[Implications of prehospital estimation of trauma patients for the treatment pathway-An evaluation of the TraumaRegister DGU®]. / Implikationen der prähospitalen Einschätzung des Traumapatienten auf den Behandlungsverlauf ­ Eine Auswertung aus dem TraumaRegister DGU®.

BACKGROUND: In the prehospital acute treatment phase of severely injured patients, the stabilization of the vital parameters is paramount. The rapid and precise assessment of the injuries by the emergency physician is crucial for the initial treatment and the selection of the receiving hospital. OBJECTIVE: The aim of this study was to determine whether the prehospital emergency medical assessment has an influence on prehospital and emergency room treatment. MATERIAL AND METHODS: Data from the TraumaRegister DGU® between 2015 and 2019 in Germany were evaluated. The prehospital emergency medical assessment of the injury pattern and severity was recorded using the emergency physician protocol and compared with the in-hospital documented diagnoses using the abbreviated injury scale. RESULTS: A total of 47,838 patients with an average injury severity score (ISS) of 18,7 points (SD 12.3) were included. In summary, 127,739 injured body regions were documented in the hospitals. Of these, a total of 87,921 were correctly suspected by the emergency physician Thus, 39,818 injured body regions were not properly documented. In 42,530 cases a region of the body was suspected to be injured without the suspicion being confirmed in the hospital. Traumatic brain injuries and facial injuries were mostly overdiagnosed (13.5% and 14.7%, respectively documented by an emergency physician while the diagnosis was not confirmed in-hospital). Chest injuries were underdocumented (17.3% missed by an emergency physician while the diagnosis was finally confirmed in-hospital). The total mortality of all groups was very close to the expected mortality calculated with the revised injury severity classification II(RISC II)-score (12.0% vs. 11.3%). CONCLUSION: In the prehospital care of severely injured patients, the overall injury severity is often correctly recorded by the emergency physician and correlates well with the derived treatment, the selection of the receiving hospital as well as the clinical course and the patient outcome; however, the assessment of injuries of individual body regions seems to be challenging in the prehospital setting.

Health care utilization and excess costs after pelvic fractures among older people in Germany.

Our study demonstrates a strong increase in utilization of inpatient health care and clear excess costs in older people in the first year after pelvic fracture, the latter even after adjustment for several confounders. Excess costs were particularly high in the first few months and mainly attributable to inpatient treatment. INTRODUCTION: We aimed to estimate health care utilization and excess costs in patients aged minimum 60 years up to 1 year after pelvic fracture compared to a population without pelvic fracture. METHODS: In this retrospective population-based observational study, we used routine data from a large statutory health insurance (SHI) in Germany. Patients with a first pelvic fracture between 2008 and 2010 (n=5685, 82% female, mean age 80±9 years) were frequency matched with controls (n=193,159) by sex, age at index date, and index month. We estimated health care utilization and mean total direct costs (SHI perspective) with 95% confidence intervals (CIs) using BCA bootstrap procedures for 52 weeks before and after the index date. We calculated cost ratios (CRs) in 4-week intervals after the index date by fitting mixed two-part models including adjustment for possible confounders and repeated measurement. All analyses were further stratified for men/women, in-/outpatient-treated, and major/minor pelvic fractures. RESULTS: Health care utilization and mean costs in the year after the index date were higher for cases than for controls, with inpatient treatment being particularly pronounced. CRs (95% CIs) decreased from 10.7 (10.2-11.1) within the first 4 weeks to 1.3 (1.2-1.4) within week 49-52. Excess costs were higher for inpatient than for outpatient-treated persons (CRs of 13.4 (12.9-13.9) and 2.3 (2.0-2.6) in week 1-4). In the first few months, high excess costs were detected for both persons with major and minor pelvic fracture. CONCLUSION: Pelvic fractures come along with high excess costs and should be considered when planning and allocating health care resources.

Detection of missed fractures of hand and forearm in whole-body CT in a blinded reassessment.

BACKGROUND: We examined the visibility of fractures of hand and forearm in whole-body CT and its influence on delayed diagnosis. This study is based on a prior study on delayed diagnosis of fractures of hand and forearm in patients with suspected polytrauma. METHODS: Two blinded radiologists examined CT-scans of patients with fractures of hand or forearm that were diagnosed later than 24 h after admission and control cases with unremarkable imaging of those areas. They were provided with clinical information that was documented in the admission report and were asked to examine forearm and hands. After unblinding, the visibility of fractures was determined. We examined if time of admission or slice thickness was a factor for late or missed diagnoses. RESULTS: We included 72 known fractures in 36 cases. Of those 65 were visible. Sixteen visible fractures were diagnosed late during hospital stay. Eight more fractures were detected on revision by the radiologists. Both radiologists missed known fractures and found new fractures that were not reported by the other. Missed and late diagnoses of fractures occurred more often around 5 pm and 1 am. Slice thickness was not significantly different between fractures and cases with fractures found within 24 h and those found later. CONCLUSIONS: The number of late diagnosis or completely missed fractures of the hand and forearm may be reduced by a repeated survey of WBCT with focus on the extremities in patients with suspected polytrauma who are not conscious. LEVEL OF EVIDENCE: III.

[Resuscitation room management for trauma patients]. / Schockraummanagement bei traumatologischen Patienten.

Resuscitation rooms in central emergency admissions are the first point of contact for potentially severely or multiply injured patients. Here priority is given to the interdisciplinary treatment of these patients, which includes the structured and standardized hospital admission as well as the appropriate initial diagnostics and treatment of potentially life-threatening conditions. The resuscitation room is a central vital link between the prehospital and internal hospital treatment chain. This article describes the core tasks of the resuscitation room team as well as concepts and strategies of initial treatment of severely injured and polytrauma patients.

[Differences in injury patterns in motorcycle accidents involving children and adolescents]. / Unterschiede der Verletzungsmuster bei Motorradunfällen von Kindern und Jugendlichen.

BACKGROUND: Traffic accidents and the traumatic injury consequences are frequent causes of mortality and irreversible damage in children and young adults. In motorcycle accidents the injury patterns differ depending on the age of the patient. OBJECTIVE: The aim of this study was to describe the typical injury patterns after motorcycle accidents involving children and adolescents as these can have a decisive influence on the prevention and the adequate treatment in the respective patient groups. MATERIAL AND METHODS: The study included 22,923 patients from the years 2002-2018 which were extracted from the TraumaRegister DGU®. Injury patterns of 4 age categories were analyzed: group 1 (4-15 years), group 2 (16-17 years), group 3 (18-20 years) and group 4 (21-50 years). RESULTS: In both younger age groups, limb injuries mostly of the lower extremities, showed the highest incidence. Moreover, younger patients with traumatic brain injury showed better outcomes despite of initially poor conditions. Ribcage, abdominal, pelvic and spinal injuries are the least frequent in younger patients. In terms of diagnostics, children are less likely to undergo whole-body computed tomography (CT) diagnostics than adults. CONCLUSION: The study revealed age-specific differences with respect to injury patterns in patients involved in motorcycle accidents, either as drivers or co-drivers. Furthermore, the analysis of preclinical and in-hospital treatment elucidated the relevance of preventive and protective measures.

[Platelet-rich plasma combined with autologous cancellous bone : An alternative therapy for persistent non-union?]. / Platelet-rich-Plasma in Kombination mit autologer Spongiosa : Eine Alternative bei therapierefraktären Pseudarthrosen?

BACKGROUND: In addition to a stabile osteosynthesis autologous cancellous bone graft remains an essential therapy option in persistent non-union. Despite this therapy regimen persistent non-union can occasionally occur. The aim of this study was to evaluate the treatment of persistent non-union with a combination of platelet-rich plasma (PRP) and autologous cancellous bone. MATERIAL AND METHODS: In this prospective study 17 patients with persistent non-union of long bones were treated by a combination of PRP and autologous iliac crest bone. Inclusion criteria were a minimum of one previously failed cancellous bone transplantation and an atrophic non-union persisting for 6-14 months (mean 9 months). The patients were examined clinically and radiologically at intervals of 3, 6 and 9 months postoperatively. RESULTS: After an average time of 17 months (range 15-23 months) the patients were treated by a combination of PRP and autologous cancellous bone. In all cases the non-union was successfully treated and osseous bridging was found radiologically after an average of 5 months (range 4-7 months) without any complications. CONCLUSION: The combination of PRP and autologous cancellous bone appears to be a safe and effective method for treatment of persistent non-union. The use of PRP does not result in substantial additional costs. Allergies and graft versus host reactions are not expected because of the autologous origin.

Quantitative modeling of biochemical networks.

Today different database systems for molecular structures (genes and proteins) and metabolic pathways are available. All these systems are characterized by the static data representation. For progress in biotechnology, the dynamic representation of this data is important. The metabolism can be characterized as a complex biochemical network. Different models for the quantitative simulation of biochemical networks are discussed, but no useful formalization is available. This paper shows that the theory of Petrinets is useful for the quantitative modeling of biochemical networks.

Possible risk factors for acute and chronic deep periprosthetic joint infections in primary total knee arthroplasty. Do BMI, smoking, urinary tract infections, gender, and ASA classification have an impact?

PURPOSE: Aim of this retrospective study was to evaluate the impact of the patient related factors body mass index (BMI), urinary tract infection, current smoking, gender, and American Society of Anesthesiologists (ASA) classification on the incidence of acute and chronic deep periprosthetic joint infections (PJI) in total knee arthroplasty (TKA). METHODS: All patients undergoing revision surgery for a deep PJI of primary TKA between July 2012 and December 2016 were included in this study. All relevant data was collected from the medical records. Acute deep PJI was defined when PJI was diagnosed within the first 6 weeks after primary TKA, chronic PJI was defined when patients demonstrated PJI later than 6 weeks after primary TKA. RESULTS: A total of 57 patients was included in this study with 13 cases of acute PJI and 44 of chronic PJI. Overweight patients (BMI > 25 kg/m2) represent a significantly larger proportion in both PJI groups (p < 0.05). Current smokers had an significantly increased risk for acute and chronic PJI (p < 0.05). In the acute PJI group 46.2% patients had an postoperative urinary tract infection. CONCLUSION: An elevated BMI (>25 kg/m2), current smoking and urinary tract infection are possible risk factors for acute and chronic deep PJI. After primary TKA screening for urinary tract infection is recommendable to prevent predominantly acute deep PJI.

Loosening of total knee arthroplasty - always aseptic?

PURPOSE: When revision surgery is needed in total knee arthroplasty (TKA) the most frequent reasons are aseptic loosening (AL) and periprosthetic joint infection (PJI). However preoperative distinction between AL and PJI remains challenging. Aim of this study is to determine the incidence of PJI in patients with suspected AL after TKA and to evaluate a diagnostic algorithm for reliable differential diagnosis. METHODS: In this study a total of 149 symptomatic patients with radiographic signs of prosthetic loosening and suspected AL were included. Preoperatively all patients underwent a standardized diagnostic algorithm. For each patient demographics, as well as the results of laboratory and microbiological testing were collected from the medical records. RESULTS: Of the included patients 117 (78.5%) were diagnosed with AL and 32 (21.5%) with PJI. The latency period from primary arthroplasty to the presentation with symptomatic implant loosening was significantly shorter for PJI compared to AL (p < 0.05). The initial CRP values were significantly higher in patients with PJI compared to patients with AL (p < 0.05). Elevated count of white blood cells or percentage of neutrophils within the synovial fluid support the diagnosis of PJI. The sensitivity of synovial cell count (CC) count for PJI in patients with radiographic signs of loosening was 0.84 (CI 0.81-0.87) with a specificity of 0.96 (CI 0.92-0.98). The single best measure for the diagnosis of PJI was synovial fluid cultures with a specificity of 1, however this measure provides poor sensitivity. CONCLUSION: Patients with radiographic signs of loosening in TKA need thorough diagnostics. Information about primary TKA, serological testing, and results of joint aspiration can rule out a PJI in most cases.

[Functional and subjective results following subtalar dislocations]. / Funktionelle und subjektive Ergebnisse nach subtalaren Luxationen.

BACKGROUND: The objective of our study is to evaluate the functional and subjective results following subtalar dislocations without any associated bone injuries and to examine whether the direction of dislocation has any effect on the post-traumatic results. METHODS: Over the period from February 1998 to May 2006, 56 patients with a subtalar dislocation were enrolled in the study. A subtalar dislocation without any associated bone injuries was only present in 13 patients. Follow-up examination after an average of 39.8 months was performed using the AOFAS Ankle-Hindfoot scale. The adapted classification developed by Altman was used to assess the post-traumatic degree of arthrosis radiologically. RESULTS: The average AOFAS score was 81, with good results in 11 patients and satisfactory results in 2 patients. The range of motion (ROM) for the ankle-hindfoot joint was 39.2 degrees . CONCLUSION: Despite the severity of the injury, the functional and subjective results of subtalar dislocations without any bone injuries are good. Generally, no early post-traumatic arthrosis occurs if there are no associated bone injuries. No differences were established between medial and lateral subtalar dislocations.

[Distal radius fractures : Current treatment concepts and controversies]. / Die distale Radiusfraktur : Aktuelle Behandlungskonzepte und Kontroversen.

Distal radius fractures represent the most frequent bone fractures in humans. Although the treatment was dominated for decades by conservative measures or closed surgical procedures, such as percutaneous wire osteosynthesis, a paradigm shift was instigated by the introduction and rapid dissemination of volar locking plate osteosynthesis (VLP). The novel procedure was soon proclaimed to be the gold standard and applied for practically all forms of fractures of the distal radius. In addition to clinical mishaps, e.g. failure to address dorsal edge fragments or the occurrence of extensor and flexor tendon irritation, the publication of various prospective randomized studies and meta-analyses led to a certain degree of disillusionment. In comparison to percutaneous wire osteosynthesis, no differences in the clinical result could be established for VLP 1 year postoperatively. It was therefore obvious that not all problems of the distal radius could be solved using the innovative instrument of volar locking plates. This article gives an overview on the current insights and reflects the current expert opinion on the present concepts for the treatment of distal radius fractures. This is illustrated by comprehensive case presentations.

Constitutive expression of stromal derived factor-1 by mucosal epithelia and its role in HIV transmission and propagation.

HIV particles that use the chemokine receptor CXCR4 as a coreceptor for entry into cells (X4-HIV) inefficiently transmit infection across mucosal surfaces [1], despite their presence in seminal fluid and mucosal secretions from infected individuals [2] [3] [4]. In addition, although intestinal lymphocytes are susceptible to infection with either X4-HIV particles or particles that use the chemokine receptor CCR5 for viral entry (R5-HIV) during ex vivo culture [5], only systemic inoculation of R5-chimeric simian-HIV (S-HIV) results in a rapid loss of CD4(+) intestinal lymphocytes in macaques [6]. The mechanisms underlying the inefficient capacity of X4-HIV to transmit infection across mucosal surfaces and to infect intestinal lymphocytes in vivo have remained elusive. The CCR5 ligands RANTES, MIP-1alpha and MIP-1beta suppress infection by R5-HIV-1 particles via induction of CCR5 internalization, and individuals whose peripheral blood lymphocytes produce high levels of these chemokines are relatively resistant to infection [7] [8] [9]. Here, we show that the CXCR4 ligand stromal derived factor-1 (SDF-1) is constitutively expressed by mucosal epithelial cells at sites of HIV transmission and propagation. Furthermore, CXCR4 is selectively downmodulated on intestinal lymphocytes within the setting of prominent SDF-1 expression. We postulate that mucosally derived SDF-1 continuously downmodulates CXCR4 on resident HIV target cells, thereby reducing the transmission and propagation of X4-HIV at mucosal sites. Moreover, such a mechanism could contribute to the delayed emergence of X4 isolates, which predominantly occurs during the later stages of the HIV infection.

Hyperbaric oxygen therapy improves angiogenesis and bone formation in critical sized diaphyseal defects.

Besides the use of autologous bone grafting several osteoconductive and osteoinductive methods have been reported to improve bone healing. However, persistent non-union occurs in a considerable number of cases and compromised angiogenesis is suspected to impede bone regeneration. Hyperbaric oxygen therapy (HBO) improves angiogenesis. This study evaluates the effects of HBO on bone defects treated with autologous bone grafting in a bone defect model in rabbits. Twenty-four New-Zealand White Rabbits were subjected to a unilateral critical sized diaphyseal radius bone defect and treated with autologous cancellous bone transplantation. The study groups were exposed to an additional HBO treatment regimen. Bone regeneration was evaluated radiologically and histologically at 3 and 6 weeks, angiogenesis was assessed by immunohistochemistry at three and six weeks. The additional administration of HBO resulted in a significantly increased new bone formation and angiogenesis compared to the sole treatment with autologous bone grafting. These results were apparent after three and six weeks of treatment. The addition of HBO therapy to autologous bone grafts leads to significantly improved bone regeneration. The increase in angiogenesis observed could play a crucial role for the results observed.

Employment of telemedicine in emergency medicine. Clinical requirement analysis, system development and first test results.

OBJECTIVES: Demographic change, rising co-morbidity and an increasing number of emergencies are the main challenges that emergency medical services (EMS) in several countries worldwide are facing. In order to improve quality in EMS, highly trained personnel and well-equipped ambulances are essential. However several studies have shown a deficiency in qualified EMS physicians. Telemedicine emerges as a complementary system in EMS that may provide expertise and improve quality of medical treatment on the scene. Hence our aim is to develop and test a specific teleconsultation system. METHODS: During the development process several use cases were defined and technically specified by medical experts and engineers in the areas of: system administration, start-up of EMS assistance systems, audio communication, data transfer, routine tele-EMS physician activities and research capabilities. Upon completion, technical field tests were performed under realistic conditions to test system properties such as robustness, feasibility and usability, providing end-to-end measurements. RESULTS: Six ambulances were equipped with telemedical facilities based on the results of the requirement analysis and 55 scenarios were tested under realistic conditions in one month. The results indicate that the developed system performed well in terms of usability and robustness. The major challenges were, as expected, mobile communication and data network availability. Third generation networks were only available in 76.4% of the cases. Although 3G (third generation), such as Universal Mobile Telecommunications System (UMTS), provides beneficial conditions for higher bandwidth, system performance for most features was also acceptable under adequate 2G (second generation) test conditions. CONCLUSIONS: An innovative concept for the use of telemedicine for medical consultations in EMS was developed. Organisational and technical aspects were considered and practical requirements specified. Since technical feasibility was demonstrated in these technical field tests, the next step would be to prove medical usefulness and technical robustness under real conditions in a clinical trial.

The early phase influence of bone marrow concentrate on metaphyseal bone healing.

Bone marrow concentrate (BMC) contains high densities of progenitor cells. Therefore, in critical size defects BMC may have the potency to support bone healing. The aim of this study was to investigate the effect of BMC in combination with calcium phosphate granules (CPG) on bone defect healing in a metaphyseal long bone defect in mini-pigs. A metaphyseal critical-size bone defect at the proximal tibia of 24 mini-pigs was filled with CPG combined with BMC, CPG solely (control group) or with an autograft. Radiological and histomorphometrical evaluations after 6 weeks (42 days) showed significantly more bone formation in the BMC group in the central area of the defect zone and the cortical defect zone compared to the CPG group. At the same time the resorption rate of CPG increased significantly in the BMC group. Nevertheless, compared to the BMC group the autograft group showed a significantly higher new bone formation radiologically and histomorphometrically. In BMC the count of mononuclear cells was significantly higher compared to the bone marrow aspirate (3.5-fold). The mesenchymal progenitor cell characteristics of the cells in BMC were confirmed by flow cytometry. Cells from BMC created significantly larger colonies of alkaline phosphatase-positive colony forming units (CFU-ALP) (4.4-fold) compared to cells from bone marrow aspirate. Nevertheless, even in the BMC group complete osseous bridging was only detectable in isolated instances of the bone defects. Within the limitations of this study the BMC+CPG composite promotes bone regeneration in the early phase of bone healing significantly better than the isolated application of CPG. However, the addition of BMC does not lead to a solid fusion of the defect in the early phase of bone healing an still does not represent an equal alternative to autologous bone.

Fixed-angle plate osteosynthesis of the patella - an alternative to tension wiring?

BACKGROUND: The goal of this study is carry out a biomechanical evaluation of the stability of a bilateral, polyaxial, fixed-angle 2.7 mm plate system specifically designed for use on the patella. The results of this approach are then compared to the two currently most commonly used surgical techniques for patella fractures: modified anterior tension wiring with K-wires and cannulated lag screws with anterior tension wiring. METHODS: A transient biomechanical analysis determining material failure points of all osteosyntheses were conducted on 21 identical left polyurethane foam patellae, which were osteotomized horizontally. Evaluated were load (N), displacement (mm) and run-time (s) as well as elastic modulus (MPa), tensile strength (MPa) and strain at failure (%). FINDINGS: With a maximum load capacity of 2396 (SD 492) N, the fixed-angle plate proved to be significantly stronger than the cannulated lag screws with anterior tension wiring (1015 (SD 246) N) and the modified anterior tension wiring (625 (SD 84.9) N). The fixed-angle plate displayed significantly greater stiffness and lower fracture gap dehiscence than the other osteosyntheses. Additionally, osteosynthesis deformation was found to be lower for the fixed-angle plate. INTERPRETATION: A bilateral fixed-angle plate was the most rigid and stable osteosynthesis for horizontal patella fractures with the least amount of fracture gap dehiscence. Further biomechanical trials performed under cycling loading with fresh cadaver specimen should be done to figure out if a fixed-angle plate may be an alternative in the surgical treatment of patella fractures.

[Radial nerve palsy associated with humeral shaft fractures - early exploration or expectant procedure? An analysis concerning current strategies of treatment]. / Die primäre N.-radialis-Parese bei Humerusschaftfrakturen - revidieren oder zuwarten? Eine Analyse der Versorgungsrealität in Deutschland.

BACKGROUND: With a prevalence from 11.8 to 18% no fracture is as often associated with nerve damage as the humeral shaft fracture. Whether the radial nerve should be surgically explored in association with a palsy in humeral shaft fractures in order to exclude an interposition or discontinuity is being discussed controversially. The aim of this study was to assess the strategies for primary care of radial nerve palsies associated with humeral shaft fractures in Germany. MATERIAL AND METHODS: In a standardised survey 495 traumatological and 134 neurosurgical clinics were interviewed regarding the treatment of primary radial nerve palsies after humeral shaft fractures. The distribution of the survey included all level-one trauma centres. Statistics were based on the supply strategies, the number of observed contusions, discontinuities and inter-position of the N. radialis in the fracture gap. Moreover, the results were recorded after primary neurorrhaphy. RESULTS: The evaluable response rate to the questionnaire was 56% (university hospitals 77%, level-one trauma centres 63%, level-two trauma centres 70%, level-three trauma centres 44%). 6097 humeral shaft fractures have been treated per year, the incidence of primary radial nerve palsy was 8.6%. Regarding the management strategies, 59% of the hospitals advocated exploration of the nerve, while 25% reported that the decision depends on the individual case. 16% reject the exploration in case of a primary nerve palsy. In the case of an exploration, contusions (74%) of the nerve were largely seen, followed by nerve interpositions in the fracture gap (19%) and discontinuity (7%). In the case of neurorrhaphy, a partial or complete remission was found in 87% of cases. DISCUSSION: Although a primary expectant procedure is recommended in the literature due to the high spontaneous remission rate of 90%, an early exploration of the nerve is often preferred in clinical practice. In these cases, the use of an interlocking intramedullary nail as a minimally invasive treatment option does not appear useful due to the direct exposure of the fracture zone and the radial nerve. Interestingly, the feared discontinuity occurs rarely. The impact of nerve interposition in the fracture gap without surgical exploration remains unclear due to the lack of visibility. CONCLUSION: There is no consensus concerning the treatment of radial nerve palsies after humeral shaft fractures in Germany. Discontinuities are rare, the rate of spontaneous recoveries is high. Whether and when an exploration of the radial nerve is obligatory in primary radial palsy remains unclear and should be clarified by prospective randomised trials.

Quantitative modeling of biochemical networks.

Today different database systems for molecular structures (genes and proteins) and metabolic pathways are available. All these systems are characterized by the static data representation. For progress in biotechnology the dynamic representation of this data is important. The metabolism can be characterized as a complex biochemical network. Different models for the quantitative simulation of biochemical networks are discussed, but no useful formalization is available. This paper shows that the theory of Petrinets is useful for the quantitative modeling of biochemical networks.

Influence of the pulse duration of an Er:YAG laser system on the ablation threshold of dental enamel.

The present study examines the dependence of the ablation threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (lambda=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 micro m. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm(2), while the duration of the pulses applied was changed in four steps from 100 micro s to 700 micro s. The irradiated tooth surfaces were examined for visible signs of ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which ablation sets in is reduced by up to approx. 3 J/cm(2). This expands the ablation threshold range of Er:YAG laser radiation to between 6 and 10 J/cm(2). In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the ablation threshold (logistic regression, p<0.0001). Although the ablation threshold of the dental enamel can be changed by varying the pulse duration of the Er:YAG laser, no clinical consequences can be expected, as the shift is only slight.

Membrane-potential-dependent changes of the lipid microviscosity of mitochondria and phospholipid vesicles.

The effects of a transmembrane potential difference upon the lipid microviscosity of cytochrome oxidase vesicles (COVs) and rat liver mitochondria (RLM) were investigated. COVs and RLM were labelled with the fluorescent probe 1,6-diphenylhexa-1,3,5-triene (DPH). The fluorescence polarization of the probe was then measured when potentials of different magnitudes were induced across the membranes of these particles. It was shown that the absolute value of the microviscosity changes to quite a significant extent, owing to the imposition of large membrane potentials. On relaxation of the membrane potential the lipid microviscosity was also shown to return to the value before the induction of the potential. The largest change in lipid microviscosity was observed when coupled respiration was initiated. This occurred in both the COV system and the RLM system. The absolute value of the lipid microviscosity was shown to change by as much as 22% with the induction of membrane potentials, owing to respiration. To confirm the viscosity measurements made with DPH, lipid microviscosity was also measured with the spin-labelled fatty acid 5-doxyl stearate. Measurements of the order parameters indicated that, in agreement with the results of fluorescence experiments, viscosity changes occurred that were due to the induction of a membrane potential. The significance of these findings to the regulation of metabolism is briefly discussed, the main conclusion being that, although there is certainly a significant variation of lipid microviscosity with electric field, mechanistic interpretations will require further studies.