Biomedical subjects

P G Niblett

Publications and source records attributed to P G Niblett.

8 recordsLinked to original sources

PubMed2005

The clinical effectiveness of hand held Doppler examination for diagnosis of reflux in patients with varicose veins.

OBJECTIVE: To assess the accuracy of hand held Doppler (HHD) as a rapid screening test for selecting varicose vein patients for duplex imaging. DESIGN: Prospective single blind study of consecutive patients in a randomised trial. MATERIALS: Use of hand held Doppler and duplex ultrasound scanners. METHODS: One thousand two hundred and eighteen legs (943 patients) were examined by HHD and then duplex. HHD examiners recorded whether they would normally have requested duplex. RESULTS: HHD results of one Clinical Assistant (166 limbs) were significantly poorer than all others and his results were excluded from analysis. Duplex would not have been requested in 645 of 1052 (62%) limbs. Among these HHD missed significant reflux in the long saphenous vein in 18 (3%) and the short saphenous in 25 (4%). Reasons for requesting duplex were popliteal fossa reflux (202); recurrent (94) or atypical (86) varicose veins; and possible previous thrombosis (67). Differences were observed between staff and units in requests for duplex; and in thoroughness and style of duplex reporting. CONCLUSIONS: Selective use of HHD can avoid duplex imaging for many patients, with a low failure rate for detecting correctable venous reflux. Observed variations between individuals and units in results of HHD and duplex imaging have implications for the increasing use of duplex by clinicians.

Adolescent↗

PubMed1998

Pressure-permeability relationships in basement membrane: effects of static and dynamic pressures.

The glomerular basement membrane (GBM) is an important component of the filtration barrier that is the glomerular capillary wall. Previously GBM permeability has been investigated only under static pressures and often within a supraphysiological range. We used Matrigel as a model of GBM and formed membranes at the base of filtration chamber. We measured membrane permeability under static and dynamic pressures. Matrigel membranes were size and charge selective toward neutrally and negatively charged dextrans. Their permeability (as measured by hydraulic conductivity) was found to decrease from 1.61 +/- 0.06 to 0.75 +/- 0.07 x 10(-6) cm.s-1.cmH2O-1 as static pressure increased from 6 to 78 cmH2O, an effect attributed to membrane compression. In comparison to static pressure, sinusoidal pressure waves with a mean pressure of 50 cmH2O decreased membrane permeability, e.g., fluid flux was reduced by a maximum of 2% to a value of 5.47 +/- 0.38 x 10(-5) cm/s; albumin clearance was reduced by a maximum of 5.2% to a value of 9.63 +/- 1.06 x 10(-6) ml.cm-2.s-1. Such changes were affected by the frequency of pressure wave application and could be attributed to a switching on and off of the membrane compression effect.

Animals↗

PubMed1997

Hand-held Doppler as a screening test in primary varicose veins.

BACKGROUND: Hand-held Doppler is in common use for evaluating varicose veins, but its accuracy in identifying the exact sites of venous reflux is inferior to that of duplex scanning. It has been suggested that duplex should be used to investigate all varicose veins, but this is currently impractical, and should be unnecessary if hand-held Doppler examination were shown to be an adequate screening test. METHODS: Eighty-five patients (122 legs) with primary varicose veins were evaluated using a hand-held Doppler in the outpatient clinic, according to a protocol. Patients then had venous duplex imaging. RESULTS: Different methods of assessing the long saphenous vein (LSV) (tourniquet and tapping tests, and examination at and below the groin) had similar sensitivities for detecting reflux (75-86 per cent), and together detected 91 per cent of cases. Six of the nine missed had a competent saphenofemoral junction, and five had low-velocity reflux. Hand-held Doppler assessment missed 11 cases of popliteal fossa reflux; only four involved the short saphenous vein (SSV), and most had low-velocity popliteal vein reflux. CONCLUSION: Hand-held Doppler examination missed LSV or SSV incompetence in 11 per cent of legs, but these included cases with short-duration and low-velocity reflux of dubious clinical importance.

Adult↗

PubMed1996

The place of duplex scanning for varicose veins and common venous problems.

Duplex scanning has become the 'gold standard' for confirming reflux and demonstrating anatomy in cases of lower limb venous disease. However, the large numbers of patients presenting with varicose veins (or with skin changes and ulcers) mean that routine use of duplex is impractical, and this investigation has still not become well established in many hospitals. In order to determine the proportion of patients likely to require duplex scanning (and other special tests-photoplethysmography and ascending venography) we reviewed a consecutive series of 201 patients referred to the vascular clinic of a district general hospital with 283 symptomatic limbs affected by varicose veins and/or skin changes and ulcers. Patients were examined clinically and with hand-held Doppler. Duplex scanning was then requested to check for reflux in the popliteal fossa and to examine the groin and residual long saphenous vein in some cases of recurrent varicose veins. Duplex scanning was required in 51 (18%) limbs, venography in 8 (3%), and photoplethysmography in only one limb. In total, special tests were needed in 60 (21%) limbs. Subsequently, 198 (70%) limbs were referred for surgery. We would now (in 1996) duplex scan every case with popliteal fossa reflux and most recurrences. Had all these been scanned, then 79 (28%) would have had special tests. This knowledge should help in planning the implications of a duplex scanning service for varicose veins, skin changes and ulcers.

Adolescent↗

PubMed1992

Reinforced vascular grafts: a comparative study.

Reinforced vascular grafts are designed to resist compression and flexion forces, for example in axillo-femoral or below-knee femoropopliteal reconstruction. This study compared eight types of 6-mm reinforced grafts (five polytetrafluoroethylene (PTFE) and 3 Dacron). On a specially designed rig, graft diameter and flow were measured during compression by a standard series of weights up to 3.6 kg, and on another rig grafts were flexed through 135 degrees. Meadox Microvel graft resisted compression best (p less than 0.05) but there were no important differences between the other grafts (Vascutek; Bard; Goretex Standard, Thin Walled and Removable Ring; Impra Standard and Thin Wall). Flexion produced no significant changes in flow through the grafts. In addition, five general surgeons were asked to score the ease of removal of reinforcement, passage of sutures, and the tendency of sutures to cut out of each graft. Removal of reinforcement and passage of sutures were easier with the PTFE grafts, but the Dacron was more resistant to sutures cutting out. This study shows that these grafts resist flexion and compression well. Their different handling characteristics and data on patency at different sites should remain the main determinants in choice of graft.

Blood Flow Velocity↗

PubMed1990

Which balloon embolectomy catheter?

This study compared seven makes of balloon embolectomy catheter currently available, testing the most commonly used 4 Fr catheters. The volume of fluid and inflation pressure required to burst balloons of each type were measured. All balloons showed a similar shape of inflation curve, but compliance varied considerably, and the pressure required to burst different balloon types varied from 1060 to 1920 cmH2O. Two balloon types consistently fragmented when they burst in free space. On a specially designed mechanical rig balloon catheters were pulled through a 6 mm tube containing a fixed stenosis, with continuous measurement of traction force and intraballoon pressure. Traction force varied from 34 to 129 g (median 40 g) during passage along the tube, and from 254 to 463 g (median 350 g) during passage through the stenosis. The shear force imparted by the balloon to the tube wall was also calculated. This study provides comparative data which may help to guide surgeons in their choice of balloon embolectomy catheter.

Catheterization↗

PubMed1988

Provisional study to quantify and compare parameters of urine leakage in stress and instability incontinence.

Apart from measuring the total volume of urine leaked over prescribed periods of time, the characteristics of urine losses have been ignored. In this provisional study, conducted on 217 female patients, parameters such as the number and volume of the individual losses contributing to the total have been measured and related to the simultaneous pressure changes recorded during natural-filling urodynamic investigations. Each episode of incontinence can thus be attributed unequivocally to stress or to detrusor instability. This enables the quantified parameters of urine losses of both groups to be compared. The results indicate that interesting differences exist between the two types of incontinence, the recognition of which might be valuable for diagnostic purposes and for the design, development and suggested usage of incontinence aids.

Exercise↗

PubMed1987

The vagina as an alternative to the rectum in measuring abdominal pressure during urodynamic investigations.

Pressure in the vagina as well as within the bladder and rectum was measured during urodynamic investigations. Rectal pressure is normally used to represent changes in abdominal pressure which, when subtracted from the total bladder pressure, provides a method of assessing detrusor function. This study showed that vaginal pressure represented changes in abdominal pressure more accurately and consistently than did rectal pressure, and the vagina is therefore recommended as an alternative site in conducting urodynamic studies.

Abdomen↗