Microfluidic ratio metering devices fabricated in PMMA by CO2 laser.

We describe microfluidic fabrication results achieved using a 10.6 µm CO2 engraving laser on cast PMMA, in both raster and vector mode, with a 1.5″ lens and a High Power Density Focussing Optics lens. Raster written channels show a flatter base and are more U-shaped, while vector written channels are V shaped. Cross-sectional images, and, where possible, stylus profilometry results are presented. The sides of V-grooves become increasing steep with laser power, but broader shallower channels may be produced in vector mode by laser defocus, as illustrated. Smoothing of raster engraved channels by heated IPA etch, and transparency enhancement by CHCl3 vapour treatment are briefly discussed. An asymmetric Y meter is discussed as one method of diluting acid into seawater for dissolved CO2 analysis. Alternatively, microfluidic snake channel restrictors of different lengths in 2 channels may achieve the same result. Samples are fabricated with bases bonded by CHCl3 vapour treatment, and the devices are flow tested with either dilute food dye or DI water. Microfluidics fabricated in this manner have applications in ocean sensing of dissolved CO2 and other analytes, as well as broader sensing measurements, including biomedical sensors.

The analysis of dissolved inorganic carbon in liquid using a microfluidic conductivity sensor with membrane separation of CO2.

Autonomous continuous analysis of oceanic dissolved inorganic carbon (DIC) concentration with depth is of great significance with regard to ocean acidification and climate change. However, miniaturisation of in situ analysis systems is hampered by the size, cost and power requirements of traditional optical instrumentation. Here, we report a low-cost microfluidic alternative based on CO2 separation and conductance measurements that could lead to integrated lab-on-chip systems for ocean float deployment, or for moored or autonomous surface vehicle applications. Conductimetric determination of concentration, in the seawater range of 1000-3000 µmol kg-1, has been achieved using a microfluidic thin-film electrode conductivity cell and a membrane-based gas exchange cell. Sample acidification released CO2 through the membrane, reacting in a NaOH carrier, later drawn through a sub-µL conductivity cell, for impedance versus time measurements. Precision values (relative standard deviations) were ~ 0.2% for peak height measurements at 2000 µmol kg-1. Comparable precision values of ~ 0.25% were obtained using a C4D electrophoresis headstage with similar measurement volume. The required total sample and reagent volumes were ~ 500 µL for the low volume planar membrane gas exchange cell. In contrast, previous conductivity-based DIC analysis systems required total volumes between 5000 and 10,000 µL. Long membrane tubes and macroscopic wire electrodes were avoided by incorporating a planar membrane (PDMS) in the gas exchange cell, and by sputter deposition of Ti/Au electrodes directly onto a thermoplastic (PMMA) manifold. Future performance improvements will address membrane chemical and mechanical stability, further volume reduction, and component integration into a single manifold.

Long-term hydrolytically stable bond formation for future membrane-based deep ocean microfluidic chemical sensors.

Future ocean profiling of dissolved inorganic carbon and other analytes will require miniaturised chemical analysis systems based on sealed gas membranes between two fluid channels. However, for long-term deployment in the deep ocean at high pressure, the ability to seal incompatible materials represents an immense challenge. We demonstrate proof of principle high strength bond sealing. We show that polydimethylsiloxane (PDMS) is a preferred membrane material for rapid CO2 transfer, without ion leakage, and report long-term stable bonding of thin PDMS membrane films to inert thermoplastic poly(methyl methacrylate) (PMMA) patterned manifolds. Device channels were filled with 0.01 M NaOH and subjected to repeated tape pull and pressure - flow tests without failure for up to six weeks. Bond formation utilised a thin coating of the aminosilane bis-[3-trimethoxysilylpropyl]amine (BTMSPA) conformally coated onto PMMA channels and surfaces and cured. All surfaces were subsequently plasma treated and devices subject to thermocompressive bond annealing. Successful chemically resistant bonding of membrane materials to thermoplastics opens the possibility of remote environmental chemical analysis and offers a route to float-based depth profiling of dissolved inorganic carbon in the oceans.

A two centre observational study of simultaneous pulse oximetry and arterial oxygen saturation recordings in intensive care unit patients.

The influence of variables that might affect the accuracy of pulse oximetry (SpO2) recordings in critically ill patients is not well established. We sought to describe the relationship between paired SpO2/SaO2 (oxygen saturation via arterial blood gas analysis) in adult intensive care unit (ICU) patients and to describe the diagnostic performance of SpO2 in detecting low SaO2 and PaO2. A paired SpO2/SaO2 measurement was obtained from 404 adults in ICU. Measurements were used to calculate bias, precision, and limits of agreement. Associations between bias and variables including vasopressor and inotrope use, capillary refill time, hand temperature, pulse pressure, body temperature, oximeter model, and skin colour were estimated. There was no overall statistically significant bias in paired SpO2/SaO2 measurements; observed limits of agreement were +/-4.4%. However, body temperature, oximeter model, and skin colour, were statistically significantly associated with the degree of bias. SpO2 <89% had a sensitivity of 3/7 (42.9%; 95% confidence intervals, CI, 9.9% to 81.6%) and a specificity of 344/384 (89.6%; 95% CI 86.1% to 92.5%) for detecting SaO2 <89%. The absence of statistically significant bias in paired SpO2/SaO2 in adult ICU patients provides support for the use of pulse oximetry to titrate oxygen therapy. However, SpO2 recordings alone should be used cautiously when SaO2 recordings of 4.4% higher or lower than the observed SpO2 would be of concern. A range of variables relevant to the critically ill had little or no effect on bias.

Fabrication of impedimetric sensors for label-free point-of-care immunoassay cardiac marker systems, with passive microfluidic delivery.

Miniaturised point-of-care cardiac marker sensors are being developed, based on impedimetric sensing of cardiac enzyme capture by an antibody layer immobilised on a planar gold electrode sensor. Gold/Ti-on-glass substrates have been used, in a 2 electrode configuration, with antibodies immobilised on the working electrode. Microfluidic structures have been fabricated by a CO2 laser, in 25 mum thick pressure sensitive adhesive (PSA), on a PMMA lid, and the structure bonded on top of the planar sensor. Microfluidic blood/serum delivery has been investigated using a visualisation dye. Some flow problems are observed if the sensor is exposed to air for several days, suggesting that flow channel nanopillars and hermetic encapsulation may be required to guarantee flow properties in commercially produced modules. Work is ongoing to characterise the impedimetric signal changes for myoglobin capture by antimyoglobin, using these sensors. Fifty micron thick PSA, incorporating a robust spacer layer, will be used to give better definition of channel walls.

Complex segregation analysis for a three-allele locus: experience from an analysis of acid phosphatase activity.

A complex segregation analysis of acid phosphatase activity in 50 British families showed that the essential features of the acid phosphatase polymorphism, i.e., a major gene with three alleles, is retrieved by using the biallelic mixed model. The estimates of gene frequency and displacement obtained from segregation analysis were in agreement with those obtained from electrophoretic studies. In addition, there was evidence for a multifactorial component.

Ventilatory capacity in Nigerian school children.

Forced expiratory volume in one second (FEV1.0) and forced vital capacity (FVC) were determined in 1001 healthy Nigerian school children, aged between four and 16 years. The results were analysed with respect to the ages, heights, weights and body surface areas of the subjects. Among the variables used, weight showed the best correlation with FEV1.0 in both sexes and with FVC in males. Conversely, height showed the best correlation with FVC in females. However, the differences between these correlations were not significant. The median values obtained were lower than those reported in caucasian children at all height levels, but similar to the only available data in the literature for African children. Median FEV1.0 and FVC values were higher in males than in females at most ages, particularly the younger ones. Formulae for the medians and corresponding 2.5 and 97.5% points have been produced, using either height or weight as independent variable.

Total anomalous pulmonary venous connection. Repair using deep hypothermia and circulatory arrest in 44 consecutive infants.

Forty-four consecutive infants aged from 3 days to 10 months underwent repair of total anomalous pulmonary venous connection using deep hypothermia with circulatory arrest. There were eight (18%) early hospital deaths. Using multivariate analysis no significant association could be shown between early mortality and age or weight at operation, preoperative pulmonary or systemic pressure, and preoperative condition for patients undergoing operation during the most recent five year period. Late pulmonary venous obstruction developed in four (11%) of the survivors and all of these patients died.

The current status of reactions to intravenous contrast media.

A prospective 12-month survey in 272 United Kingdom hospitals was performed and data are presented on the incidence of adverse reactions following intravenous urography, contrast CT scanning, and intravenous cholangiography. Minor and intermediate reactions are commonest in young adults, but severe and fatal reactions predominate in the older age group. There is an increased risk of severe reactions in patients with a history of allergy or previous reaction to contrast media and in patients with heart disease. The risk of severe reaction is also increased in certain ethnic groups. There appears to be an association between the incidence of severe reactions and contrast medium dose. Etiology, prevention and treatment of reactions are briefly discussed.

Chlamydial infection of the cervix in contacts of men with nongonococcal urethritis.

An investigation of chlamydial infection in sexual contacts of patients with nongonococcal urethritis (NGU) was carried out to determine the clinical signs of infection in the cervix, and their response to chemotherapy, and the incidence of cervical infection in the presence of ectopy and oral contraception. In 202 consecutive female contacts of NGU the isolation rate of Chlamydia trachomatis was 35%. Hypertrophic ectopy and endocervical mucopus were present in 19% and 37% of chlamydia-positive patients respectively and, in all but one, resolved after treatment. Only 14% of those followed up after treatment developed yeast infections. The chlamydial isolation rate was significantly higher in patients with hypertrophic ectopy and endocervical mucopus. Cervical ectopy and oral contraceptives acted additively, each producing a significant effect on the chlamydial isolation rate in the presence of the other but not when present alone.

The value of signs and symptoms in the diagnosis of enlarged adenoids.

The purpose of this study is to investigate the relationship between preoperative signs and symptoms and the actual size of the adenoid found at operation in a group of children listed for adenoidectomy.