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PubMed2002

Collapsibility of the upper airway during anesthesia with isoflurane.

BACKGROUND: The unprotected upper airway tends to obstruct during general anesthesia, yet its mechanical properties have not been studied in detail during this condition. METHODS: To study its collapsibility, pressure-flow relationships of the upper airway were obtained at three levels of anesthesia (end-tidal isoflurane = 1.2%, 0.8%, and 0.4%) in 16 subjects while supine and spontaneously breathing on nasal continuous positive airway pressure. At each level of anesthesia, mask pressure was transiently reduced from a pressure sufficient to abolish inspiratory flow limitation (11.8 +/- 2.7 cm H(2)O) to pressures resulting in variable degrees of flow limitation. The relation between mask pressure and maximal inspiratory flow was determined, and the critical pressure at which the airway occluded was recorded. The site of collapse was determined from simultaneous measurements of nasopharyngeal, oropharyngeal, and hypopharyngeal and esophageal pressures. RESULTS: The airway remained hypotonic (minimal or absent intramuscular genioglossus electromyogram activity) throughout each study. During flow-limited breaths, inspiratory flow decreased linearly with decreasing mask pressure (r(2) = 0.86 +/- 0.17), consistent with Starling resistor behavior. At end-tidal isoflurane of 1.2%, critical pressure was 1.1 +/- 3.5 cm H O; at 0.4% it decreased to -0.2 +/- 3.6 cm H(2)O ( < 0.05), indicating decreased airway collapsibility. This decrease was associated with a decrease in end-expiratory esophageal pressure of 0.6 +/- 0.9 cm H(2)O ( < 0.05), suggesting an increased lung volume. Collapse occurred in the retropalatal region in 14 subjects and in the retrolingual region in 2 subjects, and did not change with anesthetic depth. CONCLUSIONS: Isoflurane anesthesia is associated with decreased muscle activity and increased collapsibility of the upper airway. In this state it adopts the behavior of a Starling resistor. The decreased collapsibility observed with decreasing anesthetic depth was not a consequence of neuromuscular activity, which was unchanged. Rather, it may be related to increased lung volume and its effect on airway wall longitudinal tension. The predominant site of collapse is the soft palate.

Adult↗
PubMed1985

The detection of inflammation in collapsed lung by alterations in proton nuclear magnetic relaxation times.

The purpose of this study was to establish the proton NMR relaxation times of collapsed but otherwise normal lung tissue and to determine whether an inflammatory process within a collapsed lung can be detected by alterations in relaxation times. The lungs of three groups of rabbits were studied: group A (n = 7) had a sterile collapse of one lung for two days. The two other groups also had one lung collapsed, but with bacterial (group B, n = 6) or chemically induced (group C; n = 6) pneumonitis superimposed. The contralateral lung, which was acutely deflated at the time of thoracotomy, served as a control in each animal. T1, T2 and the total water content were measured on freshly excised lung samples. In group A, there was no significant difference in T1 (606 +/- 14* ms vs. 595 +/- 18 ms;* = SEM) or T2 (80.6 +/- 1.7 ms vs. 78.4 +/- 2.6 ms) between the collapsed and the control lung tissue. In each animal in groups B and C, T2 was longer in the collapsed lung with superimposed pneumonitis than in the control lung tissue (group B: 116.8 +/- 6.9 ms vs. 82.9 +/- 1.8 ms, P less than .001; group C: 120.5 +/- 5.9 ms vs. 86.0 +/- 1.5 ms, P less than .001). T1 changes were similar, but less marked. There was a linear relationship between the relaxation times and the total water content of the lung samples (T1:r = 0.87; T2:r = 0.91). It is concluded that proton NMR may have a potential in detecting disease such as inflammation in collapsed lung tissue based on differences in relaxation parameters compared with normal lung areas.

Animals↗
PubMed2001

Inelastic collapse in simple shear flow of a granular medium.

Previous investigations have shown that inelastic collapse is a common feature of inelastic, hard-sphere simulations of nondriven (or unforced) flows, provided that the coefficient of restitution is small enough. The focus of the current effort is on a driven system, namely, simple shear flow. Two-dimensional, hard-sphere simulations have been carried out over a considerable range of restitution coefficients (r), solids fractions (nu), and numbers of particles (N). The results indicate that inelastic collapse is an integral feature of the sheared system. Similar to nondriven systems, this phenomenon is characterized by a string of particles engaging in numerous, repeated collisions just prior to collapse. The collapsed string is typically oriented along a 135 degrees angle from the streamwise direction. Inelastic collapse is also found to be more likely in systems with lower r, higher nu, and higher N, as is true for unforced systems. Nonetheless, an examination of the boundary between the collapsed and noncollapsed states reveals that the sheared system is generally more "resistant" to inelastic collapse than its nondriven counterpart. Furthermore, a dimensionless number V* is identified that represents the magnitude of the initial fluctuating velocities relative to that of a characteristic steady-state velocity (i.e., the product of shear rate and particle diameter). For values of V*>>O(1), the transient portion of the simulation is found to be more reminiscent of a nondriven system (i.e., isotropic particle bunching is observed instead of diagonal particle bands).

Journal Article↗
PubMed2002

Specific and nonspecific collapse in protein folding funnels.

Experiments with fast folding proteins are beginning to address the relationship between collapse and folding. We investigate how different scenarios for folding can arise depending on whether the folding and collapse transitions are concurrent or whether a nonspecific collapse precedes folding. Many earlier studies have focused on the limit in which collapse is fast compared to the folding time; in this work we focus on the opposite limit where, at the folding temperature, collapse and folding occur simultaneously. Real proteins exist in both of these limits. The folding mechanism varies substantially in these two regimes. In the regime of concurrent folding and collapse, nonspecific collapse now occurs at a temperature below the folding temperature (but slightly above the glass transition temperature).

Amino Acid Sequence↗
PubMed1989

Siphon mechanism in collapsible tubes: application to circulation of the giraffe head.

Controversy exists over the principles involved in determining blood flow to the head of a giraffe, specifically over the role of gravity pressure (pgh) in the collapsible jugular vein in facilitating uphill flow in arteries. This study investigated the pressures within vertically oriented models containing both rigid and collapsible tubes. An inverted U tube was constructed (height = 103 cm) of thick rubber tubing in the ascending limb and collapsible dialysis tubing in the descending limb. Water flow was induced by a variable speed pump maintained at the reservoir level such that the descending limb was partially collapsed. Pressure measurements were made at various levels within the U tube by two methods: 1) with the transducer at same level as the tip of the water-filled catheter and 2) with the transducer at the reservoir level. During flow, the pressure at any point was nearly atmospheric along the length of the descending limb. Such methods of obtaining pressure indicated that the pressure gradient within the partially collapsed descending limb was the sum of viscous flow pressure (P1-P2 of Poiseuille) and gravitational pressure (pgh). To study the facilitatory effect of a siphon, the descending limb was compared with a horizontally placed limb (length = 100 cm), and the flow was kept constant. Calculations of hydraulic "work" (pressure x flow) indicated that with a partially collapsed descending limb, work of the pump was reduced by 15% compared with uphill flow to the elevated horizontal position. It is concluded that the siphon mechanism operates in a partially collapsed descending limb of a siphon loop.

Animals↗
PubMed1993

Determining the site of airway collapse in obstructive sleep apnea with airway pressure monitoring.

Twenty patients with obstructive sleep apnea (OSA) underwent complete polysomnography and simultaneous upper airway pressure monitoring with a custom-made, soft silicone-covered catheter measuring 2.3 mm in diameter. The catheter had four solid-state microtip pressure sensors positioned in the posterior nasopharynx, immediately caudal to the tip of the uvula, at the level of the hyoid bone, and in the midesophagus. The level(s) of airway collapse was determined by changes in the pressure patterns between transducers. In 14 of the 20 patients, airway collapse was confined or initiated at the oropharyngeal region. The obstruction extended to the base of tongue in 7 and to the entire collapsible upper airway in 2 patients. Four patients had collapse at the base of the tongue and 2 had collapse at the hypopharynx. The site of airway collapse remained fairly constant through various sleep stages and positions. Uvulopalatopharyngoplasty (UPPP) and postoperative polysomnography were performed in 4 patients (2 with hypopharyngeal, 1 with base of tongue, and 1 with oropharyngeal airway collapse). Two patients had a favorable response to UPPP.

Female↗
PubMed2003

A randomized prospective clinical trial of the effect of infant orthopedics in unilateral cleft lip and palate: prevention of collapse of the alveolar segments (Dutchcleft).

OBJECTIVE: To study the effect of infant orthopedics (IO) on maxillary arch form and position of the alveolar segments. DESIGN: Prospective two-arm randomized, controlled trial in parallel with three participating academic cleft palate centers. Treatment was assigned by means of a computerized balanced allocation method. SETTING: Cleft palate centers of Amsterdam, Nijmegen, and Rotterdam, the Netherlands. PATIENTS, PARTICIPANTS: Infants with complete unilateral cleft lip and palate and no other malformations. INTERVENTIONS: One group (IO+) wore passive maxillary plates during the first year of life; the other group (IO-) did not. All other interventions were the same. MAIN OUTCOME MEASURE(S): The presence of contact and/or overlap (collapse) between the maxillary segments at maxillary casts made shortly after birth, at 15, 24, 48, 58, and 78 weeks. Survival experience of contact and collapse with time as well as the frequencies of different arch forms and severity of collapse were evaluated. RESULTS: Comparable arch forms with no contact or overlap of the maxillary segments were seen at birth in both groups. With time the frequency of collapse increased, with no significant differences between groups. No significant group differences were found with respect to the survival experience of contact and collapse or for the severity of collapse at the end of the observational period. CONCLUSIONS: Infant orthopedics does not prevent collapse and can be abandoned as a tool to improve maxillary arch form.

Alveolar Process↗
PubMed2005

Articular cartilage degeneration in post-collapse osteonecrosis of the femoral head. Radiographic staging, macroscopic grading, and histologic changes.

BACKGROUND: Osteonecrosis of the femoral head is a debilitating condition characterized by progressive degeneration of bone that eventually leads to collapse of the femoral head in the majority of patients. Femoral head-sparing procedures have been more successful in pre-collapse stages of osteonecrosis than in post-collapse stages, although some patients with early post-collapse disease have had no additional progression of the disorder. Nevertheless, the effects of collapse on the articular cartilage are not well understood, and radiographic staging of femoral head collapse does not address the condition of the articular cartilage. METHODS: In the current study, we investigated the relationship between the mechanical properties of post-collapse articular cartilage and the histologic findings and macroscopic grades of the articular cartilage from hips with stage-IV osteonecrosis, those with stage-V osteonecrosis, and those without osteonecrosis. RESULTS: The cartilage from both stage-IV and stage-V hips showed significant degeneration compared with the normal control cartilage, but there was no significant difference between the two stages. There was significant variability in the histologic and mechanical properties of these samples that correlated strongly with the gross appearance of the cartilage surface but not with the lesion size. CONCLUSIONS: These results suggest that articular cartilage that appears macroscopically normal may remain mechanically functional even in patients with large osteonecrotic lesions or a late radiographic stage of the disease.

Biomechanical Phenomena↗
PubMedDate not supplied

[Collapsing glomerulopathy: a new entity associated with nephrotic syndrome and end-stage renal failure].

Collapsing glomerulopathy is an aggressive form of glomerular disease defined for its histopathological features of glomerular collapse, visceral epithelial cell damage and tubulointerstitial changes that are characteristic. Patients with collapsing glomerulopathy present with severe nephrotic syndrome, marked proteinuria, generally more than 10 g/day and rapid progression to chronic renal failure, or death due to complications of nephrotic syndrome, despite any form of treatment. Collapsing glomerulopathy presents as de novo or recurrent disease in the renal allograft. There is slight predominance in males and strong predominance in blacks as renal diseases in general. Collapsing glomerulopathy shares several clinical and histopathological features with focal and segmental glomerulosclerosis and HIV-nephropathy; nevertheless, there is enough evidence to support collapsing glomerulopathy as a different entity. It must be mentioned that collapsing glomerulopathy, focal and segmental glomerulosclerosis and HIV-nephropathy may have a similar pathophysiological mechanism of damage to the visceral epithelial cell.

Diagnosis, Differential↗
PubMed2002

Differentiation of malignant vertebral collapse from osteoporotic and other benign causes using magnetic resonance imaging.

INTRODUCTION: Elderly patients presenting with backache and vertebral collapse are a diagnostic challenge. Plain X-rays, computed tomography and radionuclide bone scans have not always reliably distinguished between benign and malignant causes. Magnetic resonance imaging (MRI) may be able to do so. MATERIALS AND METHODS: Patients who underwent MRI evaluation for vertebral collapse were retrospectively studied. Over a 21-month period from January 1995 to September 1996, 47 patients with 58 vertebral collapses were studied. Benign and malignant aetiologies were established by serial imaging, clinical outcome and histology. Imaging was performed with T1 and T2-weighted sequences, with contrast enhancement in some patients. Collapsed vertebrae were examined for appearance of marrow on T1 and T2-weighted sequences and after contrast administration, signal intensity of adjacent discs, degree of marrow involvement, involvement of posterior elements, presence or absence of paraspinal mass and end-plate integrity. Agreement between the final and radiological diagnosis was evaluated. RESULTS: There were 36 benign vertebral collapses (20 osteoporotic, 7 post-traumatic, 9 infective) and 22 malignant ones (20 metastatic carcinoma, 2 multiple myeloma). Features which pointed to malignant cause were hypointense marrow on T1-weighted images, marrow enhancement after intravenous contrast, greater than 50% marrow involvement and involvement of posterior elements. Of the vertebral collapses due to infection, 78% showed end-plate disruption. CONCLUSIONS: This study shows that MRI can be used to accurately differentiate between benign and malignant causes of vertebral collapse. Further differentiation between an osteoporotic, traumatic or infective cause can be done with the help of clinical history and evaluation of end-plate integrity.

Adult↗
PubMedDate not supplied

Management of severe bilateral nasal wall collapse.

OBJECTIVE: The aim of this study was to examine and analyze the pathology contributing to severe bilateral nasal wall collapse seen in certain revision rhinoplasty patients and identify those surgical maneuvers in the previous nasal surgery, which may have contributed to this complication; suggest alternatives or modifying steps in nasal surgery to prevent lateral wall collapse; analyze consecutive revision rhinoplasties and identify those patients who have complete bilateral nasal collapse at the internal nasal valve; and analyze the results achieved after surgical reconstruction of complete bilateral nasal collapse. PATIENTS: We identified 49 patients, who presented from 1990 to 2000 for revision surgery, who had bilateral collapse of the upper lateral cartilage. All patients had at least one previous rhinoplasty and all but 14 patients had undergone two or more procedures. The patients were reconstructed with a conchal cartilage graft placed through an external rhinoplasty approach. RESULTS: All patients complained of nasal obstruction with forced nasal inspiration. The collapse was visualized on inspiration and when prevented with intranasal positioning of a bayonet, all patients experienced an immediate improvement in nasal breathing. Postoperatively, all patients experienced this same improvement in their nasal airway. Collapse was not identified in any of the patients after surgery. Two patients underwent revision because of cosmetic asymmetries. CONCLUSION: We strongly recommend a cartilage overlay to reconstitute the rigid midline continuity of the upper lateral cartilages. Unfortunately, with any significant hump removal, this structural interruption is, to varying degrees, inevitable in most rhinoplasty techniques. The upper lateral cartilages can be sutured to circumvent some of the inferior drift, but this will not reconstitute the rigid lateral cantilever effect of the intact cartilage.

Adult↗
PubMed2006

Surveillance for World Trade Center disaster health effects among survivors of collapsed and damaged buildings.

PROBLEM/CONDITION: Survivors of collapsed or damaged buildings from the attack on the World Trade Center (WTC) were among those most exposed to injury hazards, air pollution, and traumatic events. REPORTING PERIOD: This report summarizes data from health outcomes collected during interviews conducted from September 5, 2003, to the close of the World Trade Center Health Registry (WTCHR) enrollment on November 20, 2004. DESCRIPTION OF SYSTEM: WTCHR will be used to monitor periodically the mental and physical health of 71,437 enrollees for 20 years. The analysis is limited to 8,418 adult survivors of collapsed buildings (n = 5,095) and buildings with major or moderate damage (n = 3,323), excluding those who were involved in rescue and recovery. RESULTS: A total of 62.4% of survivors of collapsed or damaged buildings were caught in the dust and debris cloud that resulted from the collapse of the WTC towers, and 63.8% experienced three or more potentially psychologically traumatizing events. Injuries were common (43.6%), but few survivors reported injuries that would have required extensive treatment. More than half (56.6%) of survivors reported experiencing new or worsening respiratory symptoms after the attacks, 23.9% had heartburn/reflux, and 21.0% had severe headaches. At the time of the interview, 10.7% of building survivors screened positive for serious psychological distress (SPD) using the K6 instrument. After multiple adjustments, data indicated that survivors caught in the dust and debris cloud were more likely to report any injuries (adjusted odds ratio [AOR] = 3.9; p< or =0.05); any respiratory symptom (AOR = 2.7; p< or =0.05); severe headaches (AOR = 2.0; p< or =0.05); skin rash/irritation (AOR = 1.7; p< or =0.05); hearing problems or loss (AOR = 1.7; p< or =0.05); heartburn (AOR = 1.7; p< or =0.05); diagnosed stroke (AOR = 5.6; p< or =0.05); self-reported depression, anxiety, or other emotional problem (AOR = 1.4; p< or =0.05); and current SPD (AOR = 2.2; p< or =0.05). Adjustment for SPD did not diminish the observed associations between dust cloud exposure and physical health outcomes. Building type and time of evacuation were associated with injuries on September 11, 2001 and reported symptoms; building type (collapsed versus damaged) also was associated with mental distress. INTERPRETATION: Two to three years after September 11, survivors of buildings that collapsed or that were damaged as a result of the WTC attack reported substantial physical and mental health problems. The long-term ramifications of these effects are unknown. Many survivors were caught directly in the dust and debris of collapsing towers, a dense cloud of particulate matter that might have produced or exacerbated these health effects. PUBLIC HEALTH ACTION RECOMMENDED: Long-term follow-up of building survivors and all other persons enrolled in WTCHR should be maintained, with particular attention to those persons exposed to the dust cloud. Some of these findings might lead to building designs that can minimize injury hazards.

Adult↗
PubMed2006

Oropharyngeal collapse predicts treatment response with oral appliance therapy in obstructive sleep apnea.

STUDY OBJECTIVES: To examine whether primary oropharyngeal collapse of the upper airway during sleep predicts treatment success with oral appliance therapy in patients with obstructive sleep apnea. DESIGN: Prospective physiologic study. SETTING: Multidisciplinary sleep disorders clinic in a university teaching hospital. PATIENTS: Twelve treatment-naïve adult patients with obstructive sleep apnea (apnea-hypopnea index > or = 10/h and at least 2 of the following symptoms: snoring, fragmented sleep, witnessed apneas, or daytime sleepiness). INTERVENTION: Custom-made mandibular advancement splint (MAS). MEASUREMENTS AND RESULTS: A baseline diagnostic polysomnogram confirmed AHI > or = 10 per hour. During the following acclimatization period, a custom-made adjustable MAS was incrementally advanced until maximum comfortable mandibular protrusion was reached. A second polysomnogram with MAS in situ determined efficacy. Following a 1-week washout period, a final sleep study was performed using multisensor catheters (with and without MAS, in random order during the same night) to determine upper-airway closing pressures and the site or sites of upper-airway collapse. MAS resulted in significant improvements, mean +/- SEM, in AHI (22.0 +/- 2.6 vs 9.2 +/- 1.9/h, p < .01) and upper-airway closing pressures during stage 2 non-rapid eye movement sleep (-1.1 +/- 0.3 vs -2.8 +/- 0.5 cm H2O, p < .01). All 4 patients with primary oropharyngeal collapse achieved an AHI < 5 per hour. Only 1 of the 8 patients with primary velopharyngeal collapse achieved an AHI < 5 per hour. Oropharyngeal collapse, compared with velopharyngeal collapse, predicted treatment success with MAS (p < .02). CONCLUSIONS: These preliminary data suggest that primary oropharyngeal collapse of the upper airway during sleep is an important predictor of treatment outcome with MAS therapy.

Adult↗
PubMed1986

Comparison of resuscitation of sheep and dogs after bupivacaine-induced cardiovascular collapse.

This study evaluated interspecies sensitivity and ability to resuscitate pentobarbital anesthetized sheep and dogs after cardiovascular toxic doses of bupivacaine. Every minute, 3 mg/kg of bupivacaine was injected into the right atrium over the course of 10 sec until cardiovascular collapse occurred. While the bupivacaine was given, the animals were made apneic for 90 sec and then ventilated with 100% oxygen. After the bupivacaine administration, cardiovascular collapse occurred in the form of electromechanical dissociation progressing to asystole in dogs, whereas in sheep the predominant rhythm was ventricular fibrillation leading to asystole. Resuscitation was performed using open chest heart massage, bretylium for treatment of ventricular tachycardia and fibrillation, and epinephrine with atropine for treatment of electromechanical dissociation or asystole. The initial dose of bupivacaine used to cause cardiovascular collapse was 3.5 +/- 1.2 mg/kg in sheep and 24.6 +/- 8.5 mg/kg in dogs (P less than 0.01). All sheep and dogs were resuscitated from the first cardiovascular collapse. The resuscitation time was 2.1 +/- 1.0 min in dogs and 36.9 +/- 15.4 min in sheep (P less than 0.01). All dogs could be resuscitated after two additional cardiovascular collapses induced by bupivacaine, but no sheep could be resuscitated after a second cardiovascular collapse. Concentrations of bupivacaine in cardiac tissue and serum levels of bupivacaine after the last resuscitation attempt were significantly greater in the dogs than in the sheep. We conclude that sheep are more sensitive to bupivacaine than dogs, but that even sheep can be resuscitated after cardiovascular collapse produced by bupivacaine.

Animals↗
PubMed1994

Collapse of intertrochanteric hip fractures fixed with sliding screws.

A retrospective analysis of postoperative fracture collapse was performed using data from 142 patients with intertrochanteric hip fractures fixed anatomically with sliding screws. Of the 142 patients, 80 had unstable, three- or four-part hip fractures. Significant collapse (as defined by strict radiographic criteria relating the height of the femoral head to the greater trochanter and by Doppelt's criteria) was seen in 26 of the unstable fractures. The degree of collapse was classified as type I (minimal), type II (moderate), and type III (severe). Average follow-up was 31 months. An in-depth clinical and radiographic analysis was performed evaluating pain, limp, abductor weakness, and leg-length discrepancy. The numerical degree of both vertical and horizontal fracture collapse was also analyzed. Of the patients with moderate or severe collapse, 93% had a poor functional result, whereas all the patients with minimal collapse remained asymptomatic. Although postoperative fracture impaction of hips fixed with sliding screws may promote early healing, a high rate of union, and a low rate of hardware failure, excessive collapse is a problem that needs to be addressed.

Aged↗
PubMed1994

Increased thallium-201 uptake in collapsed lung: a pitfall in scintigraphic evaluation of central bronchogenic carcinoma.

UNLABELLED: This study evaluated whether 201Tl scintigraphy can differentiate a central bronchogenic cancer from a distal collapse consolidation. METHODS: Nine patients with squamous carcinoma with collapse confirmed by surgery and pathology were included. All patients underwent SPECT 1 hr after an intravenous injection of 3 mCi of 201Tl. Four-hour delayed SPECT was performed in five of the nine patients. The thallium activity in tumor and collapse was visually assessed on the basis of the pathologic findings. The specimens were prepared to have the same orientation and level with the SPECT image. RESULTS: The tumor activity appeared higher than that of the collapse in four patients, equal in three patients and lower in two patients. Both collapsed lung with and without superimposed inflammation also showed increased thallium activity. Delayed SPECT aided in tumor detection within a collapsed lung in only two of the five patients. CONCLUSION: Our study illustrates the need for caution in the interpretation of thallium scintigraphy in patients with central bronchogenic cancer and distal collapse.

Aged↗
PubMed1994

Nasal reconstruction with conchal cartilage. Correcting valve and lateral nasal collapse.

OBJECTIVE: To analyze the causes and the subsequent management of a collapsed valve and lateral nasal wall. The causes, including both predisposing anatomy and the surgical contributions, are presented. DESIGN: Analysis of consecutive patients with lateral nasal wall collapse corrected surgically with autogenous conchal cartilage grafts. PATIENTS: Fifty-six patients (37 women and 19 men; age range, 19 to 71 years) with nasal wall collapse were operated on. Forty-one of these patients had undergone at least one previous nasal procedure. The collapse of the nasal wall as a result of senescence was repaired in 13 patients. Two instances of nasal collapse were thought to be due to trauma. Forty-five patients had bilateral involvement. RESULTS: All 56 patients showed subjective improvement in nasal airway breathing. Rhinomanometry was performed in 24 patients and documented the improvement in all 24. Fifty-three patients noted an improvement in the appearance of their noses. Minimal morbidity was noted and no major complications were seen. Follow-up ranged from 18 months to 13 years. CONCLUSION: Surgery is very beneficial in cases of severe nasal collapse. This major functional complication warrants this major surgical reconstructive procedure and, as the results of this study demonstrate, predictable positive results with little morbidity and no major complications are possible.

Adult↗
PubMed1996

Molecular collapse: the rate-limiting step in two-state cytochrome c folding.

Experiments with cytochrome c (cyt c) show that an initial folding event, molecular collapse, is not an energetically downhill continuum as commonly presumed but represents a large-scale, time-consuming, cooperative barrier-crossing process. In the absence of later misfold-reorganization barriers, the early collapse barrier limits cyt c folding to a time scale of milliseconds. The collapse process itself appears to be limited by an uphill search for some coarsely determined transition state structure that can nucleate subsequent energetically downhill folding events. An earlier "burst phase" event at strongly native conditions appears to be a non-specific response of the unfolded chain to reduced denaturant concentration. The molecular collapse process may or may not require the co-formation of the amino- and carboxyl-terminal helices, which are present in an initial metastable intermediate directly following the rate-limiting collapse. After the collapse-nucleation event, folding can proceed rapidly in an apparent two-state manner, probably by way of a predetermined sequence of metastable intermediates that leads to the native protein structure (Bai et al., Science 269:192-197, 1995).

Cytochrome c Group↗