Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “COLLAPSE”

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 217 records · Page 12Linked to original sources
PubMed1991

Differentiation of central lung tumor from postobstructive lobar collapse by rapid sequence computed tomography.

When central lung tumor is associated with lobar collapse, discrimination of tumor from atelectasis is important for determining operability or for field planning should radiation therapy be utilized. Because tumor and collapsed lung have similar attenuation values, they cannot always be distinguished with usual contrast-enhanced CT. The article describes separation of tumor from collapsed lung by means of RSCT with bolus injection of nonionic contrast medium. With this technique collapsed lung is appreciably enhanced, but tumor enhancement is slow and minimal. The difference is most marked from 40 seconds to 2 minutes after scanning begins. This phenomenon is probably related to the marked increase in blood flow per unit area of collapsed lung due to crowding of relatively large pulmonary arteries compared to tumor blood supply through small bronchial arteries. Tumor can also be delineated from atelectasis by differences in internal structure with this technique.

Aged↗
PubMed1996

Computed tomography correlation in atypical (peripheral) right upper lobe collapse: the minor fissure as an explanation for the pleural-based density.

Peripheral right upper lobe collapse describes the unusual plain film finding in which the collapsed lobe simulates a peripheral, pleural-based mass. Most investigators have postulated that the peripheral opacity is explained by the interface between the superior segment of the lower lobe and the posterior aspect of the collapsed upper lobe, which does not swing as far medial as in the normal pattern of collapse. In our patient, using computed tomography (CT) correlation, we demonstrated that the finding is explained by the interface between the middle lobe and the anterior aspect of the collapsed upper lobe.

Humans↗
PubMed1998

De novo collapsing glomerulopathy in renal allografts.

BACKGROUND: Collapsing glomerulopathy is a recently described form of glomerular injury characterized by capillary collapse and visceral epithelial hypercellularity associated with nephrotic range proteinuria and a rapid, progressive decline in renal function. The lesion has rarely been described in allografts. METHODS: We reviewed 892 allograft biopsies from a population of 1079 recipients who received renal transplants between 1978 and 1996. RESULTS: Five cases of de novo collapsing glomerulopathy were identified (0.6% of biopsies; 3.2% since 1993). None occurred before 1993. The patients were 31 to 66 years of age and they presented 6 to 25 months after transplantation. The 24-hr urinary protein ranged from 1.8 to 11.8 g. All patients and donors were negative for the human immunodeficiency virus and had no risk factors for human immunodeficiency virus infection. Diffuse or focal, global or segmental collapse of glomerular capillaries, swelling and hypercellularity of the visceral epithelium, hyaline arteriolosclerosis, and interstitial fibrosis were characteristic histologic features. Two cases had concomitant glomerular immune complex deposits. Progressive decline in allograft function occurred within 2-24 months after diagnosis, culminating in return to dialysis in all patients. CONCLUSION: Collapsing glomerulopathy can arise in renal allografts as a de novo disease. Although its pathogenesis remains to be clarified, it is important to distinguish this lesion in allografts as it can be associated with rapidly progressive graft failure.

Adult↗
PubMed1999

Survival-time distribution for inelastic collapse.

In a recent publication [Phys. Rev. Lett. 81, 1142 (1998)] it was argued that a randomly forced particle that collides inelastically with a boundary can undergo inelastic collapse and come to rest in a finite time. Here we discuss the survival probability for the inelastic collapse transition. It is found that the collapse-time distribution behaves asymptotically as a power law in time, and that the exponent governing this decay is nonuniversal. An approximate calculation of the collapse-time exponent confirms this behavior and shows how inelastic collapse can be viewed as a generalized persistence phenomenon.

Journal Article↗
PubMed2000

Four-dimensional polymer collapse: pseudo-first-order transition in interacting self-avoiding walks

In an earlier work we provided the first evidence that the collapse, or coil-globule transition of an isolated polymer in solution can be seen in a four-dimensional model. Here we investigate, via Monte Carlo simulations, the canonical lattice model of polymer collapse, namely, interacting self-avoiding walks, to show that it not only has a distinct collapse transition at finite temperature but that for any finite polymer length this collapse has many characteristics of a rounded first-order phase transition. However, we also show that there exists a "straight theta point" where the polymer behaves in a simple Gaussian manner (which is a critical state), to which these finite-size transition temperatures approach as the polymer length is increased. The resolution of these seemingly incompatible conclusions involves the argument that the first-order-like rounded transition is scaled away in the thermodynamic limit to leave a mean-field second-order transition. Essentially this happens because the finite-size shift of the transition is asymptotically much larger than the width of the pseudotransition and the latent heat decays to zero (algebraically) with polymer length. This scenario can be inferred from the application of the theory of Lifshitz, Grosberg, and Khokhlov (based upon the framework of Lifshitz) to four dimensions: the conclusions of which were written down some time ago by Khokhlov. In fact it is precisely above the upper critical dimension, which is 3 for this problem, that the theory of Lifshitz may be quantitatively applicable to polymer collapse.

Journal Article↗
PubMed2003

Collapses and explosions in self-gravitating systems.

Collapse and explosion (reverse to collapse) transitions in self-gravitating systems are studied by molecular dynamics simulations. A microcanonical ensemble of point particles confined to a spherical box is considered. The particles interact via an attractive soft Coulomb potential. It is observed that a collapse indeed takes place when the energy of the uniform state is set near or below the metastability-instability threshold (collapse energy) as predicted by the mean-field theory. Similarly, an explosion occurs when the energy of the core-halo state is increased above the explosion energy, where according to the mean-field predictions the core-halo state becomes unstable. For systems consisting of 125-500 particles, the collapse takes about 10(5) single-particle crossing times to complete, while a typical explosion is by an order of magnitude faster. A finite lifetime of metastable states is observed. It is also found that the mean-field description of the uniform and core-halo states is exact within the statistical uncertainty of the molecular dynamics data.

Journal Article↗
PubMed2005

Kinetics of the polymer collapse transition: the role of hydrodynamics.

We investigate numerically the dynamical behavior of a polymer chain collapsing in a dilute solution. The rate of collapse is measured with and without the presence of hydrodynamic interactions. We find that hydrodynamic interactions accelerate polymer collapse. We present a scaling theory describing the physical process responsible for the collapse kinetics. Predicted collapse times in a hydrodynamic (tauH approximately N(4/3)) and a Brownian heat bath (tauB approximately N2) agree well with the numerical results (tauH approximately N(1.40+/-0.08) and tauB approximately N(1.89+/-0.09)) where N denotes chain length. The folding kinetics of Go models of proteins is also examined. We show that for these systems, where many free energy minima compete, hydrodynamics has little effect on the kinetics.

Journal Article↗
PubMed2006

Laryngeal collapse in seven brachycephalic puppies.

OBJECTIVES: To document the histories, clinical findings, and management of seven puppies with laryngeal collapse occurring secondarily to brachycephalic airway syndrome. METHODS: Seven brachycephalic puppies aged between 4.5 and six months underwent surgery for management of brachycephalic airway syndrome following presentation for exercise intolerance and increased respiratory noise and effort. RESULTS: Stenotic nares of varying severity and an elongated soft palate were common to all dogs. All dogs had tracheal hypoplasia and this was severe in four dogs. Laryngeal collapse was present in all dogs. Two dogs had stage I, four dogs stage II, and one dog stage III laryngeal collapse. The dog with stage III laryngeal collapse and one dog with stage II laryngeal collapse died. There was no apparent association between the changes evident on thoracic radiographs or the degree of tracheal hypoplasia and postoperative outcome. CLINICAL SIGNIFICANCE: The development of severe secondary laryngeal changes in dogs aged six months or less supports the suggestion that immature brachycephalic dogs should undergo assessment and, if indicated, surgery as soon as any clinical signs of BAS are apparent.

Airway Obstruction↗
PubMed2005

The flow field downstream of an oscillating collapsed tube.

A two-component laser Doppler anemometer was used to determine the velocity of aqueous flow in the region from 0.25 to 2.5 diameters downstream of a collapsible tube while the tube was executing vigorous repetitive flow-induced oscillations. The Reynolds number for the time-averaged flow was 10,750. A simultaneous measurement of the pressure at the downstream end of the tube was used to align all the results in time at sixty locations in each of the two principal planes defined by the axes of collapse of the flexible tube upstream. The raw data of seed-particle velocity were used to create a periodic waveform for each measured velocity component at each location by least-squares fitting of a Fourier series. The results are presented as both velocity vectors and interpolated contours, for each of ten salient instants during the cycle of oscillation. In the plane of the collapse major axis, the dominant feature is the jet which emerges from each of the two tube lobes when it collapses, but transient retrograde flow is observed on both the central and lateral edges of this jet. In the orthogonal, minor-axis plane, the dominant feature is the retrograde flow, which during part of the cycle extends over the whole plane. All these features are essentially confined to the first 1.5 diameters of the rigid pipe downstream of the flexible tube. These data map the temporal and spatial extent of the highly three-dimensional reversing flow just downstream of an oscillating collapsed tube.

Animals↗
PubMed1992

Possible sources of discrepancy between sphygmomanometer cuff pressure and blood pressure quantified in a collapsible-tube analogue.

This paper examines the assumption that the audible events detected as Korotkov sounds in sphygmomanometry occur when blood pressure equals arm-cuff pressure. Several effects that contribute to discrepancy between these pressures are quantified using an idealised arm-and-cuff system consisting of a thick-walled collapsible tube subject to external compression along a central part of its length. The effects studied are (1) transverse pressure difference, resulting from tissues sustaining a part of the external compression through (a) circumferential bending stiffness and (b) longitudinal curvature of the tensed localised neck at the site of initial collapse, (2) longitudinal pressure difference between upstream pressure and pressure at the collapse point due to both (a) viscous and (b) inertial pressure drop. These effects are found to compensate partially for each other; the pressure within the vessel at the collapse point is less than the cuff pressure, but is also less than the blood pressure at the upstream end of the cuff. All four of the contributing terms increase proportionally to the flow-rate raised to a power greater than one, except the viscous pressure drop. Owing to a progressive shortening of the collapsed neck as flow-rate increases, the viscous term is almost independent of the flow-rate. The overall discrepancy displays less flow-rate dependency and is smaller than some of the terms which contribute to it. This means that considerable accuracy is needed if measurements of the effects are to be used to correct the raw data on cuff pressure at the time of Korotkov sound emission so as to obtain an improved estimate of the blood pressure.

Auscultation↗
PubMed2005

Spontaneous homologous recombination is induced by collapsed replication forks that are caused by endogenous DNA single-strand breaks.

Homologous recombination is vital to repair fatal DNA damage during DNA replication. However, very little is known about the substrates or repair pathways for homologous recombination in mammalian cells. Here, we have compared the recombination products produced spontaneously with those produced following induction of DNA double-strand breaks (DSBs) with the I-SceI restriction endonuclease or after stalling or collapsing replication forks following treatment with thymidine or camptothecin, respectively. We show that each lesion produces different spectra of recombinants, suggesting differential use of homologous recombination pathways in repair of these lesions. The spontaneous spectrum most resembled the spectra produced at collapsed replication forks formed when a replication fork runs into camptothecin-stabilized DNA single-strand breaks (SSBs) within the topoisomerase I cleavage complex. We found that camptothecin-induced DSBs and the resulting recombination repair require replication, showing that a collapsed fork is the substrate for camptothecin-induced recombination. An SSB repair-defective cell line, EM9 with an XRCC1 mutation, has an increased number of spontaneous gammaH2Ax and RAD51 foci, suggesting that endogenous SSBs collapse replication forks, triggering recombination repair. Furthermore, we show that gammaH2Ax, DSBs, and RAD51 foci are synergistically induced in EM9 cells with camptothecin, suggesting that lack of SSB repair in EM9 causes more collapsed forks and more recombination repair. Furthermore, our results suggest that two-ended DSBs are rare substrates for spontaneous homologous recombination in a mammalian fibroblast cell line. Interestingly, all spectra showed evidence of multiple homologous recombination events in 8 to 16% of clones. However, there was no increase in homologous recombination genomewide in these clones nor were the events dependent on each other; rather, we suggest that a first homologous recombination event frequently triggers a second event at the same locus in mammalian cells.

Animals↗
PubMed2005

Tracheobronchomalacia: comparison between end-expiratory and dynamic expiratory CT for evaluation of central airway collapse.

PURPOSE: To compare dynamic expiratory and end-expiratory computed tomography (CT) for depicting central airway collapse in patients with acquired tracheobronchomalacia (TBM). MATERIALS AND METHODS: Institutional review board approval was obtained, and informed consent was not needed. Retrospective review was performed of all patients with a CT diagnosis of TBM in a 10-month period (n = 34) who underwent evaluation of airway disease by means of three different sequences at multi-detector row CT: end inspiration, dynamic expiration, and end expiration (the latter was performed only at the levels of the aortic arch, carina, and bronchus intermedius). Fourteen patients (11 men, three women; age range, 19-79 years) who had comparable images obtained with all three sequences at any of these three levels were included in the study. The degree of airway collapse was measured by two thoracic radiologists in consensus by calculating the percentage change in the area of the airway between inspiratory and expiratory scanning. Statistical analysis was performed by using the paired t test. RESULTS: Dynamic expiratory CT elicited a significantly greater degree of airway collapse than end-expiratory CT at all three levels (P < .005). The mean percentages of airway collapse at each of the three levels were as follows: aortic arch, 53.9% with dynamic expiration versus 35.7% with end expiration (P = .0046); carina, 53.6% with dynamic expiration versus 30.9% with end expiration (P < .0001); and bronchus intermedius, 57.5% with dynamic expiration versus 28.6% with end expiration (P = .0022). CONCLUSION: Dynamic expiratory CT elicits a significantly greater degree of airway collapse than standard end-expiratory CT in patients with TBM.

Adult↗
PubMed1982

Role of carotid artery resistance to collapse during high-intrathoracic-pressure CPR.

The driving force for carotid artery flow during high-intrathoracic-pressure cardiopulmonary resuscitation is a peripheral arteriovenous pressure gradient resulting from differential transmission of the high intrathoracic pressure to the carotid artery but not to the jugular vein. To study the role of carotid artery resistance to collapse in establishing this differential pressure transmission, we manipulated the upstream, downstream, and surrounding pressures and measured the resultant carotid artery flow in both intact dogs and in excised arteries. Stepwise reductions in downstream pressure produced a narrowing near the outlet from the high-pressure chamber (the thorax in vivo), but increments in flow continued despite the presence of a positive (outside--inside) transmural pressure gradient. Flow limitation occurred only when downstream pressure was further decreased. Resistance to collapse was indexed by the transmural pressure at the onset of flow limitation (Pcrit), which was 7.2 +/- 1.6 mmHg in eight intact dogs. After administration of norepinephrine Pcrit increased by 2.6 +/- 0.7 mmHg, P less than 0.001). Seven excised carotid arteries also demonstrated resistance to collapse which was enhanced somewhat with norepinephrine. Thus resistance of the carotid artery to collapse is a critical factor in maintaining forward flow during high intrathoracic pressure. This resistance to collapse is also seen in vitro and can be enhanced by vasoconstricting agents.

Animals↗
PubMed2002

Modulation of upper airway collapsibility during sleep: influence of respiratory phase and flow regimen.

We hypothesized that upper airway collapsibility is modulated dynamically throughout the respiratory cycle in sleeping humans by alterations in respiratory phase and/or airflow regimen. To test this hypothesis, critical pressures were derived from upper airway pressure-flow relationships in six tracheostomized patients with obstructive sleep apnea. Pressure-flow relationships were generated by varying the pressure at the trachea and nose during tracheostomy (inspiration and expiration) (comparison A) and nasal (inspiration only) breathing (comparison B), respectively. When a constant airflow regimen was maintained throughout the respiratory cycle (tracheostomy breathing), a small yet significant decrease in critical pressure was found at the inspiratory vs. end- and peak-expiratory time point [7.1 +/- 1.6 (SE) to 6.6 +/- 1.9 to 6.1 +/- 1.9 cmH(2)O, respectively; P < 0.05], indicating that phasic factors exerted only a modest influence on upper airway collapsibility. In contrast, we found that the inspiratory critical pressure fell markedly during nasal vs. tracheostomy breathing [1.1 +/- 1.5 (SE) vs. 6.1 +/- 1.9 cmH(2)O; P < 0.01], indicating that upper airway collapsibility is markedly influenced by differences in airflow regimen. Tracheostomy breathing was also associated with a reduction in both phasic and tonic genioglossal muscle activity during sleep. Our findings indicate that both phasic factors and airflow regimen modulate upper airway collapsibility dynamically and suggest that neuromuscular responses to alterations in airflow regimen can markedly lower upper airway collapsibility during inspiration.

Adult↗
PubMed2002

Dysregulation of podocyte phenotype in idiopathic collapsing glomerulopathy and HIV-associated nephropathy.

BACKGROUND: Idiopathic collapsing glomerulopathy (ICG) and HIV-associated nephropathy (HIV-AN) are characterized by severe nephrotic syndrome, collapse and sclerosis of the glomerular tuft with prominent podocyte alterations and extensive tubulointerstitial lesions. We previously showed phenotypic changes in podocytes from patients with diffuse mesangial sclerosis, a severe glomerulopathy sharing several morphological features with collapsing glomerulopathy. The aim of this study was to analyze the podocyte phenotype in ICG and HIV-AN. METHODS: Using immunohistochemical techniques, we studied the podocyte expression of the transcription factor WT1 and its target PAX2, GLEPP1, synaptopodin and vimentin as markers of podocyte maturity and of proliferating cell nuclear antigen (PCNA) as a marker of proliferation. Apoptosis was analyzed by the TUNEL method. Results from renal biopsies of ICG and HIV-AN were compared with those obtained from normal kidney, minimal change nephrotic syndrome (MCNS), focal and segmental glomerulosclerosis (FSGS) and membranous glomerulonephritis (MGN). RESULTS: Abnormal distribution of WT1 and PAX2 and extensive loss of podocyte markers were observed in ICG and HIV-AN; this dysregulation was associated with podocyte proliferation without detectable apoptosis. In contrast, no podocyte changes were detected in MCNS or MGN. In FSGS, phenotypic changes, without proliferation, were restricted to podocytes surrounding focal and segmental glomerular lesions. Increased PCNA expression and apoptosis were observed in ICG and HIV-AN tubular cells. CONCLUSION: Dysregulation of podocyte phenotype and proliferation are present in both ICG and HIV-AN. This suggests that, whatever their etiology, both types of collapsing glomerulopathy share a common pathogenic pathway. Upregulation of cell proliferation and apoptosis observed in tubular epithelial cells is probably involved in the occurrence of severe tubulointerstitial lesions in collapsing glomerulonephritis.

AIDS-Associated Nephropathy↗
PubMed1996

The influence of collapse of the lung parenchyma on the morphology of pulmonary blood vessels in the rat.

During a search for resident subendothelial smooth muscle cells in pulmonary vessels of the rat we found that in expanded lungs the muscular pads in the veins, considered by some authors as sphincters, were hardly visible whereas in collapsed lungs they were very conspicuous. In a separate study intended to quantify the degree of collapse or expansion the left lung was examined in 5 rats with a collapsed and in 5 rats with an expanded lung: the expansion was produced by filling the airways by gravity with Methacarn fixative. The degree of expansion was determined by morphometry measuring the volume density of the tissue fraction of the pulmonary parenchyma in the microscopic sections: in the expanded lung the mean value was 8.5% (range 6.7-12.6%), in the collapsed lung 20.1% (range 18.7-22.3%), a highly significant difference (p < 0.000). Serial sections generally 60-100, 6-microns-thick, were stained by PAS, Sirius red hematoxylin and Verhoeff's elastic stains. Immunohistochemical staining was done with monoclonal antibody against alpha smooth muscle cell actin and desmin. Graphic reconstructions of representative vessels were performed. It was shown that the muscular media of the veins was interrupted and that the muscular pads corresponded to the contracted smooth muscle cell segments alternating with the noncontracted segments devoid of muscle. In the expanded lungs muscular pads were flattened and often hardly detectable. This indicates that the structures considered as sphincters are postmortem contraction rings in collapsed lungs.

Actins↗
PubMed1976

Correlation between lung function and tracheobronchial collapse.

In 30 unselected male patients, bronchoscopic aspect and lung function parameters (notch in FEV1, FEV1/FIV1%, discrepancy between airways resistance and FEV1, club-shaped resistance curves) were correlated to determine the validity of lung function in the diagnosis of a central bronchial collapse. There were no strong correlations; only the club-shaped resistance curve and FEV1/FIV1% less than 60 were a little more often seen in the presence of central bronchial collapse. It is concluded from these results, and with regard to the known results from bronchial pressure measurements, that the functional parameters mentioned above are good indicators of a flaccid tracheobronchial system but not typical for a central bronchial collapse alone. Additional methods (bronchoscopy, bronchial pressure measurements) are needed to locate the major pressure drop and to select the adequate therapy (conservative in the case of pure peripheral or most mixed situations, chirurgical in special cases with pure central bronchial collapse). The reactions of a collapsible tracheobronchial system to bronchodilating drugs are described and their help in location of the major pressure drop is discussed.

Bronchial Diseases↗
PubMed1998

Effect of different pressure levels on the dynamics of lung collapse and recruitment in oleic-acid-induced lung injury.

The effects of different inspiratory and expiratory airway pressures (Paw) on the dynamics of lung collapse and recruitment were studied in 14 anesthetized, mechanically ventilated, pigs with oleic-acid-induced lung injury. Repetitive CT scans of the same slice were obtained every 0.8 s during different inspiration and expiration hold procedures. The mean lung density and amount of atelectasis were measured in each scan. Inspiration to a Paw of 15 cm H2O above PEEP resulted in recruitment of collapsed lung tissue, mainly within 1.4 s. During expiration lung density increased rapidly and at an almost even rate within the first 1.4 s, whereas a rapid increase of atelectasis occurred after an initial delay period of 0.6 s with PEEP = 10 or 15 cm H2O. PEEP of 20 or 25 cm H2O almost prevented lung collapse during expiration. Thus, in order to avoid cyclic alveolar collapse during mechanical ventilation in oleic-acid-induced lung injury, a PEEP level >= 20 cm H2O or an expiration time <= 0.6 s is required. Long inspiratory time intervals, as used in inverse ratio ventilation, seem to be of minor importance for the recruitment of collapsed lung tissue in this experimental model.

Analysis of Variance↗