Browsing by Author "Bunn, Anthony E"

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    A plethysmographic device for determining human body volume and body density
    (1992) Cronjé, Thomas Frederick; Bunn, Anthony E
    The measurement of total body volume (V) (excluding lung volume) together with total body mass (m) is required in order to determine body density (d = m/V). From this, and using certain simplifying assumptions, it is possible to derive body composition in terms of fat mass (FM) and fat free mass (FFM) for the two-compartment model. The standard method for determining body volume (and hence body composition) is the densitometric (underwater weighing) technique based on Archimedes' principle. Three variables, notably residual lung volume (RV), total body mass (m) and submerged body mass are measured. RV is normally determined using a gas dilution technique while total body mass is simply measured using an accurate weighing scale. The submerged body mass is measured while the subject is totally submerged in a tank of water. This method, although relatively accurate, requires substantial apparatus and is time consuming. An alternative method, based on a polytropic thermodynamic process, is described for body volume measurement and thereby for body composition assessment. Previous use of this method by Taylor, et al. (1985) and Gundlach and Visscher (1986) were successful, but complex in terms of operating system. The described system comprises of a Perspex, sealed chamber. A cycling piston communicates with the chamber and imposes a minute sinusoidal pressure variation which is then measured. With a subject situated inside the chamber an increased pressure variation, caused by the decreased chamber volume, is then measured and processed to yield the displaced, or body volume. Subject comfort, above all, is greatly enhanced, in comparison to the underwater weighing method. A substantial advantage of the method appears to be that RV need no longer be measured. Variables such as a rise of temperature and humidity caused by the subject, as well as pressure variations due to respiration, were expected and found. These were analyzed both theoretically and experimentally and where necessary the data were modified to account for these variables using a personal computer. Calibration and preliminary validation of the instrument has been carried out using underwater weighing, bioimpedance and skinfold analyses and the error of measurement assessed. It appears that the described plethysmographic method is capable of measuring body volume and thus compares favourably to the underwater weighing method. Even though other groups have succeeded in employing similar principles, a substantially simpler mechanism has been used here.
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    Single frequency whole-body impedance studies in children with diarrhoeal disease and development of a variable frequency system
    (1993) Moshal, David Clive; Moshal, David Clive; Bunn, Anthony E
    Diarrhoeal disease is a major cause of infant mortality in this and other developing countries. The assessment of the degree of dehydration in these children is often based on subjective findings alone. These have been shown to be inaccurate as an assessment of the degree of dehydration. Whole-body impedance (WBI) is a method of measuring total body water which is used to assess body composition. This WBI technology, which operates at a single frequency, has been applied to the assessment of dehydration in children with diarrhoeal disease. The normal range of WBI was determined on a group of normally hydrated children and was found to have a mean of 746 Ω, a standard deviation of 85 Ω and 95 % confidence interval for the mean from 720 Ω to 772 Ω. WBI did not depend on age, mass, height or sex. The WBI of a group of children dehydrated from infantile gastroenteritis was measured both before and after rehydration. The dehydrated group had a mean WBI on admission of 1089 Ω and a standard deviation of 149 Ω with a 95 % confidence interval for the mean from 950 Ω to 1109 Ω. This value was significantly greater than that of the normal group. The WBI of the dehydrated group after rehydration was not significantly different from the normal group. In addition a variable frequency bioimpedance analyser was designed and tested. It was found to have an error of less than 1 % over the frequency range 1 to 100 kHz. The device was evaluated on 11 normal and dehydrated children. Four dehydrated children were tested before and after rehydration and this data was compared to a standard electrical model for WBI. It was found that the model could represent the measured data over this frequency range. The extracellular resistive element of the model was mainly responsible for the changes seen during rehydration, suggesting that dehydration in gastroenteritis is mainly due to fluid loss from the ECF compartment.
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    A system for the acquisition and digital analysis of lower limb flow waveforms
    (1994) Smith, Leonard; Capper, Wayne L; Bunn, Anthony E; Immelman, E J
    A PC based waveform acquisition and analysis system has been developed for use in aorta-iliac arterial assessment. A Motorola DSP56001 based system containing dual Analog to Digital converters is used to sample phase quadrature demodulated signals from a commercially available continuous wave Doppler unit. The Power Spectral Density is calculated using an autoregressive model from which the mean velocity waveform is calculated. This waveform is used to calculate the damping factor, vessel compliance and runoff resistance of a simple electrical model of the lower limb arterial circulation using a non-linear regression technique of curve fitting in the time domain. A pilot study using the system shows a significant separation (p < 0.001 Mann Whitney U-test) between the damping factors of a normal control group (quartile range = 0. 15 - 0.25 ; median = 0. 19) and a patient group with angiographically determined aorta-iliac arterial disease (quartile range = 0.45 - 0.89 ; median= 0.49).