On-line high-performance liquid chromatography/mass spectrometric investigation of amyloid-beta peptide variants found in Alzheimer's disease

Abeta peptides are the major components of amyloid deposits in Alzheimer's disease. The presence of N-terminally truncated Abeta variants in amyloid may be a critical factor in Alzheimer's disease pathogenesis. These Abeta variants are less soluble and more amyloidogenic than full-length Abeta, making their separation, purification and identification difficult. High-performance liquid chromatography (HPLC) at elevated temperatures, coupled to electrospray ionization (ES) mass spectrometry (MS), enables rapid separation and identification of N-terminally truncated Abeta variants. This methodology provides a potential tool for exploring the importance of these Abeta variants in both the pathogenesis and diagnosis of Alzheimer's disease.

Peak expiratory flow rate guided protocol did not improve outcome in emergency room asthma

BACKGROUND AND AIMS OF STUDY: All current international practice guidelines recommend that treatment of acute asthma in the emergency room (ER) should be guided by the peak expiratory flow rate (PEFR). The aim of this study was to assess the efficacy of a PEFR guided protocol in treating ER asthma.

METHODS

We compared two different management protocols in adult asthmatics who presented to the ER with acute exacerbations. The routine protocol (RP) assessed and dispensed patients according to overall subjective and clinical response without predetermined criteria. The peak protocol (PP) used serial measurements of PEFR to guide intensity of bronchodilator treatment and fitness for hospital discharge. On the PP, a threshold PEFR of > or = 60% predicted had to be achieved before the patient could be discharged from the ER.

RESULTS

There were 79 patients in the RP group and 70 in the PP group. There was no significant difference between the two groups in baseline PEFR, PEFR after treatment and percentage increase in PEFR with treatment. The PP resulted in a higher hospital admission rate than RP.

CONCLUSION

We conclude that in the management of acute asthma in the ER, a PEFR guided protocol neither improved overall PEFR response to treatment nor reduced admission rates when compared with current management as it is practised in Singapore.

Efficacy of the conventional diagnostic approach to pulmonary tuberculosis

OBJECTIVE

The aim of this study was to evaluate the efficacy of the current clinical approach to the diagnosis of culture positive pulmonary tuberculosis (PTB) in hospitalised adult patients.

METHOD

We examined the case records and chest X-rays (CXR) of 199 adult patients with culture positive PTB diagnosed from 1993 to 1995. Patients were divided into two groups: early treatment (ET) and delayed treatment (DT) of PTB. DT were patients who received treatment only after respiratory specimens had returned with positive culture results. We also compared the CXR of the DT group with a group of age, sex matched patients who did not have PTB (control). Usual CXR pattern for PTB was defined as: upper lobe acinar shadows, upper lobe cavitation or miliary pattern.

RESULTS

There were 199 patients with a mean age of 56 (19). One patient was HIV antibody positive and 27% were diabetics. There were 143 (72%) patients in the ET group and 56 (28%) in the DT group. The ET group was significantly younger and more likely to show usual features and cavitary disease on the CXR than the DT group. The diabetic patients had significantly more frequent cavitation than non-diabetics. When compared to a control group without PTB, the DT group was significantly more likely to show usual CXR pattern and less likely to have a clear CXR.

CONCLUSIONS

The conventional approach to the diagnosis of PTB is reasonably accurate and efficient enough for the majority of patients. The delay in the diagnosis and treatment of PTB was more common among elderly patients, patients with negative smear results and atypical CXR features. If PTB is suspected in elderly patients, an early decision should be made between empiric treatment and further diagnostic testing.

Absorption effect in the calculation of a second-order nonlinear coefficient from the data of a maker fringe experiment

The effect of light absorption by sample in the analysis of Makerfringe data for estimating a second-order nonlinear coefficient hasbeen studied experimentally. Two theories, one by Jerphagnon andKurtz that neglects the absorption effect and one by Herman and Haydenthat takes into account the absorption effect, were compared with theexperimental results. It was found that Jerphagnon and Kurtz'sformula was unable to predict correctly not only the magnitude but alsothe incident angle dependence or the sample thickness dependence of thesecond harmonic signal generated by the sample with strong absorption, whereas the theory by Herman and Hayden was able to make thosepredictions fairly well. It was also found that the error in theestimated nonlinear coefficient when one uses Jerphagnon and Kurtz'sformula could be as large as 2-4 times the true value, depending onsample thickness.

Ventilatory strategies for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a severe condition that has a high mortality. Mechanical ventilation is required and concepts have evolved over the last few decades as to the methods and principles guiding such ventilatory support. In particular, volutrauma as a feature of ventilator-associated lung injury has been well documented, leading to pressure-limited strategies with consequent permissive hypercapnia. Such an approach is in direct contrast to traditional ventilatory teaching of high tidal volumes and normal PaCO2. Current strategies therefore emphasis lower tidal volumes, adequate positive end-expiratory pressure (PEEP), minimum FiO2, and the use of pressure-control modes (plus or minus inverse-ratio ventilation). Hypercapnia is allowed to develop, and adjunctive methods are employed to improve oxygenation in order to minimise the "pressure-cost" of maintaining adequate oxygenation. With such an approach, overall mortality is reported to be around 40%.

Efficient Single-Mode GaAs/AlGaAs W Waveguide Phase Modulator with a Low Propagation Loss

We report a single-mode P-P-p-i-n-N-N GaAs/AlGaAs W waveguide phase modulator with a high phase modulation efficiency and a low propagation loss. The phase modulator with a W-shaped refractive-index profile utilizes a novel epilayer structure to reduce the propagation loss associated with doped layers and to obtain a phase modulation efficiency larger than those of P-i-N double heterostructure modulators. The phase shift and propagation loss were measured with a Fabry-Perot resonance method at 1.31-mum wavelength. A phase modulation efficiency as high as 34.6 degrees /V mm was measured for TE polarized light. Also propagation losses of less than 0.6 dB/cm were achieved. As a result, the W waveguide phase modulator that exhibits a high phase modulation efficiency and a low propagation loss have been experimentally realized for the first time as far as we know.

Emerging pathogens for pneumonia in Singapore

The death rate from pneumonia in Singapore has increased steadily over the past decade. The emerging respiratory pathogens may have contributed to this increased mortality. New challenges have arisen from changes in the characteristics of the host and the susceptibilities of the various pathogens to antibiotics. There has been a 60-fold increase in the incidence of penicillin resistance in Streptococcus pneumoniae, the major pathogen for community-acquired pneumonia (CAP). Gram-negative bacilli are the major pathogens in severe CAP with Klebsiella pneumonia being the most frequently isolated organism. There has been a small increase in the number of cases of Legionnaire's disease and a marked increase in the incidence of melioidosis. While the overall incidence of tuberculosis has been unchanged, the number of non-residents with tuberculosis has doubled in the past 5 years. The rising prevalence of human immunodeficiency Virus infection is reflected in an increasing number of apparently healthy young men who present with CAP caused by Pneumocystis carinii. There is increasing resistance to antibiotics among gram-negative bacilli and Staphylococcus aureus, the dominant pathogens in hospital-acquired pneumonia. New strategies are urgently needed to prevent the emergence of pathogens in the hospital environment which may be resistant to all known antibiotics.

Severe asthma

OBJECTIVE

To determine the morbidity and mortality of severe asthmatic patients needing intensive care in Singapore.

DESIGN

Retrospective review of admissions from January 1987 to March 1993.

SETTING

Urban teaching hospital.

PATIENTS

Forty-eight patients with forty-nine admissions with severe asthma requiring admission into the medical intensive care unit.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Forty-eight patients with forty-nine admissions with severe asthma requiring admission into the medical intensive care unit were identified during the study period. The majority (69%) were admitted directly into the intensive care from the emergency room, and 16 cases (33%) had cardiorespiratory arrest, of whom half survived hypoxic brain damage. Mechanical ventilation was needed in 30 cases (61%), with a mean duration of 3.3 days, and 2 pneumothoraces were recorded. Those who needed mechanical ventilation had significantly higher arterial pCO2 (98 mmHg vs 62 mmHg) and a lower arterial pH (7.1 vs 7.3). However, not all patients with hypercapnia (> 50 mmHg) needed mechanical ventilation. Hospital mortality was 12% (6 cases), while two others with hypoxic brain damage died shortly after hospital discharge. Mortality was not predicted by previous need for mechanical ventilation, length of asthma, or age. For the ventilated group alone, hospital mortality was higher at 20%. On an average follow-up of 133 weeks, there was only one death. Mean potassium level was 3.9 mmol/L with 13 cases (28%) of hypokalemia (< 3.6 mmol/L).

CONCLUSION

Severe asthma was associated with an appreciable mortality. Hypercapnia did not guarantee the need for mechanical ventilation. For those that survived their acute episode, there was one mortality out of 40 survivors after an average of 2 years of follow-up.

Excessive bronchoconstriction induced by histamine and effects of volume history in patients with bronchial asthma

The aim of this study was to examine the inter-relationships between the different effects of deep breaths and histamine provocation on airway function in patients with bronchial asthma. Group 1 consisted of 38 consecutive out-patients with newly diagnosed mild asthma, group 2 consisted of 20 patients with bronchial asthma of varying severity who were studied during clinical remission. We measured bronchial responsiveness (BR) to histamine inhalation as the dose of histamine which provoked a 20% fall in FEV1 (PD20). The fall in forced vital capacity (FVC) after inhaling the highest dose of histamine during each BR test was calculated and expressed as percentage of the value measured at baseline (delta FVC in percentage). We studied the effects of deep breaths on airway caliber in group 2 patients by comparing isovolumic flow rates on partial (P) and maximal (M) forced expiratory flow volumes curves expressed as the M/P ratio. The changes in residual volume (RV) after deep breaths (delta RV) were expressed as a percentage of the largest VC measured on the composite M and P curves. The patients in group 1 had significantly higher PD20 and lower delta FVC than patients in group 2. There was, however, no significant correlation between PD20 and delta FVC measurements in individual patients (r < 0.1, P > 0.05). The M/P ratio was significantly related to delta FVC (r = -0.6, P < 0.006). There was also a significant positive relation between the magnitude of increase in residual volume following deep breaths (delta RV) and the degree of fall in FVC following histamine inhalation (delta FVC) (r = 0.65, P = 0.001). This significant relationship between the degree of airway closure after a deep breath and airway closure after histamine challenge is a new finding. In patients with bronchial asthma, the effects of a deep breath on airway function may be indicative of the tendency for airway closure during BR testing.

Controlled trial of intrapleural streptokinase in the treatment of pleural empyema and complicated parapneumonic effusions

OBJECTIVE

To compare the efficacy of adjunctive intrapleural streptokinase (SK) with simple closed chest tube drainage (Drain) in the treatment of empyemas and complicated parapneumonic effusions.

METHOD

This was a controlled study of 52 patients (mean age, 57 years; 41 men) with pleura space sepsis. Forty patients (77%) had empyema and 12 had complicated parapneumonic effusions. Twenty-nine patients were treated with Drain only while 23 received, in addition, repeated daily SK, 250,000 U in saline solution (mean, 5.3 days).

RESULTS

The two groups of patients had comparable degrees of peripheral blood leukocytosis, frequency of loculated effusions, pleural fluid pH, and lactate dehydrogenase levels. Infective organisms were isolated in 54% of which 32% were anaerobic and 21% were polymicrobial infections. The incidence of surgical decortication was 17% and mortality was 15%. A significantly larger volume of pleural fluid was drained from patients in the SK treatment group (2.0 [1.5] L) than those in the Drain treatment group (1.0 [1.01] L). There were no significant differences, however, between the two treatment groups in terms of duration before defervescence, duration of hospital stay, the need for surgical intervention, or mortality rates.

CONCLUSION

We conclude that thrombolytic therapy increased the volume of fluid drained from pleural empyemas but did not markedly reduce morbidity and mortality.

Electrochemical disinfection of drinking water using an activated-carbon-fiber reactor capable of monitoring its microbial fouling

An electrochemical reactor employing activated carbon fibers (ACF) was constructed for the disinfection of bacteria in drinking water. The application of an alternating potential of 1.0 V and -0.8 V versus a saturated calomel electrode, for disinfecting and desorbing bacteria, enabled reactor operation for 840 h. Drinking water was passed through the reactor in stop/flow mode: 300 ml/min flow for 12 h and no flow for 12 h, alternately. The bacterial cell density in treated water was always been less than 20 cells/ml. It was also found that the formation of biofilm on the ACF reactor caused an increase in current, enabling the self-detection of microbial fouling.

Treatment of complicated parapneumonic effusions and pleural empyema: a four-year prospective study

We studied prospectively the microbiologic findings, management, including the use of intrapleural streptokinase to improve pleural drainage, and outcome of 33 patients with complicated parapneumonic effusions (6) frank empyema (27) treated by our unit over a 4-year period. The mean age was 61 years, with more male (26) than female (7) patients. Seventy-nine percent of the patients had some form of underlying illness, especially chronic lung disease (46%), followed by diabetes mellitus (23%). Fifteen percent of the pleural collections were loculated. Pleural fluid cultures were positive in 58%, Staph aureus and Kleb pneumoniae being the most prevalent aerobic isolates. The incidence of anaerobic isolates was 32%. Besides empirical antibiotics, all patients had drainage of the pleural collections at diagnosis. Four patients were treated with needle aspiration; 28 (85%) required thoracostomy tube drainage for a mean of 8 days, 5 of these went on to surgical decortication. Thirteen patients received intrapleural streptokinase (SK) to facilitate drainage, with significant increase in the volume drained. The mean duration of stay for the whole group was 22 days. The administration of intrapleural SK did not significantly shorten the duration of hospital stay. There were six deaths (18%), none as a direct result of the empyema. We describe a therapeutic approach to parapneumonic effusions and empyema which tailors the interventional modality to the clinical stage of disease.

Treatment of severe exacerbation of chronic obstructive pulmonary disease with mask-applied continuous positive airway pressure

The efficacy of mask-applied continuous positive airway pressure (CPAP) in the treatment of patients with acute severe exacerbations of chronic obstructive pulmonary disease (COPD) was examined. Ten patients with severe exacerbation of COPD who had deteriorated during conventional therapy were treated with face-mask delivered CPAP (+5 cmH2O; Downs Vital signs Inc., New Jersey, USA) instead of tracheal intubation and mechanical ventilation. The patients that were selected required mental alertness, intact upper airway reflexes, the clinical signs of dynamic hyperinflation and a positive end-expiratory pressure auto-(PEEP) manifested as expiratory wheeze and grunting. Nine out of 10 patients responded promptly to mask-CPAP with less distress, better oxygenation, lower respiratory and pulse rates. There was no significant change in arterial carbon dioxide tension with mask-CPAP treatment. One patient deteriorated on mask-CPAP and required intubation and mechanical ventilation. Three patients died (none of these patients died during the acute period of exacerbation). It was concluded that Mask-CPAP may be an alternative to mechanical ventilation in the treatment of selected patients with severe hypercapnic exacerbations of COPD.

Severe community-acquired pneumonia in Singapore

BACKGROUND

There has been no previous study documenting the aetiology and prognosis of severe community-acquired pneumonia in Singapore. Patients with severe community-acquired pneumonia (SCAP) needing admission to a medical intensive care unit in Singapore were studied retrospectively.

METHODS

All patients admitted to the medical intensive care unit at National University Hospital from June 1991 to February 1993 with a diagnosis of community-acquired pneumonia were entered into the study. All patients had blood cultures, sputum cultures, serologies for Legionella and mycoplasma drawn on admission. APACHE II scores were determined prospectively.

RESULTS

Fifty-nine consecutive cases from June 1991 to February 1993 were identified with a mean age of 61 (SD 17) years. Nearly all the cases needed mechanical ventilation (90%) and overall mortality was 63%. An aetiological agent was identified in the majority of cases (68%), with Klebsiella pneumoniae being the most common agent (9 cases, 15%). Haemophilus influenzae and Streptococcus pneumoniae were identified in 8% (5 cases) and 5% (3 cases) of cases respectively. Pseudomonas pseudomallei was identified in 4 cases (7%) with a 100% mortality. Overall, gram-negative organisms were identified in 47% of cases. APACHE II was significantly higher in non-survivors. Age, creatinine levels, and the presence of bacteraemia were not prognostic features.

CONCLUSION

SCAP in Singapore carries a high mortality with the predominance of gram-negative organisms. Empiric antibiotics should include gram-positive and gram-negative coverage with specific coverage for Pseudomonas pseudomallei.

A profile of acute asthma patients presenting to the emergency room

We conducted a three-month prospective study on the profile of 70 acute adult asthmatic patients presenting to the Accident and Emergency Unit of a general hospital. The overall background asthmatic activity, clinical features of current exacerbation, maintenance drug treatment, gross psycho-social problems, previous experience of near-fatal asthma, and admission and relapse rates were documented. Ninety percent of the presentations were within 24 hours of the initial attack, with an average pre-hospital therapy duration of 6.5 hours. Sixty-seven percent sought further treatment after failure to find relief from their salbutamol metered-dose inhalers. Sixteen percent did not receive any treatment before presentation. Ten percent gave a past history of mechanical ventilation for severe or near fatal asthma. The majority (94%) had asthmatic symptoms in the mild to moderate range. About half (46%) had attended the Emergency Room (ER) at least once in the previous six months. On average, patients were on two items of drugs and 23% were on maintenance inhaled steroids. One-third (33%) of the patients were found to have psycho-social problems relating to their condition. The admission rate was 37% with relapse rate following ER discharge of 13%. The study showed a high proportion of patients with psycho-social problems relating to asthma, and a subset of patients with frequent visits to the ER. It also revealed the infrequent use of prophylactic therapy.

Granulocyte-macrophage colony-stimulating factor overrides the immunosuppressive function of corticosteroids on rat pulmonary dendritic cells

Pulmonary dendritic cells (DC) are present in extremely small numbers, but they are the most potent antigen-presenting cells in the lungs. Pure populations of DC can be isolated from the lung following collagen digestion, Percoll gradient centrifugation, removal of phagocytic cells and flow cytometric sorting for cells which exhibit high levels of surface major histocompatibility complex (MHC) class II molecules. Exogenous GM-CSF enhances this immunostimulatory capacity of the pulmonary DC. Soluble factors produced by type II airway epithelial cells and interstitial macrophages also enhance the immunostimulating capacity of pulmonary DC while alveolar macrophages suppress it. Thus, the function of DC may be regulated by locally produced cytokines. Corticosteroids are widely used as immunosuppressive agents in pharmacotherapy. While these agents are known to inhibit T cell proliferation and macrophage activation, their effects on DC are not known. We found that dexamethasone (Dex) pretreatment resulted in about a 50% reduction in the immunostimulatory capacity of rat pulmonary DC. This was associated with downregulation of MHC class II (Ia) expression. Dex-induced suppression of DC function could be restored with GM-CSF. We conclude that corticosteroids downregulate antigen-presenting capacity by direct suppression of pulmonary DC. This immunosuppressive effect of corticosteroids on DC may, however, be abrogated by exogenous GM-CSF. Corticosteroids and GM-CSF are therapeutic agents with potent direct immunomodulating effects on DC.

Simplified method for measuring urinary leukotriene E4

The conventional method for measuring urinary leukotriene E4 (LTE4) is by reversed-phase high-performance liquid chromatography (RP-HPLC), followed by radioimmunoassay (RIA) or enzyme immunoassay (EIA). We measured urinary LTE4 levels by two methods, HPLC with EIA and EIA alone after initial crude extraction of urine using an octadecyl reversed-phase extraction cartridge (Sep-Pak). Ninety-three urine samples from normal subjects and patients with bronchial asthma and adult respiratory distress syndrome were tested. The results showed that urinary LTE4 levels measured by EIA significantly correlated with those measured by HPLC plus EIA in the three groups (r = 0.88, 0.85, 0.68). The absolute values of urinary LTE4 measured by EIA without HPLC purification were higher than by EIA with HPLC purification. This suggests that HPLC may not be necessary for routine urinary LTE4 quantitation in different clinical situations.

Single-mode GaAs/AIGaAs W waveguides with a low propagation loss

We have designed a low-loss single-mode GaAs/AIGaAs optical waveguide with a symmetric five-layer heterostructure at the 1.31-µm wavelength by use of an effective-index method. Waveguides with a W-shaped refractive-index profile have been grown by use of a metallo-organic chemical vapor deposition technique and fabricated with a chemical wet-etching method. Propagation loss has been measured by use of the Fabry-Perot resonance method and a sequential-cleaving experiment. The measured loss is as low as 0.19 dB/cm for waveguides with 2.3-µm thickness and 4.3-µm width, which is comparable to the lowest-loss semiconductor waveguides yet reported. These waveguides could be used to make low-loss modulators for guided-wave devices.

Mirabilins (A-F): New Alkaloids From a Southern Australian Marine Sponge, Arenochalina mirabilis

An Australian marine sponge Arenochalina mirabilis (Lendenfeld 1887) collected from the Great Australian Bight has been found to contain six tricyclic alkaloids, mirabilins A-F (5)-(10), isolated and identified as their N-acetyl derivatives (11)-(16). Structures for the mirabilins were secured by detailed spectroscopic analysis.