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Biomedical subjects

S R Dodds

Publications and source records attributed to S R Dodds.

14 recordsLinked to original sources
PubMed2006

Measuring sub-bandage pressure: comparing the use of pressure monitors and pulse oximeters.

OBJECTIVE: To test the use of low-cost sub-bandage pressure monitors and pulse oximeters as part of a quality-control measure for graduated compression bandaging in leg ulcer clinics. METHOD: Twenty-five healthy volunteers (mean age 40 years) providing 50 limbs were bandaged with a four-layer compression bandaging system. The ankle systolic pressure (ASP) was measured using a pulse oximeter (Nellcor NBP-40) before applying the graduated compression bandages. Interface pressure was measured by placing pressure sensors on the skin at three points (2cm above the medial malleolus; the widest part of the calf; and a point midway between them) in the supine and standing positions. The ASP was measured again with the pulse oximeter after the bandage had been applied, and the effect of the bandage on the ASP was recorded. The actual pressure created by the bandage was compared with the required pressure profile. RESULTS: Interface pressures varied with change of position and movement. With the operator blinded to the pressure monitors while applying the bandages, the target pressure of 35-40mmHg at the ankle was achieved in only 36% of limbs ([mean +/- 95% confidence interval]; 32.3 +/- 1.6mmHg [supine]; 38.4 +/- 2.4mmHg [standing position]). With the help of the pressure monitors, the target pressure was achieved in 78% of the limbs. There was no correlation between the pressure monitors and pulse oximeter pressures, demonstrating that the pulse oximeter is not a useful tool for measuring sub-bandage pressures. CONCLUSION: The results suggest a tool (interface pressure monitors) that is easy to operate should be available as part of quality assurance for treatment, training of care providers and education.

Adult↗
PubMed2006

Use of ulcer size and initial responses to treatment to predict the healing time of leg ulcers.

OBJECTIVE: To test the following two hypotheses: the initial healing profiles of individual leg ulcers determine the longer-term outcome; healing time can be predicted from an initial ulcer size measurement and a sequence of further measurements recorded after treatment has started. METHOD: Twenty-three patients with venous leg ulcers were studied (10 male, 13 female). Digital images of the ulcers were taken at weekly intervals; ulcer size was measured electronically and the information stored in an electronic patient record. The healing profile for each ulcer was analysed by linear regression using the correlation coefficient (r) to indicate linearity. For [r] > 0.85 ([r] = modulus of r, [where r is negative], that is good linearity and hence wound healing), the predicted healing time was calculated from the initial size (cm2) and initial healing rate (cm2/week), and was compared with the actual healing time. RESULTS: The majority of ulcers (17/23) healed with linearity ([r] > 0.85). For these ulcers there was agreement between the predicted healing time and the actual healing time (correlation coefficient 0.95). CONCLUSION: Venous ulcers that respond to treatment appear to heal at a near constant rate. The initial response to treatment can be used to reliably estimate the healing time.

Aged↗
PubMed2003

The haemodynamics of multiple sequential stenoses and the criteria for a critical stenosis.

INTRODUCTION: Occlusive arterial disease is usually multi-focal but the cumulative functional effect of multiple arterial stenoses is not fully understood. We tested the hypothesis that a non-linear pressure/flow model (DeltaP=k1Q+k2Q2) that has been validated for single stenoses is also valid for multiple stenoses arranged in series. METHOD: The pressure/flow characteristics of three dissimilar modelled stenoses were measured individually and in different combinations using a hydraulic flow rig. RESULTS: The combined effect of multiple stenoses fitted the non-linear model accurately (R2=0.99) and approximated to the sum of the k1 and k2 parameters for each individual stenosis. For multiple stenoses the cumulative k1 was less than the predicted and the series order of the individual stenoses consistently altered the combined effect. CONCLUSIONS: A sequence of multiple stenoses is functionally equivalent to a single equivalent stenosis of greater functional severity and can be represented by a single viscous (k1) and inertial (k2) pressure loss coefficient. This finding allows the term 'critical stenosis' to be defined precisely in terms of the functional effect rather than the anatomical appearance, particularly where disease is multi-focal.

Arterial Occlusive Diseases↗
PubMed2002

The haemodynamics of asymmetric stenoses.

OBJECTIVE: Occlusive arterial disease is usually irregular with both symmetric (concentric) and asymmetric (eccentric) stenoses. Knowledge of the effect of stenosis geometry on stenosis haemodynamics is necessary to correctly interpret tests that measure stenosis severity anatomically. The independent haemodynamic effect of stenosis asymmetry has not been described. DESIGN: In vitro flow-rig measurement of the steady pressure/flow behaviour of rigid, 20mm long, square-ended symmetric and asymmetric stenoses in a 6.7-mm diameter tube using a blood analogue (40% glycerol). RESULTS: All stenoses, irrespective of geometry, had a linear resistance (R) to flow (Q) relationship such that R=k(1)+ k(2)Q where k(1) and k(2) are constants (corr>0.99, p<0.05). Asymmetry was found to have a significant haemodynamic effect if the stenosis severity is expressed as a diameter reduction but no effect if stenosis severity is expressed as an area reduction. The maximum flow for an inflow pressure of 90mmHg (Q(90)) fell from 2050 to 280ml/min as stenosis area reduction increased from 80% to 96%. CONCLUSIONS: Arterial stenoses exhibit flow-dependent resistance irrespective of their geometry. The effect of stenosis asymmetry can only be ignored if anatomical severity is expressed as a percentage area reduction. A clinically useful measure of stenosis severity is the maximum flow for a given inflow pressure.

Arterial Occlusive Diseases↗
PubMed1997

Early effect of carotid endarterectomy on arterial blood pressure measured with an ambulatory monitor.

BACKGROUND: Carotid artery disease and hypertension are associated, and carotid endarterectomy is often followed by acute changes in blood pressure. As the carotid sinus is responsible for short-term blood pressure control, occlusive carotid disease may contribute to the mechanism of preoperative hypertension. METHODS: Ten patients undergoing carotid endarterectomy and eight having a peripheral bypass procedure were studied 2 weeks before and 2 weeks after operation, using home ambulatory blood pressure measurement. RESULTS: A significant fall in both mean systolic (-14.4 mmHg) and mean diastolic (-12.7 mmHg) pressure was observed after carotid endarterectomy (P < 0.006), whereas no change was seen in controls. CONCLUSION: These results suggest that there is an increase in carotid sinus activity in patients following carotid endarterectomy and supports the hypothesis that carotid sinus dysfunction contributes to hypertension in patients with carotid artery disease.

Aged↗
PubMed1996

Effect of flow on the resistance of modelled femoral artery stenoses.

An accurate model of the pressure-flow relationship of a stenosis is necessary for the correct interpretation of haemodynamic measurements. Modelled femoral artery stenoses were tested in vitro and the pressure drop: flow ratio (resistance) was most accurately represented by a fixed component (Rf) combined with a variable component (Rv) that increased linearly with flow (Q) such that Rv = SvQ. For stenoses of 68-94 per cent area, Rf increased from 3.2 to 77.7 milliperipheral resistance units (mPRU), while Sv increased from 0.009 to 0.578 mPRU ml-1 min and Rv was dominant for physiological flow rates. It was concluded that the approximation of a significant stenosis to a fixed resistance is incorrect.

Blood Flow Velocity↗
PubMed1996

An objective evaluation of the effectiveness of different methods of displaying three-dimensional information with medical x-ray images.

RATIONALE AND OBJECTIVES: The authors determine the effectiveness of stereoscopy and vertical-axis rotation for displaying three-dimensional (3-D) information in x-ray images. METHODS: Simple x-ray images were simulated using ray tracing and computer-displayed in monoscopic static (MS), monoscopic rotating (MR), stereoscopic static (SS), and stereoscopic rotating (SR) formats. In two experimental tasks, participants including experts (radiologists and radiographers) were shown images displayed in these four formats. Performance was measured by participants' accuracy of judgment, amount of time taken, and confidence in each response. The experts also informally evaluated the displays using complex fluoroscopic skull images and a simulated diagnostic task. RESULTS: The results from both tasks were consistent and showed MS to be least effective and SR to be most effective on all measures. There was no difference in performance between the nonexperts and experts, whose informal feedback consolidated the experimental findings. CONCLUSIONS: It was found that rotational stereoscopic fluoroscopy is feasible and is an effective way of portraying 3-D information using x-rays.

Computer Simulation↗
PubMed1996

A survey of post-operative care after day case surgery.

A prospective survey of patients undergoing day surgery was performed with the main aim of identifying the need for post-operative follow-up after minor or intermediate surgery. The degree of patient satisfaction and the increased workload that this group of patients caused general practitioners was also analysed. Patients underwent either varicose vein surgery, inguinal hernia repair or vasectomy and were asked to return a prepaid reply questionnaire two weeks after surgery. Ninety-eight patients were recruited into the survey, 89 (90.8 per cent) correctly completed forms were returned. Of these patients 58 (69 per cent) believed that they would not benefit from an outpatient appointment, 19 (21.3 per cent) made one or more visits to their general practitioner but had no continuing problem at two weeks postoperation. Six (6.7 per cent) continued to have a problem and thought they would benefit from a surgical outpatient appointment. Of the five patients given routine follow-up appointments before discharge four expected no benefit from an outpatient appointment and only one wished to be seen. This survey suggests that patients should be given the option of an outpatient appointment after minor or intermediate surgery via a postal questionnaire. Unnecessary appointments would thereby be reduced.

Adult↗
PubMed1995

Neural networks.

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Attitude to Computers↗