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H van Urk

Publications and source records attributed to H van Urk.

At least 91 records · Page 5Linked to original sources
PubMed1991

Assessment of arterial disease and arterial reconstructions by intravascular ultrasound.

Clinical application of intravascular ultrasound to assess arterial atherosclerotic disease was introduced in humans after extensive in vitro and in vivo animal studies. Real-time images, obtained with a 30 MHz element mounted on a 5 F catheter, consistently confirmed angiographic images, up till now considered to be the gold standard. In addition to these data, ultrasonic cross-sectional imaging provided information on the composition of atheroselectic lesions and the size and shape of the lumen. Based on the experimentally derived criteria for tissue characterization, a better insight into arterial morphology could be obtained, allowing improved planning of interventional or reconstructional procedures. Moreover intravascular ultrasound has proved valuable as a post-interventional procedure to monitor and assess the quality of interventional results. The ultrasound images are clearly superior to angiographic studies, albeit the ultrasonic information is an adjunct to angiography and, as yet, not a substitute. We present our initial experience with intravascular ultrasound obtained in patients with substantial peripheral arterial disease.

Angioplasty, Balloon↗
PubMed1991

Validation of quantitative analysis of intravascular ultrasound images.

This study investigated the accuracy and reproducibility of a computer-aided method for quantification of intravascular ultrasound. The computer analysis system was developed on an IBM compatible PC/AT equipped with a framegrabber. The quantitative assessment of lumen area, lesion area and percent area obstruction was performed by tracing the boundaries of the free lumen and original lumen. Accuracy of the analysis system was tested in a phantom study. Echographic measurements of lumen and lesion area derived from 16 arterial specimens were compared with data obtained by histology. The differences in lesion area measurements between histology and ultrasound were minimal (mean +/- SD: -0.27 +/- 1.79 mm2, p greater than 0.05). Lumen area measurements from histology were significantly smaller than those with ultrasound due to mechanical deformation of histologic specimens (-5.38 +/- 5.09 mm2, p less than 0.05). For comparison with angiography, 18 ultrasound cross-sections were obtained in vivo from 8 healthy peripheral arteries. Luminal areas obtained by angiography were similar to those by ultrasound (-0.52 +/- 5.15 mm2, p greater than 0.05). Finally, intra- and interobserver variability of our quantitative method was evaluated in measurements of 100 in vivo ultrasound images. The results showed that variations in lumen area measurements were low (5%) whereas variations in lesion area and percent area obstruction were relatively high (13%, 10%, respectively). Results of this study indicate that our quantitative method provides accurate and reproducible measurements of lumen and lesion area. Thus, intravascular ultrasound can be used for clinical investigation, including assessment of vascular stenosis and evaluation of therapeutic intervention.

Angiography↗
PubMed1991

Femoro-popliteal vein bypass grafts studied by intravascular ultrasound.

The usefulness of intra-operative intravascular ultrasound (30 MHz) was evaluated in three patients who underwent a femoropopliteal vein bypass. Intravascular echography analysis of the surgical procedure revealed a normal uneventful result in one patient. In two other patients obstructions in the vein grafts were identified either caused by internal obstruction or external compression. Angiography in these two patients provided equivocal data. We conclude that intravascular ultrasound imaging may be a useful adjunct to angiography and may offer important clinical data to facilitate the surgeons in analysing the results of the interventional procedures.

Aged↗
PubMed1991

Acute management of traumatic forequarter amputations: case reports.

Traumatic forequarter amputation is a rare and very devastating injury. The arm, including the scapula, clavicle, and pectoral muscle, is torn from the body by a tremendous traction force, usually combined with a counteracting force from the body. The cases of three patients are presented. One patient was caught by the axle of a harvesting machine, resulting in a forequarter amputation of his right extremity and amputation of his left arm at the level of the upper arm. The other two patients had their arms caught in conveyer belts. All patients survived. Closure of the defect was performed acutely using a local pedicled musculocutaneous flap in one case and free vascularized musculocutaneous flaps from the amputated limbs in the two other cases.

Accidents, Occupational↗
PubMed1989

Localization and kinetics of pyruvate-metabolizing enzymes in relation to aerobic alcoholic fermentation in Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621.

The role of pyruvate metabolism in the triggering of aerobic, alcoholic fermentation in Saccharomyces cerevisiae has been studied. Since Candida utilis does not exhibit a Crabtree effect. this yeast was used as a reference organism. The localization, activity and kinetic properties of pyruvate carboxylase (EC 6.4.1.1), the pyruvate dehydrogenase complex and pyruvate decarboxylase (EC 4.1.1.1) in cells of glucose-limited chemostat cultures of the two yeasts were compared. In contrast to the general situation in fungi, plants and animals, pyruvate carboxylase was found to be a cytosolic enzyme in both yeasts. This implies that for anabolic processes, transport of C4-dicarboxylic acids into the mitochondria is required. Isolated mitochondria from both yeasts exhibited the same kinetics with respect to oxidation of malate. Also, the affinity of isolated mitochondria for pyruvate oxidation and the in situ activity of the pyruvate dehydrogenase complex was similar in both types of mitochondria. The activity of the cytosolic enzyme pyruvate decarboxylase in S. cerevisiae from glucose-limited chemostat cultures was 8-fold that in C. utilis. The enzyme was purified from both organisms, and its kinetic properties were determined. Pyruvate decarboxylase of both yeasts was competitively inhibited by inorganic phosphate. The enzyme of S. cerevisiae was more sensitive to this inhibitor than the enzyme of C. utilis. The in vivo role of phosphate inhibition of pyruvate decarboxylase upon transition of cells from glucose limitation to glucose excess and the associated triggering of alcoholic fermentation was investigated with 31P-NMR. In both yeasts this transition resulted in a rapid drop of the cytosolic inorganic phosphate concentration. It is concluded that the relief from phosphate inhibition does stimulate alcoholic fermentation, but it is not a prerequisite for pyruvate decarboxylase to become active in vivo. Rather, a high glycolytic flux and a high level of this enzyme are decisive for the occurrence of alcoholic fermentation after transfer of cells from glucose limitation to glucose excess.

Candida↗
PubMed1989

Arterial wall characteristics determined by intravascular ultrasound imaging: an in vitro study.

The feasibility of assessing arterial wall configuration with an intravascular 40 MHz ultrasound imaging device was investigated in an in vitro study of 11 autopsy specimens of human arteries. The system consists of a single element transducer, rotated with a motor mounted on an 8F catheter tip. Cross sections obtained with ultrasound were matched with the corresponding histologic sections. The arterial specimens were histologically classified as of the muscular or elastic type. Muscular arteries interrogated with ultrasound presented with a hypoechoic media, coinciding with the smooth muscle cells. In contrast, the media of an elastic artery densely packed with elastin fibers was as echogenic as the intima and the adventitia. On the basis of the cross-sectional image, it was possible to determine the nature of the atherosclerotic plaque. The location and thickness of the lesion measured from the histologic sections correlated well with the data derived from the corresponding ultrasound images. This study indicates that characterization of the type of artery and detection of arterial wall disease are possible with use of an intravascular ultrasound imaging technique.

Adult↗
PubMed1989

Extracranial carotid artery aneurysms.

Aneurysms of the extracranial carotid arteries are uncommon vascular lesions. During the period 1976 to 1986 we encountered 18 extracranial carotid aneurysms in 14 patients. The aneurysms were atherosclerotic (12 in 9 patients), congenital (3 in 2 patients), mycotic (1) and secondary (false aneurysms) after previous carotid surgery (2 in 2 patients). The patients presented with neurological symptoms (11) or a pulsating mass in the neck (2). In one patient the aneurysm was detected accidentally during angiography. From this study it became clear that "carotid aneurysm" is not a well defined entity. The "normal" configuration of the carotid bulb with its usually larger diameter, is in part a cause of the problem of definition. A recently described technique for predicting normal vessel diameters in stenosing lesions of the carotid arteries was retrospectively applied to all our patients with aneurysms. With these measurements, made on standard preoperative angiograms, it was possible to quantify the degree of dilatation, and confirm the diagnosis of aneurysm. Eleven of the 14 patients were operated on without mortality, no neurological deficits were seen as a result of the operation and minimal morbidity occurred in six patients. From this study we conclude that surgical correction of accessible carotid artery aneurysms is a relatively safe procedure and these lesions should be operated on irrespective of symptoms. This is the first report that gives clear guidelines for measuring dilatation of the extracranial carotid arteries and based on these guidelines we suggest criteria for the discrimination between physiological dilatation and pathological aneurysm formation, the latter condition being an indication for operation.

Adolescent↗
PubMed1989

Intravascular ultrasonic imaging: histologic and echographic correlation.

The feasibility of assessing arterial wall characteristics with an intravascular 40 MHz ultrasonic imaging device was determined in vitro. Ten autopsy specimens of human arteries, with and without atherosclerosis, were studied. A close relationship was observed between the histologic section and the corresponding ultrasonic cross-section with regard to the location, maximum plaque thickness and extent of the atherosclerotic lesion along the circumference of the vessel wall. Based on echogenicity of the atherosclerotic lesion, ultrasound could distinguish four basic types of atherosclerotic plaque components: 1. hypoechoic: a reflection of lipid deposits; 2. soft echoes: reflective of fibromuscular tissue; 3. bright echoes: representative of fibrous tissue; 4. bright echoes with shadowing behind the lesion: representative of calcium deposits. It is anticipated that development of such a catheter-tip imaging system combined with recanalisation methods will be of immense benefit for the precise localisation and identification of vessel wall pathology, precise positioning of a recanalisation instrument (laser device, atherectomy catheter) and subsequent use of this recanalisation procedure and for assessing the effect of recanalisation.

Adult↗
PubMed1989

Glucose transport in crabtree-positive and crabtree-negative yeasts.

The kinetic parameters of glucose transport in four Crabtree-positive and four Crabtree-negative yeasts were determined. The organisms were grown in aerobic glucose-limited chemostats at a dilution rate of 0.1 h-1. The results show a clear correlation between the presence of high-affinity glucose transport systems and the absence of aerobic fermentation upon addition of excess glucose to steady-state cultures. The presence of these H+-symport systems could be established by determination of intracellular accumulation of 6-deoxy-[3H]glucose and alkalinization of buffered cell suspensions upon addition of glucose. In contrast, the yeasts that did show aerobic alcoholic fermentation during these glucose pulse experiments had low-affinity facilitated-diffusion carriers only. In the yeasts examined the capacity of the glucose transport carriers was higher than the actual glucose consumption rates during the glucose pulse experiments. The relationship between the rate of sugar consumption and the rate of alcoholic fermentation was studied in detail with Saccharomyces cerevisiae. When S. cerevisiae was pulsed with low amounts of glucose or mannose, in order to obtain submaximal sugar consumption rates, fermentation was already occurring at sugar consumption rates just above those which were maintained in the glucose-limited steady-state culture. The results are interpreted in relation with the Crabtree effect. In Crabtree-positive yeasts, an increase in the external glucose concentration may lead to unrestricted glucose uptake by facilitated diffusion and hence, to aerobic fermentation. In contrast, Crabtree-negative yeasts may restrict the entry of glucose by their regulated H+-symport systems and thus prevent the occurrence of overflow metabolism.

Biological Transport↗
PubMed1988

Diagnosis and management of graft-enteric fistulae.

During a 7-year period 20 patients underwent operation for a graft-enteric fistula after implantation of an intra-abdominal vascular prosthesis months or years before. Eighteen patients had gastrointestinal blood loss as their first symptom; 12 were in shock on admission. Fourteen patients had a fistula between the proximal anastomosis and the duodenum. Graft excision followed by axillobifemoral bypass was performed in 10 patients and four patients underwent local repair. A fistula between the distal anastomosis and the bowel was found in the remaining six patients and a local repair was carried out. Proximal graft-enteric fistula carries a particularly high postoperative mortality rate of more than 50 per cent.

Aged↗
PubMed1988

Assessment of peripheral vascular obliterative disease by transcutaneous oxygen tension tests.

By repeated measurements in each of ten normal subjects and ten patients with mild intermittent claudication, the performance of three transcutaneous oxygen tension (PtcO2) test in the diagnosis of obliterative peripheral arterial disease was studied. PtcO2 resting value, PtcO2 response to oxygen breathing and PtcO2 reperfusion response after tourniquet obstruction were all measured on the dorsum of the foot. We found that PtcO2 resting values were not different between patients and controls, while responses to 100% oxygen breathing and reperfusion responses differed significantly between the two groups. The most prominent difference between the two groups was observed in the latency of PtcO2 rise after reperfusion. Therefore the reperfusion response test may have a place in the assessment of claudication by PtcO2 measurement.

Aged↗
PubMed1987

Late results of mesocaval interposition shunting for bleeding oesophageal varices.

Survival, encephalopathy and shunt patency were studied in 64 consecutive patients who underwent mesocaval shunting with a wide-calibre Dacron prosthesis. Half of the patients were operated as emergency cases. Operative blood loss in patients who had emergency procedures was significantly higher than during elective operations. Overall, 30-day mortality was 27 per cent. Survival was 61 per cent after 1 year and 39 per cent after 5 years. Serious encephalopathy requiring hospital admission occurred in 5 patients (11 per cent of patients surviving more than 1 month). Shunt patency was assessed by scintisplenoportography and ultrasonography. Cumulative shunt occlusion rate was 16 per cent after 1 year, 33 per cent after 5 years and 52 per cent after 8 years of follow-up. Out of 17 patients with an occluded shunt, 9 had persistent or recurrent bleeding, while 3 patients had recurrent bleeding despite a patent shunt. We conclude that the mesocaval Dacron interposition shunt should not be recommended as the procedure of first choice for portosystemic shunting.

Adult↗
PubMed1987

Monitoring heparin and haemostasis during reconstruction of the abdominal aorta.

In spite of its unpredictable kinetics, heparin is still not generally monitored during peripheral vascular surgery. To evaluate heparin levels and neutralisation, plasma heparin concentrations were measured using a chromogenic substate method during 20 consecutive operations on the Abdominal Aorta. This was combined with measuring activated partial thromboplastin time (APTT), thrombin time (ThT), prothrombin time (PT), antithrombin-III (AT-III) and fibrinogen concentration. Heparin concentration 5 min after administration and the elimination rate showed a wide variation. Using a standard dosage for all patients resulted in plasma heparin levels that are potentially too low in some patients. The APTT and ThT were found to be unsuitable for an exact calculation of heparin levels. Protamine administration based on the surgeon's judgement of haemostasis was inadequate. Furthermore an intraoperative decrease of AT-III and fibrinogen was seen in eight patients. It is advisable and possible to have direct monitoring of heparin concentration during peripheral vascular surgery.

Aorta, Abdominal↗