Biomedical subjects
Publications and source records attributed to S Smye.
Thirty-four vascular and general surgical patients were recruited to a pilot study exploring skin blood flow using laser Doppler imaging and clinical assessment of skin erythema in relation to pressure sore development. Brief details of the results, sample size calculations and main study methodology are described in this mid-term report of the Tissue Viability Society Research Fellowship (1998-2000).
AIM: To investigate deposition patterns and to assess the delivery rate of two nebuliser systems in children with cystic fibrosis (CF). METHODS: Thirty three children with CF on regular treatment with nebulised antibiotics had radioisotope scans performed using technetium-99m labelled aerosol antibiotic generated by a Ventstream nebuliser (median mass diameter (MMD), 3.3 microm; delivery rate, 0. 075 ml/min) under conditions similar to their routine home practice. The inhomogeneity of the images was scored on a 1-10 rating scale (a low score indicating even distribution of the antibiotic), and stomach deposition was measured as a percentage of overall deposition. Twenty patients had a repeat scan using an Optimist nebuliser (MMD, 1.8 microm; delivery rate, 0.02 ml/min). RESULTS: The mean inhomogeneity scores were 5.4 in the Ventstream group and 3. 5 in the Optimist group. Mean stomach deposition was 17.3% in the 33 patients using the Ventstream nebuliser. There was an inverse relation between height and stomach deposition (r = 0.69). In the 20 patients who had both nebulisers, the mean percentages of stomach deposition for the Ventstream and Optimist nebulisers were 11.8% and 1.6%, respectively. The Ventstream nebuliser delivered antibiotic at an average 2.8 times faster rate than the Optimist nebuliser. IMPLICATIONS: A smaller particle size results in a more homogenous distribution of the antibiotic in the lungs with decreased stomach deposition. This should not be seen as a recommendation to use the Optimist nebuliser because more antibiotic was delivered to most parts of the lung with the Ventstream because of its increased delivery rate.
During saccadic motion the eyewall moves in a manner similar to a sinusoid or at least can be represented by a sine Fourier series. Motion of the vitreous is induced by the saccade and the vitreo-retinal interface is subjected to a time-dependent shear. This force may be a significant factor for retinal tearing in the neighbourhood of small retinal holes or tears. An analytical viscoelastic model and a numerical, Newtonian model of the motion of the vitreous are presented and compared. Under sinusoidal boundary motion the analytical model shows that a viscous wave propagates inward toward the axis of rotation and the characteristic length of this wave is a function of the Womersley number. The numerical solution indicates that the vitreous moves similarly to the analytical result with small secondary motion; however, this motion allows complete recirculation of the vitreous over large timescales. Excellent agreement is found between the analytical and numerical models. The time-dependent fluid shear is evaluated and from the analytical solution the maximum value of this is found to be proportional to R0 square root of v(omega)3, where R0 is the eye radius, v the modified complex viscosity and omega the sinusoidal frequency. This indicates that myopes have a larger shear force exerted on them by virtue of the larger eye size. Further work is directed toward a model which links the stress found in the sclera to that exerted on the vitreo-retinal interface by the vitreous fluid motion.
Myopia or short sightedness, is the most important predisposing factor to retinal detachment. The relative risk of detachment rises with increasing myopia. The model characterizes that because the severity of myopia increases with the axial length (antero-posterior diameter) of the eyeball, the relative risk of retinal detachment rises with increasing eye size. We present a mathematical model of the time-dependent shear stress force that occurs in the thin eye wall shell supporting the vitreous humour inside the eye globe during the acceleration and deceleration phases of saccadic eye movement. Results show that the shear force increases as the thickness of the eye wall decreases. It is common for myopes to have thinner eye wall tissue than emmetropes. In addition, if account is taken of the increased force required to provide normal saccadic movement of myopic (larger) eyes, then the shear force is up to seven times greater than that experienced for emmetropes.
Mathematical models that simulate the exchange of solute between multiple body compartments have been used to study the distribution, elimination, and transport of urea, water, electrolytes, and other substances in the dialysis patient. Within a compartment, such substances are assumed to be uniformly distributed while exchange between compartments or with the environment may occur in a number of different ways. Diffusion in response to concentration gradients between, for example, intracellular and extracellular spaces, and convection due to blood flow have been identified as the most important transport mechanisms. Any system with more than one compartment may develop nonuniform solute distribution or solute disequilibrium between compartments. The minimum number of compartments required to model a kinetic process such as urea removal during hemodialysis depends on the accuracy and temporal resolution required, with higher resolution calling for more compartments. A two-compartment model is adequate for most clinical purposes. The physiological meaning or anatomic counterparts of the mathematical compartments remain uncertain as both flow and diffusion transport mechanisms contribute to the disequilibrium. Processes such as access and cardiopulmonary recirculation may be represented as additional compartments with small distribution volumes and high mass transport rates. Failure to recognize the effect of multiple compartments will result in an inaccurate measurement of dialysis dose and an inadequate hemodialysis prescription with a predictably poor clinical outcome. Allowance for compartment effects is particularly important in patients receiving treatment with a high ratio of dialyzer clearance to total body water, now commonly encountered during short-time, high-efficiency dialysis.
Four patients with advanced hepatic malignancy have been investigated with a view to intra-arterial treatment with degradable starch microspheres (DSM) and mitomycin-C (MMC). Computer-assisted interpretation of data gathered during the administration of technetium-labelled albumin allows the degree of arteriovenous shunting within the liver to be measured. In a similar way, the effectiveness of DSM in blocking hepatic arterial flow is determined. Two patients showed unacceptably high levels of shunting (75% and 100%) and were excluded from further study. One patient with hepatocellular carcinoma shunted only 24% of the macroaggregated albumin, and flow through the liver was reduced to 48% by DSM therapy. This patient has undergone four courses of MMC without significant toxic complications. The last patient had 25% shunting. The DSM titration and the first MMC administration had to be abandoned because of severe abdominal pain and nausea related to a fracture of the intra-arterial catheter. Complications directly associated with the procedures have been acceptable. The relationship between flow reduction and the amount of DSM administered is non-linear, and the appropriate dose of DSM for each treatment must be titrated against both the patient's symptoms and the computer-generated flow indices.