14 research outputs found

    A review of scattering models for ultrasonic propagation in the trabecular bone

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    The use of ultrasound transmission measurements for the assessment of properties of bone in normal and diseased states

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    SIGLEAvailable from British Library Document Supply Centre-DSC:DX190561 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

    Effects of changes in packed cell volume on the specific heat capacity of blood: implications for studies measuring heat exchange in extracorporeal circuits

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    Extracorporeal circuits such as cardiopulmonary bypass (CPB) and renal dialysis machines cause active and/or passive loss of body heat. Attempts to quantify this heat loss are generally based on the Fick principle which requires knowledge of the specific heat capacity (SHC) of blood. As changes in packed cell volume are common, we investigated the effect of these changes on the SHC of blood over a range of packed cell volumes (PCV) from whole blood at 43.1% (3594 J kg-1 degrees C-1) to pure Hartmann's solution (4153 J kg-1 degrees C-1). The SHC of other fluids used during CPB was also measured and found to be 4139 J kg-1 degrees C-1 and 4082 J kg-1 degrees C-1 for normal saline and Gelofusine, respectively. The maximum variability in SHC over the range of PCV values encountered during CPB was calculated to be small (5.5%). We conclude that use of a constant value of SHC for calculation of thermal energy transfer is currently justified

    Development and application of a general purpose ambulatory monitor

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    This paper details the development and application of a multi-channel, general purpose, lightweight, portable monitor. The monitor is constructed with separate analogue and digital circuitry so that a dedicated analogue board may be developed for each new application with the same general purpose digital board, the latter requiring only changes to the firmware. At the heart of the digital circuit is an Arizona Microchip PIC 16C64 microcontroller, which can communicate with a computer via a serial port and perform both simple and relatively complex data analysis prior to storing data in memory. The low-power design enables the circuit to operate for potentially longer than a week on one set of batteries. Designed with medical applications in mind, preliminary data from three studies utilising the monitor are described. These include measurements of bladder pressure, personal exposure to pollutant gases and body temperature. The studies demonstrate the system's versatility in a variety of investigations requiring different signal processing and sampling protocols. It is hoped that, in the future, this ambulatory device will contribute to the diagnosis, treatment and understanding of a wide variety of disease conditions

    Effects of respiratory gas composition on transthoracic impedance

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    The transthoracic current generated during defibrillation comprises a cardiac and extracardiac component. Changes in impedance of transthoracic pathways will alter the transmyocardial current and may thus affect the outcome from defibrillation. The lungs comprise a large component of extracardiac tissue but the effects of different respiratory gases on transthoracic impedance has not been documented. We therefore measured transthoracic impedance (TTI) using different respiratory gas mixtures. TTI across self-adhesive defibrillation pads placed in the antero-apical position was measured at end-expiration using a 30 kHz low amplitude AC current. Ten healthy subjects aged 22-34 years (eight male) were studied whilst breathing alternate mixtures of air, 100% oxygen. 70% helium in 30% oxygen, and 70% nitrous oxide in 30% oxygen administered in a random sequence. There was no significant difference in TTI between any of the four respiratory gases. Therefore transthoracic current during defibrillation is unlikely to be affected by different respiratory gases. This is the first study to document that these respiratory gases do not change the impedance of transthoracic pathways
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