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PubMed1990

Effects of ouabain and EGTA on the inhibitory effect of Ca2+ on guinea pig stomach smooth muscle ('Ca reversal').

Guinea pig stomach smooth muscle is known to show sustained contraction when treated with carbachol (CCh) in Ca-free solution containing 2 X 10(-3) M EGTA ('Ca-free contraction'). After pretreatment of the muscle with a Ca antagonist (D-600, nicardipine or nifedipine), addition of 10(-4) M Ca2+ (pCa 4.0) relaxed this CCh-induced Ca-free contraction ('Ca reversal'), but without pretreatment with a Ca antagonist, Ca2+ evoked contraction. In a Ca buffer containing 2 X 10(-3) M EGTA, low concentrations of Ca2+, 10(-8)-3 X 10(-7) M (pCa 8.0-6.5), relaxed the Ca-free contraction dose dependently ('Ca reversal'), whereas concentrations higher than 10(-6) M Ca2+ (pCa 6.0-) reversed this relaxation back to contraction. EGTA at 5 X 10(-3) or 10(-2) M potentiated the Ca reversal, whereas no reversal occurred in a Ca buffer containing 10(-3) M EGTA. This Ca reversal was inhibited in K(+)-depleted, Ca-free solution and by ouabain in Ca buffer containing EGTA (5 X 10(-3) or 10(-2) M). These results show that Ca reversal of guinea pig stomach smooth muscle occurs at low concentrations of Ca2+ and that its mechanism is related to ouabain-sensitive processes, such as the function of Na(+)-K+ ATPase.

Animals↗
PubMed1986

Biochemical heterogeneity of reverse transcriptase purified from the AIDS virus, HTLV-III.

The reverse transcriptase from AIDS virus, HTLV-III, was purified and characterized. The purified enzyme has a very high affinity for template primers (rC)n X (dG)12 and (rCm)n X (dG)12 compared to that for (rA)n X (dT)12. In addition, the HTLV-III reverse transcriptase was able to transcribe (rAm)n X (dT)12 very efficiently. The ionic requirements are unique in the sense that HTLV-III reverse transcriptase prefers Mg2+ as divalent ions to transcribe (rC)n X (dG)12 and (rA)n X (dT)12. The Mr of the enzyme is 95 000-98 000. Unlike the HTLV-I reverse transcriptase, the HTLV-III enzyme is highly stable and has a much higher activity in the presence of (rC)n X (dG)12; the Vmax for HTLV-III reverse transcriptase is several-fold higher than that for HTLV-I enzyme. The enzyme activity of the purified reverse transcriptase from HTLV-III was resolved into two peaks on a preparative isoelectric column, one at pH 5.75 and the other at pH 6.25. This leads us to conclude that the reverse transcriptase of HTLV-III is biochemically heterogeneous.

Cations, Divalent↗
PubMed1994

Resulting long-term intestinal motility in dogs following construction of a reversed jejunal segment after extensive small bowel resection.

To evaluate the long-term function and effective motility of a reversed jejunal segment after extensive small bowel resection, the authors continuously measured postoperative bowel motility during interdigestive and postprandial periods in conscious dogs 6 to 10 months after surgery. The long-term findings were compared with previously reported short-term results measured 2 to 4 weeks after the operation. In the long-term follow-up dogs with a 20-cm reversed jejunal segment constructed after extensive (75% to 80%) small bowel resection, the fasting duodenal migrating myoelectric (or motor) complex (MMC) was often interrupted in the jejunum above the reversed segment, and did not migrate smoothly to the reversed segment or terminal ileum. The MMCs arising from the duodenum predominantly propagated to the ileum through the inherent anatomic continuity of the bowel. In addition, brief small discordant contractions were frequent in the reversed segment and the jejunum, above the proximal anastomosis. These findings are similar to those of the MMC propagation pattern noted 2 to 4 weeks after surgery. However, the postprandial duration without duodenal MMC activity was significantly shorter in the dogs with long-term follow-up than in those with short-term follow-up (both were longer than in control dogs). Marked dilatation of the jejunum and reversed jejunal segment was noted across the proximal anastomosis. These results suggest that the transit time and passage of intestinal contents can be delayed and stagnated for at least 10 months after extensive small bowel resection with a 20-cm reversed jejunal segment.(ABSTRACT TRUNCATED AT 250 WORDS)

Anastomosis, Surgical↗
PubMed1992

Effects of various chemical compounds on spontaneous and hydrogen peroxide-induced reversion in strain TA104 of Salmonella typhimurium.

In experiments designed to determine which active oxygen species contribute to hydrogen peroxide (HP)-induced reversion in strain TA104 of Salmonella typhimurium, 1,10-phenanthroline (an iron chelator, which prevents the formation of hydroxyl radicals from HP and DNA-bound iron by the Fenton reaction), sodium azide (a singlet oxygen scavenger), and potassium iodide (an hydroxyl radical scavenger) inhibited HP-induced reversion. These results indicate that hydroxyl radicals generated from HP by the Fenton reaction, and perhaps singlet oxygen, contribute to HP-induced reversion in TA104. However, reduced glutathione (reduces Fe3+ to Fe2+ and/or HP to water), diethyldithiocarbamic acid (an inhibitor of superoxide dismutase), diethyl maleate (a glutathione scavenger), and 3-amino-1,2,4-triazole (an inhibitor of catalase) did not inhibit HP-induced reversion in TA104. Thus, superoxide radical anions and HP itself do not appear to be the cause of HP-induced reversion in this strain. In experiments on the effect of 5 common dietary compounds (beta-carotene, retinoic acid, and vitamins A, C and E), chlorophyllin (CHL), and ergothioneine, the frequency of revertants in TA104 increased above the spontaneous frequency in the presence of beta-carotene or vitamin C (about 2-fold) or vitamin A (about 3-fold). The 5 dietary antimutagens and CHL did not inhibit HP-induced reversion in TA104. However, L-ergothioneine inhibited HP-induced reversion in this strain. Therefore, it is likely that L-ergothioneine is a scavenger of hydroxyl radicals or an inhibitor of their formation, and perhaps of singlet oxygen, at the concentrations tested in TA104.

Ascorbic Acid↗
PubMed1985

Flicker and movement constituents of the pattern reversal response.

A counterphase-modulated (i.e. contrast reversing) pattern will affect hypothetical neural elements sensitive to motion as well as hypothetical elements sensitive to changes in contrast and other elements sensitive to local luminance. Attempts to describe visual evoked potentials (VEPs) to contrast reversal entirely in terms of luminance change or entirely in terms of contrast change have been unsuccessful; strong interactions between responses to contrast decrease and increase had to be postulated ad hoc in order to account for the contrast reversal VEP, and no explanation for these interactions has been proposed. Rather than attempting to separate the reversal VEP into responses to contrast decrease and increase, we attempt here to analyze the reversal VEP into responses to motion onset and offset. We find that VEPs to an abrupt displacement of less than one square's width of a checkerboard pattern are qualitatively similar to the contrast reversal VEP, and that the displacement VEP can be seen as the limiting case of a motion onset response shortly followed by a motion offset response. When displacement occurs during steady motion, the displacement and motion responses interact. We conclude that the contrast reversal VEP is better described in terms of motion onset and offset response than in terms of contrast onset and offset responses.

Adaptation, Ocular↗
PubMed1987

Reversal of opioid-induced muscular rigidity in rats: evidence for alpha-2 adrenergic involvement.

Compounds from several different pharmacological classes were tested for their ability to reverse the muscular rigidity induced by an intravenous dose of fentanyl that also caused loss of the righting reflex (LOR). Opioid antagonists reversed the entire syndrome--LOR and rigidity but, generally, rigidity could be reversed nonspecifically by doses of compounds that caused LOR by themselves (e.g., CNS depressants). Muscle relaxants and agonists of histamine, which appeared to be acting peripherally, were also effective. On the other hand, serotonergic drugs and dopamine agonists were not. However, dopaminergic antagonists with adrenolytic activity (i.e., chlorpromazine, haloperidol) reversed rigidity, whereas sulpiride did not. Moreover, rigidity reversed by neuroleptics could be restored by piperoxane, an alpha-2 adrenergic antagonist. In addition, clonidine and other alpha-2 agonists selectively reversed only rigidity following systemic or central administration at doses several orders of magnitude lower than other compounds tested. It is proposed that opioid-induced rigidity is reversed by inhibition of sympathoadrenal outflow which can be accomplished selectively, centrally, by alpha-2 agonists.

Adrenergic alpha-Agonists↗
PubMed1992

Incomplete reversibility of an experimentally induced hypocholinergic state: biochemical and physiological, but not behavioral, recovery.

In previous reports, we described the experimental development of a hypocholinergic state in rats following the total replacement of dietary choline by an artificial isostere, N-aminodeanol (NADe). NADe shares most of the physicochemical and biochemical characteristics of choline (Ch) but is utilized less efficiently in pathways leading to the formation of both acetylcholine and phospholipids. This experimental model mimics many of the features of human degenrative dementias. We now discuss the behavioral and physiological effects of restoring a normal diet after the hypocholinergic state has become well established. The procedure by which that state was induced has been described in detail in earlier publications. After replacing Ch in the diets of weanling rats for 270 days, NADe replaced 70-85% of the phospholipid-bound Ch in plasma, brain, and peripheral tissue. When dietary NADe was removed and Ch was restored in the diet, NADe disappeared and plasma and erythrocyte (RBC) choline levels returned to normal within 30-60 days. Quinuclidinyl benzilate (QNB) binding showed that muscarinic receptors continued to be depressed in animals remaining on the NADe diet, but returned to control levels in the reversal group. There were no differences in cholinesterase activity among the three treatments. Choline acetyltransferase activity returned to control levels, while continuing to be lower in the NADe animals. Liver lipids were elevated in the latter and not significantly different in the control and reversal groups. Among physiological functions, body weight increased more rapidly in the reversal group than in animals continuing on the NADe diet. Brain weights of the reversal animals were significantly greater than those of animals not reversed, but less than controls. Core body temperatures did not differ from controls at any time during the reversal period. Behaviorally, nociceptive thresholds indicative of sensory-reflexive and sensory-perceptual responses remained significantly below normal, that is, a hyperalgesic state. Reversal animals also remained hyperactive and displayed memory significantly poorer than those on the normal diet, that is, no improvement over animals continuing on NADe. In general, the results suggest that behavioral losses induced by NADe reflect persisting changes in the CNS, despite essentially complete recovery of biochemical parameters. The changes may be morphological or be associated with adaptive changes in other neurochemical events in the CNS.

Animals↗
PubMed1989

Reversion to normal phenotype induced by SV40 in a spontaneously transformed malignant Chinese hamster cell line.

By using a selection procedure that excluded the transforming effect of SV40, reversions to several properties of normal phenotype were for the first time obtained in a transformed Chinese hamster cell line after SV40 infection. The value of induction to recovery of contact inhibition was typical for SV40-induced reverse gene mutations. Thirteen of 15 isolated revertant clones were T-antigen positive, thus synthesizing the product of viral oncogene. Therefore, in the majority of clones reversion occurred in spite of the presence of viral transforming protein. Dot hybridization revealed the presence of SV40 DNA in all revertants including those expressing no T antigen. The virus rescued from one T-antigen positive and two negative clones proved to be infectious. Reversion to contact inhibition was followed by reversion as regards serum requirements and growth in soft agar. However, in all cases reversion was partial. Karyologic analysis of revertant clones showed that six clones maintained the hypodiploid karyotype of the parental clone, six revertants were near-tetraploid, and one was near triploid. The possible events underlying the SV40-induced reversions to normal phenotype and the role of virus-induced mutations in viral carcinogenesis are discussed.

Animals↗
PubMed1988

Murine cytomegalovirus binds reversibly to mouse embryo fibroblasts: implications for quantitation and explanation of centrifugal enhancement.

In a study of the infection of mouse embryo fibroblasts with murine cytomegalovirus (MCMV), we found that plaque number is directly related to virus concentration and not to the total amount of virus contained in the inoculum. These results suggested that virus binding was reversible and that during infection a binding equilibrium is established which limits the amount of bound virus. Further analysis revealed three categories of plaque based on reversibility after virus adsorption. One group was removed simply by washing cell monolayers after virus removal. A second group of plaques was lost gradually with time, giving complete reversal after 5 min at 37 degrees C. The rate of reversal was temperature dependent, and probably represented true virus dissociation. The final group was irreversible plaques, the number of which increased with increasing infection time. The number of reversible plaques remained constant with time of infection, and represented about 70% of the total plaques after 1 h of virus adsorption. Centrifugation of the virus inoculum onto the fibroblast monolayer at 1000 X g increased plaque numbers up to 100-fold, but had little effect on plaque number when carried out after the virus inoculum was removed. In contrast centrifugation increased the number of reversible plaques, suggesting an increase in the number of virus particles attached to the cell monolayers. We suggest that centrifugation enhances MCMV infection by three mechanisms related to reversibility of binding: (1), it increases the rate of virus association; (2), it decreases the rate of dissociation; (3), by increasing the length of time each virus particle is bound it increases the probability of virus being taken into the cell.

Adsorption↗
PubMed1983

Follitropin binding to receptors in testis: studies on the reversibility and thermodynamics of the reaction.

Studies were designed to assess the extent to which binding of follitropin (FSH) to its receptor is a reversible process. [125I]hFSH was allowed to interact with membrane receptors from calf testis for 2 h at various temperatures by which time significant specific binding of [125I]hFSH had taken place in all instances. Unlabeled FSH was then added (delayed addition) and the amount of [125I]hFSH remaining bound was monitored as a function of time. In order to assess reversibility, [125I]hFSH binding in the latter samples was compared to that occurring when unlabeled FSH had not been added or when unlabeled FSH was present from the start of the incubation. Binding was essentially fully reversible at 4 degrees C, but reversibility decreased with increasing temperature. Reversibility of FSH binding decreased markedly at temperatures greater than 26 degrees C and was considered irreversible at temperatures above 30 degrees C. At 4 degrees C essentially full reversibility (greater than 90%) was observed when the unlabeled hormone was added after 7 h of incubation, but decreased when added after 12 h. At warmer temperatures (22 or 30 degrees C) 'there was a progressive decrease in reversibility as the time of delay before addition of unlabeled hormone was lengthened. By determining the affinity constant (in separate experiments) at various temperatures, a thermodynamic analysis was possible. This analysis was restricted to the temperature range 4-26 degrees C in order to minimize complications arising from irreversible binding. The reaction was endothermal at low temperatures (T less than 12.5 degrees C) and exothermal at higher temperatures (T greater than 12.5 degrees C) and was associated with a decrease in heat capacity of 1800 cal [mol deg]-1 at 25 degrees C. The results are consistent with the concept that the hydrophobic effect plays an important role in FSH binding, but that the reaction is complex and may be composed of more than one step.

Animals↗
PubMed1993

Reversed closure sequence of the mitral and tricuspid valves in congestive heart failure.

OBJECTIVES: The purpose of this study was to evaluate functional and hemodynamic factors that determine the mitral-tricuspid and aortic-pulmonary valve closure sequence in patients with dilated cardiomyopathy. BACKGROUND: The physiologic factors determining closure sequence of cardiac valves in various forms of heart disease have been found to be complex. Few data exist for dilated cardiomyopathy, particularly for differentiating the effects of a conduction delay versus changes in ventricular performance. METHODS: A group of 64 patients were compared with 36 control subjects. Timing of valve closure and electromechanical intervals were determined by combined M-mode echocardiography, phonocardiography and apexcardiography. Hemodynamic data from right heart catheterization were available in 46 patients. RESULTS: In all control subjects, the aortic valve closed before the pulmonary valve and the mitral valve closed before the tricuspid valve. In the study group, 30 patients (49%) had reversed aortic-pulmonary valve closure and 27 (90%) of these had a left-sided conduction delay. There were 38 patients (60%) who had reversed mitral-tricuspid valve closure, but this was unrelated to the presence of a left-sided conduction delay. The presence of high ventricular filling pressures and poor systolic function was associated with delayed closure of both the mitral and the tricuspid valve. This caused the closure sequence to be related to the size of the difference between mean pulmonary artery wedge pressure and mean central venous pressure and also the magnitude of right ventricular dysfunction. Patients with a low wedge pressure (< 16 mm Hg) and a low central venous pressure (< 10 mm Hg) had a low prevalence of mitral-tricuspid valve closure reversal (30%). Those with a high wedge pressure (> 16 mm Hg) but a low central venous pressure had a high prevalence (86%) of reversal of mitral-tricuspid valve closure. Patients with high wedge and central venous pressures had a moderate prevalence (47%) of mitral-tricuspid valve closure reversal. Similar findings were observed for right ventricular dysfunction. If the right ventricle was normal or severely dysfunctional, a reversed closure sequence was less common (52% and 41%, respectively) than if moderate dysfunction was present (78%). CONCLUSIONS: Aortic-pulmonary valve closure sequence is strongly related to the presence of a left-sided conduction delay. The mitral-tricuspid valve closure sequence is unrelated to a conduction delay but can be reversed by relative differences in the severity of systolic dysfunction and filling pressures between the two ventricles.

Adolescent↗
PubMed2006

Surgical management of twin reversed arterial perfusion sequence.

OBJECTIVE: The purpose of this study was to review our experience in the management of twin reversed arterial perfusion sequence to derive management recommendations. STUDY DESIGN: All patients with twin reversed arterial perfusion sequence who were seen for consultation between 1993 and 2004 were studied. Criteria for umbilical cord occlusion included abdominal circumference of the twin reversed arterial perfusion fetus that was more than or equal to the pump twin, polyhydramnios (maximum vertical pocket > or = 8 cm), abnormal Doppler studies or hydrops of the pump twin, or monoamniotic twins. Various surgical and access techniques for umbilical cord occlusion were used as they were developed. RESULTS: Seventy-four patients with twin reversed arterial perfusion sequence were studied. Sixty-five patients were considered surgical candidates, of which 51 patients underwent umbilical cord occlusion attempt. The overall perinatal survival for surgical candidates who had umbilical cord occlusion was 65% (33/51 patients) versus 42.9% (6/14 patients) for the surgical candidates who did not undergo umbilical cord occlusion (P = .1). However, perinatal outcomes in surgical patients were significantly better than expectantly treated surgical candidates if the dividing membrane was not disrupted purposely (22/28 patients; 78.5%; P = .02). Surgery within the sac of the twin reversed arterial perfusion fetus was feasible in 23.5% of patients and was associated with no incidence of premature rupture of membranes, with 83% perinatal survival, and with a significantly greater gestational age at delivery (36 weeks). There were no significant differences in perinatal outcome relative to the specific surgical technique that was used. CONCLUSION: Surgical management of twin reversed arterial perfusion sequence is indicated in high-risk patients. The surgical approach and the surgical technique should be tailored to the specific clinical presentation, preferably by performing the surgery within the sac of the twin reversed arterial perfusion sequence fetus and avoiding disruption of the dividing membrane.

Arteries↗
PubMed2005

fsi zebrafish show concordant reversal of laterality of viscera, neuroanatomy, and a subset of behavioral responses.

Asymmetries in CNS neuroanatomy are assumed to underlie the widespread cognitive and behavioral asymmetries in vertebrates. Studies in humans have shown that the laterality of some cognitive asymmetries is independent of the laterality of the viscera; discrete mechanisms may therefore regulate visceral and neural lateralization. However, through analysis of visceral, neuroanatomical, and behavioral asymmetries in the frequent-situs-inversus (fsi) line of zebrafish, we show that the principal left-right body asymmetries are coupled to certain brain asymmetries and lateralized behaviors. fsi fish with asymmetry defects show concordant reversal of heart, gut, and neuroanatomical asymmetries in the diencephalon. Moreover, the neuroanatomical reversals in reversed fsi fish correlate with reversal of some behavioral responses in both fry and adult fsi fish. Surprisingly, two behavioral asymmetries do not reverse, suggesting that at least two separable mechanisms must influence functional lateralization in the CNS. Partial reversal of CNS asymmetries may generate new behavioral phenotypes; supporting this idea, reversed fsi fry differ markedly from their normally lateralized siblings in their behavioral response to a novel visual feature. Revealing a link between visceral and brain asymmetry and lateralized behavior, our studies help to explain the complexity of the relationship between the lateralities of visceral and neural asymmetries.

Analysis of Variance↗
PubMed2005

Preoperative left ventricular dimensions predict reverse remodeling following restrictive mitral annuloplasty in ischemic mitral regurgitation.

OBJECTIVE: Ischemic mitral regurgitation can be treated with a restrictive mitral annuloplasty, with or without coronary revascularization. In this study, the extent of reverse remodeling of the left ventricle following this strategy is assessed, as well as the factors that influence it. METHODS: Eighty-seven consecutive patients with ischemic mitral regurgitation and a mean ejection fraction of 32+/-10% underwent restrictive mitral annuloplasty (downsizing by two ring sizes, median ring size 26), with additional coronary revascularization in 75 patients. All underwent transthoracic echocardiography 18 months after surgery to assess residual mitral regurgitation, mitral valve gradient and left ventricular end-systolic and end-diastolic dimensions. Univariate and multivariate analysis was performed to identify predictors for reverse remodeling, defined as a 10% reduction in left ventricular dimension. Receiver-operating characteristic analysis was used to identify cut-off values for preoperative left ventricular dimensions in predicting reverse remodeling. RESULTS: Early mortality was 8.0% (seven patients, three non-cardiac), late mortality was 7.5% (six patients, four non-cardiac). There were two reoperations (redo annuloplasty), and four readmissions for heart failure. At 29 months follow-up, NYHA class improved from 3.0+/-0.9 to 1.3+/-0.5 (P<0.01). Mitral regurgitation grade decreased from 3.1+/-0.5 to 0.6+/-0.6 at 18 months, left ventricular end-systolic dimension decreased from 52+/-8 to 44+/-11 mm (P<0.01), and end-diastolic dimension from 64+/-8 to 58+/-10mm (P<0.01). Multivariate analysis identified preoperative left ventricular end-diastolic dimension as the single best factor in predicting occurrence of reverse remodeling. For end-systolic dimension, 51mm was the optimal cut-off value to predict reverse remodeling (specificity and sensitivity 81%, area under curve 0.85); for end-diastolic dimension, the cut-off value was 65mm (specificity and sensitivity 89%, area under curve 0.92). CONCLUSIONS: Stringent restrictive mitral annuloplasty with or without revascularization provides excellent clinical results with acceptable mortality. At 18 months follow-up, there is no significant residual mitral regurgitation. Reverse remodeling occurs in the majority of patients, but is limited by preoperative left ventricular dimensions. In patients with a left ventricular end-diastolic dimension exceeding 65mm, additional surgical procedures are necessary to try and obtain reverse remodeling in this subgroup.

Adult↗
PubMed2005

Pharmacological left ventricular reverse remodeling in elderly patients receiving optimal therapy for chronic heart failure.

BACKGROUND AND AIMS: In recent years, reversal of established left ventricular (LV) dilatation has been increasingly recognized in middle-aged patients with dilated cardiomyopathy receiving angiotensin-converting enzyme (ACE) inhibitors and/or beta-blockers. We performed this prospective study to evaluate whether optimized therapy for heart failure also induces LV reverse remodeling in older patients. METHODS: One hundred and twenty-four patients aged >70 years with LV ejection fraction <40% underwent clinical and echocardiographic evaluation at baseline and after 1 year. During the early stage of follow-up, pharmacological therapy was optimized. LV reverse remodeling was defined as a reduction in LV end-diastolic volume >25% from baseline to final evaluation. RESULTS: LV reverse remodeling was recognized in 32 patients (26%). Compared to the subjects who did not improve LV geometry, those with reverse remodeling had, at baseline, higher arterial blood pressure, lower serum creatinine levels, shorter duration of symptoms of heart failure, more frequently received beta-blocker therapy and had predominantly nonischemic aetiology. The variables associated with the development of reverse remodeling in the multivariate analysis were shorter duration of symptoms of heart failure (Odds ratio: 7.7; CI: 2.5-23.3, p=0.0001) and beta-blocker therapy (Odds ratio: 6.0; CI: 1.6-23.3, p=0.01). CONCLUSIONS: LV reverse remodeling takes place in elderly as well as in younger heart failure patients. A significant proportion of elderly patients undergoes this favourable process which occurs prevalently in patients receiving beta-blocker therapy with a short history of cardiac disease.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Grammont reverse prosthesis: design, rationale, and biomechanics.

Combined destruction of the rotator cuff and the glenohumeral joint may lead to a painful and pseudo-paralyzed shoulder. In this situation a nonconstrained shoulder prosthesis yields a limited functional result or may even be contraindicated. Previous constrained prostheses (ball-and-socket or reverse ball-and-socket designs) have failed because their center of rotation remained lateral to the scapula, which limited motion and produced excessive torque on the glenoid component, leading to early loosening. The reverse prosthesis designed by Paul Grammont, unlike any previous reverse ball-and-socket design, has introduced 2 major innovations that have led to its success: (1) a large glenoid hemisphere with no neck and (2) a small humeral cup almost horizontally oriented with a nonanatomic inclination of 155 degrees, covering less than half of the glenosphere. This design medializes and stabilizes the center of rotation, minimizes torque on the glenoid component, and helps in recruiting more fibers of the anterior and posterior deltoid to act as abductors. Furthermore, the humerus is lowered relative to the acromion, restoring and even increasing deltoid tension. The Grammont reverse prosthesis imposes a new biomechanical environment for the deltoid muscle to act, thus allowing it to compensate for the deficient rotator cuff muscles. The clinical experience does live up to the biomechanical concept: the reverse prosthesis restores active elevation above 90 degrees in patients with a cuff-deficient shoulder. However, external rotation often remains limited, particularly in patients with an absent or fat-infiltrated teres minor. Internal rotation is also rarely restored after a reverse prosthesis. Failure to restore sufficient tension in the deltoid may result in prosthetic instability. The design does appear to protect against early loosening of the glenoid component, but impingement of the humeral cup on the scapular neck can lead to scapular notching and polyethylene wear. This is a cause for concern, especially as the notch is often more extensive than can be explained by impingement alone. Bony lysis of the scapula may also be related to a polyethylene granuloma. Further follow-up is required to ensure that loosening does not become a problem in the long term, and it has been recommended to limit its use to elderly patients, arguably those aged over 70 years. Despite these concerns, the reverse prosthesis, based on the biomechanical Grammont concept, offers a true surgical option in several situations where only limited possibilities were previously available: cuff tear arthrosis, persistent shoulder pseudo-paralysis due to a massive and irreparable cuff tear, severe fracture sequelae, prosthetic revision in a cuff-deficient shoulder, and tumor surgery. Finally, surgeons must be aware that results are less predictable and complication/revision rates are higher in revision surgery.

Biomechanical Phenomena↗
PubMed2004

Transcervical carotid stenting with internal carotid artery flow reversal: feasibility and preliminary results.

OBJECTIVE: Transfemoral carotid artery stenting (CAS), with or without distal protection, is associated with risk for cerebral and peripheral embolism and access site complications. To establish cerebral protection before crossing the carotid lesion and to avert transfemoral access complications, the present study was undertaken to evaluate a transcervical approach for CAS with carotid flow reversal for cerebral protection. METHODS: Fifty patients underwent CAS through a transcervical approach. All patients with symptoms had greater than 60% internal carotid artery (ICA) stenosis, and all patients without symptoms had greater than 80% ICA stenosis. Twenty-one patients (42%) had symptomatic disease or ipsilateral stroke, and 8 patients (16%) had contralateral stroke. Four patients (8%) had recurrent stenosis, 7 patients (14%) had contralateral ICA occlusion, and 1 patient (2%) had undergone previous neck radiation. Twenty-seven procedures (54%) were performed with local anesthesia, and 23 (46%) with general anesthesia. Using a cervical cutdown, flow was reversed in the ICA by occluding the common carotid artery and establishing a carotid-jugular vein fistula. Pre-dilation was selective, and 8-mm to 10-mm self-expanding stents were deployed and post-dilated with 5-mm to 6-mm balloons in all cases. RESULTS: The procedure was technically successful in all patients, without significant residual stenoses. No strokes or deaths occurred. There was 1 wound complication (2%). All patients were discharged within 2 days of surgery. Mean flow reversal time was 21.4 minutes (range, 9-50 minutes). Carotid flow reversal was not tolerated in 2 patients (4%). Early in the experience, carotid flow reversal was not possible in 1 patient, and there were 1 major and 3 minor common carotid artery dissections, which resolved after stent placement. One intraoperative transient ischemic attack (2%) occurred in 1 patient in whom carotid flow was not reversed, and 1 patient with a contralateral ICA occlusion had a contralateral transient ischemic attack. At 1 to 12 months of follow-up, all patients remained asymptomatic, and all but 1 stent remained patent. CONCLUSION: Transcervical CAS with carotid flow reversal is feasible and safe. It can be done with the patient under local anesthesia, averts the complications of the transfemoral approach, and eliminates the increased complexity and cost of cerebral protection devices. Transcervical CAS is feasible when the transfemoral route is impossible or contraindicated, and may be the procedure of choice in a subset of patients in whom carotid stenting is indicated.

Aged↗
PubMed2006

Voluntary control of Necker cube reversals modulates the EEG delta- and gamma-band response.

Reversible figures such as the Necker cube make up a well-known class of visual phenomena in which an invariant stimulus pattern gives rise to at least two different perceptual interpretations. Former EEG studies of our research group demonstrated a reversal-related delta response and a frontal enhancement of gamma activity during multistable perception which has been interpreted as signaling attentional top-down processes. The aim of the present study was to investigate the functional involvement of delta and gamma activity in top-down processes more explicitly by asking 21 healthy participants to bring the reversal rate under voluntary control during viewing of the Necker cube. Slowing down the reversal rate should be accomplished by focussing attention to the currently perceived alternative while speeding up should be accomplished by shifting attention as rapidly as possible from one perspective to the other. EEG was recorded from frontal, central, parietal, and occipital locations of both hemispheres. The data was analysed on the single-sweep level in the delta and gamma frequency range. The results showed that both delta response and gamma power were larger during slowing down than speeding up the reversal rate. These findings may indicate that more attentional resources have to be allocated by the cognitive system in order to prevent a reversal by means of focussed attention than to initiate a reversal by attentional shifts.

Adolescent↗