Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Reversibility”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources
PubMed1996

Effect of multiple discrimination reversals on acquisition of a drug discrimination task in rats.

There are many similarities between exteroceptive stimuli and interoceptive stimuli. Nevertheless, it has been suggested that behavior maintained by drug stimuli might be more difficult to reverse than behavior controlled by exteroceptive stimuli. Once a discrimination is established with an exteroceptive stimulus, it can be reversed by switching the reinforcement contingencies, and repeated reversals result in progressively faster relearning of the discrimination. To determine whether faster relearning of successive discrimination reversals also occurs when the discrimination is controlled by an internal drug stimulus, we trained rats to discriminate 3.2mg/kg phencyclidine-(PCP) from saline, in a two-lever food-reinforced operant task. After this discrimination was acquired, the reinforcement contingencies were reversed. A number of such discrimination reversals were performed to determine whether fewer trials would be needed to reach criterion performance with each reversal. Each time the reinforcement contingencies were switched, fewer training sessions were required for the subjects to reach criterion. These results are similar to those observed when a discrimination has been established with exteroceptive stimuli. The present study provides further evidence of the similarity between interoceptive drug stimuli and exteroceptive sensory stimuli.

Journal Article↗
PubMed2002

Laparoscopically assisted reversal of Hartmann's procedure revisited.

Reversal of Hartmann's procedure is a major operation, associated with substantial morbidity and mortality. In light of this, many patients elect not to undergo reversal (44-49%). In recent years, enthusiasm for laparoscopic reversal of Hartmann's procedure has increased, with the outcomes of many series suggesting that it has a reduced morbidity and mortality compared with the open procedure. We present our initial experience of four cases of laparoscopically assisted reversal of Hartmann's procedure and review the literature on this technique. Laparoscopic reversal was successful in all but one case. Literature review shows reduced postoperative hospital stay compared with the traditional, open approach and suggests that laparoscopic reversal is associated with lower morbidity and mortality rates. Laparoscopic reversal of Hartmann's procedure is feasible with potential advantages for the patient.

Aged↗
PubMed2003

Reverse selection for differential response to the locomotor stimulant effects of ethanol provides evidence for pleiotropic genetic influence on locomotor response to other drugs of abuse.

BACKGROUND: Addictive drugs share the ability to induce euphoria, which may be associated with their potential for abuse. Replicate mouse lines with high (FAST-1, FAST-2) and low (SLOW-1, SLOW-2) sensitivity to ethanol-induced psychomotor stimulation (a possible animal model for the euphoria experienced by humans) have provided evidence for common genetic influences (pleiotropy) on sensitivity to the effects of ethanol and of GABA-A receptor acting compounds on locomotor activity. Differences between FAST and SLOW mice in locomotor response to certain other drugs were found later in selection. Reverse selection produced lines (r-FAST-1, r-FAST-2, r-SLOW-1, r-SLOW-2) with similar locomotor responses to ethanol. These lines are well suited for asking whether the same alleles that influence sensitivity to ethanol are also responsible for these later arising differences in drug sensitivity. METHODS: Two replicate sets of forward- and reverse-selected FAST and SLOW lines were tested for the effects of multiple doses of morphine, cocaine, methamphetamine, nicotine, and scopolamine on their locomotor behavior. We predicted that differences in drug sensitivity between the FAST and SLOW lines would be reduced or eliminated in the reverse-selected lines. RESULTS: Differences in sensitivity to morphine, cocaine, methamphetamine, and nicotine that arose in earlier generations of the FAST-1 and SLOW-1 lines ultimately also appeared in the FAST-2 and SLOW-2 lines. However, some differences between the FAST-2 and SLOW-2 lines (those in response to cocaine and methamphetamine) were not seen until several generations after selection had been relaxed. In lines reverse-selected for sensitivity to ethanol, differences in sensitivity to the other drugs were decreased, eliminated, or even reversed. No differences in scopolamine response were found in the replicate 1 forward- or reverse-selected lines. However, a small difference in scopolamine response in the replicate 2 lines was reversed. CONCLUSIONS: Genes that influence the locomotor response to ethanol also influence locomotor response to other drugs with stimulant effects in the FAST and SLOW mice. The current data most strongly support this conclusion for sensitivity to morphine and nicotine.

Animals↗
PubMed2004

Telomerase reverse transcriptase subunit expression is associated with chondrosarcoma malignancy.

Expression of the telomerase reverse transcriptase subunit telomerase reverse transcriptase gene is associated with most human malignancies. Because telomerase reverse transcriptase is rarely expressed in normal tissue, its presence in pathologic specimens is considered a marker of transformed cells. Moreover, high levels of expression have been correlated with poor prognosis in many cancers. Although telomerase activity has been found in chondrosarcomas, its prognostic significance in these malignant cartilage tumors is unknown. Malignancy in cartilage-derived tumors is assessed routinely by histomorphologic grading, but even well differentiated, low-grade lesions can metastasize. This unpredictable behavior greatly complicates the clinical treatment of cartilage tumors, making better prognostic indicators desirable. To address this issue we used immunohistochemistry to compare telomerase reverse transcriptase expression in a collection of 61 tumors consisting of malignant chondrosarcomas of varying grade and benign enchondromas. Associated case histories were reviewed to test the hypothesis that telomerase reverse transcriptase expression levels correlated with subsequent tumor recurrence. We found that the relative abundance of telomerase reverse transcriptase-expressing cells correlated significantly with grade and recurrence. These findings indicate that telomerase reverse transcriptase immunostaining may be a useful adjunct to the conventional three-level grading system.

Biomarkers, Tumor↗
PubMed1997

A complex structure in the mRNA of Tf1 is recognized and cleaved to generate the primer of reverse transcription.

All retroviruses and LTR-containing retrotransposons are thought to require specific tRNA molecules to serve as primers of reverse transcription. An exception is the LTR-containing retrotransposon Tf1, isolated from Schizosaccharomyces pombe. Instead of requiring a tRNA, the reverse transcriptase of Tf1 uses the first 11 bases of the Tf1 transcript as the primer for reverse transcription. The primer is generated by a cleavage that occurs between bases 11 and 12 of the Tf1 mRNA. Sequence analysis of the 5' untranslated region of the Tf1 mRNA resulted in the identification of a region with the potential to form an RNA structure of 89 bases that included the primer binding site and the first 11 bases of the Tf1 mRNA. Systematic mutagenesis of this region revealed 34 single-point mutants in the structure that resulted in reduced transposition activity. The defects in transposition correlated with reduced level of Tf1 reverse transcripts as determined by DNA blot analysis. Evidence that the RNA structure did form in vivo included the result that strains with second site mutations that restored complementarity resulted in increased levels of reverse transcripts and Tf1 transposition. The majority of the mutants defective for reverse transcription were unable to cleave the Tf1 mRNA between bases 11 and 12. These data indicate that formation of an extensive RNA structure was required for the cleavage reaction that generated the primer for Tf1 reverse transcription.

Base Composition↗
PubMed2004

FEV1 reversibility does not adequately predict effect of formoterol via Aerolizer in chronic obstructive pulmonary disease.

Evaluation of patients with chronic obstructive pulmonary disease (COPD) often includes the use of post-bronchodilator reversibility testing to guide treatment decisions. Recommendations for reversibility testing differ and there is no universally accepted method or outcome criterion. A survey of recent clinical trials with beta2-agonists in COPD illustrates the diversity of methods used to assess reversibility and highlights the difficulty of comparing data from such trials. Two recent studies demonstrated the benefits of treatment with the long-acting beta2-agonist bronchodilator formoterol (Foradil Aerolizer) in patients with COPD. When patients were classified according to their degree of reversibility as partially or poorly reversible, improvements were observed in both groups irrespective of the definition applied. These results suggest that bronchodilator reversibility testing should not be used as a rigid basis for treatment decisions with beta2-agonists in COPD patients. There is a pressing need for the role of reversibility testing to be clearly defined.

Administration, Inhalation↗
PubMed1996

Conditions to optimise the reversal action of neostigmine upon a vecuronium-induced neuromuscular block.

BACKGROUND: Since neostigmine was introduced for reversal of neuromuscular block, there has been controversy about the optimum dose for antagonizing neuromuscular block. The purpose of this study was to characterise recovery of neuromuscular transmission following a vecuronium-induced block 15 min after neostigmine administration using different stimulation patterns, and to determine the effects of different doses of neostigmine given at various pre-reversal twitch heights. METHODS: Adductor pollicis (AP) mechanical activity in response to low (0.1 and 2 Hz) and high (50 and 100 Hz) frequency stimulation, was recorded 15 min after 20, 40 and 80 micrograms/kg neostigmine, given to reverse a vecuronium-induced block at 10, 25 and 50% pre-reversal twitch height (TH). Fifty four ASA class I and II anaesthetised (methohexital, fentanyl, N2O/O2) young adult patients were studied and randomly allocated into 9 groups of 6 patients each. RESULTS: In contrast to twitch height (TH) and residual force after 50 Hz, 5 s tetanic stimulation (RF50Hz), the greater sensitivity of train-of-four (TOF) ratio and residual force after 100 Hz, 5 s tetanic stimulation (RF100Hz) points out the best reversal conditions (prereversal TH and the optimal neostigmine dose) (P < 0.001, two-way analysis of variance). The highest reversal scores (about 0.9 TOF ratio and RF100Hz) were obtained when 40 micrograms/kg of neostigmine was given at 25 and 50% TH. A 0.9 TOF ratio was also observed when 40 micrograms/kg of neostigmine was given at 10% TH, but, under these conditions, RF100Hz was only 0.6 (P < 0.05, Duncan test). CONCLUSION: To optimise the reversal action of neostigmine in order to obtain the highest neuromuscular transmission recovery (0.9 TOF ratio and RF100Hz) during a vecuronium-induced neuromuscular block, the 40 micrograms/kg dose has to be given at 25 to 50% recovery of TH.

Adolescent↗
PubMed2005

Relationship of interleukin-6 with semen characteristics and oxidative stress in vasectomy reversal patients.

This prospective study was performed to evaluate the relationship between interleukin-6 (IL-6), oxidative stress and sperm function following vasectomy reversal. We included 22 patients who underwent vasectomy reversal and 15 healthy sperm donors (controls) with normal sperm morphology criteria. Levels of IL-6 in the semen were measured by the enzyme-linked immunosorbent assay, and levels of reactive oxygen species (ROS) and total antioxidant capacity were measured by the chemiluminescence assay. The mean sperm concentration in the vasectomy reversal group was significantly lower than control group (45.3 +/- 39.1 versus 63.1 +/- 28.5; P = 0.02). Motility was also significantly lower in the vasectomy reversal group (32.1 +/- 19.9 versus 54.6 +/- 18.9; P = 001). Levels of IL-6 were significantly higher in the vasectomy reversal group (2.09 +/- 0.87 versus 0.99 +/- 0.97; P = 0.007) as were mean ROS levels (2.25 +/- 0.97 versus 1.2 +/- 0.7; P = 0.009). Significant positive correlation was observed between the IL-6 and ROS levels in vasectomy reversal patients compared with donors (r = 0.41, P = 0.05 versus r = 0.38, P = 0.15). We conclude that patients who undergo vasectomy reversal have elevated levels of IL-6 and ROS, which may contribute to decreased sperm motility and concentration and possibly lead to sub-fertility.

Adult↗
PubMed1980

Action of enkephalin analogues and morphine on brain acetylcholine release: differential reversal by naloxone and an opiate pentapeptide.

1 Methionine (Met)-enkephalin, leucine (Leu)-enkephalin and their synthetic analogues were tested for effects on the spontaneous release of cortical acetylcholine (ACh) in vivo. The ability of naloxone to reverse the action of enkephalins on ACh release was compared with its action against morphine. An enkephalin analogue, structurally related to Met-enkephalin, was tested for opiate antagonistic activity in ACh release experiments. 2 Intraventricular administration of Met-enkephalin, Leu-enkephalin, D-Ala2-Met5-enkephalinamide (DALA) and D-Ala2-D-Leu5-enkephalin (DALEU) produced a dose-related inhibition of cortical ACh release. Met- and Leu-enkephalin were very similar both in their potency and the time course of their action on ACh release. Both DALA and DALEU were more potent and had a longer duration of action than Leu-enkephalin. Systemic injections of two pentapeptides, D-Met2-Pro5-enkephalinamide and D-Ala2-MePhe4-Met5(O)-ol-enkephalin (33,824), produced a sustained inhibition of cortical ACh release. 3 Naloxone, administered systemically following the depression of ACh release induced by either intraventricular injections of enkephalins (DALA or DALEU), or systemic injections of enkephalins (D-Met2-Pro5-enkephalinamide or 33,824), reversed this depression and restored the release to baseline levels. The effect of D-Met2-Pro5-enkephalinamide on the release of ACh was reversed by naloxone with difficulty. Naloxone also reversed the inhibitory effect of systemic morphine and this reversal was associated with a large overshoot of ACh release. The latter was never observed in the enkephalin experiments. 4 Intraventricular injection of the pentapeptide, D-Ala2-D-Ala3-Met5-enkephalinamide (TAAPM), at doses that did not influence the basal ACh release, blocked or reversed the inhibitory effect of morphine on this release. This peptide did not block the effect of the non-opiate, chlorpromazine, under similar conditions. In two experiments TAAPM failed to reverse the inhibition of ACh release produced by systemically injected enkephalin, D-Met2-Pro5-enkephalinamide. 5 Effects of morphine and enkephalin on ACh release are discussed in terms of their action on difference opiate receptors.

Acetylcholine↗
PubMed1998

Mechanisms of induction of typical and reversed atrial flutter.

INTRODUCTION: Typical flutter is due to reentry around caval veins and terminal crest. In patients with typical flutter, reversed (clockwise) reentry can be induced. We studied mechanisms of typical and reversed flutter induction. METHODS AND RESULTS: Thirteen patients (11 men) underwent 16 radiofrequency (RF) ablation procedures for typical (12) or reversed flutter (1). High right atrium (RA) stimulation included 1 to 3 extrastimuli over cycle lengths 600 to 250 msec, and burst. We recorded simultaneously from three levels of septal and anterior RA. RF was delivered to the inferior vena cava-tricuspid isthmus (CTI). Of 25 inductions, 4 were a result of single, 9 double, and 11 triple extrastimuli, and 1 burst. Clinical basal flutter was induced (7 typical, 1 reversed). After RF, typical flutter was reinduced in 9 cases and reversed flutter in 7, with only typical flutter seen clinically. All flutters were interrupted by ablation or catheter pressure on the CTI. Typical flutter began by low RA septal activation block, preceded by repetitive responses in 12 instances, atypical flutter in 1, and directly from stimuli in 4. Reversed flutter started in 8 instances by low RA block of a stimulated front descending the anterior wall and in 1 by repetitive responses. CONCLUSION: Septal activation block was the usual mechanism of typical flutter induction by RA extrastimuli. Facilitation of reversed flutter after RF application is probably due to a new area of block in the CTI. Flutter induction without intermediate rhythms confirms the presence of block at the terminal crest at baseline.

Atrial Flutter↗
PubMed2005

Impact of reversibility of no reflow phenomenon on 30-day mortality following percutaneous revascularization for acute myocardial infarction-insights from a 1,328 patient registry.

BACKGROUND: Occurrence of no reflow phenomenon during percutaneous coronary intervention (PCI) is associated with increased mortality. Although intracoronary medications can improve coronary flow, the effect on mortality is not known. METHODS: Patients who had PCI for myocardial infarction (MI) at the Singapore National University Hospital from January 2000 to March 2004 were studied. Our analysis stratified patients into three groups according to the occurrence and persistence of no reflow during PCI. (1) Adequate reflow: without no reflow occurrence; (2) Reversible no reflow: no reflow occurred, but final thrombolysis in myocardial infarction (TIMI) 3 flow restored after intracoronary medications; and (3) Refractory no reflow: no reflow occurred and persisted, final TIMI flow < 3 despite medications. Thirty-day mortality was determined for each group. RESULTS: A total of 1,328 patients (82% male), 703 (53%) underwent primary PCI and 625 (47%) rescue PCI were analyzed. Among the study patients, no reflow (including reversible and refractory) occurred in 135 patients (10.2%). Intracoronary verapamil, adenosine, nitroprusside, or a combination of drugs were used to treat the no reflow in 70.0%, 17.7%, 3.5%, and 8.8% of cases, respectively. Intracoronary medications successfully restored final TIMI 3 in 108 patients (80%, reversible no reflow). The remaining 27 patients (20%) have final TIMI < 3 (refractory no reflow). In comparison with the adequate reflow and reversible no reflow groups, those with refractory no reflow had an increased 30-day mortality (3.7% vs 2.8% vs 32.0%, P < 0.001). Logistic regression analyses showed that patients with refractory no reflow had a significantly higher 30-day mortality compared to patients with adequate reflow (P < 0.001) and reversible no reflow (P = 0.001), but no significant differences in the 30-day mortality between patients with adequate reflow and reversible no reflow (P = 0.157) were detected after adjusting for relevant covariates. CONCLUSION: Among patients undergoing PCI for MI, reversible no reflow was associated with a significantly lower 30-day mortality compared with the refractory counterpart.

Angioplasty, Balloon, Coronary↗
PubMed1996

Reversible photobleaching of fluorescein conjugates in air-saturated viscous solutions: singlet and triplet state quenching by tryptophan.

Fluorescence recovery after photobleaching (FRAP) measurements on air-saturated aqueous solutions of fluorescein made viscous with glycerol or sucrose revealed a rapid component of fluorescence recovery with exponential time constants of 30-120 microseconds at viscosities of 15-300 cP. The rapid recovery process was not related to fluorophore translational diffusion and was insensitive to fluorophore concentration and the additive used to increase solution viscosity. At constant viscosity, the rate of reversible photobleaching recovery increased 2.5-fold in an O2- vs N2-saturated solution. The relative efficiency of reversible-to-irreversible photobleaching decreased with increasing photobleaching time and/or beam intensity. Reversible photobleaching was also detected for conjugates of fluorescein with dextrans and proteins in viscous media. In screening triplet state quenchers that might influence the reversible recovery, it was found that tryptophan enhanced the rate of reversible photobleaching recovery (two-fold increase at 8 mM) and quenched the fluorescein singlet state (Stern-Volmer constant, 12 M-1). Analysis of fluorescein lifetimes and photobleaching parameters for a series of fluorescein-labeled proteins with different numbers of tryptophans were also carried out. The results provide evidence for an oxygen-dependent, reversible photobleaching mechanism for the fluorescein chromophore involving triplet state relaxation. The identification of reversible fluorescein photobleaching has important implications for FRAP measurements of rapid solute diffusion in biological systems.

Fluoresceins↗
PubMed1991

Sulphate conjugation enhances reversible binding of drug to human serum albumin.

Reversible binding of model compounds, their conjugated metabolites (sulphates and glucuronides), and also derivatives of the compounds, to human serum albumin (HSA) has been examined using an ultrafiltration method. p-Nitrophenol (p-NP), alpha-naphthol (alpha-NA) and beta-naphthol (beta-NA) were used as model compounds. Reversible binding of 500 microM p-NP sulphate to 4% HSA (96.6 +/- 0.35%, mean +/- s.d. n = 3) was significantly higher (P less than 0.001), whereas reversible binding of p-NP glucuronide to 4% HSA (33.3 +/- 9.82%) was much lower (P less than 0.001) than that of 500 microM p-NP (90.9 +/- 0.60%). Reversible binding of 500 microM p-NP glucopyranoside to 4% HSA (25.8 +/- 2.82%) was comparable with that of the glucuronide, with which it is structurally similar. In contrast, reversible binding of 500 microM p-NP phosphate, an anionic compound like p-NP sulphate, to 4% HSA (61.4 +/- 5.28%) was significantly lower than that of p-NP (P less than 0.001). Similar results were observed in reversible binding of sulphates of alpha-NA and beta-NA. Significant differences of dissociation constants for HSA binding were observed between the parent compound (alpha- or beta-NA) and its sulphate conjugate (P less than 0.005 for alpha-NA and alpha-NA sulphate, P less than 0.001 for beta-NA and beta-NA sulphate), but the number of binding sites was the same. These results indicated that sulphate conjugation enhances reversible binding of a parent compound to HSA by increasing the binding affinity of the parent compound to HSA. This enhancement appeared to be advantageous for preventing random distribution of this metabolite to organs in the body.

Acetaminophen↗
PubMed1974

Reversal of the physiological effects of monocular deprivation in kittens: further evidence for a sensitive period.

1. It was confirmed that suturing the lids of one eye (monocular deprivation), until only 5 weeks of age, leaves virtually every neurone in the kitten's visual cortex entirely dominated by the other eye. On the other hand, deprivation of both eyes causes no change in the normal ocular dominance of cortical neurones, most cells being clearly binocularly driven.2. Kittens were monocularly deprived until various ages, from 5 to 14 weeks, at which time reverse suturing was performed: the initially deprived right eye was opened and the left eye closed for a further 9 weeks before recording from the visual cortex.3. Reverse suturing at 5 weeks caused a complete switch in ocular dominance: every cell was dominated by the initially deprived right eye. Reverse suturing at 14 weeks, however, had almost no further effect on ocular dominance: most cells were still driven solely by the left eye. Animals reverse sutured at intermediate ages had cortical neurones strongly dominated by one eye or the other, and they were organized into clear columnar groups according to ocular dominance.4. Thus, between 5 weeks and 4 months of age, there is a period of declining sensitivity to both the effects of an initial period of monocular deprivation and the reversal of those effects by reverse suturing.5. The small proportion of binocular cells in reverse sutured kittens (which have never had simultaneous binocular vision) often differed considerably in their receptive field properties in the two eyes. In particular, if the cells were orientation selective in both eyes the two preferred orientations could differ by up to 70 degrees .6. The relative importance of innate and environmental contributions to the properties of cortical cells is discussed.

Action Potentials↗
PubMed1980

Motoneurone projection patterns in the chick hind limb following early partial reversals of the spinal cord.

1. The development of motoneurone projection patterns in the chick hind limb from reversed spinal cord segments was studied from the onset of axonal outgrowth (St. 24) to the establishment of mature connectivity patterns (St. 36). Approximately the first three lumbosacral cord segments were reversed along the anterior-posterior axis at St. 15-16. 2. Projection patterns from reversed cord segments were assessed electrophysiologically by direct spinal cord and spinal nerve stimulation and anatomically by retrograde horseradish peroxidase (HRP) labelling of motoneurones in St. 30-36 embryos. In younger embryos, paths taken by reversed axons were characterized by orthograde HRP labelling of motoneurones in specific reversed cord segments. 3. Lumbosacral motoneurones formed appropriate functional connexions with individual limb muscles in spite of anterior-posterior shifts in their spinal cord position aned consequent shifts in their spinal nerve entry point into the limb bud. Reversed motoneurones supplying individual hind limb muscles formed discrete nuclei in the transverse plane of the cord. Each nucleus and the lateral motor column as a whole showed reversed topographical characteristics when compared to control embryos. These observations were made before (St. 30) and after (St. 35-36) the major period of motoneurone cell death. 4. Correct connectivity resulted from specific alterations in axonal pathways within the plexus or major nerve trunks proximal to the branching of individual muscle nerves. Further such directed outgrowth was present from the earliest times that axons could be traced into the limb which is before the onset of motoneurone cell death and muscle cleavage. 5. It is concluded that motoneurones are specified to project to individual muscles or to follow particular pathways prior to motoneurone birthdays and limb bud formation. The establishment of specific motoneurone connectivity can not be accounted for by passive or mechanical guidance models alone. Rather, motoneurones must also actively respond to cues within the limb or interact among themselves on the basis of an early central specification.

Animals↗
PubMed2004

Nitric oxide is significantly reduced in ex vivo porcine arteries during reverse flow because of increased superoxide production.

Oscillatory and negative flows occur normally in the cardiovascular system, which predispose those regions to atherosclerosis. Nitric oxide (NO) production increases in proportion to the magnitude of flow and is known to be athero-protective. What is not known, however, is the effect of flow reversal on NO concentration ([NO]). The hypothesis of the present study is that [NO] is reduced in reverse flow. An additional hypothesis is that the reduction in [NO] is mediated through an increase in superoxide production during flow reversal. These hypotheses were tested in an ex vivo preparation of porcine elastic and muscular arteries. The flow of a physiological solution through the vessels was regulated in the forward and reverse direction and the effluent was assayed for nitrite levels using a combination of a diazo coupling method and high performance liquid chromatography. Our results show that [NO] is significantly reduced during reverse flow. Furthermore, addition of tempol (superoxide dismutase-mimetic) which is a superoxide scavenger returns the [NO] during reverse flow to mirror those of forward flow. These results have important implications since the action of superoxide is implicated in many cardiovascular diseases, and the present finding suggests that flow reversal should be added to the list.

Animals↗
PubMed2005

Time-reversal imaging for classification of submerged elastic targets via Gibbs sampling and the Relevance Vector Machine.

Time-reversal imaging (TRI) is analogous to matched-field processing, although TRI is typically very wideband and is appropriate for subsequent target classification (in addition to localization). Time-reversal techniques, as applied to acoustic target classification, are highly sensitive to channel mismatch. Hence, it is crucial to estimate the channel parameters before time-reversal imaging is performed. The channel-parameter statistics are estimated here by applying a geoacoustic inversion technique based on Gibbs sampling. The maximum a posteriori (MAP) estimate of the channel parameters are then used to perform time-reversal imaging. Time-reversal implementation requires a fast forward model, implemented here by a normal-mode framework. In addition to imaging, extraction of features from the time-reversed images is explored, with these applied to subsequent target classification. The classification of time-reversed signatures is performed by the relevance vector machine (RVM). The efficacy of the technique is analyzed on simulated in-channel data generated by a free-field finite element method (FEM) code, in conjunction with a channel propagation model, wherein the final classification performance is demonstrated to be relatively insensitive to the associated channel parameters. The underlying theory of Gibbs sampling and TRI are presented along with the feature extraction and target classification via the RVM.

Journal Article↗
PubMed2005

Release from informational masking by time reversal of native and non-native interfering speech.

In many studies, the influence of intelligibility of the interfering speech is avoided by reversing it in time. Usually, intelligibility with time-reversed interfering speech indeed is higher compared to that with normal interfering speech. However, due to the nature of speech, reversed speech also gives rise to increased forward masking. The latter will result in a decrease in intelligibility. Thus, differences in intelligibility as a consequence of reversing speech in time are due to two opposite effects. This paper describes a speech reception threshold (SRT) test with intelligible and unintelligible interfering speech played normally and time-reversed. With Dutch listeners, Swedish reversed interfering speech gave a rise in SRT of 2.3 dB compared with the Swedish interfering speech (played normally). The difference can be attributed to differences in forward masking. Dutch time-reversed interfering speech gave a decrease in SRT of 4.3 dB compared to (intelligible) Dutch interfering speech. The latter is the result of both a release from informational masking and an increase in forward masking. Therefore, the amount of informational masking is larger than 4.3 dB and, if one assumes similar differences in forward masking for Dutch and Swedish speech, may amount to 6.6 dB.

Acoustic Stimulation↗