The effect of gradually increased blood flow on ischemia-reperfusion 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.

The Effect of Nerolidol Renal Dysfunction following Ischemia-Reperfusion Injury in the Rat

Efforts to decrease the deleterious effects of renal ischemia-reperfusion injury (IRI) are ongoing. Recently, there has been increasing interest in using natural phytochemical compounds as alternative remedies in several diseases. Nerolidol is a natural product extracted from plants with floral odors and has been proven to be effective for the treatment of some conditions. We investigated the effect of nerolidol in a rat model of renal IRI. Nerolidol was dissolved in a vehicle and administered orally as single daily dose of 200 mg/kg for 5 days prior to IRI and continued for 3 days post IRI. G-Sham (n = 10) underwent sham surgery, whereas G-IRI (n = 10) and G-IRI/NR (n = 10) underwent bilateral warm renal ischemia for 30 min and received the vehicle/nerolidol, respectively. Renal functions and histological changes were assessed before starting the medication, just prior to IRI and 3 days after IRI. Nerolidol significantly attenuated the alterations in serum creatinine and urea, creatinine clearance, urinary albumin and the urinary albumin-creatinine ratio. Nerolidol also significantly attenuated the alterations in markers of kidney injury; proinflammatory, profibrotic and apoptotic cytokines; oxidative stress markers; and histological changes. We conclude that nerolidol has a renoprotective effect on IRI-induced renal dysfunction. These findings might have clinical implications.

Protection of multiple ischemic organs by controlled reperfusion

Reperfusion injury (RI) is a harmful complication that takes place during recanalization treatment of ischemic organs. Currently, there are no efficacious treatments for protecting the organs against RI. Therefore, it is necessary to discover new strategies to prevent RI. As a novel intervention technique, controlled reperfusion has promising effects on protecting multiple organs from RI, and it is done by adjusting physical parameters of blood flow or chemical compositions of the reperfusion liquid. In this brief review, the status of various controlled reperfusion methods is presented, as well as their application in the protection of ischemic organs.

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.

The effect of neprilysin and renin inhibition on the renal dysfunction following ischemia-reperfusion injury in the rat

The natriuretic peptide (NP) system counter-regulates the renin-angiotensin system (RAS), so enhancing the activity of natriuretic peptides (NPs) may be beneficial in conditions when RAS is activated such as ischemia-reperfusion injury (IRI). Neprilysin is the key enzyme responsible for the degradation of NPs. The effects of neprilysin inhibition or the combination of neprilysin inhibition and RAS inhibition on renal IRI-induced renal dysfunction have not been investigated yet. To investigate this, rats underwent sham surgery or bilateral IRI for 20 min. G-Als, G-Scb, and G-Als+Scb underwent similar protocol but received aliskiren (renin inhibitor), sacubitril (neprilysin inhibitor) or a combination of both pre- and post-IRI, respectively. IRI caused significant alterations in all renal functional parameters, markers of acute renal injury, pro-inflammatory and pro-fibrotic cytokines, and histological features. All these alterations were significantly attenuated in G-Als, G-Scb, and G-Als+Scb. The attenuations in the alterations in serum creatinine, creatinine clearance, and histological features were larger in G-Als+Scb compared to either G-Als or G-Scb. We conclude that RAS blockade by a renin inhibitor (aliskiren) or neprilysin inhibition by sacubitril separately led to significant attenuation in the renal IRI-induced renal dysfunction. The combination of aliskiren and sacubitril was more effective than either one alone.

An advanced magnetic resonance imaging perspective on the etiology of deep tissue injury

Early diagnosis of deep tissue injury remains problematic due to the complicated and multifactorial nature of damage induction and the many processes involved in damage development and recovery. In this paper, we present a comprehensive assessment of deep tissue injury development and remodeling in a rat model by multiparametric magnetic resonance imaging (MRI) and histopathology. The tibialis anterior muscle of rats was subjected to mechanical deformation for 2 h. Multiparametric in vivo MRI, consisting of T2, T2*, mean diffusivity (MD), and angiography measurements, was applied before, during, and directly after indentation as well as at several time points during a 14-day follow-up. MRI readouts were linked to histological analyses of the damaged tissue. The results showed dynamic change in various MRI parameters, reflecting the histopathological status of the tissue during damage induction and repair. Increased T2 corresponded with edema, muscle cell damage, and inflammation. T2* was related to tissue perfusion, hemorrhage, and inflammation. MD increase and decrease was reported on the tissue’s microstructural integrity and reflected muscle degeneration and edema as well as fibrosis. Angiography provided information on blockage of blood flow during deformation. Our results indicate that the effects of a single damage-causing event of only 2 h of deformation were present up to 14 days. The initial tissue response to deformation, as observed by MRI, starts at the edge of the indentation. The quantitative MRI readouts provided distinct and complementary information on the extent, temporal evolution, and microstructural basis of deep tissue injury-related muscle damage.

NEW & NOTEWORTHY We have applied a multiparametric MRI approach linked to histopathology to characterize damage development and remodeling in a rat model of deep tissue injury. Our approach provided several relevant insights in deep tissue injury. Response to damage, as observed by MRI, started at some distance from the deformation. Damage after a single indentation period persisted up to 14 days. The MRI parameters provided distinct and complementary information on the microstructural basis of the damage.

Trends of reactive hyperaemia responses to repetitive loading on skin tissue of rats - Implications for pressure ulcer prevention

Tissue recovery is important in preventing tissue deterioration, which is induced by pressure and may lead to pressure ulcers (PU). Reactive hyperaemia (RH) is an indicator used to identify people at risk of PU. In this study, the effect of different recovery times on RH trend is investigated during repetitive loading. Twenty-one male Sprague-Dawley rats (seven per group), with body weight of 385-485 g, were categorised into three groups and subjected to different recovery times with three repetitive loading cycles. The first, second, and third groups were subjected to short (3 min), moderate (10 min), and prolonged (40 min) recovery, respectively, while fixed loading time and pressure (10 min and 50 mmHg, respectively). Peak hyperaemia was measured in the three cycles to determine trends associated with different recovery times. Three RH trends (increasing, decreasing, and inconsistent) were observed. As the recovery time is increased (3 min vs. 10 min vs. 40 min), the number of samples with increasing RH trend decreases (57% vs. 29% vs. 14%) and the number of samples with inconsistent RH trend increases (29% vs. 57% vs. 72%). All groups consists of one sample with decreasing RH trend (14%). Results confirm that different recovery times affect the RH trend during repetitive loading. The RH trend may be used to determine the sufficient recovery time of an individual to avoid PU development.

Protective effects of udenafil citrate, piracetam and dexmedetomidine treatment on testicular torsion/detorsion-induced ischaemia/reperfusion injury in rats

The aim of this study was to investigate the antioxidant properties of udenafil citrate (1.4 mg kg(-1) -2.8 mg kg(-1) ), dexmedetomidine 25 μg kg(-1) and piracetam 200 mg kg(-1) administered on ipsilateral/contralateral testes after ischaemia in a rat model of testicular torsion/detorsion (T/D) and define its protective effect histologically. Fifty-six Wistar albino rats were included and randomly assigned into 6 groups. No intervention was performed in control group (Group 1, n = 8) and in torsion/detorsion group, (Group 2, n = 8). Udenafil 1.4 mg kg(-1) was given to torsion/detorsion group (Group 3, n = 10), udenafil 2.8 mg kg(-1) was given to torsion/detorsion group (Group 4, n = 10), piracetam 200 mg kg(-1) was given to torsion/detorsion group (Group 5, n = 10) and dexmedetomidine 25 μg kg(-1) was given to torsion/detorsion group (Group 6, n = 10) intraperitoneally after 60 mins of testicular torsion. Biochemical and histopathological testicular injury were evaluated. When the tissue was examined by TOS values, Group 3, Group 4 and Group 5 were significantly lower than Group 2. In contrary Group 6 values were significantly higher than Group 2. The increasing doses of udenafil demonstrated antioxidant properties on the testis tissue and histopathological that protects the testicles.

Identifying the right surface for the right patient at the right time: generation and content validation of an algorithm for support surface selection

Support surfaces are an integral component of pressure ulcer prevention and treatment, but there is insufficient evidence to guide clinical decision making in this area. In an effort to provide clinical guidance for selecting support surfaces based on individual patient needs, the Wound, Ostomy and Continence Nurses Society (WOCN®) set out to develop an evidence- and consensus-based algorithm. A Task Force of clinical experts was identified who: 1) reviewed the literature and identified evidence for support surface use in the prevention and treatment of pressure ulcers; 2) developed supporting statements for essential components for the algorithm, 3) developed a draft algorithm for support surface selection; and 4) determined its face validity. A consensus panel of 20 key opinion leaders was then convened that: 1.) reviewed the draft algorithm and supporting statements, 2.) reached consensus on statements lacking robust supporting evidence, 3.) modified the draft algorithm and evaluated its content validity. The Content Validity Index (CVI) for the algorithm was strong (0.95 out of 1.0) with an overall mean score of 3.72 (out of 1 to 4), suggesting that the steps were appropriate to the purpose of the algorithm. To our knowledge, this is the first evidence and consensus based algorithm for support surface selection that has undergone content validation.

A new pressure ulcer conceptual framework

AIM

This paper discusses the critical determinants of pressure ulcer development and proposes a new pressure ulcer conceptual framework.

BACKGROUND

Recent work to develop and validate a new evidence-based pressure ulcer risk assessment framework was undertaken. This formed part of a Pressure UlceR Programme Of reSEarch (RP-PG-0407-10056), funded by the National Institute for Health Research. The foundation for the risk assessment component incorporated a systematic review and a consensus study that highlighted the need to propose a new conceptual framework.

DESIGN

Discussion Paper.

DATA SOURCES

The new conceptual framework links evidence from biomechanical, physiological and epidemiological evidence, through use of data from a systematic review (search conducted March 2010), a consensus study (conducted December 2010-2011) and an international expert group meeting (conducted December 2011).

IMPLICATIONS FOR NURSING

A new pressure ulcer conceptual framework incorporating key physiological and biomechanical components and their impact on internal strains, stresses and damage thresholds is proposed. Direct and key indirect causal factors suggested in a theoretical causal pathway are mapped to the physiological and biomechanical components of the framework. The new proposed conceptual framework provides the basis for understanding the critical determinants of pressure ulcer development and has the potential to influence risk assessment guidance and practice. It could also be used to underpin future research to explore the role of individual risk factors conceptually and operationally.

CONCLUSION

By integrating existing knowledge from epidemiological, physiological and biomechanical evidence, a theoretical causal pathway and new conceptual framework are proposed with potential implications for practice and research.

Activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf-2-dependent genes by ischaemic pre-conditioning and post-conditioning: new adaptive endogenous protective responses against renal ischaemia/reperfusion injury

AIM

To investigate the impact of ischaemic pre-conditioning (Ipre) and post-conditioning (Ipost) on expression of nuclear factor erythroid 2-related factor 2 (Nrf2) gene and its dependent genes, haem oxygenase-1 (HO-1) and NADPH-quinone oxidoreductase-1 (NQO-1); inflammatory cytokines TNF-α, IL1β and ICAM-1; and apoptotic markers such as caspase-3 in renal ischaemia/reperfusion (I/R) injury.

METHODS

One hundred and fifty male Sprague Dawley rats were classified into five groups (each consisted of 30 rats): sham, control (I/R), Ipre + I/R, Ipre without I/R and Ipost + I/R. Serum creatinine and blood urea nitrogen (BUN) were measured at 2, 24 and 48 h after ischaemia. In kidney tissues, mRNA of Nrf2, HO-1, NQO-1, TNF-α, IL-1β and ICAM-1 and immunohistochemical expression of Nrf2 and caspase-3 were assessed.

RESULTS

Serum creatinine and BUN improved significantly in Pre + I/R group; however, they did not show any significant improvement in Post + I/R group. Also, Ipre-I/R group showed non-significant change in serum creatinine and BUN. The expression of Nrf2, HO-1 and NQO-1 is increased significantly in Pre + I/R and Pre - I/R groups, while the enhancement in Post + I/R group was non-significant. Moreover, the expression of proinflammatory cytokines (TNF-α, IL-1 and ICAM-1) and apoptotic (caspase-3) markers showed high significant attenuation in Pre + I/R group, but slight significant attenuation in Pre + I/R group.

CONCLUSION

The renoprotective action of Ipre might include early activation and enhanced expression of Nrf2 gene and its dependent antioxidant genes, HO-1 and NOQ1, as endogenous adaptive renoprotective genes, as well as reduction in TNF-α, IL-1β, ICAM-1 and caspase-3.

The effectiveness of three types of alternating pressure air mattresses in the prevention of pressure ulcers in Belgian hospitals

To compare the effectiveness of multi-stage and one-stage alternating low-pressure air mattresses (ALPAM) and alternating pressure air mattress (APAM) overlays in preventing pressure ulcers among hospitalized patients, data were pooled (N = 617) from a study of patients allocated to multi-stage ALPAM (n = 252) or one-stage ALPAM (n = 264), and another study of patients allocated to APAM overlay (n = 101). Cumulative pressure ulcer incidence was 4.9% (n = 30) over 14 days. Fewer ulcers developed on multi-stage ALPAM compared with APAM overlay (OR = 0.33; 95% CI [0.11, 0.97]), but no difference was found between one-stage ALPAM and APAM overlay (OR = 0.40; 95% CI [0.14, 1.10]). Time to develop ulcers did not differ by mattress type.

An improved postconditioning algorithm: gradually increased reperfusion provides improved cardioprotection in rats

The aim of the present study was to investigate whether a gradually increasing reperfusion algorithm, in which the brief reperfusion was lengthened as the duration of each reperfusion/reocclusion cycle remained fixed, enhances cardioprotection. Rats were randomized into 5 groups: the sham, reperfusion injury (R/I), gradually decreased reperfusion (GDR; 30/10‑25/15‑15/25‑10/30 sec of reperfusion/reocclusion), equal reperfusion (ER; 4 20/20‑sec reperfusion/reocclusion cycles) and gradually increased reperfusion (GIR; 10/30‑15/25‑25/15‑30/10 sec of reperfusion/reocclusion). The rats were sacrificed to measure serum markers, apoptotic indices and infarct size. Western blot analyses were used to analyze the expression of molecules involved in important signaling pathways. All the three postconditioning patterns were found to provide cardioprotection (P<0.05 compared with the R/I group). GIR provided optimum cardioprotection, followed by ER and then GDR. Apoptotic index and serum marker levels were significantly reduced in the GIR compared with the ER group (P<0.05). The enhanced cardioprotection provided by GIR was accompanied by significantly increased levels of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and Bcl‑2, as well as lower levels of p38/c‑Jun N‑terminal kinase (JNK) phosphorylation, tumor necrosis factor α (TNFα), caspase‑8, Bax, caspase‑9 and cytochrome c (Cyt‑c) in the cytoplasm of rats (P<0.05, all compared with ER). The infarct size in the rats of the GIR group was also smaller compared with that in the rats of the ER group, but this difference was not significant (16.30±5.22 vs. 20.57±6.32%, P>0.05). All the variables measured in the present study were significantly improved in the GIR group compared with the GDR group (P<0.05). In conclusion, the association between brief reperfusion and reocclusion is an important factor in postconditioning algorithms. Additionally, GIR results in improved cardioprotection compared with that achieved by the remaining algorithms examined.

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.

The long-term protective effects of short-interval postconditioning in testicular ischemia-reperfusion injury in rats

AIM

Even with prompt diagnosis and treatment, testicular torsion may lead to infertility and atrophy after testicular salvage. The aims of this study were to investigate the long-term protective effects of short-interval postconditioning on testicular atrophy and to optimize the reperfusion period.

MATERIALS AND METHODS

Forty adult male rats were divided into 5 subgroups: sham operated; torsion + detorsion; torsion + postconditioning, 5 seconds (PC5); torsion + postconditioning, 10 seconds; and torsion + postconditioning, 20 seconds. Torsion was created by rotating the left testis 1080° counterclockwise and then fixing the testis to the scrotum with 3 sutures. Torsion was maintained for 4 hours. The testicular artery was visualized, and an atraumatic vascular clamp was applied to prevent reperfusion in all study groups. Detorsion of the testis was then performed. In the torsion + detorsion group, the clamp was released just after detorsion. In all the other intervention groups, the subsequent procedures were repeated 10 times. In the PC5 group, the clamp was released for 5 seconds and applied for 10 seconds; in the torsion + postconditioning, 10 seconds group, the clamp was released for 10 seconds and applied for 10 seconds; and in the torsion + postconditioning, 20 seconds group, the clamp was released for 20 seconds and applied for 10 seconds. Then, reperfusion was allowed. After 60 days, rats in all study groups were killed, both testes were removed, and the histopathology was evaluated. The χ(2) test was used for statistical analysis.

RESULTS

Compared with the other groups, the extent of tissue injury determined by histopathologic grades according to Cosentino et al (J Androl. 1986;7:23-31) was significantly less in group PC5 (P < .05).

CONCLUSION

We conclude that short-interval postconditioning can protect against long-term testicular reperfusion injury. Furthermore, the optimal time for reperfusion during postconditioning was 5 seconds in our rat model of testicular torsion. This technique seems easily applicable, and evidence suggests that similar techniques may be useful during testicular surgery.

Pattern of presentation of pressure ulcers in traumatic spinal cord injured patients in University College Hospital, Ibadan

The neurosurgery division in University College Hospital (U.C.H.) admits approximately one traumatic spinal cord injured (SCI) patient per week, most of whom stay a minimum of 42 days on admission. A common complication in these patients is the development of pressure ulcers, which contributes to a longer hospital stay and increased hospital expenses. The purpose of this study was to investigate the pattern of presentation of pressure ulcers in patients on admission and to propose policies or protocols to reduce the incidence. It is a prospective study of traumatic SCI patients managed on the neurosurgery ward from January 2003 to June 2004. The data was analysed using descriptive statistics. Sixty-seven patients were studied. The average hospital stay was 73 days. Thirteen (20%) of the patients were admitted with pressure ulcers, 32 (47·7%) developed it after admission. As much as 87·5% of pressure ulcers seen in the course of this study which occurred on admission in U.C.H. was in the first week of admission, 6·25% in the second week and the remaining 6·25% in the third week. Pressure ulcers were distributed as follows; 69% (42) in the sacral region, 18% (11) trochanteric, 5% (3) scalp, 1·5% (1) ankle, 1·5% (1) ischial tuberosity, the remaining 5% in other sites. Preventive measures for pressure ulcers consisted of basic skin care, pressure dispersion using fenestrated foams and alternating weight-bearing sites by regular turning. Pressure ulcers are commonest in the sacral and gluteal regions and tend to occur within the first week of admission in the neurosurgical wards.

The effects of deformation, ischemia, and reperfusion on the development of muscle damage during prolonged loading

Deep tissue injury (DTI) is a severe form of pressure ulcer where tissue damage starts in deep tissues underneath intact skin. In the present study, the contributions of deformation, ischemia, and reperfusion to skeletal muscle damage development were examined in a rat model during a 6-h period. Magnetic resonance imaging (MRI) was used to study perfusion (contrast-enhanced MRI) and tissue integrity (T2-weighted MRI). The levels of tissue deformation were estimated using finite element models. Complete ischemia caused a gradual homogeneous increase in T2 (∼20% during the 6-h period). The effect of reperfusion on T2 was highly variable, depending on the anatomical location. In experiments involving deformation, inevitably associated with partial ischemia, a variable T2 increase (17–66% during the 6-h period) was observed reflecting the significant variation in deformation (with two-dimensional strain energies of 0.60–1.51 J/mm) and ischemia (50.8–99.8% of the leg) between experiments. These results imply that deformation, ischemia, and reperfusion all contribute to the damage process during prolonged loading, although their importance varies with time. The critical deformation threshold and period of ischemia that cause muscle damage will certainly vary between individuals. These variations are related to intrinsic factors, such as pathological state, which partly explain the individual susceptibility to the development of DTI and highlight the need for regular assessments of individual subjects.

The effects of short-interval postconditioning in preventing testicular ischemia-reperfusion injury in rats

AIM

Testicular torsion can lead to testicular damage. During reperfusion, tissue damage is more severe. The aim of this study was to investigate the protective effect of short-interval postconditioning and determine the optimal time of reperfusion for postconditioning.

MATERIALS AND METHODS

Thirty-five adult male rats were divided into 5 subgroups: Sh (sham operated), TD (torsion + detorsion), PC5 (torsion + postconditioning 5 seconds), PC10 (torsion + postconditioning-10 seconds), PC20 (torsion + postconditioning 20 seconds). Torsion was created by rotating the left testis counterclockwise 1080° and the testis fixed to the scrotum with 3 sutures. Torsion was maintained for 4 hours. The testicular artery was visualized, and before detorsion of the testis, an atraumatic vessel clamp was applied to prevent reperfusion in all study groups. Then, detorsion of the testis was performed. In the TD group, the clamp was released just after detorsion; in the PC5 group, the clamp was released for 5 seconds and closed for 10 seconds (10 times); in the PC10 group, the clamp was released for 10 seconds and closed for 10 seconds (10 times); and in the PC20 group, the clamp was released for 20 seconds and closed for 10 seconds (10 times). Then, all testes were reperfused for a 1-hour period in all study groups. After this period, the rats were sacrificed, and the left testes were removed and evaluated histopathologically and biochemically. The Mann-Whitney U test was used for statistical analyses.

RESULTS

Tissue malondialdehyde levels were 79.3 ± 10.6, 231.7 ± 102.3, 71.3 ± 12.6, 73.8 ± 13.7, and 124.3 ± 48.0 nmol/g tissue in the Sh, TD, PC5, PC10, and PC20 groups, respectively. Tissue malondialdehyde levels were significantly lower in the PC5 and PC10 groups (P < .05) compared to the other groups. However, mean histopathologic grade was lower in all postconditioning groups compared to the control group, but the difference was significant only in the PC5 group (P < .05).

CONCLUSION

We conclude that short-interval postconditioning can reduce reperfusion injury in ischemic tissue and the optimal mode of short-interval postconditioning is 5 seconds × 10 times. This technique seems easily applicable, and a similar technique may be used during testicular surgery.

Biomechanics of Pressure Ulcer in Body Tissues Interacting with External Forces during Locomotion

Forces acting on the body via various external surfaces during locomotion are needed to support the body under gravity, control posture, and overcome inertia. Examples include the forces acting on the body via the seating surfaces during wheelchair propulsion, the forces acting on the plantar foot tissues via the insole during gait, and the forces acting on the residual-limb tissues via the prosthetic socket during various movement activities. Excessive exposure to unwarranted stresses at the body-support interfaces could lead to tissue breakdowns commonly known as pressure ulcers, often presented as deep-tissue injuries around bony prominences or as surface damage on the skin. In this article, we review the literature that describes how the involved tissues respond to epidermal loading, taking into account both experimental and computational findings from in vivo and in vitro studies. In particular, we discuss related literature about internal tissue deformation and stresses, microcirculatory responses, and histological, cellular, and molecular observations.

Temporal effects of mechanical loading on deformation-induced damage in skeletal muscle tissue

Mechanical loading of soft tissues covering bony prominences can cause skeletal muscle damage, ultimately resulting in a severe pressure ulcer termed deep tissue injury. Recently, by means of an experimental-numerical approach, it was shown that local tissue deformations cause tissue damage once a deformation threshold is exceeded. In the present study, the effects of load exposure time and intermittent load relief on the development of deformation-induced muscle damage were investigated. The data showed that a 2 h loading period caused more damage than 10 min loading. Intermittent load reliefs of 2 min during a 2 h loading period had minimal effect on the evolution of skeletal muscle damage. In addition, a local deformation threshold for damage was found, which was similar for each of the loading regimes applied in this study. For short loading periods, these results imply that local tissue deformations determine whether muscle damage will develop and the exposure time influences the amount of tissue damage. Temporary load reliefs were inefficient in reducing deformation-induced damage, but may still influence the development of ischemia-induced damage during longer loading periods.

[Effect of postconditioning in major vascular operations on rats]

BACKGROUND

Postconditioning - using alternating brief cycles of reperfusion/reocclusion applied just at the very beginning of reperfusion - has recently been described as a potent therapeutic technique, attenuating ischaemia-reperfusion injury. In vascular surgery, certain elective interventions involve cross-clamping of major arteries, resulting in temporary ischaemia in large peripheral organs, which thus suffer ischaemia-reperfusion injury. Patients undergoing these operations may develop also serious systemic complications such as multiple distant organ dysfunctions, SIRS, detrimental redistribution of the circulation or even shock, a phenomenon called reperfusion-syndrome. We studied the effects of postconditioning on reperfusion-syndrome in a rodent experimental model.

MATERIAL AND METHODS

Anaesthetized male Wistar rats underwent 180 minutes of bilateral lower limb ischaemia and 4 hours of reperfusion using an infrarenal cross-clamping of the abdominal aorta. Control animals underwent no additional intervention. Postconditioning consisted of 6 cycles of 10-second aortic occlusion/10-second declamping starting at the beginning of reperfusion. Haemodynamic parameters were observed with invasive arterial manometer, microcirculation of the lower limb was detected with laser-Doppler-flowmeter. After 4 hours of reperfusion serum, urine, and histological samples were collected.

RESULTS

180-minute ischaemia resulted in significant haemodynamic changes after reperfusion. Postconditioning affected the character of the microcirculatory flow curves, the limb circulation stabilized with hyperaemia after reperfusion. Postconditioning caused a significant reduction in systemic inflammatory response (TNF-alpha, oxygen-derived free radicals). The laboratory and histological samples implied a significant decrease in remote organ (lung and renal) dysfunctions after postconditioning.

CONCLUSION

Postconditioning proves to be capable in conferring protection against different organ injuries caused by longer circulatory occlusions during elective major vascular surgeries.

Gradual detorsion of torsioned rat testis attenuates ischemia reperfusion injury

AIM

This study was designed to investigate effect of gradual detorsion on testicular ischemia reperfusion injury.

MATERIALS AND METHODS

A total of 21 male rats were divided into 3 groups, each containing 7 rats. Torsion was created by rotating the left testis 720 degrees in a clockwise direction. Group 1 underwent sham operation. Group 2 (sudden detorsion) served as a torsion/detorsion group, receiving 2 hours torsion and 2 hours detorsion. In group 3, 360 degrees detorsion was done for 20 minutes after 720 degrees torsion for 2 hours. Then, testis was done full detorsion for 100 minutes. At the end of the experiments (fourth hour), left orchiectomy was performed to measure the tissue levels of malondialdehyde (MDA), superoxide dismutase, and glutathione peroxidase and to perform histologic examination in testes.

RESULTS

The MDA levels of testis tissues were significantly increased in the sudden detorsion group as compared with the sham group. We found decrease of the MDA level in gradual detorsion group, but it was not a statistically significant amount. Significant decrease was found in the superoxide dismutase and glutathione peroxidase activities in the sudden detorsion group as compared with the sham and gradual detorsion groups. Histologic examinations were in accordance with the testicular tissue MDA levels.

CONCLUSION

In the light of our biochemical and histopathologic findings, we can say that gradual detorsion has a trend to decrease the degree of testicular reperfusion injury in the rat torsion/detorsion model.

Temporal differences in the influence of ischemic factors and deformation on the metabolism of engineered skeletal muscle

Prolonged periods of tissue compression may lead to the development of pressure ulcers, some of which may originate in, for example, skeletal muscle tissue and progress underneath intact skin, representing deep tissue injury. Their etiology is multifactorial and the interaction between individual causal factors and their relative importance remain unknown. The present study addressed the relative contributions of deformation and ischemic factors to altered metabolism and viability. Engineered muscle tissue was prepared as previously detailed ( 14 ) and subjected to a combination of factors including 0% oxygen, lactic acid concentrations resulting in pH from 5.3 to 7.4, 34% compression, and low glucose levels. Deformation had an immediate effect on tissue viability {[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) assay}, which increased with time. By contrast, hypoxia evoked metabolic responses (glucose and lactate levels) within 24 h, but viability was only reduced after 48 h. In addition, lactic acidification downregulated tissue metabolism up to an acid concentration (∼23 mM) where metabolism was arrested and cell death enhanced. A similar tissue response was observed during glucose deprivation, which, at negligible concentration, resulted in both a cessation of metabolic activity and a reduction in cell viability. The combination of results suggests that in a short-term (<24 h) deformation, extreme acidification and glucose deprivation increased the level of cell death. By contrast, nonextreme acidification and hypoxia influenced tissue metabolism, but not the development of cell death. These data provide more insight into how compression-induced factors can lead to the onset of deep tissue injury.

Impact of gradual blood flow increase on ischaemia-reperfusion injury in the rat cremaster microcirculation model

INTRODUCTION

We aimed to evaluate the impact of gradual blood reperfusion on ischaemia-reperfusion injury and to explain the pathophysiology of reperfusion injury in a rat cremaster muscle microcirculation model.

MATERIALS AND METHODS

Twenty-four Sprague-Dawley rats weighing 150-200 g were evaluated in three groups. Cremaster muscles were prepared for microcirculatory observations. Group I (n=8, control): no ischemia was induced. Group II (n=8, acute reperfusion): microclamps were applied to the right external iliac vessels for 150 min, then venous and arterial clamps were released at once. Group III (n=8, gradual reperfusion): microclamps were applied to the right external iliac vessels for 150 min, and then the first venous clamp was released; the arterial clamp was opened gradually by a specially designed microclamp holder (Sheey ossicle holding clamp). In all groups, following a wait of 150 min blood flow velocity was measured for 15 min and then the animals were reperfused freely for 1h. Next, red blood cell velocity, vessel diameters, functional capillary perfusion and endothelial oedema index were analysed, and rolling, migrating and adhesing leukocytes and lymphocytes were counted. All observations were videotaped for slow-motion replay. Muscle damage was evaluated histologically.

RESULTS

In the acute clamp release group, blood velocities increased up to 600% of their pre-ischaemic values during the post-ischaemia-reperfusion period. The numbers of rolling, adhering and transmigrating leukocytes were significantly higher and histological evaluation revealed more tissue damage in the acute reperfusion group.

CONCLUSION

Depending on histological and microcirculatory findings, gradual reperfusion was confirmed to reduce the intensity of reperfusion injury.

The effect of gradually increased blood flow on ischemia-reperfusion injury in rat kidney

BACKGROUND

Gradually increased blood flow to the ischemic rat kidney was studied to assess the ability to diminish ischemia-reperfusion injury.

METHODS

The left renal artery and vein were isolated in 25 rats. Microclamps were applied for 45 minutes and were released at once (group II) or gradually (group III). Renal arterial blood flow and K+ activity were measured. Bilateral kidneys were harvested for histopathology and for malonyldealdehyde and myeloperoxidase levels.

RESULTS

Increased K+ activity returned to preischemic values faster in group III than in group II. No statistically significant difference existed in malonyldealdehyde and myeloperoxidase levels; histopathologic scoring showed less tissue damage in group III (P < .05). Contralateral kidney samples showed signs of ischemia in group II.

CONCLUSIONS

Gradually increased blood flow to the ischemic kidney decreases ischemic changes. Ischemic insult to 1 kidney causes histopathologically detectable changes to the contralateral kidney, which can be diminished by gradual reperfusion.