Complications of total temporomandibular joint replacement: a systematic review and meta-analysis

The aim of this systematic review was to determine the most prevalent complications resulting from total temporomandibular joint (TMJ) replacement. An electronic search was performed using the Embase, LILACS, MEDLINE (via PubMed), SciELO, Scopus, and Web of Science databases up to June 2022. Prospective and retrospective clinical studies on patients who underwent TMJ replacement were included. Two reviewers performed the study selection, data extraction, and individual risk of bias assessment using the Joanna Briggs Institute Critical Appraisal Tools. The pooled prevalence of each complication was calculated through a proportion meta-analysis using the random-effects model. Twenty-eight studies met the eligibility criteria and were included in the review. All of the eligible studies had a low risk of bias. The results of the meta-analysis revealed that the most prevalent complication was paresis or paralysis of the facial nerve branches (7.8%; 95% confidence interval (CI) 2.6-15.1%, I2 = 94.5%), followed by sensory alterations (1.8%; 95% CI 0.6-4.9%, I2 = 88.8%), heterotopic bone formation (1.0%; 95% CI 0.1-2.5%, I2 = 75.8%), and infection (0.7%; 95% CI 0.1-1.6%, I2 = 22.7%). In conclusion, TMJ replacement has a low prevalence of complications, and most of them can be managed successfully.

Impact of donor and prolonged cold ischemia time of neonatal pig pancreas on neonatal pig islet transplant outcome

BACKGROUND

Genetically modified pigs (GMP) have been developed to alleviate the shortage of donors in human islet transplantation and rejection. In this study, we characterized and compared the islets from GalTKO, GalTKO/hCD46, GalTKO/hCD46/hCD39, and wild-type (WT) neonatal pigs.

METHODS

Islets were isolated from GMP and WT pig pancreases that have been packaged with ice pack for at least 24 hours. The difference in gene expression and function of islets were evaluated by microarray analysis and transplantation of islets under the kidney capsule of streptozotocin-induced diabetic immune-deficient mice, respectively. Blood glucose levels of these mice were monitored weekly post-transplantation for >100 days, and islet grafts were collected and evaluated for the presence of endocrine cells.

RESULTS

The genes involved in extracellular components, cell adhesion, glucose metabolism, and inflammatory response are differentially expressed between GMP and WT pig islets. Variation in the ability of pig islets in correcting the diabetic state of the mouse recipients appears to be dependent on the pig donor. In addition, prolonged cold ischemia time had a negative effect on the transplant outcome. All normoglycemic mice were able to respond well to glucose challenge despite the initial differences in the ability of islet transplants to reverse their diabetic state. Islet xenografts of normoglycemic mice contained abundant insulin- and glucagon-positive cells.

CONCLUSION

The effect of GMP and WT neonatal pig islet transplants on hyperglycemia in mice appears to be dependent on the pig donor, and prolonged cold ischemia time negatively affects the neonatal pig islet transplant outcome.

Quantitative bone imaging biomarkers to diagnose temporomandibular joint osteoarthritis

Bone degradation of the condylar surface is seen in temporomandibular joint osteoarthritis (TMJ OA); however, the initial changes occur in the subchondral bone. This cross-sectional study was performed to evaluate 23 subchondral bone imaging biomarkers for TMJ OA. The sample consisted of high-resolution cone beam computed tomography scans of 84 subjects, divided into two groups: TMJ OA (45 patients with TMJ OA) and control (39 asymptomatic subjects). Six regions of each mandibular condyle scan were extracted for computation of five bone morphometric and 18 grey-level texture-based variables. The groups were compared using the Mann-Whitney U-test, and the receiver operating characteristics (ROC) curve was determined for each variable that showed a statically significance difference. The results showed statistically significant differences in the subchondral bone microstructure in the lateral and central condylar regions between the control and TMJ OA groups (P< 0.05). The area under the ROC curve (AUC) for these variables was between 0.620 and 0.710. In conclusion, 13 imaging bone biomarkers presented an acceptable diagnostic performance for the diagnosis of TMJ OA, indicating that the texture and geometry of the subchondral bone microarchitecture may be useful for quantitative grading of the disease.

Alpha-gal syndrome: Implications for cardiovascular disease

Alpha-gal syndrome (AGS) refers to a potentially life-threatening allergy to the molecule galactose-α1,3-galactose (gal), which is expressed on most mammalian tissues but, importantly, is not expressed by humans. This syndrome can manifest as an allergic reaction to mammalian meat products, but other sources of mammalian tissue can also provoke an immune response, including injectable and implantable medical products. This syndrome has been linked to coronary atherosclerosis, and medical products that express gal are routinely used in cardiology and cardiac surgery. This article seeks to discuss potential implications of alpha syndrome as it relates to cardiovascular health and to heighten awareness in the cardiovascular community about this emerging public health issue.

Asylum seekers’ healthcare in Italy: policies and practices among different regions

Background

The Italian law provides for international protection and universal health-care coverage for asylum seekers (AS). Indeed, they are entitled to be regularly registered at the National Healthcare Service. Before submitting the application for refugee status, medical assistance to migrants is up to local administration. Our aim was to describe and compare policies and protocols regulating AS healthcare from their arrival to their application for refugee status, at national and regional level. Moreover, we investigated the daily healthcare practice addressing potential gaps between policies and practice.

Methods

The research team is a subgroup of the Inequality working group of the Italian hygiene society and it is composed of public health residents. The research involved also local health workers and other professionals belonging to regional groups of Italian migrant medicine society (SIMM). We collected national, regional and local policies and protocols and we compared them using a specific framework. Furthermore, we achieved a mapping of daily practice implementation at local health organization (LHO) level using a checklist.

Results

The most relevant findings were that regional policies themselves vary notably from each other and, as regard practices, LHO implement differently the same regional legislation. Furthermore, we found some critical issues: the delayed inclusion in primary care assistance and lack of continuity of care and of a computerized system of recording information.

Conclusions

The lack of uniformity concerning policies and practices of AS healthcare might also result in unawareness and uncertainty about how to access to healthcare services by migrants. An enhanced cooperation between groups dealing with migrants’ issues may lead to avoid variability at the implementation. Finally, a computerized system for data collection might facilitate the continuity of care and the assessment of the real health needs of the AS population.

Key messages

It is a priority challenge for health systems to strengthen the interventions aimed at overcoming the linguistic, economic, cultural and administrative barriers to the health services access. It is crucial to improve the recording information system to detect the real health needs of AS, their change and the inequalities in access and to improve collaboration between groups and university.

Comparative Decellularization and Recellularization of Wild-Type and Alpha 1,3 Galactosyltransferase Knockout Pig Lungs: A Model for Ex Vivo Xenogeneic Lung Bioengineering and Transplantation

BACKGROUND

A novel potential approach for lung transplantation could be to utilize xenogeneic decellularized pig lung scaffolds that are recellularized with human lung cells. However, pig tissues express several immunogenic proteins, notably galactosylated cell surface glycoproteins resulting from alpha 1,3 galactosyltransferase (α-gal) activity, that could conceivably prevent effective use. Use of lungs from α-gal knock out (α-gal KO) pigs presents a potential alternative and thus comparative de- and recellularization of wild-type and α-gal KO pig lungs was assessed.

METHODS

Decellularized lungs were compared by histologic, immunohistochemical, and mass spectrometric techniques. Recellularization was assessed following compartmental inoculation of human lung bronchial epithelial cells, human lung fibroblasts, human bone marrow-derived mesenchymal stromal cells (all via airway inoculation), and human pulmonary vascular endothelial cells (CBF) (vascular inoculation).

RESULTS

No obvious differences in histologic structure was observed but an approximate 25% difference in retention of residual proteins was determined between decellularized wild-type and α-gal KO pig lungs, including retention of α-galactosylated epitopes in acellular wild-type pig lungs. However, robust initial recellularization and subsequent growth and proliferation was observed for all cell types with no obvious differences between cells seeded into wild-type versus α-gal KO lungs.

CONCLUSION

These proof of concept studies demonstrate that decellularized wild-type and α-gal KO pig lungs can be comparably decellularized and comparably support initial growth of human lung cells, despite some differences in retained proteins. α-Gal KO pig lungs are a suitable platform for further studies of xenogeneic lung regeneration.

Comparison of hematologic, biochemical, and coagulation parameters in α1,3-galactosyltransferase gene-knockout pigs, wild-type pigs, and four primate species

BACKGROUND

The increasing availability of genetically engineered pigs is steadily improving the results of pig organ and cell transplantation in non-human primates (NHPs). Current techniques offer knockout of pig genes and/or knockin of human genes. Knowledge of normal values of hematologic, biochemical, coagulation, and other parameters in healthy genetically engineered pigs and NHPs is important, particularly following pig organ transplantation in NHPs. Furthermore, information on parameters in various NHP species may prove important in selecting the optimal NHP model for specific studies.

METHODS

We have collected hematologic, biochemical, and coagulation data on 71 α1,3-galactosyltransferase gene-knockout (GTKO) pigs, 18 GTKO pigs additionally transgenic for human CD46 (GTKO.hCD46), four GTKO.hCD46 pigs additionally transgenic for human CD55 (GTKO.hCD46.hCD55), and two GTKO.hCD46 pigs additionally transgenic for human thrombomodulin (GTKO.hCD46.hTBM).

RESULTS

We report these data and compare them with similar data from wild-type pigs and the three major NHP species commonly used in biomedical research (baboons, cynomolgus, and rhesus monkeys) and humans, largely from previously published reports.

CONCLUSIONS

Genetic modification of the pig (e.g., deletion of the Gal antigen and/or the addition of a human transgene) (i) does not result in abnormalities in hematologic, biochemical, or coagulation parameters that might impact animal welfare, (ii) seems not to alter metabolic function of vital organs, although this needs to be confirmed after their xenotransplantation, and (iii) possibly (though, by no means certainly) modifies the hematologic, biochemical, and coagulation parameters closer to human values. This study may provide a good reference for those working with genetically engineered pigs in xenotransplantation research and eventually in clinical xenotransplantation.

Anti-gal antibodies in α1,3-galactosyltransferase gene-knockout pigs

Serum anti-galactose-α1,3-galactose (Gal) IgM and IgG antibody levels were measured by ELISA in α1,3-galactosyltransferase gene-knockout (GTKO) pigs (78 estimations in 47 pigs). A low level of anti-Gal IgM was present soon after birth, and rose to a peak at 4-6 m, which was maintained thereafter even in the oldest pigs tested (at >2 yr). Anti-Gal IgG was also present at birth, peaked at 3 m, and after 6 m steadily decreased until almost undetectable at 20 m. No differences in this pattern were seen between pigs of different gender. Total IgM followed a similar pattern as anti-Gal IgM, but total IgG did not decrease after 6m. The data provide useful baseline data for future experimental studies in GTKO pigs, e.g., relating to the antibody response to WT pig allografts.

The effects of multiple freeze-thaw cycles on the biomechanical properties of the human bone-patellar tendon-bone allograft

Soft tissue allografts, such as the bone-patellar tendon-bone (BPTB) graft, have been frequently used for anterior cruciate ligament (ACL) reconstruction. As allografts are subjected to freezing and thawing for multiple cycles, the objective of this study was to measure the changes of the biomechanical properties of the human BPTB allograft after 4 and 8 freeze-thaw cycles in comparison to a single freeze-thaw cycle. Three BPTB specimens were procured from 21 human donors and divided into three groups: 1, 4, or 8 freeze-thaw cycles. Each freeze-thaw cycle consisted of freezing at -20 ± 10°C for more than 6 h and thawing at 22 ± 3°C for at least 6 h. Tensile testing of the BPTB specimens consisted of loading between 50 N and 250 N for 100 cycles and then loading to failure. Cyclic loading revealed a similar amount of creep (∼0.5 mm) among the three freeze-thaw cycles groups (p = 0.38). The stiffness of the BPTB graft for the 1, 4, and 8 freeze-thaw cycle groups were 244 ± 42 N/mm, 235 ± 39 N/mm, and 231 ± 40 N/mm, respectively (p = 0.43). Similar findings were obtained for the ultimate load of the BPTB graft (p = 0.14) and the tangent modulus of the PT substance (p = 0.41). The results of this study suggest that there would be little measurable effect on the structural properties of the BPTB graft or mechanical properties of the PT tissue substance following 8 freeze-thaw cycles. These BPTB allografts could potentially be re-frozen without a loss in their biomechanical properties, given appropriate storage and care.

The cleansing of superficial traumatic wounds

Patients with skin injuries account for 15% of accident and emergency (A&E) admissions (Leaman, 1991). Although there is evidence to suggest that wound cleansing is not always necessary (Thomlinson, 1987), no diagnostic test exists to allow healthcare practitioners to identify whether the bacterial load in the wound is capable of causing infection (Chrisholm, 1992). For this reason, all wounds in A&E should undergo some form of cleansing to decrease the bacterial inoculum in the wound to levels that can be managed by host defences (Chrisholm, 1992). Heyworth (1997) postulates that successful management of the contaminated wound must remove contaminants while inflicting minimal injury to tissue. This article reviews the research on the preparation and cleansing of superficial lacerations. Wound closure and indications for oral antibiotics will not be discussed.

Allergic contact dermatitis in venous leg ulcer patients

Our aim was to determine the frequency and nature of contact sensitivity in venous leg ulcer patients in Lanarkshire. We performed patch testing with the European standard series, antimicrobials and medicaments on 200 patients referred to our leg ulcer clinics. Positive patch tests were found in 136 (68%) patients. Multiple allergies occurred in 102 (51%). The most frequent allergen groups were fragrances (30.5%), antimicrobials (19.5%), topical excipients (19.5%), rubber accelerators (13.5%) and topical corticosteroids (8%). We also found a high prevalence of positive patch tests to Intrasite gel (9.5%) and Hioxyl cream (8.5%), medicaments which are commonly used to treat leg ulcers in our area. Contact sensitivity is common in venous leg ulcer patients and has important implications for patient management. The allergens involved vary depending on local nursing practice. We suggest that all venous leg ulcer patients be patch tested with a locally relevant patch test series.

Use of rotational tomography for assessing internal resorption

The authors describe the use of tomography, a relatively simple and well-established radiographic technique, for determining the buccolingual extent of internal resorptive lesions. The procedure may be a useful adjunct in selected cases to determine whether root canal therapy for the treatment of internal resorption followed by restoration of the tooth is likely to be successful.

Cadexomer-iodine in the treatment of venous leg ulcers: what is the evidence?

Studies on the use of cadexomer-iodine in venous leg ulcers have found some evidence of its benefits over other treatments, but most are dated and some used products now contraindicated.

Iodoflex and Iodosorb in the treatment of venous leg ulcers

This article reviews the use of Iodoflex and Iodosorb in chronic venous leg ulcers. A description of prevalence and quality of life issues is given. Application and method of use of Iodoflex and Iodosorb in venous leg ulcers is then detailed along with relevant clinical evidence. A case study describes the use of Iodoflex in a difficult-to-heal venous leg ulcer.

In vivo, thyroid and lens surface exposure with spiral and conventional computed tomography in dental implant radiography

OBJECTIVE

To compare the surface dose exposure to the lens of the eye and the thyroid gland received by patients undergoing spiral and conventional computed tomography (CT) examinations during dental implant pretreatment evaluation in critical radiosensitive structures of the maxillofacial region.

STUDY DESIGN

Two groups of 10 patients each had a dental implant CT examination performed, with 5 patients in each group having maxillary and 5 having mandibular examinations. One group was examined with conventional CT and the other with spiral CT. Seven examination parameters were standardized to both types of examinations. Lithium fluoride thermoluminescent dosimeters were placed over the thyroid gland, lateral orbit, and infraorbital foramen of each patient to measure the surface dose. The Wilcoxon rank sum test was used to compare doses, with statistical significance set at P <.05.

RESULTS

For the maxillary examination, there was a 57.4% reduction in the surface dose at the lateral orbit, 47% at the infraorbital foramen, and 60.8% at the thyroid when spiral CT was used instead of conventional CT with the same parameters. Similarly, for the mandibular examination, there was a 57.4% reduction at the lateral orbit, 60% reduction at the infraorbital foramen, and 70.9% at the thyroid. All the dose reductions were statistically significant at P <.05.

CONCLUSION

The use of spiral CT for preimplant evaluation reduces the surface absorbed dose in certain critical structures of the maxillofacial region compared with conventional CT.

The management of a patient with lymphoedema of the legs

Lymphoedema is a much under-publicised condition, yet it affects many people. Janice Bianchi and Marie Todd outline the implications of the condition and examine the treatment options of a typical case study.

Pulse oximetry: a new tool to assess patients with leg ulcers

The objective of the study was to investigate pulse oximetry as a guide to assessing patients with leg ulcers before treatment. Graduated elastic compression is the treatment of choice for uncomplicated venous leg ulcers, but is contra-indicated in patients with significant arterial disease. The standard assessment of arterial insufficiency by Doppler ultrasound ankle branchial pressure index (ABPI) has shortcomings which prompted this investigation of pulse oximetry as a possible additional, or alternative, method of assessment of patients with leg ulcers, prior to treatment with compression. The study, carried out on a population of patients attending hospital leg ulcer clinics, was designed to evaluate pulse oximetry assessment in the selection and monitoring of patients with venous leg ulceration leading to a prospective controlled study of ulcer healing in groups of patients with reduced and normal ABPI, selected for compression therapy by pulse oximetry criteria. Outcome measurement required follow-up of patients selected for compression therapy by pulse oximetry to record time to healing and rate of healing of leg ulcers. Results from the study show a fair correlation between the toe-finger oximetry index (TFOI) and Doppler ABPI. There is no difference between ulcer healing in patients with reduced and normal ABPI selected for treatment on the basis of pulse oximetry maximum compression pressure (MCP). In conclusion, pulse oximetry is an aid to the selection of patients who will benefit from compression therapy, but would be excluded on the basis of Doppler ABPI.

The management of leg ulcers in a patient with B cell cutaneous lymphoma

Some patients suffer the consequences of skin ulceration more severely than others. Patients with B cell cutaneously lymphoma are one such group and this article reviews their special needs.

Cortical photostimulation with filtered visible light as a treatment for rheumatoid arthritis

Not all extraocular photoreceptors in the human brain have been identified or their functions determined. The efferent and afferent fibres between the orbital frontal cortex and the hypothalamus cannot be overlooked in the context of the neuro-endocrine-immune feedback loop. It is suggested here that there are extraocular photoreceptors in the orbital frontal cortex, conceivably crucial for immunoregulation. The orbital frontal cortex of 7 volunteers with rheumatoid arthritis (RA) was photostimulated through the roof of the orbits with filtered visible light in sessions of 12, 14 and 16 minutes for a period of 6 weeks. Within 5 weeks, a significant decrease in the rheumatoid factor titres of 6 subjects was observed together with marked clinical improvement in 4 cases.

The gluteal compartment syndrome

The gluteal compartment syndrome is a rare, often unrecognized condition which, left untreated, can lead to renal failure, sepsis, and death. The etiology, physiology, and manifestations are similar to those seen in the more common and readily recognized compartment syndromes of the lower leg and forearm. The large gluteal muscle mass confined by the fascia lata of the thigh and tensor fascia lata can, under the right conditions, produce muscle necrosis, acidosis, elevations of creatinine phosphokinase, and ultimately renal failure. A gluteal compartment syndrome most commonly occurs in individuals with an altered mental status due to drugs or alcohol who remain in one position for an extended period of time. This prolonged compression leads to muscle damage, edema, and a full-blown compartment syndrome. Due to its anatomic location and rarity, diagnosis is missed or delayed, resulting in significant morbidity and possible mortality. The mainstay of treatment consists of fasciotomy and debridement.

Phenol red is a thromboxane A2/prostaglandin H2 receptor antagonist in canine lingual arteries and human platelets

Phenol red (PR) is used as a pH indicator in cell culture medium. We found that cell culture medium containing PR relaxed canine lingual arteries (LA) contracted by the thromboxane A2/prostaglandin endoperoxide (TPE) receptor agonist (15S)-hydroxy-11-alpha-9-alpha- (epoxymethano)prosta-5Z,13E-dienoic acid (U46619). We tested the effect of PR and the TPE receptor antagonist ONO-3708 on U46619, prostaglandin F2 alpha (PGF2 alpha), phenylephrine (PE) and potassium chloride (KCl)-induced contraction of the LA and on human platelet aggregation to U46619, ADP, arachidonic acid (AA), A23187 and thrombin. U46619, PGF2 alpha, KCl and PE produced equal tension development of the LA. PR relaxed the LA contracted with U46619 and PGF2 alpha with IC50 concentrations of 18.3 +/- 10 and 37.3 +/- 8.8 microM, respectively. ONO-3708 inhibited the contractions to U46619 and PGF2 alpha with IC50 of 9.4 +/- 2.2 and 12.2 +/- 2.2 nM, respectively. However, PR (300 microM) and ONO-3708 (300 nM) did not affect contraction of the LA to KCl or PE. PR inhibited human platelet aggregation, in vitro, to AA and U46619 and second wave aggregation to ADP but did not affect thrombin or first wave ADP-mediated platelet aggregation. PR inhibited U46619 and AA-induced changes in cyclic AMP and Fura-2 calcium transients in platelets and LA. However, PR did not affect the activation of cyclic AMP or intracellular calcium ion in platelets or calcium influx and the release of intracellular calcium ion in canine LA produced by ryanodine, KCl and PE. The concentration of PR in many culture media is between 40 and 70 microM. The data support the conclusion that PR, in concentrations used as a pH indicator, is a selective antagonist of TPE receptors.

Biologic esthetic restorations

Cases of serious coronal destruction were treated by bonding parts of extracted teeth to the coronal remnants by means of adhesives and photo-activated composite resins. The long-term clinical results have revealed very satisfactory clinical performance of the compounded restorations. No detrimental effects have been identified.

Restoration of severely damaged teeth with resin bonding systems: case reports

In cases of severe coronal destruction, conventional dentistry must resort to complex techniques and combinations of prosthetic materials. In addition, execution and placement of the restoration results in more destruction of sound dental tissue. This paper presents an alternative technique that utilizes the adhesive capabilities of new materials in combination with strategic placement of parts of extracted human teeth to achieve better esthetics and more conservation of sound dental tissue.

Determination of infundibular innervation and amine receptor content in cyanotic and acyanotic myocardium: relation to clinical events in tetralogy of Fallot

Right ventricular myocardium was assessed for cholinergic and adrenergic innervation, as well as alpha-adrenergic, beta-adrenergic, and muscarinic receptors, in 18 cyanotic patients with tetralogy of Fallot (TOF) and four acyanotic control patients with ventricular septal defect, each of whom underwent a cardiac repair from June through December 1987. Neurons containing acetylcholine (ACH), neuron-specific enolase (NSE), S-100 protein, neuropeptide-Y (NPY), dopamine-beta-hydroxylase (DBH), and calcitonin gene-related polypeptide (CGRP) were detected surrounding arterioles and myocytes in all specimens. NSE and S-100 immunoreactivities were also identified in the cytoplasm of TOF cardiocytes, possibly indicating a neuroendocrine origin of these cells. Cardiocyte size was increased in TOF (p = 0.05). Acetylcholine (cholinergic) (p = 0.04) and CGRP (cholinergic) positive neurons (p = 0.07) were decreased in the TOF as compared to controls. Adrenergic fiber content (p = 0.15) and beta receptors (p = 0.21) were similar in both groups. There was an increase in muscarinic receptors in the controls (p = 0.002), and a marked increase in alpha receptors in TOF (p = 0.019). There were no intragroup differences in the TOF patients according to degree of cyanosis. In conclusion, there were important differences in neuronal and amine receptor content between TOF and control patients. Increased alpha receptors in TOF could account for differences in clinical and hemodynamic events.

A comparison of the electrophysiologic effects of acute and chronic amiodarone administration on canine Purkinje fibers

The electrophysiologic effects of acutely and chronically administered amiodarone on canine Purkinje fibers were assessed using microelectrode techniques to record intracellular action potentials. Chronically treated dogs received amiodarone for 3 weeks (serum levels, 0.91 +/- 0.09 microgram/ml or 1.42 X 10(-6) M). Acute studies were performed using fibers from untreated dogs superfused for 1 h with 5 X 10(-5) M amiodarone (32 micrograms/ml) in Tyrode's solution (KCl = 4 mM). Acute superfusion shortened the action potential duration to 50 and 90% repolarization by 41 and 8%, respectively (p less than 0.01), and decreased Vmax of phase 0 from 418 +/- 20 to 309 +/- 23 V/s (p less than 0.01) (paced cycle length of 500 ms). Prominent use-dependent depression of Vmax was noted. Acute exposure of fibers from untreated dogs to blood from dogs chronically treated with amiodarone using the blood cross-perfusion technique decreased the action potential duration to 50% repolarization and Vmax, similar to acute exposure in Tyrode's solution. Blood cross-perfusion was used to study fibers from treated dogs superfused with blood from another amiodarone-treated dog. Chronic amiodarone prolonged the action potential duration to 90% repolarization by 13% (p less than 0.02) and did not change Vmax when compared to control studies using fibers obtained from untreated dogs superfused with blood from untreated dogs. Thus, the effects of acutely superfused amiodarone on action potentials of canine Purkinje fibers differ from the effects of chronically administered amiodarone.

A canine model to assess the electrical stability of the transplanted heart

The electrophysiological stability of the transplanted heart under conditions of myocardial ischemia is largely unknown. This problem was studied using a canine model of total cardiac denervation as a substitute for transplantation. Group 1 (N = 3) served as control with placement of ventricular pacing wires only. Group 2 (N = 3) underwent total cardiac denervation with placement of ventricular wires. Group 3 (N = 8) underwent total cardiac denervation with subsequent ligation of the left anterior descending coronary artery and collaterals to the apex. Group 4 (N = 9) underwent coronary artery ligation only. Chronic electrophysiological studies were conducted in all groups in the conscious state. Electrophysiological variables were determined from continuous Holter monitoring of the ECG, determination of strength-interval curves, and assessment of the inducibility of ventricular tachycardia by premature programmed pacing. In general, the denervated, infarcted group (Group 3) consistently demonstrated a greater level of electrical stability than the infarcted animals with normal innervation (Group 4).

Total denervation stabilizes the infarcted canine myocardium

The effect of total cardiac denervation upon the electrophysiology of infarcted canine myocardium was studied at both organ and cellular levels. Fifteen dogs underwent coronary ligation to produce an infarct at the apex of the left ventricle (Group 1, n = 15). A second group of dogs (Group 2, n = 14) underwent total intrapericardial denervation with subsequent infarct 15.0 +/- 0.3 (mean +/- SEM) days later. All animals had bipolar epicardial pacing electrodes placed on the right ventricle and the infarct border zone of the left ventricle. Strength-interval curves were performed one or two times per week in conscious animals to assess cardiac excitability. Animals were sacrificed 18.1 +/- 0.5 days following infarct and histologic studies were performed to determine infarct size. Standard microelectrode techniques were also utilized to determine cellular parameters. Denervation was found to lengthen the absolute refractory period and prevent increases in the relative refractory period which were observed in innervated animals following infarct. Isolated tissue data including measurements of maximal rate of depolarization, mean diastolic potential, action potential amplitude, action potential duration at 50% repolarization, and effective refractory period indicated that denervation protects against cellular deterioration and improves electrophysiologic cellular characteristics. These studies suggest that under conditions of myocardial ischemia, denervation produces an electrically more stable myocardium which is less excitable and probably less vulnerable to lethal arrhythmias.

Dehydroascorbic acid and cell membranes: possible disruptive effects

Exposure of cellular membranes to dehydroascorbic acid can result in a loss of membrane integrity. Renal brush border or basolateral membrane vesicles pre-incubated with dehydroascorbic acid demonstrate a decrease in initial transport rates of D-glucose and a loss of intravesicular volume. The activity of brush border membrane specific leucine aminopeptidase is increased in vesiculated membrane preparations following exposure of the vesicles to either dehydroascorbic acid or Triton X-100. Erythrocytes in isotonic buffer with dehydroascorbic acid lose membrane integrity as demonstrated by a release of hemoglobin.

Dehydroascorbic acid and ascorbic acid transport systems in the guinea pig ileum

The transport properties of dehydroascorbic acid and ascorbic acid in membrane vesicle preparations of guinea pig ileum were evaluated. Na-dependent transport of ascorbic acid in the brush-border membrane was confirmed, and an Na-independent mechanism was found in the basolateral membrane. The electrically neutral oxidized form of vitamin C is transported by an Na-independent mechanism at both cell surfaces. Transport of each substrate is saturable and exhibits cis-inhibition and trans-stimulation in the presence of structural analogues. Additional studies on ascorbate metabolism will be necessary to support a comprehensive model of intestinal handling of vitamin C.

Glucose-independent transport of dehydroascorbic acid in human erythrocytes

It has been previously reported that glucose and its structural analogs inhibit dehydroascorbic acid (DHA) transport across the membranes of nonpolar cells, which led to the suggestion that the hexose transporter mediates dehydroascorbic acid transport. The present study examines the role of the erythrocyte hexose transport system in dehydroascorbic acid uptake. We have confirmed that dehydroascorbic acid may be a ligand of the hexose transport system under certain experimental conditions. However, there is an additional pathway of dehydroascorbic acid transport that is uninfluenced by external glucose. This pathway is one of facilitated diffusion, demonstrating saturation kinetics of transport, cis-inhibition, and trans-stimulation. The Km for the system is 412 microM. It is suggested that this previously undescribed sugar-independent transporter is the physiologically important route of DHA uptake in erythrocytes.

Effective use of renal cortical slices in transport and metabolic studies

The uptake and metabolism of two water-soluble vitamins were measured in rat renal cortical slices, isolated tubules, and vesicles of the brush-border and basolateral cell membranes to determine (a) whether it is possible to produce slices that have open tubules and, (b) whether slices and tubules metabolize vitamins similarly. Transport of ascorbic acid is sodium-dependent in slices and in brush-border vesicles but is sodium-independent in basolateral vesicles, suggesting that the brush-border membrane of slices is accessible to components of the bathing solution. Nicotinic acid was metabolized similarly (97-98%) in both slices and isolated tubules. Oxygen consumption by slices maintained in a closed chamber was constant as pO2 decreased from 88% to 58%. Slices are concluded to be a suitable model for transport and metabolic studies providing that care is taken in their preparation and use.

Transport of L-ascorbic acid and dehydro-L-ascorbic acid across renal cortical basolateral membrane vesicles

The uptake of L-ascorbic acid and dehydro-L-ascorbic acid into renal cortical basolateral membrane vesicles has been characterized. The uptake systems for both solutes demonstrate saturation kinetics. The presence of structural analogs of L-ascorbic acid and dehydro-L-ascorbic acid results in cis-inhibition and trans-stimulation. Uptake of each substrate is Na+-independent, proceeding to an endpoint of substrate equilibrium across the vesicular membrane. The transport mechanism(s) for L-ascorbic acid and dehydro-L-ascorbic acid appears to be facilitated diffusion.

Na+-independent dehydro-L-ascorbic acid uptake in renal brush-border membrane vesicles

A membrane preparation enriched in the brush-border component of the plasma membrane was isolated from rat renal superficial cortex by a divalent cation precipitation procedure. Uptake of dehydro-L-ascorbic acid, the oxidized form of L-ascorbic acid, by the brush-border membrane vesicles was studied. The uptake mechanism was found to be sodium-independent and insensitive to the trans-membrane electrical potential difference. Uptake was saturable and subject to cis-inhibition. Concentrative uptake was demonstrated only under conditions of trans-stimulation by structural analogs. The results suggest a mechanism of facilitated diffusion for the uptake of dehydro-L-ascorbic acid in renal brush-border membranes.

Tachycardia and apparent sino-atrial block due to concealed sinus node re-entry

The role of the middle intercaval area ("internodal pathway") in the genesis of atrial re-entry was studied using microelectrode techniques and the extrastimulus method in the rabbit heart. Following surgical interruption of the anterior and posterior internodal tracts, two patterns of re-entry were observed using the middle internodal pathway manifesting alternatively as tachy- and brady-arrhythmias. Re-entry which was produced by critically timed extrastimulation at the septal branch of the crista terminalis (CT) caused tachycardia reciprocating between the sinus node (SN) and intercaval area. Spontaneous re-entrant impulses were also observed, particularly following the addition of cedilanid (0.04 mg/L). In addition, in association with critical prolongation of conduction in the sino-septal area, premature discharge of the dominant pacemaker fibers was observed and resulted in the appearance of bradyarrhythmias. These were commonly manifest as bigeminy and trigeminy on the surface septal electrogram. Hence concealed sinus node re-entry could manifest itself as apparent sino-atrial block or sino-atrial re-entry tachycardia.

Atrioventricular nodal conduction during atrial fibrillation in rabbit heart

Atrial fibrillation was induced in 15 superfused rabbit atrial-atrioventricular nodal preparations in which surface bipolar electrograms were recorded simultaneously from the crista terminalis, interatrial septum, and His bundle along with microelectrode action potentials from cells in the atrionodal (AN), nodal (N), and nodal-His (NH) regions of the atrioventricular node. Effective engagement of the atrioventricular node with propagation to the His bundle was critically dependent on the relative timing of activation at the crista terminalis and interatrial septal input regions of the atrioventricular node. Conduction through the AN and N regions appeared dependent on the relative timing of activation wave fronts emerging from the two input regions. Asynchronous engagement of AN and N regions resulted in both distortion of action potentials and concealed conduction, with delayed conduction and block to the NH region and His bundle. Successful engagement of the NH region always produced a 1:1 NH-to-His bundle relationship. It is concluded that during atrial fibrillation 1) activation of the AN region occurs as a result of the variable interaction of inputs from the crista terminalis and interatrial septum; 2) predictably, effective synchronous engagement of the AN and consequently the N region is responsible for conduction to the NH and His bundle regions; 3) conversely, asynchronous activation inputs from the crista terminalis and interatrial septum result in fragmented, asynchronous as well as concealed conduction within the AN and N regions with block in the atrioventricular node and variable conduction to the His bundle.

Conduction disturbances in the middle internodal tract of the rabbit heart

Conduction properties between the sinus node and the septal branch of the crista terminalis, the so-called middle internodal tract, were studied in the isolated rabbit right atrium. Recordings were obtained from two simultaneously impaled microelectrodes using the extrastimulation technique after cutting the anterior and posterior internodal tracts. Several types of conduction block were observed associated with steplike prepotentials and distortions of perinodal fibers in the absence of pharmacological intervention. Prolongation of sino-septal conduction time occurred with decreasing coupling intervals. The return cycle of the atria gradually increased with prolongation of the retrograde conduction time of premature impulses to the SN until entrance block was seen. Several observations in this data demonstrate the influence of concealed or manifest retrograde conduction into the perinodal fibers of the sinus node after premature stimulation of the atria, as critical delay within the perinodal region could alter conduction time of the premature depolarization, reset the sinus node, and influence subsequent antegrade conduction alone or in various combinations.