Cell-level temperature distributions in skeletal muscle post spinal cord injury as related to deep tissue injury

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.

Biomarkers of local inflammation at the skin's surface may predict both pressure and diabetic foot ulcers

This commentary considers the similarities which exist between pressure ulcers (PUs) and diabetic foot ulcers (DFUs). It aims to describe what is known to be shared-both in theory and practice-by these wound types. It goes on to detail the literature surrounding the role of inflammation in both wound types. PUs occur following prolonged exposure to pressure or pressure in conjunction with shear, either due to impaired mobility or medical devices. As a result, inflammation occurs, causing cell damage. While DFUs are not associated with immobility, they are associated with altered mobility occurring as a result of complications of diabetes. The incidence and prevalence of both types of lesions are increased in the presence of multimorbidity. The prediction of either type of ulceration is challenging. Current risk assessment practices are reported to be ineffective at predicting when ulceration will occur. While systemic inflammation is easily measured, the presence of local or subclinical inflammation is harder to discern. In patients at risk of either DFUs or PUs, clinical signs and symptoms of inflammation may be masked, and systemic biomarkers of inflammation may not be elevated sufficiently to predict imminent damage until ulceration appears. The current literature suggests that the use of local biomarkers of inflammation at the skin's surface, namely oedema and temperature, may identify early tissue damage.

Risk factors for the development and evolution of deep tissue injuries: A systematic review

AIMS

The aim of this systematic review is to identify the current epidemiological evidence indicating the unique risk factors for deep tissue injury (DTI) compared to grade I-IV pressure injury (PI), the proportion of DTI which evolve rather than resolve and the anatomical distribution of DTI.

METHODS

A systematic literature search was undertaken using the MEDLINE and CINAHL Plus databases using the search terms 'Deep tissue injury OR DTI [Title/abstract]'. A google scholar search was also conducted in addition to hand searches of relevant journals, websites and books which were identified from reference lists in retrieved articles. Only peer-reviewed English language articles published 2009-2021 were included, with full text available online.

RESULTS

The final qualitative analysis included nine articles. These included n = 4 retrospective studies, n = 4 prospective studies and n = 1 animal study.

CONCLUSION

The literature indicates that the majority of DTI occur at the heel and sacrum although in paediatric patients they are mainly associated with medical devices. Most DTI are reported to resolve, with between 9.3 and 27% deteriorating to full thickness tissue loss. Risk factors unique to DTI appear to include anaemia, vasopressor use, haemodialysis and nicotine use although it is unclear if these factors are unique to DTI or are shared with grade I-IV PI. Factors associated with deterioration include cooler skin measured using infrared thermography and negative capillary refill. With 100% of DTI showing positive capillary refill in one study resolving without tissue loss (p = 0.02) suggesting this may be an effective prognostic indicator. More prospective studies are required focusing on establishing causal links between risk factors identified in earlier retrospective studies. Ideally these should use statistically powered samples and sufficient follow up periods allowing DTI outcomes to be reached. Further work is also needed to establish reliable diagnostic criteria for DTI in addition to more studies in the paediatric population.

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.

Modeling, Fabrication and Integration of Wearable Smart Sensors in a Monitoring Platform for Diabetic Patients

The monitoring of some parameters, such as pressure loads, temperature, and glucose level in sweat on the plantar surface, is one of the most promising approaches for evaluating the health state of the diabetic foot and for preventing the onset of inflammatory events later degenerating in ulcerative lesions. This work presents the results of sensors microfabrication, experimental characterization and FEA-based thermal analysis of a 3D foot-insole model, aimed to advance in the development of a fully custom smart multisensory hardware-software monitoring platform for the diabetic foot. In this system, the simultaneous detection of temperature-, pressure- and sweat-based glucose level by means of full custom microfabricated sensors distributed on eight reading points of a smart insole will be possible, and the unit for data acquisition and wireless transmission will be fully integrated into the platform. Finite element analysis simulations, based on an accurate bioheat transfer model of the metabolic response of the foot tissue, demonstrated that subcutaneous inflamed lesions located up to the muscle layer, and ischemic damage located not below the reticular/fat layer, can be successfully detected. The microfabrication processes and preliminary results of functional characterization of flexible piezoelectric pressure sensors and glucose sensors are presented. Full custom pressure sensors generate an electric charge in the range 0-20 pC, proportional to the applied load in the range 0-4 N, with a figure of merit of 4.7 ± 1 GPa. The disposable glucose sensors exhibit a 0-6 mM (0-108 mg/dL) glucose concentration optimized linear response (for sweat-sensing), with a LOD of 3.27 µM (0.058 mg/dL) and a sensitivity of 21 µA/mM cm2 in the PBS solution. The technical prerequisites and experimental sensing performances were assessed, as preliminary step before future integration into a second prototype, based on a full custom smart insole with enhanced sensing functionalities.

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.

Local Cooling as a Step of Treatment for Tissue Ischemia Caused by Hyaluronic Acid Injection-induced Embolism-A Report of 9 Cases

Hyaluronic acid injection is 1 of the most popular procedures in facial rejuvenation and augmentation. It is widely popular in the cosmetic surgery due to several advantages, which include rapid effect, minimal injury, and a short postoperative recovery period. With continuous increase in hyaluronic acid injections, many cases of hyaluronic acid injection-induced embolism have been reported. At present, methods for early treatment of hyaluronic acid injection-induced embolism include local injection of hyaluronidase, topical application of nitroglycerin ointment, massage, hot compression, and intravenous injections of antibiotics and hormones. Although early warm massage may facilitate hyaluronic acid degradation by hyaluronidase, local application of heat will also increase metabolic rate in the tissue, thereby reducing the ischemic tolerance of the tissue. Therefore, in this study, warm massage was limited to the first 30 minutes after hyaluronidase injection and was followed by local cooling using a gauze pad soaked with antibiotic saline solution. Excellent therapeutic effects were achieved with this approach. The methods of treatment for tissue ischemia caused by hyaluronic acid injection-induced embolism and clinical cases are introduced in the article.

Microvascularization is not a limiting factor for exercise in adults with cerebral palsy

Muscle contractures are a common complication in patients with central nervous system (CNS) lesions which limit range of movement and cause joint deformities. Furthermore, it has previously been shown that muscles with contractures have a reduced number of capillaries, indicating decreased tissue vascularization. The aim of the present study was to investigate the microvascular volume (MV) at rest and after acute exercise in the muscle tissue of individuals with cerebral palsy (CP) and healthy control individuals. Contrast-enhanced ultrasound (CEUS) was used before and after 30 min of walking or running on a treadmill in 10 healthy control participants and 10 individuals with CP to detect MV of their skeletal muscle tissue. A significant increase in the MV was observed after exercise both in the adult CP group (21–53 yr) and in the control group (21–52 yr) (1.8 ± 0.8 ΔdB to 3.1 ± 0.9 ΔdB or 42.9% and 1.5 ± 0.6 ΔdB to 2.5 ± 0.9 ΔdB or 39.0%, respectively). Furthermore, a difference in the resting MV was observed between the most severe cases of CP [gross motor function classification scale (GMFCS) 3 and 4] (2.3 ± 0.5 ΔdB) and the less severe cases (GMFCS 1 and 2) (1.5 ± 0.2 ΔdB). When the CP group was walking (3.4 km/h), the lactate levels, Borg score, and heart rate matched the level of controls when they were running (9.8 km/h). In conclusion, individuals with CP become exhausted at much lower exercise intensities than healthy individuals. This is not explained by impaired microvascularization, since the MV of the individuals with CP respond normally to increased O2 demand during acute exercise.

NEW & NOTEWORTHY Cerebral palsy (CP) patients were less physically active compared with typically developed individuals. This may affect the microvascularization. We observed that the CP group became exhausted at much lower exercise intensities compared with healthy individuals. However, impaired microvascularization was not the reason for the decreased physical activity as the CP group responded normally to increased O2 demand during acute exercise. These results indicate that walking may be recommended as an intervention to train and maintain skeletal muscle tissue in individuals with CP.

In Vivo Ischemia Detection by Luminescent Nanothermometers

There is an urgent need to develop new diagnosis tools for real in vivo detection of first stages of ischemia for the early treatment of cardiovascular diseases and accidents. However, traditional approaches show low sensitivity and a limited penetration into tissues, so they are only applicable for the detection of surface lesions. Here, it is shown how the superior thermal sensing capabilities of near infrared-emitting quantum dots (NIR-QDs) can be efficiently used for in vivo detection of subcutaneous ischemic tissues. In particular, NIR-QDs make possible ischemia detection by high penetration transient thermometry studies in a murine ischemic hindlimb model. NIR-QDs nanothermometers are able to identify ischemic tissues by means of their faster thermal dynamics. In addition, they have shown to be capable of monitoring both the revascularization and damage recovery processes of ischemic tissues. This work demonstrates the applicability of fluorescence nanothermometry for ischemia detection and treatment, as well as a tool for early diagnosis of cardiovascular disease.

Effects of Biowastes Released by Mechanically Damaged Muscle Cells on the Propagation of Deep Tissue Injury: A Multiphysics Study

Deep tissue injuries occur in muscle tissues around bony prominences under mechanical loading leading to severe pressure ulcers. Tissue compression can potentially compromise lymphatic transport and cause accumulation of metabolic biowastes, which may cause further cell damage under continuous mechanical loading. In this study, we hypothesized that biowastes released by mechanically damaged muscle cells could be toxic to the surrounding muscle cells and could compromise the capability of the surrounding muscle cells to withstand further mechanical loadings. In vitro, we applied prolonged low compressive stress (PLCS) and short-term high compressive stress to myoblasts to cause cell damage and collected the biowastes released by the damaged cells under the respective loading scenarios. In silico, we used COMSOL to simulate the compressive stress distribution and the diffusion of biowastes in a semi-3D buttock finite element model. In vitro results showed that biowastes collected from cells damaged under PLCS were more toxic and could compromise the capability of normal myoblasts to resist compressive damage. In silico results showed that higher biowastes diffusion coefficient, higher biowastes release rate, lower biowastes tolerance threshold and earlier timeline of releasing biowastes would cause faster propagation of tissue damage. This study highlighted the importance of biowastes in the development of deep tissue injury to clinical pressure ulcers under prolonged skeletal compression.

Physiological Capillary Regression is not Dependent on Reducing VEGF Expression

Investigations into physiologically controlled capillary regression report the provocative finding that microvessel regression occurs in the face of persistent elevation of skeletal muscle VEGF expression. TSP-1, a negative angiogenic regulator, is increasingly being observed to temporally correlate with capillary regression, suggesting that increased TSP-1 (and not reduction in VEGF per se) is needed to initiate, and likely regulate, capillary regression. Based on evidence being gleaned from physiologically mediated regression of capillaries, it needs to be recognized that capillary regression (and perhaps capillary rarefaction with disease) is not simply the reversal of factors used to stimulate angiogenesis. Rather, the conceptual understanding that angiogenesis and capillary regression each have specific and unique requirements that are biologically constrained to opposite sides of the balance between positive and negative angioregulatory factors may shed light on why anti-VEGF therapies have not lived up to the promise in reversing angiogenesis and providing the cure that many had hoped toward fighting cancer. Emerging evidence from physiological controlled angiogenesis suggest that cases involving excessive or uncontrolled capillary expansion may be best treated by therapies designed to increase expression of negative angiogenic regulators, whereas those involving capillary rarefaction may benefit from inhibiting negative regulators (like TSP-1).

Circulating angiogenic biomolecules at rest and in response to upper-limb exercise in individuals with spinal cord injury

OBJECTIVE

Individuals with spinal cord injury (SCI) show structural and functional vascular maladaptations and muscle loss in their lower limbs. Angiogenic biomolecules play important roles in physiological and pathological angiogenesis, and are implicated in the maintenance of muscle mass. This study examined the responses of angiogenic molecules during upper-limb aerobic exercise in patients with SCI and in able-bodied (AB) individuals.

METHODS

Eight SCI patients with thoracic lesions (T6-T12, ASIA A) and eight AB individuals performed an arm-cranking exercise for 30 minutes at 60% of their VO2max. Plasma concentrations of vascular endothelial growth factor (VEGF-A165), VEGF receptor 1 (sVEGFr-1), VEGF receptor 2 (sVEGFr-2), metalloproteinase 2 (MMP-2), and endostatin were measured at rest, after exercise, and at 1.5 and 3.0 hours during recovery.

RESULTS

The two-way analysis of variance showed non-significant main effects of "group" and significant main effects of "time/exercise" for all angiogenic biomolecules examined (P < 0.01-0.001). The arm-cranking exercise significantly increased plasma concentrations of VEGF, sVEGFr-1, sVEGFr-2, MMP-2, and endostatin in both groups (P < 0.001-0.01). The magnitude of the increase was similar in both patients with SCI and AB individuals, as shown by the non-significant group × time interaction for all angiogenic parameters.

CONCLUSIONS

Upper-limb exercise (arm-cranking for 30 minutes at 60% of VO2max) is a sufficient stimulus to trigger a coordinated circulating angiogenic response in patients with SCI. The response of angiogenic molecules to upper-limb aerobic exercise in SCI appears relatively similar to that observed in AB individuals.

Heat transfer model for deep tissue injury: a step towards an early thermographic diagnostic capability

BACKGROUND

Deep tissue injury (DTI) is a class of serious lesions which develop in the deep tissue layers as a result of sustained tissue loading or pressure-induced ischemic injury. DTI lesions often do not become visible on the skin surface until the injury reaches an advanced stage, making their early detection a challenging task.

THEORY

Early diagnosis leading to early treatment mitigates the progression of the lesion and remains one of the priorities in clinical care. The aim of the study is to relate changes in tissue temperature with key physiological changes occurring at the tissue level to develop criteria for the detection of incipient DTIs.

METHOD

Skin surface temperature distributions of the damaged tissue were analyzed using a multilayer tissue model. Thermal response of the skin surface to a cooling stress, was computed for deep tissue inflammation and deep tissue ischemia, and then compared with computed skin temperature of healthy tissue.

RESULTS

For a deep lesion situated in muscle and fat layers, measurable skin temperature differences were observed within the first five minutes of thermal recovery period including temperature increases between 0.25 °C to 0.9 °C during inflammation and temperature decreases between -0.2 °C to -0.5 °C during ischemia.

CONCLUSIONS

The computational thermal models can explain previously published thermographic findings related to DTIs and pressure ulcers. It is concluded that infrared thermography can be used as an objective, non-invasive and quantitative means of early DTI diagnosis.

VIRTUAL SLIDES

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1461254346108378.

Effectiveness of local cooling for enhancing tissue ischemia tolerance in people with spinal cord injury

OBJECTIVE

To investigate the effects of localized cooling and cooling rate on pressure-induced ischemia for people with and without neurological deficits.

DESIGN

A 2 × 3 mixed factorial design with two groups: (1) people with spinal cord injury (SCI) and (2) people without neurological deficits (control), and three test conditions: (1) pressure only, (2) pressure with fast cooling (-4°C/min), and (3) pressure with slow cooling (-0.33°C/min).

SETTING

University laboratory.

PARTICIPANTS

Fourteen controls and 14 individuals with SCI.

INTERVENTIONS

Pressure on the sacrum was 0.4 kPa for 5 minutes, then 8 kPa for 20 minutes, and finally 0.4 kPa for 15 minutes. Fast and slow cooling to 25°C applied during 8 kPa of pressure.

OUTCOME MEASURES

Reactive hyperemia and its spectral densities in the metabolic, neurogenic, and myogenic frequency ranges.

RESULTS

In controls, reactive hyperemia was greater in pressure only as compared with both cooling conditions. No change was noted in all spectral densities in both cooling conditions, and only neurogenic spectral density increased without cooling. In subjects with SCI, no difference was noted in reactive hyperemia among conditions. However, metabolic and myogenic spectral densities increased without cooling and all spectral densities increased with slow cooling. No change was noted in all spectral densities with fast cooling.

CONCLUSION

Local cooling reduced the severity of ischemia in controls. This protective effect may be masked in subjects with SCI due to chronic microvascular changes; however, spectral analysis suggested local cooling may reduce metabolic vasodilation. These findings provide evidence towards the development of support surfaces with temperature control for weight-bearing soft tissues.

HEAT TRANSFER MODEL AND QUANTITATIVE ANALYSIS OF DEEP TISSUE INJURY

Deep tissue injuries (DTI) are serious lesions which may develop in deep tissue layers as a result of sustained tissue loading or ischemic injury. These lesions may not become visible on the skin surface until the injury reaches an advanced stage making their early detection a challenging task. Early diagnosis leading to early treatment mitigates the progression of lesion and remains one of the priorities in management. The aim of this study is to examine skin surface temperature distributions of damaged tissue and develop criteria for the detection of incipient DTI. A multilayer quantitative heat transfer model of the skin tissue was developed using finite element based software COMSOL Multiphysics. Thermal response of the skin surface was computed during deep tissue inflammation and deep tissue ischemia and then compared with that of healthy tissue. In the presence of a DTI, an increase of about 0.5°C in skin surface temperatures was noticed during initial phase of deep tissue inflammation, which was followed by a surface temperature decrease of about 0.2°C corresponding to persistent deep tissue ischemia. These temperature differences are large enough to be detected by thermographic imaging. This study, therefore, also enhances the understanding of the previously detected thermographic quantitative changes associated with DTI.