Moreover, they emphasize the importance of studying shear loading in addition to normal loading in attempting to understand the pathophysiology of this disease.

Deformation of the gluteal soft tissues during sitting

BACKGROUND

Excessive deformation of soft tissues is considered to be one of the major contributing factors to discomfort and injury for individuals who sit for long periods of time. Soft tissue deformation in research has been measured under the assumption that tissues deform uniaxially below the ischium, with very small or negligible deformations taking place in other directions. Therefore, this study describes the deformation of the gluteus maximus muscle and surrounding fat tissues in the buttock region for seated subjects.

METHODS

In vivo measurements of the deformation for the gluteal soft tissues were obtained from MRI scans of six seated subjects. Each subject was scanned in weight-bearing and non-weight-bearing sitting postures using a Positional MRI scanner (Fonar 0.6 Tesla Indomitable™). Deformations were measured below the ischium and the proximal femur. Deformation of the gluteus maximus was also measured in the distal direction along the thigh for each subject.

FINDINGS

Our data suggest that soft tissues undergo three-dimensional deformation with considerable components below the ischium (mean of 21.4mm) and in the distal direction along the thigh (mean of 20.3mm). Differences in muscle deformation below the ischium were also observed between obese (mean of 27.4mm) and non-obese subjects (mean of 16.5mm).

INTERPRETATION

Findings of this study demonstrate that tissue deformations in sitting include complex three-dimensional motions that are not well approximated by two-dimensional models.

Effect of tilt and recline on ischial and coccygeal interface pressures in people with spinal cord injury

OBJECTIVE

Clinicians commonly recommend that power wheelchair users with spinal cord injury perform wheelchair tilt and recline maneuvers to redistribute seating loads away from the ischial tuberosities. However, ischial pressure reduction may be accompanied by coccygeal pressure increases. Although the coccyx is among the most common sites of pressure ulcers, few studies have reported coccygeal interface pressure. The purpose of this study was to investigate both ischial and coccygeal interface pressures in response to changes in wheelchair tilt and recline angles.

DESIGN

Thirteen power wheelchair users were recruited into this study. Six combinations of wheelchair tilt (15, 25, and 35 degrees) and recline (10 and 30 degrees, corresponding to traditional recline conventions of 100 and 120 degrees, respectively) angles were tested in random order. Each combination was tested with 5 mins of upright sitting, 5 mins of tilt and recline, as well as 5 mins of maximal pressure relief recovery. Peak pressure indices were calculated at the ischial and coccygeal sites.

RESULTS

Ischial pressures monotonically decreased in response to increasing combinations of tilt and recline. Increments of 15 degrees of tilt did not produce significant differences under either recline angle, whereas increments of 25 degrees of tilt produced significant differences under both recline angles. Coccygeal pressures increased in response to the four smallest (of six) combinations of tilt and recline, whereas they decreased in response to the largest two combinations.

CONCLUSIONS

Ischial pressures seemed to be redistributed to the coccyx in response to the four smallest angle combinations and redistributed to the back support in response to the two largest angle combinations. Future work should confirm this pressure redistribution to the back support and determine the back support locations of redistribution.

Investigation of peak pressure index parameters for people with spinal cord injury using wheelchair tilt-in-space and recline: methodology and preliminary report

The purpose of this study was to determine the effect of the sensel window's location and size when calculating the peak pressure index (PPI) of pressure mapping with varying degrees of wheelchair tilt-in-space (tilt) and recline in people with spinal cord injury (SCI). Thirteen power wheelchair users were recruited into this study. Six combinations of wheelchair tilt (15°, 25°, and 35°) and recline (10° and 30°) were used by the participants in random order. Displacements of peak pressure and center of pressure were extracted from the left side of the mapping system. Normalized PPI was computed for three sensel window dimensions (3 sensels × 3 sensels, 5 × 5, and 7 × 7). At least 3.33 cm of Euclidean displacement of peak pressures was observed in the tilt and recline. For every tilt angle, peak pressure displacement was not significantly different between 10° and 30° recline, while center of pressure displacement was significantly different (P < .05). For each recline angle, peak pressure displacement was not significantly different between pairs of 15°, 25°, and 35° tilt, while center of pressure displacement was significantly different between 15° versus 35° and 25° versus 35°. Our study showed that peak pressure displacement occurs in response to wheelchair tilt and recline, suggesting that the selected sensel window locations used to calculate PPI should be adjusted during changes in wheelchair configuration.

Comparison of changes in heart rate variability and sacral skin perfusion in response to postural changes in people with spinal cord injury

The current clinical practice has established guidelines to assess influences of severity of autonomic injury on the control of heart and blood pressure following spinal cord injury (SCI). However, the influences of SCI-induced autonomic impairment on microvascular dysfunction have not yet been established. Heart rate variability (HRV) has been shown to be a potential tool for quantifying residual sympathovagal regulation of the cardiovascular system following SCI and may be used to assess the effect of autonomic injury on skin microvascular dysfunction. A total of 26 people were recruited into the study, including 12 people with SCI and 14 nondisabled controls. HRV and sacral skin intervals and sacral skin perfusion were continually recorded during 10 min upright and 10 min prone postures. The sympathovagal balance was defined as the ratio of the power of the low frequency to the high frequency of HRV. The results showed that postural changes of nondisabled people produced significant changes in the sympathovagal balance; lower sympathovagal balance was associated with higher skin perfusion (p < 0.05). People with SCI did not show a significant change of HRV and skin perfusion in response to postural changes. In this study, we have demonstrated that the sympathovagal balance assessed by HRV was associated with the skin vasoconstrictive response to postural changes.

Is a computer-based measurement method superior to a recommended manual method by the ROHO(®) Group to assess pressure in the sitting position?

BACKGROUND

In clinical practice, a manual-based assessment is standard procedure to adjust the air pressure in the ROHO(®) cushion in seated position. Recently, a computerized pressure system method was developed to support the clinical adjustment of air in the ROHO(®) cushion to reduce the pressure in the seated position. To our knowledge, no studies have investigated the reliability between the manual method mostly used in clinical practice and the alternative computer-based assessment of the pressure in the seated position.

AIM

The objective was to test intra-tester and inter-tester reliability and evaluate if a computer-based measurement method is superior to a manual method to reduce pressure in the seated position. The cushion used was a Roho Quadtro select(®) high profile.

METHODS

An intra-tester and inter-tester reliability study was conducted in 2010 at the Department of Occupational Therapy and Physiotherapy, Aalborg Hospital, Aarhus University Hospital, Denmark. Subjects included were two occupational therapists and 20 healthy subjects. The outcome measures were obtained using a pressure imaging system that could register pressure distribution in the sitting area.

RESULTS

The study did not show high intra-class correlation coefficients neither in the intra-tester nor in the inter-tester reliability for manual or computer-based methods in reducing pressure in the seating position.

CONCLUSIONS

The current company-recommended air pressure adjustment procedure seems unreliable. The technical superiority of the computer-based method over the manual method has not been established.

Skin blood flow dynamics and its role in pressure ulcers

Pressure ulcers are a significant healthcare problem affecting the quality of life in wheelchair bounded or bed-ridden people and are a major cost to the healthcare system. Various assessment tools such as the Braden scale have been developed to quantify the risk level of pressure ulcers. These tools have provided an initial guideline on preventing pressure ulcers while additional assessments are needed to improve the outcomes of pressure ulcer prevention. Skin blood flow function that determines the ability of the skin in response to ischemic stress has been proposed to be a good indicator for identifying people at risk of pressure ulcers. Wavelet spectral and nonlinear complexity analyses have been performed to investigate the influences of the metabolic, neurogenic and myogenic activities on microvascular regulation in people with various pathological conditions. These findings have contributed to the understanding of the role of ischemia and viability on the development of pressure ulcers. The purpose of the present review is to provide an introduction of the basic concepts and approaches for the analysis of skin blood flow oscillations, and present an overview of the research results obtained so far. We hope this information may contribute to the development of better clinical guidelines for the prevention of pressure ulcers.

Comparison of muscle and skin perfusion over the ischial tuberosities in response to wheelchair tilt-in-space and recline angles in people with spinal cord injury

OBJECTIVE

To compare the efficacy of wheelchair tilt-in-space and recline on enhancing muscle and skin perfusion over the ischial tuberosities in people with spinal cord injury (SCI).

DESIGN

Repeated-measures and before-after trial design.

SETTING

University research laboratory.

PARTICIPANTS

Power wheelchair users with SCI (N=20).

INTERVENTIONS

Six combinations of wheelchair tilt-in-space and recline angles were presented to participants in a random order. The testing protocol consisted of a baseline 5 minutes sitting with no tilt/recline and 5 minutes positioned in a tilted and reclined position at each of 6 conditions, including: (1) 15° tilt-in-space and 100° recline, (2) 25° tilt-in-space and 100° recline, (3) 35° tilt-in-space and 100° recline, (4) 15° tilt-in-space and 120° recline, (5) 25° tilt-in-space and 120° recline, and (6) 35° tilt-in-space and 120° recline.

MAIN OUTCOME MEASURES

Muscle and skin perfusion were assessed by near-infrared spectroscopy and laser Doppler flowmetry, respectively.

RESULTS

Muscle perfusion was significantly increased at 25° and 35° tilt-in-space when combined with 120° recline, and skin perfusion was significantly increased at 3 tilt-in-space angles (15°, 25°, 35°) when combined with 120° recline and at 35° tilt-in-space when combined with 100° recline (P<.05). Even in the positions of increased muscle perfusion and skin perfusion (25° and 35° of tilt-in-space combined with 120° of recline), the amount of muscle perfusion change was significantly lower than the amount of skin perfusion change (P<.05).

CONCLUSIONS

Our results indicate that a larger angle of tilt-in-space and recline is needed to improve muscle perfusion compared with skin perfusion. A position of 25° tilt-in-space combined with 120° recline is effective in enhancing muscle and skin perfusion of weight-bearing soft tissues at the ischial tuberosities.

Effect of durations of wheelchair tilt-in-space and recline on skin perfusion over the ischial tuberosity in people with spinal cord injury

OBJECTIVE

To compare the efficacy of various durations of wheelchair tilt-in-space and recline on enhancing skin perfusion over the ischial tuberosity in people with spinal cord injury (SCI).

DESIGN

Repeated-measures, intervention and outcomes measure design.

SETTING

University research laboratory.

PARTICIPANTS

Power wheelchair users with SCI (N=9).

INTERVENTIONS

Three protocols of various durations (3min, 1min, and 0min) of wheelchair tilt-in-space and recline were randomly assigned to the participants. Each protocol consisted of a baseline 15-minute sitting, a duration of 0- to 3-minute reclined and tilted, a second 15-minute sitting, and a 5-minute recovery. The position at the baseline and the second sitting was no tilt/recline of the participant and at the reclined and tilted and recovery was at 35° tilt-in-space and 120° recline.

MAIN OUTCOME MEASURES

Skin perfusion response to tilt and recline was assessed by laser Doppler and was normalized to mean skin perfusion at the baseline sitting.

RESULTS

The results showed that mean skin perfusion during recovery at the 3-minute duration was significantly higher than that at the 1-minute duration (P<.017) and mean skin perfusion was not significantly different between the 1-minute and 0-minute durations (not significant). Skin perfusion during the second sitting was significantly higher at the 3-minute duration than at the 1-minute and 0-minute durations (P<.017).

CONCLUSIONS

Our findings suggest that performing the 3-minute duration of wheelchair tilt-in-space and recline is more effective than the 1-minute duration in enhancing skin perfusion of weight-bearing soft tissues.

A system utilizing metal hydride actuators to achieve passive motion of toe joints for prevention of pressure ulcers: a pilot study

This paper describes the influence of human toe movement on blood flow and the design of a toe joint passive motion system for preventing pressure ulcers. First, we measured lower extremity blood flow in the foot during active and passive motion of the toe to facilitate the design of new rehabilitation equipment. Also, the flexion and extension angles and the force of the toe joints were measured to determine appropriate specifications for the system. Increases in blood flow were observed at the external malleolus during movement. Flexion and extension angles and the force of the toe joints were found to differ significantly among participants. It is shown that a toe joint passive motion system can be effective in preventing pressure ulcers. On the basis of these results, a device using alloys of metal hydride (MH) as an actuator that is suitable for the system to initiate toe motion, was developed.

Modelling the effect of repositioning on the evolution of skeletal muscle damage in deep tissue injury

Deep tissue injury (DTI) is a localized area of tissue necrosis that originates in the subcutaneous layers under an intact skin and tends to develop when soft tissue is compressed for a prolonged period of time. In clinical practice, DTI is particularly common in bedridden patients and remains a serious issue in todays health care. Repositioning is generally considered to be an effective preventive measure of pressure ulcers. However, limited experimental research and no computational studies have been undertaken on this method. In this study, a methodology was developed to evaluate the influence of different repositioning intervals on the location, size and severity of DTI in bedridden patients. The spatiotemporal evolution of compressive stresses and skeletal muscle viability during the first 48 h of DTI onset was simulated for repositioning schemes in which a patient is turned every 2, 3, 4 or 6 h. The model was able to reproduce important experimental findings, including the morphology and location of DTI in human patients as well as the discrepancy between the internal tissue loads and the contact pressure at the interface with the environment. In addition, the model indicated that the severity and size of DTI were reduced by shortening the repositioning intervals. In conclusion, the computational framework presented in this study provides a promising modelling approach that can help to objectively select the appropriate repositioning scheme that is effective and efficient in the prevention of DTI.

Physiological measurements of tissue health; implications for clinical practice

Pressure mapping alone insufficiently describes tissue health. Comprehensive, quantitative non invasive assessment is crucial. Interface pressures (IPs) and transcutaneous blood gas levels [transcutaneous tissue oxygen (T(c) PO(2) )] were simultaneously assessed over both ischia and the sacrum to investigate the hypotheses: (i) tissue oxygenation decreases with sustained applied pressure; (ii) tissue oxygen and IP are inversely correlated in loaded soft tissues; (iii) multisite assessments are unnecessary because healthy individuals are symmetrical. Measurements were taken at 5-minute intervals for 20 minutes in both sitting and supine lying for a cohort of 20 able-bodied adults. There were no statistically significant changes over time for either variable in 96% of timepoint comparisons. Specifically, no significant differences were seen between 10 and 20 minutes in either position. These findings imply that a 10-minute assessment can reliably indicate tissue health and that tissue may adapt to applied load over time. No statistically significant correlations between T(c) PO(2) and IP were observed. However, the left and right ischia were significantly different for both variables in supine lying (P < 0.001) and for sitting IP (P < 0.010). Thus, even in this healthy cohort, postural symmetry was not observed and should not be assumed for other populations with restricted mobility. If a multisite technique cannot be used, repeated tissue health assessments must use the same anatomic location.

Outdoor dynamic subject-specific evaluation of internal stresses in the residual limb: hydraulic energy-stored prosthetic foot compared to conventional energy-stored prosthetic feet

The prosthetic foot plays an important role in propelling, breaking, balancing and supporting body loads while the amputee ambulates on different grounds. It is therefore important to quantify the effect of the prosthetic foot mechanism on biomechanical parameters, in order to prevent pressure ulcers and deep tissue injury. Our aim was to monitor the internal stresses in the residuum of transtibial amputation (TTA) prosthetic-users ambulating on different terrains, which the amputees encounter during their daily activities, i.e. paved floor, grass, ascending and descending stairs and slope. We specifically aimed to compare between the internal stresses in the TTA residuum of amputees ambulating with a novel hydraulic prosthetic foot compared to conventional energy storage and return (ESR) prosthetic feet. Monitoring of internal stresses was accomplished using a portable subject-specific real-time internal stress monitor. We found significant decrease (p<0.01) in peak internal stresses and in the loading rate of the amputated limb, while walking with the hydraulic foot, compared to walking with ESR feet. The loading rate calculated while ambulating with the hydraulic foot was at least three times lower than the loading rate calculated while ambulating with the ESR foot. Although the average decrease in internal stresses was ≈ 2-fold larger when replacing single-toe ESR feet with the hydraulic foot than when replacing split-toed ESR feet with the hydraulic foot, the differences were statistically insignificant. Our findings suggest that using a hydraulic prosthetic foot may protect the distal tibial end of the TTA residuum from high stresses, therefore preventing pressure-related injury and pain.

Infantile Ischemic Occipital Scalp Ulcers May Mimic Impact Sites

The clinical or forensic pathologic evaluation of an infant with an apparently inflicted head injury can be challenging, particularly when objective findings are limited to the classic triad ascribed to “Shaken Baby Syndrome” – subdural and retinal hemorrhages and anoxic brain injury. These three findings together, in the absence of an apparent impact site (scalp or skull injury) have a controversial differential diagnosis. However, the discovery of an impact site of virtually any size is sufficient for some forensic pathologists to make the diagnosis of homicidal (impact) blunt head trauma in babies with limited additional evidence of abuse, or with the classic triad, but without careful consideration of its differential diagnosis. Although relatively uncommon in modern intensive care units, occipital scalp ulcers can and do occur, and may mimic the appearance of a blunt impact site. Two separate cases of infant death are presented to illustrate the nature and appearance of occipital pressure ulcers. Abnormalities of the occipital scalp were not detected in either infant upon hospital admission, but scalp lesions were clearly observed at autopsy. Macroscopically, these lesions closely resembled blunt impact sites. They were determined to be pressure ulcers based predominantly on the histologic findings of epidermal thinning and dermal homogenization, combined with the absence of both hemorrhage and stainable free iron. Further supportive factors were the absence of skull fractures, intracranial hemorrhages, and cerebrocortical contusions.

Clinically oriented real-time monitoring of the individual's risk for deep tissue injury

Spinal cord injury patients are under daily risk for developing deep tissue injury which is a severe pressure ulcer that initiates in soft tissues at the bones' proximity. We aimed to formulate a patient-specific biomechanical model that can continuously monitor internal tissue stresses in real time. We adopted a formulation solving an axisymmetric contact problem of a finite-thickness, elastic layer (soft tissue), and a rigid spherical indentor (ischial tuberosity). We utilized finite element analyses to expand the formulation for large deformations. Sensitivity analyses showed that the soft tissue mechanical properties are the most influential factors in this modeling. We then used synthetic surface pressure data and actual surface pressures recorded under the buttocks of five paraplegic wheelchair users to demonstrate clinical feasibility. Output parameters were designed to be simple so that they can be easily interpreted by the user. Specifically, we calculated peak and average internal von Mises stress and stress dose, under each buttock, and also a time-dependent stress asymmetry index, to account for frequency of posture adjustments. Inter-subject variability was higher than the intra-subject variability. The heaviest subject had the highest maximal and average peak internal soft tissue stress. We believe that this method holds a high potential for clinical applications.