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Biomedical subjects

H M Norwood

Publications and source records attributed to H M Norwood.

8 recordsLinked to original sources
PubMed1994

Comparison of extra-cellular fluid volume measurement in children by 99Tcm-DPTA clearance and multi-frequency impedance techniques.

Comparisons of extra-cellular fluid (ECF) volume estimates made by isotope dilution and electrical impedance techniques have been made in a group of 16 children. For each patient an estimate of ECF volume (Vt) was obtained from measurements of the blood clearance of 99Tcm-diethylene triamine penta-acetate (DPTA) which was compared with two estimates (Vi1 and Vi2) of ECF volume obtained from measurements of the whole-body electrical impedance at 50 frequencies in the range 1 kHz to 1.348 MHz and a third estimate Vh based on patient height, L, alone. The observed frequency response of the impedance measurements was fitted to a three-element equivalent-circuit model of whole-body impedance and gave a value of the ECF resistance R. Vi1 was obtained from Vi1 = a (L2/R) + b. Vi2 was given by c(W1/2L2/R)2/3 where W is the patient weight, and Vh was given by dL2 + e. The constants a, b, c, d, e were determined by comparison with Vt and were equal to 0.335 l omega m-2 (standard error = 0.01 1 omega m-2), 0.42 l (0.25 l), 0.33 l (omega 2kg-1m-4)1/2 0.007 l (omega 2kg-1m-4)1/3, 4.92 l m-2 (2.8 x 10(-5) lm-2), 0.13 l (0.41 l), respectively. Vi1, Vi2, Vh were linearly correlated with Vt (r2 = 0.98, 0.99, 0.95, respectively, p < 0.001), and upper and lower levels of agreement were given by +/- 0.95 l (Vt and Vi1), 1.44 l and -1.12 l (Vt and Vi2), +/- 1.5 l (Vt and Vh), respectively. Thus inclusion of the impedance data accounted for greater volume variation, but differences between the techniques were not significant (paired t-test and Mann-Whitney analysis) suggesting that more accurate and detailed measurements are required.

Adolescent↗
PubMed1990

Some factors influencing the efficiency of a jet nebuliser system.

The operation of a commercially available nebuliser system (Medic-Aid Ltd) is reviewed and the efficiency with which it produces an aerosol assessed. Defining the efficiency of nebulisation E as the fraction of the original mass of solution released as an aerosol it is found that the internal surface area, mass of solution used, the surface tension of the solution and the angle of tilt are important factors in determining E. Reducing the internal surface area of the nebuliser by means of Perspex inserts significantly increases E for 3 g of water from 49% for the unmodified system to 67% for the modified nebuliser (P less than 0.01). E increases with the mass of solution used but only exceeds 60% when 4.5 g water are used. Decreasing the surface tension of the solution from 7.2 x 10(-3) N m-1 (water) to 3.7 x 10(-3) N m-1 and 3.1 x 10(-3) N m-1 (using two different concentrations of a detergent in water) significantly increases E for 3 g solution from 49% to 65% and 69% respectively (P less than 0.05). Operating the nebuliser at a tilt also increases E. The measurements emphasise the importance of reducing the internal surface area of this type of nebuliser, using an adequate volume of drug solution (at least 4 ml is suggested) and operating the nebuliser at an angle to the vertical (20 degrees suggested) in order to maximise E. The surface tension of the drug solution is a further important determinant of E.

Evaluation Studies as Topic↗
PubMed1987

Monitoring of renal allografts by Doppler ultrasound.

Cyclosporin (CyA) associated renal dysfunction may be due to an arteriolopathy which reduces graft perfusion. We have prospectively monitored 27 renal allograft recipients, within 30 days of transplantation, by continuous wave Doppler ultrasound. Changes in the frequency shift waveform should indicate alterations in renal blood flow. Objective analysis was made in 112 waveforms by determining the ratio of the area under the frequency shift/time curve of the first half and the second half of the cardiac cycle (AUC 1/2 ratio). The AUC of the first half of the cycle indicates systolic blood flow plus the first part of diastolic flow, whereas the AUC of the second half indicates the remainder of diastolic flow. The AUC 1/2 ratio during ATN was not significantly different from that during stable renal function. However the ratio was significantly higher during acute rejection episodes and CyA nephrotoxicity. Although a statistical difference was demonstrated between acute rejection and CyA nephrotoxicity, the AUC 1/2 ratio alone does not differentiate these 2 conditions. These preliminary findings suggest CyA nephrotoxicity does reduce renal allograft blood flow and that this non-invasive technique may have a useful role to play in monitoring of patients immunosuppressed with CyA.

Cyclosporins↗
PubMed1984

Patient movements during radiotherapy.

A system using closed-circuit television has been developed to enable the measurement of patient movements to an accuracy of 1 mm during external beam radiotherapy. The circuitry is under the control of a microcomputer, which records the movement data on magnetic tape for later analysis. The results indicate that patients mostly remain within 1 mm of their original set-up position on the treatment couch.

Computers↗
PubMedDate not supplied

Technical note: a mains drop-out simulator.

During an investigation into mains-borne and radiated interference in the Ultrasound Department of St James's University Hospital, the need arose to determine the susceptibility of some equipment to the mains supply failing for very brief periods. This is known as 'drop-out'. A circuit was built that can drop out the mains supply to a piece of equipment for up to 15 consecutive half-cycles at a selectable repetition rate between approximately 0.4/s to 6.5/s. Circuit design was simplified by using a solid state relay (SSR), which turns on and off only at the zero crossing points in the mains supply waveform.

Electric Conductivity↗