Effect of MBE growth conditions on GaAsBi photoluminescence lineshape and localised state filling.

A series of gallium arsenide bismide device layers covering a range of growth conditions are thoroughly probed by low-temperature, power-dependent photoluminescence measurements. The photoluminescence data is modelled using a localised state profile consisting of two Gaussians. Good agreement with the raw data is achieved for all layers whilst fixing the standard deviation values of the two Gaussians and constraining the band gap using X-ray diffraction data. The effects of growth temperature and bismuth beam equivalent pressure on the localised state distributions, and other model variables, are both shown to be linked to emission linewidth and device properties. It is concluded that bismuth rich surface conditions are preferable during growth in order to produce the narrowest emission linewidths with this material. These results also show how the growth mode of a gallium arsenide bismide layer can be inferred ex-situ from low-temperature photoluminescence measurements.

Analysis of Bi Distribution in Epitaxial GaAsBi by Aberration-Corrected HAADF-STEM.

The Bi content in GaAs/GaAs1 - xBi x /GaAs heterostructures grown by molecular beam epitaxy at a substrate temperature close to 340 °C is investigated by aberration-corrected high-angle annular dark-field techniques. The analysis at low magnification of high-angle annular dark-field scanning transmission electron microscopy images, corroborated by EDX analysis, revealed planar defect-free layers and a non-homogeneous Bi distribution at the interfaces and within the GaAsBi layer. At high magnification, the qHAADF analysis confirmed the inhomogeneous distribution and Bi segregation at the GaAsBi/GaAs interface at low Bi flux and distorted dumbbell shape in areas with higher Bi content. At higher Bi flux, the size of the Bi gathering increases leading to roughly equiaxial Bi-rich particles faceted along zinc blende {111} and uniformly dispersed around the matrix and interfaces. FFT analysis checks the coexistence of two phases in some clusters: a rhombohedral pure Bi (rh-Bi) one surrounded by a zinc blende GaAs1 - xBi x matrix. Clusters may be affecting to the local lattice relaxation and leading to a partially relaxed GaAsBi/GaAs system, in good agreement with XRD analysis.

Mechanical ventilation with or without 7-day circuit changes. A randomized controlled trial.

OBJECTIVE: To determine whether a practice of not routinely changing ventilator circuits in patients who require prolonged mechanical ventilation is associated with an increased incidence of nosocomial pneumonia. DESIGN: Randomized controlled trial. SETTING: Intensive care units in two university-affiliated teaching hospitals. PATIENTS: 300 patients admitted to an intensive care unit who required mechanical ventilation for more than 5 days. INTERVENTION: Patients were randomly assigned to receive either no routine ventilator circuit changes or circuit changes every 7 days. MEASUREMENTS: The primary outcome measure was the incidence of ventilator-associated pneumonia. Other outcome measures included duration of mechanical ventilation, length of hospital stay, and hospital mortality. RESULTS: 147 patients were randomly assigned to receive no routine ventilator circuit changes, and 153 patients were randomly assigned to receive circuit changes every 7 days. The two groups were similar at the time of randomization with regard to demographic characteristics, intensive care unit admission diagnoses, and severity of illness. Ventilator-associated pneumonia was seen in 36 patients (24.5%) receiving no routine changes and in 44 patients (28.8%) receiving changes every 7 days (relative risk, 0.85 [95% CI, 0.55 to 1.17]). No statistically significant differences for hospital mortality, intensive care unit mortality, death during mechanical ventilation, death in patients with ventilator-associated pneumonia, or mortality directly attributed to ventilator-associated pneumonia were found between the two treatment groups (P > or = 0.11). Patients receiving changes every 7 days had 247 circuit changes costing a total of $7410; patients receiving no routine changes had a total of 11 circuit changes costing $330. CONCLUSION: The elimination of routine ventilator circuit changes can reduce medical care costs without increasing the incidence of nosocomial pneumonia in patients who require prolonged mechanical ventilation.

The safety and diagnostic accuracy of minibronchoalveolar lavage in patients with suspected ventilator-associated pneumonia.

OBJECTIVES: To assess the safety of minibronchoalveolar lavage done by respiratory therapists for the evaluation of suspected ventilator-associated pneumonia and to determine the diagnostic agreement between quantitative lower airway cultures obtained by the minibronchoalveolar lavage and protected specimen brush techniques. DESIGN: A prospective direct comparison of two diagnostic techniques. SETTING: An academic tertiary care center in St. Louis, Missouri. PATIENTS: 72 consecutive patients suspected of having ventilator-associated pneumonia on the basis of clinical evidence. INTERVENTIONS: Sampling of lower airway secretions using the protected specimen brush and minibronchoalveolar lavage techniques. MAIN OUTCOME MEASURES: Clinical complications and quantitative cultures of respiratory secretions. RESULTS: 72 patients suspected of having ventilator-associated pneumonia (first episode) were evaluated using minibronchoalveolar lavage. In 42 patients, lower airway secretions were also obtained using the protected specimen brush technique. No change in arterial blood oxygen saturation or heart rate occurred after minibronchoalveolar lavage (P > 0.2). Mean arterial pressure slightly increased with minibronchoalveolar lavage (baseline mean pressure, 90.1 mm Hg [CI, 88.4 to 91.7 mm Hg]; average within-person change, 2.6 mm Hg; P = 0.024). Good diagnostic agreement was shown for quantitative cultures obtained with the protected specimen brush and minibronchoalveolar lavage techniques (kappa statistic, 0.63; concordance, 83.3%); 10(3) colony forming units/mL was used as the threshold for a clinically significant culture result. CONCLUSIONS: Minibronchoalveolar lavage is a safe and technically simple procedure for obtaining quantitative lower airway cultures in patients requiring mechanical ventilation. Quantitative culture results obtained by minibronchoalveolar lavage are similar to those obtained by the protected specimen brush technique.

Hill-Sachs lesion and normal humeral groove: MR imaging features allowing their differentiation.

PURPOSE: To present a method of differentiating Hill-Sachs lesions from the anatomic groove in the posterolateral humeral head with use of magnetic resonance imaging. MATERIALS AND METHODS: A 360 degrees reference about the humeral head was established to define the locations of Hill-Sachs lesions and the anatomic groove on transaxial images. The extension of each finding along the longitudinal humeral axis was noted. Eight cadaveric specimens were sectioned and similarly analyzed. RESULTS: The locations of Hill-Sachs lesions and the anatomic groove in the circular reference frame were statistically significantly different (P < .001), yet their respective ranges overlapped. Along the longitudinal humeral axis, there was no overlap between the respective ranges of location (P < .001). CONCLUSION: A Hill-Sachs lesion is best differentiated from the anatomic groove by means of its more cephalic position along the longitudinal humeral axis.

Identification of gastric contractions from the cutaneous electrogastrogram.

OBJECTIVE: The objective of this study was to investigate whether gastric contractions in the fasting and fed state can be identified from the cutaneous electrogastrogram. METHODS: Simultaneous measurements of gastric myoelectrical and manometric activities were made in 10 healthy female volunteers from 1:00 AM to 9:45 AM. For manometric recording, a catheter incorporating solid state transducers was used. Cutaneous electrogastrography (EGG) was used for myoelectrical recording. All EGG data from 1:00 AM to 7:30 AM that occurred during motor quiescence, all EGG data that occurred during antral contractions, and 2-h EGG data after breakfast given at 7:30 AM were quantitatively analyzed and compared with each other. The EGG in three specific periods (fasting without antral contractions, fasting with contractions, and postprandial) was characterized by four parameters that include frequency, power, and stabilities of the frequency and power. RESULTS: 1) the peak power of the postprandial EGG was, respectively, 12.5 dB (about 2-fold increase in amplitude) and 6.8 dB (about 1-fold increase in amplitude) higher than that during motor quiescence (p < 0.05) and motor activity in the fasting state; 2) the dominant frequency of the postprandial EGG was, respectively, 6% and 13% higher than that during motor quiescence and motor activity (p < 0.05) in the fasting state; 3) the peak power of the fasting EGG was 48% more unstable during motor activity than motor quiescence (p < 0.05); 4) the stability of the EGG frequency was not significantly different during the three different periods. CONCLUSION: The EGG provides important and useful information for the assessment of gastric motility. An unstable EGG peak power is indicative of gastric contractions in the fasting state. An increase in EGG peak power and/or dominant frequency after a solid test meal suggests a normal postprandial gastric motility.

Objective and subjective results of a randomized, double-blind, placebo-controlled trial using cisapride to treat gastroparesis.

Cisapride, a relatively new gastrointestinal prokinetic agent, has been reported to increase gastric emptying and improve symptoms of gastroparesis. We investigated these effects of cisapride in patients with severe idiopathic and diabetic gastroparesis during an eight-week trial. The study design was a two-week single-blind placebo run in period to exclude placebo responders, followed by a six-week randomized, double-blind, placebo-controlled treatment phase. Delayed gastric emptying of solids on radionuclide scan and a minimum symptom intensity score were inclusion criteria. Forty-three patients were entered: four placebo responders and one other patient were excluded, leaving 19 patients randomized to cisapride (20 mg per os three times a day before meals), and 19 patients to placebo. Seven individual symptoms of gastroparesis were scored in a daily diary and reviewed at two-week visits. Sixteen patients in the cisapride group were able to complete the trial compared to 12 on placebo. The gastric emptying study was repeated at the end of treatment or at the time of withdrawal for those who dropped out. Cisapride significantly increased solid gastric emptying relative to baseline (P = 0.005) whereas placebo did not (P > 0.10). Cisapride did not significantly improve any symptom of gastroparesis relative to baseline or to placebo. We conclude that in a population of severe, refractory gastroparetic patients cisapride significantly accelerates gastric emptying of a solid meal without significantly reducing symptoms during a short-term treatment trial compared to placebo. Further trials of cisapride in less advanced and "end-stage" gastroparetics than studied here or combining cisapride with other prokinetic agents or antiemetics, are warranted.

Erythromycin: a motilin agonist and gastrointestinal prokinetic agent.

Erythromycin, a commonly used antibiotic, has recently emerged as a potential gastrointestinal prokinetic agent. This follows a decade of research into the mechanism of well-recognized gastrointestinal side effects of erythromycin. Early investigations demonstrated that erythromycin increased gastrointestinal motility, and more recent studies suggest that it fortuitously binds to and stimulates the receptor for the gastrointestinal peptide motilin. From this work it appears that a new and powerful class of gastrointestinal prokinetic agents will evolve from erythromycin and its derivatives. The role of motilin in the genesis of the fasting and fed patterns of gastrointestinal motility is emerging through the study of these motilin agonists.

Human sphincter of Oddi motility and cholecystokinin response following liver transplantation.

The reported incidence of sphincter of Oddi dysfunction following orthotopic liver transplantation has ranged from 3% to 7%. If sphincteric dysfunction is unrecognized, therapy may be inappropriate; when recognized, extensive surgery may be required. To prospectively identify patients with sphincteric dysfunction, we performed sphincter of Oddi motility studies through the t-tube tract three months after transplantation. Baseline sphincter motility and response to intravenous cholecystokinin were evaluated. The results of 10 subjects are reported; nine had normal basal sphincter pressure (16 +/- 5.8 mm Hg), and all had normal frequency (3.6 +/- 1/min), amplitude (86 +/- 31 mm Hg), and duration (4.5 +/- 1 sec) of phasic contractions. One subject had an elevated basal pressure (47 mm Hg). All, including the subject with elevated basal pressure, demonstrated a normal response to intravenous cholecystokinin with significant inhibition of phasic contraction frequency and amplitude. We demonstrate that simultaneous studies of the sphincter and duodenum can be obtained via the t-tube tract, providing the opportunity for prospective evaluation of sphincteric function. We conclude that sphincter of Oddi function usually remains normal following liver transplantation with choledochocholedochostomy.

The treatment of idiopathic and diabetic gastroparesis with acute intravenous and chronic oral erythromycin.

The objective of this study was to investigate the effects of intravenous erythromycin and chronic oral dosing of erythromycin on gastric emptying in patients with idiopathic or diabetic gastroparesis. Symptoms were assessed on oral dosing and during long-term follow-up in an ambulatory setting at a University referral center. Fourteen patients (10 idiopathic and four diabetic gastroparesis) were studied. Four patients left during the 4-wk study; two due to rash, one with cramps and vomiting on erythromycin, and one due to other medical problems. Ten patients completed the 4-wk study and commenced long-term therapy. Five of these patients experienced enough symptomatic relief to continue oral erythromycin long-term, being followed for an average period of 8.4 months. After initial documentation of delayed gastric emptying, patients received 6 mg/kg intravenous erythromycin lactobionate before a second gastric emptying study. Erythromycin base was then given orally at a dose of 500 mg tid-ac and qhs, with a final gastric emptying study performed after 4 wk. During long-term follow-up, erythromycin dosage was adjusted to minimize symptoms. Radionuclide-labeled gastric emptying of a solid meal was studied at baseline, following intravenous erythromycin, and after 4 wk of oral treatment with erythromycin. Symptom scores were assessed at baseline, at 4 wk, and then at 8-wk intervals. The percentage of the solid meal retained in the stomach at 2 h decreased from 85% +/- 11% (SD) at baseline to 20% +/- 29% following intravenous erythromycin (p < 0.001), and to 48% +/- 21% after 4 wk of oral therapy (p < 0.01 vs. baseline). There was a reduction in total symptom scores and a significant reduction in global assessment scores (p = 0.03). We conclude that erythromycin has a strong gastric prokinetic effect in both idiopathic and diabetic gastroparesis, and may represent a useful new therapeutic approach to this problem.

Prevention of selenite cataract by vitamin C.

Studies have been conducted to determine the efficacy of vitamin C in the prevention of cataracts induced by selenite. Administration of the latter to rat pups results in the development of advanced cataracts within 5 days. Treatment with ascorbate had a significant preventive effect. The observations indicate that selenite cataract is due to an oxidative stress to the lens. In addition, the findings are in conformity with our view that ascorbate functions as an anticataractogenic substance.

Ascorbic acid and the eye lens.

Exposure of mice to hyperbaric oxygen leads to an inhibition of the mitotic activity in the germinative epithelium of the lens. This is followed by an eventual development of cataracts. Cataracts have also been observed in human beings treated with hyperbaric oxygen for different afflictions. The lens damage and cataract formation appears to be due to in situ generation of active radicals and other active species of oxygen. These oxygen derivatives may also contribute to the multifactorial process of senile cataract formation in human beings. This hypothesis is based on in vitro experiments with rat lenses cultured in medium generating oxygen radicals, the generation of the radicals being accomplished either photochemically or enzymatically. The ability of the lens to transport rubidium and amino acids from such a medium is adversely affected. This is a recognized index of the damage to the tissue physiology. Scavengers of active oxygen species have been found to protect against this damage. Ascorbate, present in concentrations similar to that in the primate aqueous and lens, is also protective. The studies, therefore, point to an antioxidant and perhaps an anti-cataract effect of ascorbate. Pyruvate is another agent useful in this regard.

Hexose monophosphate shunt in rat lens: stimulation by vitamin C.

The metabolism of glucose through the hexose monophosphate (HMP) shunt has been studied in rat lens in vitro, in the absence and presence of ascorbic and dehydroascorbic acids. Both forms of the vitamin stimulated the utilization of glucose through the HMP shunt, the stimulatory effect of dehydroascorbate being substantially greater than that of ascorbate. The stimulatory effect of ascorbate, as well as of dehydroascorbate, was antagonized by sodium iodide, and N,N-bis (dichloroethyl)-N-nitrosourea, compounds known to inhibit glutathione reductase. N-ethylmaleimide also antagonized the stimulation. These findings, therefore, suggest that the DHA/AA redox couple acts in concert with the GSSG/GSH couple in stimulating the tissue shunt activity.

Ambulatory pulmonary arterial pressures in humans: relationship to arterial pressure and hormones.

Six healthy volunteers were studied by use of a continuous ambulatory recording technique to document the normal range and variability of pulmonary artery pressure (PAP) and to examine its relationship to systemic arterial pressure (SAP) both at rest and during standardized interventions. Vasoactive hormone levels were measured at frequent intervals. Over 8-10 h of study the mean PAP was 15.7/6.3 mmHg. Parallel changes in PAP and SAP were observed at rest and during exercise and eating. On the contrary, PAP rose and SAP fell with hypoxia, whereas smoking was associated with a rise in SAP but no change in PAP. Sympathetic nervous system activity, as gauged by plasma norepinephrine levels, may have contributed to pressure and heart rate changes during exercise and smoking, but activity of the renin-angiotensin system was not altered by any of the maneuvers. These results provide base-line information on the level of PAP and its variability in healthy volunteers under standardized conditions. Pressures within the systemic and pulmonary circuits change in parallel under some circumstances but move in opposite directions under other conditions.

Complications associated with the use of the neodymium:YAG laser.

The neodymium:YAG laser was used in a consecutive series of 93 eyes. Diagnosis was opacified posterior capsule in 81 eyes of which 52 were pseudophakic, with cystoid macular edema and vitreous strands in eight eyes, pigmented anterior hyaloid in two eyes, opacified anterior capsular flap in one eye and vitreous strand blocking an anterior chamber tube shunt to an encircling band tube in one eye. Despite significant visual improvement and reduction of cystoid macular edema, a variety of complications were seen. These included pitting of the implant in 26 eyes and cracks in four, two of which developed a vitreitis. These occurred more frequently in our earlier cases. Also seen was elevated IOP in six eyes, pupillary block in two, vitreous face rupture in five, cystoid macular edema in four, hyphemas in four, corneal injury in two and acute peripheral retinal hemorrhage in one eye.

Anterior chamber tube shunt to an encircling band in the treatment of neovascular glaucoma and other refractory glaucomas. A long-term study.

Long-term follow-up results of the anterior chamber tube shunt to an encircling band (ACTSEB) procedure are reported. Thirty eyes of 28 patients with neovascular glaucoma (Group I) and five eyes with non-neovascular refractory glaucoma (Group II) underwent this procedure. In Group I, the average preoperative intraocular pressure (IOP) was 57.1 mmHg. After surgery and average followup of 25 months 96% of eyes had a successful outcome with an average IOP of 15.8 mmHg (P less than 0.001). In Group II, despite multiple glaucoma surgical procedures, the average preoperative IOP was 54 mmHg. After surgery and average followup of 20 months 80% of eyes had a successful outcome with an average IOP of 19.8 mmHg (P less than 0.01). Revisions in our surgical technique utilizing a small entry with a 25-gauge needle into the anterior chamber and use of Healon resulted in a fully formed anterior chamber by two days. Clinical and experimental evidence is presented which suggest that aqueous filters through the tube to a reservoir around the encircling band.