Unfavorable Location Research Articles

Muscular capabilities and workload of flight attendants for pushing and pulling trolleys aboard aircraft

Increasingly in the recent years, passengers’ services are extended into the ascent and descent flight phases on short distance flights. Trolleys containing the required meal and beverage items are used for these service operations and pushed or pulled along the aisles of the aircraft. Flight attendants reported about increased musculo-skeletal disorders and had been complaining about high physical workload from handling trolleys. In order to ensure acceptable load levels for pushing or pulling operations of trolleys, the physical capabilities of the collective “flight attendants” had been investigated by means of force measurements at maximum voluntary contraction (MVC) level and associated relevant anthropometrical and biometrical data. CEN and ISO standards as well as international and national German methods were used to derive recommended force limits for pushing/pulling operations with respect to the physical capabilities of the target group “flight attendants”. Comparing these recommended limits with the force requirements per shift under various conditions of trolley handlings (inclination of the floor, type and weight of trolley, mode of handling, frequency of operation) showed that especially for higher floor inclinations and trolley weights, flight attendants work (substantially) above recommended limits. It became also apparent that the handling of half-size trolleys is unexpectedly high demanding due to high vertical force components, caused by the unfavorable location of their center of gravity. Relevance to industry On short-distance flights, passengers’ services are performed by means of trolleys from the ascent to the descent flight phases. Flight attendants had been complaining about high physical workload. This study offers recommendations on maximum force limits for the handling of trolleys with respect to the muscular capacities and work situations of flight attendants on short-distance flights.

Posterior fossa extradural hematoma: our experience and review of the literature

Background Posterior fossa EDH is an uncommon entity, accounting for only 4% to 12.9% of all EDHs It has a characteristic clinical presentation, which if detected can be life-saving. Methods We sought to study the demographic features of patients with PFEDH and assess the clinical and radiologic predictors of the outcomes of as well as evaluate the various treatment modalities for this disease. We carried out a retrospective analysis of the cases of 61 patients with PFEDH who were admitted to the National Institute of Mental Health and Neurosciences (Bangalore, India) from 1991 through 2002. We analyzed various parameters and applied Fisher's exact test for statistical analysis. Results Mostly male individuals were affected with PFEDH. Their GCS score at admission and the presence of hydrocephalus as detected by CT scan determined the outcome of the patients. The children had better outcomes than did the adults. Patients with a good GCS score could be managed conservatively. Conclusions Posterior fossa EDH is rare. The PF is an unfavorable location of a hematoma. Good GCS scores have a favorable prognosis. Children have better outcomes than do adults, and the presence of hydrocephalus on CT scan is an ominous sign.

Successful treatment of intracranial ependymoma with leptomeningeal spread with systemic chemotherapy and intrathecal liposomal cytarabine in a two-year-old child

Ependymoma is the third most common CNS tumor in children. Neuraxis dissemination at the time of diagnosis is rare and occurs in fewer than 10% of patients. Recent advances in neuroimaging, neurosurgery, and radiation therapy have improved disease control and functional outcomes for children with ependymoma. However, children under the age of 3 years with ependymoma and leptomeningeal spread historically have had worse outcomes. It is not clear if age alone, or a combination of risk factors such us unfavorable location, which may prevent gross total resection, and withholding radiation therapy may have contributed to poor outcomes in younger age groups. The reason for attempting GTR is based on results from retrospective and prospective studies, where the most important prognostic factor is extent of resection. These patients are not candidates for craniospinal irradiation. Therefore, new therapeutic approaches must be attempted. This is a case report of a posterior fossa ependymoma with leptomeningeal dissemination in a two-year-old child, successfully treated with dose intensive chemotherapy and intrathecal liposomal cytarabine.

Problems in Bank Branch Inefficiency: Management, Scale and Location

This study evaluates the operating performance of a savings bank's branches using data envelopment analysis. In addition to the identification of the inefficient branches, the study breaks down the constituent components of operating efficiency, investigates scale properties, estimates the potential resource savings and output increments as well as examines the inefficiency problems in depth for each less-productive branch. The main results indicate that the operational inefficiencies are generally contributed by a greater degree of wasteful overuse of resources and to a smaller degree by operating at an inapropriate scale. Moreover, the savings bank is estimated to be able to save annual operating expenses of between USD 3.6 and 3.7 million, and to attract added deposits of between USD 63.9 and 199.9 million as well as to provide additional loans of between USD 9.3 and 15.3 million. Finally, the less efficient branches are identified as having the following disadvantages: weaker managers, diseconomy of scale, and unfavorable location. The findings of the study are consistent with the conceptions of management and provide a verification of their perceptions.

A Ruptured Pancreaticoduodenal Artery Aneurysm Repaired by Combined Endovascular and Open Techniques

Aneurysms of the pancreaticoduodenal arteries (PDA) are rare, accounting for <2% of all visceral aneurysms. An association with celiac artery stenosis has been reported. Many present with rupture, and a high mortality can be expected. Treatment is therefore challenging. Arterial ligation, anuerysmectomy, or bypass has been the mainstay of treatment. We recently treated a patient (who had no celiac axis) with a ruptured PDA aneurysm with combined open and endovascular techniques. A 46-year-old man was transferred to our hospital with a 1-day history of abdominal pain and syncope. On admission, an abdominal and pelvis computerized tomographic (CT) scan identified a large mesenteric hematoma, a 1.9 cm PDA aneurysm, and an occluded celiac axis. Mesenteric angiography revealed no active aneurysm leak and a stenotic superior mesenteric artery (SMA) origin. All hepatic blood flow originated from the stenotic SMA via markedly enlarged PDA collaterals. The patient was brought to the operating room, where absence of the celiac axis was confirmed. An aorto-to-proper hepatic and SMA bypass was performed using a bifurcated polyester graft. The next day, the patient was brought to the angiography suite, where the PDA aneurysm was coiled. Postprocedure CT scans confirmed thrombosis of the aneurysm. Ruptured mesenteric artery aneurysms are a challenging problem for the vascular surgeon. PDA aneurysms are rare and often occur in an unfavorable location. There appears to be an association with anatomic anomalies of the mesenteric circulation. Prompt invasive and noninvasive diagnostic studies aid in the definitive management of this often fatal problem. Combined endovascular and open techniques can be used for successful treatment.

Selected best demonstrated practices in peritoneal dialysis access

Many burdensome interventions that adversely affect the utilization of peritoneal dialysis as renal replacement therapy and patient satisfaction with this treatment modality can be avoided by early peritoneal access placement with embedded catheters, implantation techniques that preempt common catheter complications, and the use of access devices that provide flexibility in exit site location. Catheter embedding consists of subcutaneously burying the external limb of the catheter tubing at the time of the insertion procedure. Interval exteriorization of the catheter is performed when dialysis is needed. Earlier commitment by patients to peritoneal dialysis can be achieved by elimination of catheter maintenance until dialysis is necessary. Catheter embedding is a practical strategy to avoid temporary hemodialysis with vascular catheters and reduces stress on operating room access by allowing more efficient scheduling as non-urgent procedures. Laparoscopic catheter placement enables proactive techniques not available to other conventional insertion methods. These techniques include rectus sheath tunneling to prevent catheter tip migration, selective prophylactic omentopexy to prevent omental entrapment, selective resection of epiploic appendages to prevent catheter obstruction, adhesiolysis to eliminate compartmentalization, and diagnosis and simultaneous repair of previously undiagnosed abdominal wall hernias. Both standard and extended 2-piece catheter systems are necessary to customize the peritoneal access to a variety of body configurations. Catheters should be able to produce lower abdominal, mid-abdominal, upper abdominal, and upper chest exit site locations that facilitate management by the patient without sacrificing deep pelvic position of the catheter tip or resulting in excessive tubing stress during passage through the abdominal wall.

Density functional calculations of Ti-enhancedNaAlH4

The crystal structure and thermodynamic stability of a number of proposed models for the inclusion of Ti in NaAlH4 have been calculated by employing density functional theory in the generalized gradient approximation. It was shown that the least unfavorable location of Ti is close to the surface, replacing Al in the host lattice. Intricate complexation is simulated around the included Ti atom, and the preferred coordination number of H around Ti is eight. The Ti content was varied by the supercell approach, and even at 3 mol % Ti the resulting cell parameters were predicted to be significantly changed from the pure alanate. In addition, the most stable configurations were found to be thermodynamically metastable compared to the pure alanate and Ti standard state phases, and an ordered doped phase with significant bulk Ti content is thus ruled out by this study. It is proposed that Ti most probably works as a catalyst, situated at the surface of the alanate.

Early-Stage Hepatocellular Carcinoma in Patients with Cirrhosis: Long-term Results of Percutaneous Image-guided Radiofrequency Ablation

To perform a prospective, intention-to-treat clinical trial to determine the long-term survival rates of patients with hepatic cirrhosis and early-stage hepatocellular carcinoma (HCC) in whom percutaneous image-guided radiofrequency (RF) ablation was used as the sole first-line anticancer treatment. The study was performed with approval of the ethics committee, and written informed consent was obtained for all patients. From June 1, 1996, to January 1, 2003, 206 patients (143 men, 63 women; age range, 51-81 years; mean age, 67 years +/- 7) who were excluded from surgery and who had Child class A or B cirrhosis with either a single HCC less than or equal to 5 cm in diameter or multiple (as many as three) HCCs less than or equal to 3 cm in diameter each were enrolled. RF ablation was performed in 187 (91%) of 206 patients; 19 (9%) were excluded from RF treatment because of unfavorable tumor location. Follow-up ranged from 3 to 78 months (mean, 24 months +/- 21) and included measurement of alpha-fetoprotein level, ultrasonography at 3-month intervals, and spiral computed tomography at 6-month intervals. Patients were observed for recurrence of the treated tumor and for the emergence of new HCC tumors. Survival probabilities were estimated with the Kaplan-Meier method, and differences between survival curves were evaluated with the log-rank test. At the end of the study, 145 patients were alive, and 61 were dead. In the intention-to-treat analysis, overall survival rates were 97% at 1 year, 67% at 3 years, and 41% at 5 years. Median survival was 49 months. In the 187 patients treated with RF ablation, overall survival rates were 97% at 1 year, 71% at 3 years, and 48% at 5 years. Median survival was 57 months. The difference between the two survival curves was not statistically significant (P=.5094). Survival of patients treated with RF ablation was dependent on Child class (P=.0006) and tumor multiplicity (P=.0133). Patients who had Child class A cirrhosis with solitary HCC (n=116) had 1-, 3-, and 5-year survival rates of 100%, 89% and 61%; median survival was 65 months. The 1-, 3-, and 5-year recurrence rates were 14%, 49%, and 81% for the emergence of new tumors and 4%, 10%, and 10% for local tumor progression. RF ablation is an effective first-line treatment for cirrhotic patients with early-stage HCC who were excluded from surgery.

Endovascular Treatment of Giant P1/P2 Aneurysm by Direct Puncture of the Vertebral Artery

Vascular access is usually achieved through a femoral arterial puncture using a modified Seldinger technique. However, selective catheterization of the great cerebral vessels by femoral approach fails completely when the vessel is tortuous or atheromatous. In case of posterior vascular circulation aneurysms, transbrachial approach or direct puncture of the vertebral artery (VA) is an alternative. The aneurysms of the posterior cerebral artery (PCA) are reported to be rare. Due to unfavorable anatomic location, the PCA aneurysms are difficult to reach during surgical procedure. Endovascular embolization is at present considered to be more effective and safer treatment of the PCA aneurysms arising from different segments, offering a viable alternative to the surgical approach. We report the case of the giant left PCA aneurysm, located at the junction of P1/P2 segments, successfully treated by parent artery occlusion achieved after the direct puncture of the right VA which was used because both VAs were tortuous, irregular and their ostia were not accessible by femoral approach. According to different authors, parent artery occlusion appears to be safe in the treatment of P2 segment aneurysms, whatever the location of the occlusion. In our case we decided to perform this kind of treatment believing it was the only possible one.

Traumatic Pseudoaneurysm of the Brachiocephalic Artery following Medianoscopy: Initial Endovascular Repair Followed by Open Surgery—A Case Report

Endovascular stent graft repair of traumatic vessel injuries is gaining worldwide acceptance as a minimally invasive alternative to open surgical repair. However, effective endovascular repair fails if the aneurysm is not completely excluded. Conversion to open surgery may be unavoidable in such cases. Herein we describe the case of a 45-year-old man who was referred to our hospital with a pseudoaneurysm of the proximal brachiocephalic artery caused by biopsy during diagnostic medianoscopy. The pseudoaneurysm was primarily treated by stent-graft implantation into the proximal brachiocephalic artery. As a result of the unfavorable location of the lesion exclusion of the aneurysm failed and the initial therapy had to be extended to open reconstruction of the brachiocephalic artery. A bypass procedure from the aortic arch to the right common carotid artery was performed with reinsertion of the right subclavian artery to exclude the pseudoaneurysm.

A pseudo‐breakup observation: Localized current wedge across the postmidnight auroral oval

This study presents a detailed description and analysis of a pseudo‐breakup, which took place in the field of view (FOV) of the Magnetometers–Ionospheric Radars–All‐sky Cameras Large Experiment (MIRACLE) network (IMAGE magnetometers, Scandinavian Twin Auroral Radar Experiment [STARE] radars, and all‐sky cameras) on 3 November 1997 at 2212 UT. The activation lasted ∼10 min, occurred during geomagnetically quiet conditions (Dst ≥ −10 nT), and was followed by a global‐scale substorm about half an hour later (at 2246 UT). Both the pseudo‐breakup and the substorm had onsets at times corresponding to the Wind satellite observations of interplanetary magnetic field (IMF) BZ northward turnings as delayed to the subsolar magnetopause. The auroral display of the pseudo‐breakup was a mesoscale spiral with a counterclockwise winding direction. Simultaneously, STARE recorded clockwise plasma flow in the spiral surroundings. Applying the method of characteristics to the MIRACLE observations revealed that the spiral was associated with a localized current wedge (less than a few hours in MLT and about 4° in latitude), tilted in the northeast‐southwest direction. The maximum upward current density at the western edge of the wedge was about 6 A/km2, which clearly exceeds the threshold of spiral buildup (2.5 A/km2) suggested by earlier theoretical studies. About an hour before the pseudo‐breakup, the energy input from the solar wind to the magnetosphere (quantified by the ϵ parameter) exceeded the substorm threshold and the ionospheric conductivity was high enough to support substorm activity. Two likely reasons for the activation to remain localized were its unfavorable location in the morning side of the Harang discontinuity region and the abrupt decrease of the solar wind energy input at its onset time.

The restriction factors in the less developed areas and their development strategies in coastal China

Regional economic difference has aroused wide interests of numerous scholars and many academic papers have been published discussing on this.Most of the papers on regional disparities in China are concentrated on the macro scale approach, namely western China, middle China and coastal China problem. For a long period of time coastal China has witnessed fairly quick development with average GDP growth rate being over 10%, along with quite a number of less developed areas coexistence in the process. According to extreme difference analyses in provinces(or cities) concerning the ratio between the highest level and lowest level about per capita GDP, Guangdong and Shandong belong to strongly differetiated areas, Jiangsu and Fujian belong to obviously differentiated areas,and Zhejiang belongs to relatively equal area. In this paper, less developed coastal areas refer to those areas where economic situation is relatively low compared with the surrounding coastal regions. Here per capita GDP is used as a principal indicator to classify economic types. Among the 72 cities, 34 of them are economically less developed areas. The distribution of the less developed coastal areas is characterized by two main aspects: first, they are situated between three highly developed economic belts of Jingjintang (Beijing-Tianjin-Tangshan) and Jiaodong (Shandong province), Yangtze Delta, Zhujiang Delta and Hongkong; second, most of the coastal less developed areas are situated along provincial boundaries. Unfavorable location, natural conditions, economic structure and regional policy are the major restirction factors that hinder their economic development.The most important task is to quicken the pace of economic development in these areas.First,the regional infrastructure construction should be improved;second,the endogenous advantageous resources should be fully made use of;and third,relevant preferential policies should be formulated.

Endotracheal and bronchial laser surgery in the treatment of malign and benign lower airway obstructions.

Lower airway obstruction usually causes a remarkable reduction in the quality of life in cases of both benign and malignant tracheobronchial intraluminal tumor growth. Often this growth can also lead to premature death because of ventilation failure or, indirectly, because of fatal infections. In combination with external radiation therapy, laser surgery has become a standard means of treatment for these patients. From 1987-1999, 102 patients were treated with 270 laser treatment sessions (89 for malignant and 13 for benign diseases) at Turku University Hospital. Treatment was performed mostly with a combination of CO(2)-Nd:YAG laser via a rigid bronchoscope but also with a CO(2) laser and fiberoptic Nd:YAG laser. The treatment was considered successful in 208 cases of 270 treatment sessions (77%). The most important single factor affecting the success of the therapy was the unfavorable location of the tumor (40 cases). In these cases, the tumor was either located too distally in the bronchial tree, or the airway obstruction was found to be caused by extraluminal compression. There were two fatal complications (0.8%). Other complications affecting the quality of the procedure were minor intraoperative bleeding in 7.4% (20/270) and intraoperative ventilation problems in 7.0% (19/270). The 1-year survival of the patients with malignant disease was 37.1% (33/89), the 2-year survival 20.2% (18/89) and the 5-year survival 9.0% (8/89). Laser treatment is an effective method in maintaining tracheobronchial ventilation as a palliative treatment modality. Serious complications are possible, but considering the fatal nature of the disease, laser treatment can be recommended. In cases of benign diseases, endobronchial laser treatment was also very successful.

Long-term follow-up of patients with conjunctival melanoma.

Data from long-term follow-up examinations of patients with conjunctival melanoma are limited. A retrospective study of survival rates and local tumor relapse rates was performed on 85 patients initially treated between 1958 and 1993. Therapeutic procedures were local excision, local excision followed by brachytherapy, local excision combined with cryotherapy, and local excision followed by either irradiation or cryotherapy and adjuvant mitomycin C (MMC) application. The Kaplan-Meier method was used to estimate cumulative survival rates and event rate curves. Clinical parameters of the patients and the tumors were obtained and analyzed for their relation to tumor recurrence and death from metastatic melanoma using the multivariate Cox hazards modeling. The median follow-up duration among the surviving patients was 13.1 years (mean 13.8 years). The cumulative 10-year survival rate of the 85 patients based on all causes of death was 62.5%, and that based on tumor-related death was 77.7%. Patient age greater than 55 years, higher TNM category, and unfavorable tumor location (palpebral conjunctiva, fornix, caruncle, corneal stroma, eyelid) were identified as prognostic factors for death from metastatic melanoma. Tumors with unfavorable location, higher TNM grade, and excision alone as initial therapy showed a higher cumulative probability of local relapse than favorably located (bulbar and limbal conjunctiva) tumors, lower TNM grade, and excision plus adjuvant therapy. The behavior of conjunctival melanomas remains unpredictable in individual cases. To minimize local recurrence rate surgical excision should be combined with an adjunctive procedure such as irradiation, cryotherapy, or local chemotherapy with MMC. Randomized prospective multicentric studies are required.

Enhanced fluorescence resonance energy transfer between spectral variants of green fluorescent protein through zinc-site engineering.

Although spectral variants of GFP should in theory be suited for fluorescence resonance energy transfer (FRET) and therefore suited for studies of protein-protein interactions, the unfavorable location of the fluorophore 15 A deep inside the GFP molecule has especially impaired this application. Here, metal-ion site engineering around the dimerization interface known from the X-ray structure of GFP is applied to the cyan and the yellow spectral variant of GFP to stabilize the heterodimeric form of these molecules and thereby increase FRET signaling. The FRET signal, determined as the ratio between the maximal emission for the yellow variant, 530 nm, and the cyan variant, 475 nm, during excitation of the cyan variant at 433 nm was increased up to 8-10-fold in the presence of 10(-4) M ZnCl2 by engineering of two symmetric metal-ion sites being either bidentate or tridentate. A similar increase in FRET signaling was however obtained in a pair of molecules in which a single bidentate metal-ion site was generated by introducing a zinc-binding residue in each of the two spectral variants of GFP and therefore creating an obligate heterodimeric pair. It is concluded that FRET signaling between spectral variants of GFP can be increased by stabilizing dimer formation and especially by favoring heterodimer formation in this case performed by metal-ion site engineering.

Regression of intracerebral rat glioma isografts by therapeutic subcutaneous immunization with interferon-gamma, interleukin-7, or B7-1-transfected tumor cells.

Progress in the definition of the roles of various costimulators and cytokines in determining the type and height of immune responses has made it important to explore genetically altered tumor cells expressing such molecules for therapeutic immunizations. We have studied the effect of therapeutic subcutaneous (s.c.) immunizations on the growth of preexisting intracerebral brain tumor isografts in the rat. Transfectant glioma cell clones expressing either rat interferon-gamma (IFN-gamma), rat interleukin-7 (IL-7), or rat B7-1 were selected. After irradiation (80 Gy) the clones were used for immunization (administered in up to four s.c. doses in a hind leg over 14-day intervals starting 1 day after the intracranial isografting of the parental tumor). Significant growth inhibition of the intracerebral parental tumors was induced by transfectants expressing IFN-gamma and IL-7, respectively. The strongest effect was observed with IFN-gamma-expressing cells, resulting in cures in 37% of the males and in 100% of the females. Immunization with IL-7 had a similar, strong initial effect, with significantly prolonged survival in the majority of the rats but a lower final cure rate (survival for >150 days). The B7-1-expressing tumor clones induced cures in seven of eight female rats; however, no cures were seen in the male rats. It was also shown that the B7-1-expressing cells were themselves strongly immunogenic in female rats, requiring high cell numbers to result in a progressively growing tumor upon s.c. isografting; this was not the case in male rats. As a whole, the results imply that despite the unfavorable location of intracerebral tumors, therapeutic s.c. immunizations with certain types of genetically altered tumor cells can induce complete regressions with permanent survival and without gross neurological or other apparent signs of brain damage. The present results demonstrate complete regressions when immunizations are initiated shortly after intracranial isografting, when the intracerebral tumor is small.

Evaluation of Scotchbond multipurpose and maleic acid as alternative methods of bonding orthodontic brackets

Damage to the enamel surface during bonding and debonding of orthodontic brackets is a clinical concern. Alternative bonding methods that minimize enamel surface damage while maintaining a clinically useful bond strength is an aim of current research. The purpose of this study was to compare the effects on bond strength and bracket failure location of two adhesives (System 1+ and Scotchbond Multipurpose, 3M Dental Products Division) and two enamel conditioners (37% phosphoric acid and 10% maleic acid). Forty-eight freshly extracted human premolars were pumiced and divided into four groups of 12 teeth, and metal orthodontic brackets were attached to the enamel surface by one of four protocols: (1) System 1+ and phosphoric acid, (2) Scotchbond and phosphoric acid, (3) System 1+ and maleic acid, and (4) Scotchbond and maleic acid. After bracket attachment, the teeth were mounted in phenolic rings and stored in deionized water at 37° C for 72 hours. A Zwick universal testing machine (Zwick GmbH & Co.) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The analysis of variance was used to compare the four groups. Significance was predetermined at p ≤ 0.05. The results indicated that there were no significant differences in bond strength among the four groups ( p = 0.386). The results of the Chi square test, evaluating the residual adhesives on the enamel surfaces, revealed significant differences among the four groups (χ 2 = 0.005). A Duncan multiple range test revealed the difference occurred between the phosphoric acid and maleic acid groups, with maleic acid having bond failures at the enamel-adhesive interface. In conclusion, the use of Scotchbond Multipurpose and/or maleic acid does not significantly effect bond strength, however, the use of maleic acid resulted in an unfavorable bond failure location. (Am J Orthod Dentofac Orthop 1997;111:498-501.)

Visualisation of intracranial aneurysms by transcranial duplex sonography.

We examined 72 patients with 89 angiographically confirmed intracranial aneurysms, using transcranial colour-coded duplex sonography (TCCD) to determine the location and size of the aneurysm. The patients were admitted for coil embolisation of their aneurysm following subarachnoid haemorrhage or because of a cranial nerve palsy. Using a 2/2.25 MHz transducer, 42 aneurysms (47%) were seen satisfactorily through the temporal bone window or foramen magnum. In 24 cases (27%) image quality was insufficient as a result of a poor bone window, of the aneurysm having a diameter of less than 6 mm or of its being in an unfavorable location. In 23 other cases (26%) it was not possible to detect the aneurysm. Thrombosed structures could be demonstrated using TCCD in 8 of 12 giant intracavernous or basilar artery aneurysms, and in 15 of 19 aneurysms treated by platinum coil embolisation. TCCD offers a noninvasive method for monitoring progressive intra-aneurysmal thrombosis following coil embolisation and for follow-up of patients with untreatable fusiform aneurysms, should this be required. Detection of small aneurysms is limited by spatial resolution and insonation angles.

Long-term follow-up of the Palmaz stent for iliac occlusive disease

Thirty-eight limbs with iliac occlusive disease were treated with Palmaz stents from 1987 through 1991. Indications for stent utilization included dissection induced by percutaneous transluminal balloon angioplasty (PTA) (10), restenosis after PTA (nine), post-PTA residual stenosis (nine), multiple stenoses or occlusion (five), and unfavorable location (five). The ankle/brachial pressure index increased from 0.53 +/- 0.27 to 0.8 +/- 0.26 after stent deployment. The intraluminal pressure gradient decreased from 31.9 +/- 16.3 to 0.9 +/- 2.2 mm Hg after stent deployment. Complications included pseudoaneurysm (one), arteriovenous fistula (one), iliac perforation (one), groin hematoma (two), and occlusion (two). Follow-up arteriogram showed stenosis proximal or distal (n = 4) or within the stents (n = 4). These were treated with PTA or stents. Two patients required an aortobifemoral graft. Nine patients have died. Life table analysis showed a 1-, 3-, and 5-year primary and secondary cumulative patency of 87% +/- 5.9%, 74% +/- 8.2%, and 63% +/- 10% and 91% +/- 5.1%, 91% +/- 5.6%, and 86% +/- 7.6%, respectively. Palmaz stents, often required to salvage a PTA failure, appear to maintain overall patency at a high level. However, intimal hyperplasia and the progression of atherosclerotic disease may result in a need for additional procedures to obtain this favorable outcome.

Exchange between alkylammonium and sodium ions at the surface of dodecylsulfate micelles

The ion exchange between sodium and a series of alkylammonium cations of the general formula R 4− Y NH Y + (with R = methyl, ethyl, propyl, butyl; Y = 0 to 4), at the surface of dodecylsulfate micelles, was studied using fluorescence techniques. The selectivity coefficients obtained indicate that all of the organic counterions considered bind more strongly to the micelles than do either sodium or ammonium ions. Replacement of hydrogen by methyl groups ( Y = 1 to 3) in the ammonium ion increases the binding strength, the free energy increment for transfer of the counterion from water to the micelle, Δμ O, being −300 ± 30 cal/mole per methyl group. For alkylammonium ions, a Δμ O for transfer of −570 ± 50 cal/mole per methylene group, irrespective of the number of alkyl chains, was found. This indicates that the binding strength of alkylammonium ions is dominated by their hydrophobicity, independent of the spatial distribution of the alkyl groups attached to nitrogen. The possible use of these results to decide between “open” or “structured” micellar models is discussed. Tetraalkyl ions show considerably lower binding affinities than might be expected from the total hydrophobicity of their chains. This result is interpreted in terms of an unfavorable location of the fourth alkyl chain.