Biomedical subjects

G H Clarke

Publications and source records attributed to G H Clarke.

5 recordsLinked to original sources

PubMed1992

Venous wall function in the pathogenesis of varicose veins.

Three theories have been proposed to explain the cause of varicose veins, citing three different factors as the primary cause: valvular incompetence, a weakness of the vein wall, and increased arterial inflow associated with multiple arteriovenous communications. This study was designed to determine the cause of varicose veins with respect to these three factors. Duplex scanning techniques were used to assess the venous valves, and simultaneous measurements of calf volume (strain-gauge plethysmography) and venous pressure made during venous occlusion plethysmography were used to determine the elasticity of the venous wall and the rate of arterial inflow. Fifty-one control legs and 36 legs with superficial venous insufficiency were examined. Risk factors were used to divide the control legs into two groups: low risk or normal (23 legs) and high risk (28 legs). The results obtained in the high-risk limbs demonstrated a significantly reduced vein wall elasticity (p less than 0.001) and increased arterial inflow (p less than 0.005) compared with the normal limbs, with no corresponding increase in the incidence of valvular incompetence. These results clearly suggest that the role of the venous valves in the development of varicose veins is secondary to changes in the elastic properties of the vein wall and the rate of arterial inflow.

Elasticity↗

PubMed1990

Experimental evidence to support the use of interposition vein collars/patches in distal PTFE anastomoses.

We have conducted three in vitro experiments (using cadaver internal mammary artery as a model for crural artery), which establish the advantage of the Miller collar and Taylor patch over direct PTFE-artery anastomoses: (1) A new method of simultaneously measuring longitudinal and circumferential elasticity in human saphenous vein (n = 16) has demonstrated the latter to be anisotropic (i.e.: greater longitudinal than transverse compliance, P less than 0.002). This suggests that benefit may be gained by aligning the saphenous vein's longitudinal axis with that of the arteriotomy--a feature of both vein interposition anastomoses. (2) We have compared maximal pulsatile and constant flow across each type of anastomosis (n = 10 of each) using a flow model incorporating standard pressure, viscosity, graft and outflow vessel length, and anastomotic angle. This experiment has demonstrated loss of anastomotic reliability only in direct PTFE-artery anastomoses (i.e. no correlation between flow and vessel diameter, r = 0.04). (3) Casts of the internal anatomy of the anastomoses (n = 10 of each) have demonstrated a greater degree of oval distortion of the toe of the outflow vessel of direct PTFE-artery anastomoses than either of the other techniques (P less than 0.01). This experimental evidence suggests that both of these vein interposition techniques optimise the mechanical properties of saphenous vein and protect small arteries from anastomotic distortion. These benefits do not occur with direct PTFE-artery anastomoses.

Anastomosis, Surgical↗

PubMed1989

Evaluation of non-invasive and invasive methods in the assessment of short saphenous vein termination.

Surgery of the short saphenous vein is associated with a high recurrence rate because of variations in the anatomy or inadequate clinical examination. To prevent this, accurate definition of the pattern and level of termination of the saphenopopliteal junction and flush ligation is necessary. Clinical examination, Doppler ultrasound, duplex scanning and peroperative venography have been compared to assess the level of termination of the short saphenous vein. In all, 64 limbs of 46 patients were examined. In 39 limbs there was primary short saphenous incompetence, in 13 limbs there was recurrent short saphenous incompetence; in ten of these there was incompetence of the gastrocnemius vein. In 12 limbs a duplex scan did not demonstrate incompetence of the short saphenous vein or gastrocnemius vein. The accuracy of these methods when locating incompetence of the short saphenous vein to within 2 cm of the saphenopopliteal junction was 56 per cent for clinical examination, 64 per cent for Doppler ultrasound and 96 per cent for duplex scanning. When there was no saphenopopliteal junction (9 per cent), duplex scanning correctly detected the pattern of the incompetent vein. The apparent success of clinical examination was because the vein was not felt above the femoral intercondylar groove and 52 per cent of the veins terminated at this level. Duplex scanning is a non-invasive technique which is almost as accurate as venography and provides additional haemodynamic information about the incompetent veins by demonstrating the presence and extent of reflux.

Female↗

PubMed1989

Quantification of venous reflux by means of duplex scanning.

Venous reflux in milliliters per second has been measured in individual veins with duplex scanning. Forty-six patients (47 legs) with symptomatic varicose veins have been studied while they were in the erect position. Nineteen legs had skin changes whereas the rest (28 legs) had only varicose veins with no skin changes. In 45 limbs, reflux was confined to one vein only: long saphenous vein in 28, short saphenous vein in nine, and femoropopliteal vein in eight. In one limb, reflux was found in the long saphenous, short saphenous, and femoropopliteal veins, and in another it was found in the long and short saphenous veins. In the latter two limbs the amount of reflux found in each vein was added to obtain the total reflux in the limb. In the limbs with skin changes, reflux (median +/- 90% tolerance levels) was 30 (10 to 53) ml/sec; whereas in limbs with no skin changes it was 10 (3 to 44) ml/sec. Reflux greater than 10 ml/sec was associated with a high incidence of skin changes (66%) irrespective of whether this was in the superficial or deep veins; reflux less than 10 ml/sec was not associated with skin changes.

Adult↗

PubMed1969

Cold urticaria.

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Adolescent↗