Showing papers by "George Hamilton published in 2002"

Acute compartment syndromes

Abstract: Background: Acute compartment syndrome is both a limb- and life-threatening emergency that requires prompt treatment. To avoid a delay in diagnosis requires vigilance and, if necessary, intracompartmental pressure measurement. This review encompasses both limb and abdominal compartment syndrome, including aetiology, diagnosis, treatment and outcome. Methods: A Pubmed and Cochrane database search was performed. Other articles were cross-referenced. Results and conclusion: Diagnosis of limb compartment syndrome is based on clinical vigilance and repeated examination. Many techniques exist for tissue pressure measurement but they are indicated only in doubtful cases, the unconscious or obtunded patient, and children. However, monitoring of pressure has no harmful effect and may allow early fasciotomy, although the intracompartmental pressure threshold for such an undertaking is still unclear. Abdominal compartment syndrome requires measurement of intra-abdominal pressure because clinical diagnosis is difficult. Treatment is by abdominal decompression and secondary closure. Both types of compartment syndrome require prompt treatment to avoid significant sequelae. © 2002 British Journal of Surgery Society Ltd

Graduated compression stockings in the prevention of venous thromboembolism

Abstract: Background: Surveys still show a wide variation in routine use of deep vein thrombosis (DVT) prophylaxis despite its established place in current patient management. This article reviews the mechanism of action, efficacy and complications of stockings in preventing DVT. Methods: Relevant publications indexed in Medline (1966–1998) and the Cochrane database were identified. Appropriate articles identified from the reference lists of the above searches were also selected and reviewed. Results and conclusion: Graduated compression stockings reduce the overall cross-sectional area of the limb, increase the linear velocity of venous flow, reduce venous wall distension and improve valvular function. Fifteen randomized controlled trials of graduated compression stockings alone were reviewed. Stockings reduced the relative risk of DVT by 64 per cent in general surgical patients and 57 per cent following total hip replacement. The effect of stockings was enhanced by combination with pharmacological agents such as heparin; the combination is recommended in patients at moderate or high risk of DVT. Knee-length stockings are as effective and should replace above-knee stockings. Complications are rare and avoidable. © 1999 British Journal of Surgery Society Ltd

Compliance properties of conduits used in vascular reconstruction.

Abstract: Background: Compliance mismatch between native artery and prosthetic graft used for infrainguinal bypass is implicated in the aetiology of graft failure. The aim was to quantify the elastic properties of a new compliant poly(carbonate)polyurethane (CPU) vascular graft, and to compare the compliance properties of grafts made from CPU, expanded polytetrafluoroethylene (ePTFE), Dacron and human saphenous vein with that of human muscular artery.Methods: A pulsatile flow phantom was used to perfuse vessel and prosthetic graft segments at physiological pulse pressure and flow. Intraluminal pressure was measured using a Millar Mikro-tip catheter transducer and vessel wall motion was determined with duplex ultrasonography using an echo-locked wall-tracking system. Diametrical compliance and a stiffness index were then calculated for each type of conduit over mean pressures ranging from 30 to 100 mmHg by 10-mmHg increments.Results: The compliance values of CPU and artery (mean over the pressure range) were similar (mean(s.d.) 8.1(0.4) and 8.0(5.9) per cent per mmHg x 10(-2) respectively), although the elastic behaviour of artery was anisotropic unlike CPU, which was isotropic. Dacron and ePTFE grafts had lower compliance values (1.8(1.2) and 1.2(0.3)per cent per mmHg x 10(-2) respectively, averaged over the pressure range). In both these cases, compliance and stiffness differed significantly from that of artery over a mean pressure range of 30-90 mmHg. Human saphenous vein exhibited anisotropic behaviour and, although compliant at low pressure (30 mmHg), was markedly incompliant at higher pressures.Conclusion: Compliant polyurethane grafts offer a greater degree of compliance match than either ePTFE or Dacron.

Improving the clinical patency of prosthetic vascular and coronary bypass grafts: the role of seeding and tissue engineering.

Abstract: In patients requiring coronary or peripheral vascular bypass procedures, autogenous vein is currently the conduit of choice. If this is unavailable, then a prosthetic material is used. Prosthetic graft is liable to fail due to occlusion of the graft. To prevent graft occlusion, seeding of the graft lumen with endothelial cells is undertaken. Recent advances have also looked at developing a completely artificial biological graft engineered from the patient's cells with properties similar to autogenous vessels. This review encompasses the developments in the two principal technologies used in developing hybrid coronary and peripheral vascular bypass grafts, that is, seeding and tissue engineering.

A review of the carotid and femoral intima-media thickness as an indicator of the presence of peripheral vascular disease and cardiovascular risk factors

Abstract: Peripheral vascular disease (PVD) is a common condition often associated with cardiovascular risk factors and events. With the aid of B-mode ultrasound scanning, evidence is emerging that these risk factors and events are significantly related to an increased carotid and femoral intima-media thickness (IMT). More importantly, treatment of these risk factors is associated with a decrease or a diminished progression of the IMT, paralleled by a reduction in cardiovascular events and an improvement in the symptoms associated with PVD. This evidence is particularly strong for lipid lowering therapy. Additional predictors of cardiovascular risk like the IMT, could now influence the decision to intervene with medication.

Development of a hybrid cardiovascular graft using a tissue engineering approach

Abstract: Tissue engineering of endothelial cells (EC) and chemical engineering with anticoagulant moieties has been undertaken in order to improve prosthetic graft patency and thrombogenicity. This was done by covalently bonding a compliant poly(carbonate-urea)urethane graft (MyoLink™) with arginine-glycine-aspartate (RGD) or/and heparin (Hep) to ascertain whether EC retention could be improved. The retention of these moieties and EC was assessed after exposure to pulsatile flow. We covalently bonded RGD, Hep, and RGD/Hep onto the luminal surface of MyoLink using spacer arm technology. Narrow-beam X-ray photoelectron spectroscopy was carried out to check the efficiency of the bonding. EC were radiolabeled and seeded onto native MyoLink and with 1) RGD-, 2) Hep-, and 3) RGD/Hep-bonded grafts and exposed to shear stress in a physiological flow circuit for 6 h, which reproduces femoral artery flow waveforms and pulsatility. Results were recorded on a gamma camera imaging system. Viability of cells was tested with a m...

In vitro stability of a novel compliant poly(carbonate-urea)urethane to oxidative and hydrolytic stress.

Abstract: Poly(ester) urethane and poly(ether)urethane vascular grafts fail in vivo because of hydrolytic and oxidative degradative mechanisms. Studies have shown that poly(carbonate)urethanes have enhanced resistance. There is still a need for a viable, nonrigid, small-diameter, synthetic vascular graft. In this study, we sought to confirm this by exposing a novel formulation of compliant poly(carbonate)urethane (CPU) manufactured by an innovative process, resulting in a stress-free. Small-diameter prosthesis, and a conventional poly(ether) urethane Pulse-Tec graft known to readily undergo oxidation in a variety of degradative solutions, and we assessed them for the development of oxidative and hydrolytic degradation, changes in elastic properties, and chemical stability. To simulate the in vivo environment, we used buffered solutions of phospholipase A(2) and cholesterol esterase; solutions of H2O2/CoCl2, t-butyl peroxide/CoCl2 (t-but/CoCl2), and glutathione/t-butyl peroxide/CoCl2 (Glut/t-but/CoCl2); and plasma fractions I-IV, which were derived from fresh human plasma centrifuged in poly(ethylene glycol). To act as a negative control, both graft types were incubated in distilled water. Samples of both graft types (100 mm with a 5.0-mm inner diameter) were incubated in these solutions at 37 degreesC for 70 days before environmental scanning electron microscopy, radial tensile strength and quality control, gel permeation chromatography, and in vitro compliance assessments were performed. Oxidative degradation was ascertained from significant changes in molecular weight with respect to a control on all Pulse-Tec grafts treated with t-but/CoCl2, Glut/ t-but/CoCl2, and plasma fractions I-III. Pulse-Tec grafts exposed to the H2O2/CoCl2 mixture had significantly greater compliance than controls incubated in distilled water (p < 0.001 at 50 mmHg). No changes in molecular weight with respect to the control were observed for the CPU samples; only those immersed in t-but/CoCl2 and Glut/t-but,/CoCl2 showed an 11% increase in molecular weight to 108,000. Only CPU grafts treated with the Glut/t-but/CoCl2 mixture exhibited significantly greater compliance (p < 0.05 at 50 mmHg). Overall, results from this study indicate that CPU presents a far greater chemical stability than poly(ether)urethane grafts do. 2001 John Wiley & Sons, Inc.

Performance of a polyurethane vascular prosthesis carrying a dipyridamole (Persantin) coating on its lumenal surface

Abstract: A porous polyurethane vascular prosthesis with an internal diameter of 5 mm was studied. The graft carries a coating of immobilized dipyridamole (Persantin®) on the surface of its lumen. Dipyridamole is a potent nontoxic inhibitor of platelet activation/aggregation, and also a strong inhibitor of vascular smooth muscle cell proliferation. The polyurethane material is also known as Chronoflex®, and already finds use as a vascular access graft. The coated vascular graft was studied in vitro (hemocompatibility, interaction with blood platelets and cultured endothelial cells), as well as in two established in vivo models. In the first in vivo study, coated grafts were implanted in goats, as a bypass of the carotid artery (four animals, eight grafts, length of the graft was approximately 12 cm). Four uncoated grafts were used as controls in otherwise identical experiments. In the second in vivo experiment, eight sheep were used. Each animal received one coated and one uncoated prosthesis as an interposition graft in the carotid artery (length of the graft was 4 cm). The in vitro experiments revealed that the dipyridamole coating has three beneficial effects: reduced thrombogenicity, reduced adherence of blood platelets, and accommodation of a confluent monolayer of endothelial cells. The goat experiments showed patency of the coated grafts in three of the eight cases. The sheep experiments were not useful for the evaluation of the dipyridamole coating because deterioration of the polyurethane material was observed. The in vivo results indicate that the dipyridamole coating may positively influence the patency rate, probably because the coating promotes the growth of an endothelial cell lining. The sheep data show, however, that the limited stability of the Chronoflex® material precludes its issue for the construction of permanent small-bore vascular grafts. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res 54: 224–233, 2001

An assessment of covalent grafting of RGD peptides to the surface of a compliant poly(carbonate-urea)urethane vascular conduit versus conventional biological coatings: its role in enhancing cellular retention.

Abstract: The aim of sodding prosthetic grafts with endothelial cells (EC) is to establish a functioning antithrombogenic monolayer of EC. Application of basement membrane proteins improves EC adherence on ePTFE grafts. Their addition to a biodurable compliant poly(carbonate-urea)urethane graft (CPU) was studied with respect to EC adherence. Preclot, fibronectin, gelatin, and collagen were coated onto CPU. RGD peptide, heparin, and both RGD and heparin were chemically bonded to CPU. Human umbilical vein EC (HUVEC) labeled with 111-Indium oxine were sodded (1.8 × 106 EC/cm2) onto native and the modified CPU. The grafts were washed after 90 min and EC retention determined. The experiments were repeated six times. EC retention on native CPU was 1.0 ± 0.2 × 105 EC/cm2. The application of preclot, fibronectin, gelatin, and collagen did not improve EC retention, which was 0.8 ± 0.1, 0.4 ± 0.1, 0.3 ± 0.08, and 0.5 ± 0.2 × 105 EC/cm2, respectively. Bonding RGD, heparin, and both RGD and heparin significantly improved EC re...

The effect of peripheral vascular disease on the serum levels of natural anti-oxidants: bilirubin and albumin.

Abstract: Background Bilirubin and albumin may act as antioxidants Their circulating levels are lower in those patients with ischemic heart disease (IHD) and could be further reduced by more extensive atherosclerosis, ie peripheral vascular disease (PVD) Methods Serum bilirubin and albumin were measured in 456 patients classified into 3 groups: 1) no clinically evident cardiovascular disease (CVD), 2) IHD present and 3) PVD present Smoking status and gender (which affect bilirubin and albumin levels in healthy individuals) were considered separately Results Bilirubin was lower in smoking men without CVD or with PVD than in non-smokers (p=002 and p=004, respectively) in the same groups Non-smoking women without CVD had significantly (p=0004) lower bilirubin levels than the corresponding group of men Frequency analysis of male non-smokers revealed significantly (p=004) more patients with a lower bilirubin (<65 μmol/l) in the PVD compared with the no CVD group Albumin levels showed the same trends Conclusions Prospective studies should consider smoking and gender when assessing the relevance of bilirubin and/or albumin levels in patients with vascular disease Our findings support those of other studies that show that low serum bilirubin and albumin levels are associated with the presence of vascular disease

Modern management of pulmonary embolism.

Abstract: Background: Pulmonary embolism is a significant cause of morbidity and death after operation. The introduction of new technologies in the diagnosis, and thrombolysis in the treatment, of pulmonary embolism has led to a need to reappraise the management of this condition. Methods: This review encompasses a comprehensive discussion of diagnostic modalities and therapeutic strategies used in the current management of pulmonary embolism. Relevant papers on the diagnosis and treatment of pulmonary embolism were identified from a Medline search for the period 1967–1998. Additional papers were derived from the reference lists of retrieved articles. Articles presenting prospectively gathered data have been referenced preferentially. Results and conclusion: Algorithms for the diagnosis and treatment of pulmonary embolism are presented. © 1999 British Journal of Surgery Society Ltd