Computationally two-dimensional finite-difference model for hollow-fibre blood-gas exchange devices

The goal of this research is to develop a predictive model with good absolute accuracy for blood-gas exchange devices. The proposed model, unlike existing models, is able to predict gas transfer to blood flowing outside oxygenating fibres without experimental data. The proposed model uses a finite-difference numerical technique to solve computationally two-dimensional gas exchange problems such as gas transfer to blood outside hollow fibres. The model is compared to bovine and human experimental data from the small test cells with microporous polypropylene fibres. The test cell flow rates range from 1 m litre min⁻¹ to 5 m litre min⁻¹ for a 72-fibre device. Shear-augmented oxygen diffusion appears to be present, although good accuracy is obtained with a nonaugmented diffusion model, particularly at lower flows. The maximum deviation of oxygen saturation predicted by a shearaugmented bovine blood model from the experimental regression line was 1·7 per cent.     

Static transducers for electrochemical dissolved-oxygen analyzers

Conclusions 1. Stationary models have been derived for planar and hemispherical cathodes, and these have been analyzed. 2. Conditions have been formulated for the devices to work in the measurement of pO₂, CO₂, Q, and K, which have been confirmed by experiment for an oxygen concentration meter. All-Union Medical Instrumentation Research Institute, Moscow. Translated from Meditsinskaya Tekhnika, No. 5, pp. 27–31, September–October, 1980.     

Design of pneumatic gas analyzers for anesthetics

Conclusions 1. The feasibility of pneumatic gas analyzers for respiratory anesthetic mixtures with a single evaporating anesthetic has been established. 2. A pneumatic gas analyzer for anesthetics satisfies the basic anesthesiological requirements and can be used as an integral part of anesthetic equipment. 3. The gas analyzer's data unit must be based on the differential principle to secure the required sensitivity and accuracy of gas analysis. 4. The need for gas analyzers for respiratory anesthetic mixtures with a single evaporating anesthetic can be satisfied by simple small-size pneumatic gas analyzers. All-Union Scientific-Research Institute for Medical Instrument Making, Moscow. Translated from Meditsinskaya Tekhnika, No. 3, pp. 18–21, May–June, 1973.     

Maximum likelihood estimation in calibrating a stereo camera setup

Motion and deformation of the cardiac wall may be measured by following the positions of implanted radiopaque markers in three dimensions, using two x-ray cameras simultaneously. Regularly, calibration of the position measurement system is obtained by registration of the images of a calibration object, containing 10-20 radiopaque markers at known positions. Unfortunately, an accidental change of the position of a camera after calibration requires complete recalibration. Alternatively, redundant information in the measured image positions of stereo pairs can be used for calibration. Thus, a separate calibration procedure can be avoided. In the current study a model is developed that describes the geometry of the camera setup by five dimensionless parameters. Maximum Likelihood (ML) estimates of these parameters were obtained in an error analysis. It is shown that the ML estimates can be found by application of a nonlinear least squares procedure. Compared to the standard unweighted least squares procedure, the ML method resulted in more accurate estimates without noticeable bias. The accuracy of the ML method was investigated in relation to the object aperture. The reconstruction problem appeared well conditioned as long as the object aperture is larger than 0.1 rad. The angle between the two viewing directions appeared to be the parameter that was most likely to cause major inaccuracies in the reconstruction of the 3-D positions of the markers. Hence, attempts to improve the robustness of the method should primarily focus on reduction of the error in this parameter.     

A fast method for calibrating video-based motion analysers using only a rigid bar

Video-camera systems are widely used in biomechanics and clinical fields to measure the 3D kinematic measurements of human motion. To be used, they need to be calibrated, that is the parameters which geometrically define the cameras have to be determined. It is shown here how this can be achieved by surveying a rigid bar in motion inside the working volume, and in a very short time: less than 15 s on a Pentium III. The exterior parameters are estimated through the coplanarity constraint, the camera focal lengths through the properties of epipolar geometry and the principal points with a fast evolutionary optimisation which guarantees convergence when the initial principal points cannot be adequately estimated. The method has been widely tested on simulated and real data. Results show that its accuracy is comparable with that obtained using methods based on points of known 3D coordinates (DLT): 0.37 mm RMS error over a volume with a diagonal ≈1.5m. A preferential absolute reference system is obtained from the same bar motion data and is used to guide an intelligent decimation of the data. Finally, the role that the principal points play in achieving a high accuracy, which is questioned in the computer vision domain, is assessed through simulations.     

Designing a public square for research computing

A set of principles is proposed for sponsors and developers of research computing applications that can increase the likelihood of successful adoption by researchers.     

The honeycomb-like structure of the bird lung allows a uniquely thin blood-gas barrier

Flying requires enormous energy and some birds have higher mass-specific maximal oxygen consumptions than any mammal. The bird lung is very efficient partly because of an extremely thin blood-gas barrier so that some birds have thinner barriers than any mammals. We show here that in addition to the total barrier being very thin, the interstitium which is responsible for the barrier's strength is extraordinarily thin. This observation is paradoxical because intense exercise raises the pressure in pulmonary capillaries and results in large stresses in the capillary walls thus predisposing them to structural failure. For example, all galloping racehorses break their pulmonary capillaries. We propose that the explanation for how the bird can be so highly energetic yet also have such apparently fragile capillaries is the mechanical support provided by the dense packing of rigid air capillaries around the blood capillaries in the gas exchanging region of the lung. This architecture is very different from that in the mammalian lung.     

Magnetic resonance imaging of thermal coagulation effects in a phantom for calibrating thermal therapy devices

A material has been developed and tested that permanently records thermal response patterns from heating devices. The material consists of a mixture of polyacrylamide and 18% w/w bovine serum albumin. Thermal denaturation is complete when the local temperature exceeds 70 degrees C, causing a large reduction in the T2 of the material. Three-dimensional distributions of "thermal damage" can be assessed using standard magnetic resonance imaging sequences. The material works well with microwave heating devices and is adaptable for use with ultrasound, radio-frequency, or laser heating devices. Suggested uses include characterizing heating devices prior to treatment and developing new clinical applications for thermal therapies.     

New techniques for calibrating the Lloyd—Haldane apparatus

1. A new way of measuring the graduation error in the stem of the Lloyd-Haldane burette is described, in which a fixed mass of water is made to occupy different parts of the stem. This gave the same answer as the gravimetric method, but was much easier.2. Two independent methods of measuring the ;meniscus error' gave values of 0.006 and 0.008 ml. respectively. It is concluded that the bulb volume can be measured gravimetrically with the burette inverted, provided that the value so obtained is corrected by adding about 0.007 ml.3. Alternatively, this estimation can be made with the burette the right way up, no correction then being needed. To do this the lower end of the burette must be blocked and a method of doing this without the need to fuse on a glass tap is described.4. After calibration by the above methods analyses on fresh air for CO(2) + O(2) gave a mean value of 20.98%, which, in the authors' view, is the correct value.5. The observer error was measured and from this the theoretical maximum accuracy of gas analysis by Haldane's method was calculated. It is concluded that the calculated% should be correct to the second decimal place in about half the analyses, the rest having an error of +/- 0.01%. Results approaching this were obtained.     

Feasibility of calibrating elongated brachytherapy sources using a well-type ionization chamber

Recently, elongated brachytherapy sources (active length >1 cm) have become commercially available for interstitial prostate implants. These sources were introduced to improve the quality of brachytherapy procedures by eliminating the migration and seed bunching associated with loose seed-type implants. However, the inability to calibrate elongated brachytherapy sources with the Wide-Angle Free-Air Chamber (WAFAC) used by the National Institute of Standards and Technology (NIST) hinders the experimental determination of dosimetric parameters of these source types. In order to resolve this shortcoming, an interim solution has been introduced for calibration of elongated brachytherapy sources using a commercially available well-type ionization chamber. The feasibility of this procedure was examined by calibrating RadioCoil 103Pd sources with active lengths ranging from 1 to 7 cm.     

Bubble-driven mixer integrated with a microfluidic bead-based ELISA for rapid bladder cancer biomarker detection

In this study, fine bubbles were successfully generated and used as a simple, low-cost driving force for mixing fluids in an integrated microfluidic bead-based enzyme-linked immunosorbent assay (ELISA) to rapidly and quantitatively detect apolipoprotein A1 (APOA1), a biomarker highly correlated with bladder cancer. A wooden gas diffuser was embedded underneath a microfluidic chip to refine injected air and generate bubbles of less than 0.3 mm. The rising bubbles caused disturbances and convection in the fluid, increasing the probability of analyte interaction. This setup not only simplifies the micromixer design but also achieves rapid mixing with a small airflow as a force. We used this bubble-driven micromixer in a bead-based ELISA that targeted APOA1. The results indicate that this micromixer reduced the time for each incubation from 60 min in the conventional assay to 8 min with the chip, resulting in a reduction of total ELISA reaction time from 3–4 h to 30–40 min. Furthermore, the concentration detection limit was 9.16 ng/mL, which was lower than the detection cut-off value (11.16 ng/mL) for bladder cancer diagnosis reported in the literature. Therefore, this chip can be used to achieve rapid low-cost bladder cancer detection and may be used in point-of-care cancer monitoring.     

Evaluation of a mathematical algorithm for analysis of platelet volume distributions provided by Coulter hematological analyzers

The human platelet volume distribution has been shown log-normal. Coulter Counter S-Plus models, as well as JT and STKS models, give mean platelet volume and platelet distribution width parameters. A computerized mathematical method, working with an IBM-XT microcomputer, was designed to calculate median and modal volumes, as well as the percentage of platelets smaller or larger than operator definable volume thresholds, on the basis of mean platelet volume and platelet distribution width. Preliminary experiments defined that the optimal stability of results was obtained in the range 2-6 hours after the blood collection; further experiments demonstrated that the results of the mathematical analysis were reproducible and accurate, by comparison to data obtained from a channel analysis in all samples, even including macroplatelets and/or microplatelets. It was thus shown that Coulter counters working with a curve fitting process may provide a complete analysis of platelet distribution curves, which could be extensively used for studying pathological conditions involving changes in platelet parameters.