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Biomedical subjects

D W Hunter

Publications and source records attributed to D W Hunter.

177 records · Page 10Linked to original sources
PubMedDate not supplied

Magnetic resonance angiography of nonferromagnetic iliac artery stents and stent-grafts: A comparative study in sheep.

PURPOSE: To compare nonferromagnetic iliac artery prostheses in their suitability for patency monitoring with magnetic resonance angiography (MRA) using conventional angiography as a reference. METHODS: In experiment 1, three Memotherm stents were inserted into the iliac arteries of each of six sheep: two "tandem" stents on one side and a single stent on the other side. In experiment 2, four prostheses (normal and low-porosity Corvita stent-grafts, Memotherm, ZA-stent) were inserted in each of 11 sheep. Patency was monitored before and 1, 3, and 6 months after insertion with 3D phase-contrast and two 2D time-of-flight sequences (TOF-1: TR/TE = 18/6.9, TOF-2: 13/2.5) with and without contrast at 1.5 T. On 206 coronal MIP images (72 pre-, 134 post-stenting), three readers analyzed 824 iliac segments (206 x 4) for patency and artifacts. RESULTS: There was no difference in the number of artifacts between tandem and single iliac Memotherm stents. The ZA-stent induced significantly fewer artifacts than the other prostheses (p < 0.00001). With MRA, patency of the ZA-stent was correctly diagnosed in 88% of cases, which was almost comparable to nonstented iliac segments (95%), patency of the Memotherm stent in 59%, and of the Corvita stent-grafts in 57% and 55%. The TOF-2 sequence with contrast yielded the best images. CONCLUSION: MRA compatibility of nonferromagnetic prostheses depends strongly on the design of the device. MRA may be used to monitor the patency of iliac ZA-stents, whereas iliac Memotherm stents and Corvita stent-grafts appear to be less suited for follow-up with MRA.

Animals↗
PubMedDate not supplied

Recirculation-type Amplatz clot macerator: determination of particle size and distribution.

PURPOSE: A high-speed mechanical clot macerator was tested in vitro, and the distributions and sizes of residual particles produced by this device were determined. MATERIALS AND METHODS: Human thrombi aged for 4 days and 10 days were macerated using a recirculation-type Amplatz thrombectomy device with an 8-F, high-speed screw propeller. The device was activated for 15, 30, and 60 seconds. Two different methods of particle measurement were used to determine overall particle distribution and to determine the size and number of large particles. RESULTS: The recirculation device liquefied 99.2% of 4-day-old and 98.8% of 10-day-old thrombi, producing particles ranging in size from 13 to 1,000 microns; all particles were smaller than 1,000 microns. Particle size and distribution results were identical for the 30-second and 60-second activation times. CONCLUSION: The recirculation-type thrombectomy device appears to perform well as a method of macerating human thrombi. Clinical trials need to be conducted to test the device further and to determine if it can be used safely on venous as well as arterial occlusions.

Humans↗
PubMedDate not supplied

Placement of the Palmaz stent with use of an 8-F introducer sheath and Olbert balloons.

PURPOSE: The authors describe a modified technique for delivering Palmaz 30-mm stents. MATERIALS AND METHODS: The modification is based on the use of an 8-mm Olbert balloon mounted on a 5.8-F shaft. The Palmaz stent is crimped onto the balloon by using finger pressure only. An 8-F introducer sheath can be used instead of a 10-F sheath. The surface material of the balloon prevents the stent from moving as it is introduced through the sheath and lesion. The balloon has a very small profile after deflation, which means it can be easily removed without dislodging the stent. The balloon can be used for placement of more than one stent. RESULTS: Nineteen Palmaz 30-mm stents have been placed with this method, and there have been no complications or difficulties related to this method. In one case, four stents were delivered by using the same balloon. CONCLUSION: This modification should reduce the complications of stent delivery, especially in small iliofemoral systems.

Arteries↗
PubMedDate not supplied

Acute clot-trapping efficiency in dogs with compacted versus elongated wires in bird's nest filters.

PURPOSE: The clot-trapping efficiency of the Bird's Nest filter was studied in dogs with the stainless steel wires in a compacted versus fully elongated configuration. MATERIALS AND METHODS: Bird's Nest filters were placed infrarenally with the wires compacted in 10 dogs and with the wires elongated in an additional 10 dogs. The dogs were separated into two groups, five dogs with each wire configuration in each group. In group 1, 10 unlabeled 6 x 30-mm blood clots were injected into the inferior vena cava. In group 2, six 6 x 10-mm, four 6 x 15-mm, and four 6 x 30-mm labeled clots were introduced. RESULTS: In group 1, clot-trapping efficiencies were 82% for the compacted versus 86% for the elongated configuration, as seen on serial cavograms and pulmonary angiograms. In group 2, clot-trapping efficiencies were 90% for the compacted versus 97% for the elongated configuration, as seen at fluoroscopy. Clot size did not affect trapping efficiency. CONCLUSION: Acute clot-trapping efficiency of Bird's Nest filters did not differ when the wires were in a compacted versus elongated configuration. This study suggests that placement of a Bird's Nest filter in the elongated configuration may be satisfactory and may not indicate placement of a second filter.

Animals↗
PubMedDate not supplied

Hemolytic effect of the Amplatz thrombectomy device.

PURPOSE: The hemolytic effect of the Amplatz thrombectomy device (ATD) was evaluated in nine dogs and in nine patients. MATERIALS AND METHODS: The device was activated for 1-2 minutes in the abdominal aorta, inferior vena cava, or femoral artery of nine dogs. The device was activated for 1-4 minutes in the nine patients in occluded lower extremity bypass grafts (n = 5), native superficial femoral artery (n = 1), a pulmonary artery embolus (n = 1), a portocaval shunt (n = 1), and an iliac vein stent (n = 1). Patients were examined for laboratory evidence of hemolysis following mechanical thrombectomy. RESULTS: In all dogs haptoglobin level decreased, free hemoglobin level in the plasma increased, and hemoglobinuria was present. There was no change in renal function. The level of haptoglobin decreased and the level of plasma free hemoglobin increased in eight patients, with hemoglobinuria detected in one. More hemolysis was observed in the animals than in the patients. CONCLUSION: The ATD has a definite transient hemolytic effect. Until further studied, it should not be used in children and should be used with caution in patients who are anemic, hypoxemic, or have potentially reversible renal insufficiency. Activation time should be monitored closely because hemolysis probably increases with increasing activation time.

Animals↗
PubMedDate not supplied

In vitro and in vivo experimental evaluation of a new vena caval filter.

PURPOSE: A new stainless steel (MP35N alloy) vena cava filter without a central stasis point was evaluated in vitro and in vivo. MATERIALS AND METHODS: The clot-trapping efficiency and hemodynamic flow pattern of the filter were assessed in a flow model and were compared with those of currently available commercial filters including the Vena Tech-LGM, Simon nitinol, Greenfield, and Bird's Nest filters. The new filter was placed in the inferior vena cava (IVC) of 31 dogs; 21 of the 31 dogs were followed up with cavography for up to 3 months. At the termination of the study, the filters and IVCs were examined grossly and histologically. An in vivo clot-trapping test was carried out in five dogs. RESULTS: The least turbulence was noted with the new filter and the titanium Greenfield filter. The stainless steel Greenfield and Simon nitinol filters caused major flow disturbances. Migration within 5 cm of initial placement occurred in two animals (9.5%). There were no IVC thromboses, perforations, or filter embolizations. An in vivo clot-trapping study showed an 80% efficiency for small thrombi (3 x 20 mm) and 100% efficiency for large thrombi (6 x 20 mm) with the new filter. The Simon and the new filter had the best clot-trapping capabilities. The Vena Tech-LGM and Bird's Nest filters were slightly inferior and the Greenfield filter demonstrated by far the lowest trapping capacity. CONCLUSION: The new vena cava filter is easily introduced percutaneously through a 12-F sheath and appears to be very promising due to its high filtering capability, low turbulence, nonmagnetic properties, good mechanical stability, and hypothrombogenicity. Clinical trials are warranted.

Alloys↗
PubMedDate not supplied

Chronic iliac artery occlusions: primary recanalization with endovascular stents.

PURPOSE: The authors describe treatment of chronic iliac artery occlusions with primary stent placement without prior thrombolysis or angioplasty. PATIENTS AND METHODS: Eight patients with chronic iliac artery occlusions (six men and two women) underwent primary stent placement without prior use of thrombolytic agents or angioplasty. Palmaz stents were placed in seven patients and a Wallstent device was placed in one. RESULTS: In all patients, revascularization was successful without residual stenoses or pressure gradients. There was no angiographic evidence of distal embolization. CONCLUSION: Primary stent placement for chronic iliac artery occlusions without prior thrombolysis or angioplasty appears to be safe and efficacious and is potentially cost effective.

Adult↗
PubMedDate not supplied

Iliofemoral deep venous thrombosis: safety and efficacy outcome during 5 years of catheter-directed thrombolytic therapy.

PURPOSE: To prospectively evaluate the angiographic and clinical results of using catheter-directed thrombolytic therapy for the treatment of acute iliofemoral deep venous thrombosis (IFDVT). MATERIALS AND METHODS: All consecutive patients with acute IFDVT referred for thrombolytic treatment from July 1990 to December 1995 were included in this clinical data analysis. Infusions of urokinase were administered via a multisidehole infusion catheter. Angioplasty, stent placement, mechanical thrombectomy, and other procedures were often performed in conjunction with the thrombolytic procedure. RESULTS: Seventy-seven patients and 87 limbs were treated. The overall technical success rate was 79%, and was 86% for iliac veins and 63% for femoral veins. The primary and secondary patency rates at 1 year were 63% and 78%, respectively, for the iliac veins, and 40% and 51%, respectively, for the femoral veins. Patients with malignant disease fared worse. Patients requiring stent placement appeared to have inferior outcomes. A previous history of DVT did not appear to affect the results. Bleeding requiring transfusion and hematomas were the major complications encountered. Pulmonary embolus was not a significant problem. Technical success rates were lower in patients who had had symptoms for more than 4 weeks compared to those who had a more recent onset of symptoms. CONCLUSION: Current data suggest that catheter-directed thrombolytic therapy is safe and effective in achieving intermediate-term venous Patency. The long-term clinical benefits of this procedure remain, however, to be established.

Angioplasty↗
PubMedDate not supplied

Changes in tunneled catheter tip position when a patient is upright.

PURPOSE: To determine the relative changes in position of tunneled catheters from supine to upright patient position and factors affecting catheter tip migration. MATERIALS AND METHODS: One hundred forty-six different tunneled catheters were placed through the subclavian or jugular veins radiologically, and catheter positions were documented with use of cine radiography at the time of placement. Follow-up chest radiographs were obtained with the patient in the upright position within 48 hours after placement. Catheter tip positions were numbered from 1 to 8, with 1 representing the innominate/superior vena cava junction and 8, the lower right atrium. Patient sex and weight, the site of catheter entry, and the size and type of catheter were correlated with the relative change in position on the follow-up chest radiogrpahs. RESULTS: There was a statistically significant (P < .0001) change in catheter position on the follow-up chest radiographs, with a mean difference of 1.5 catheter positions (usually mid-right atrium initially to low superior vena cava on follow-up). Catheter tip migration was greater for catheters in the subclavian veins, in females, and in obese patients. CONCLUSIONS: The catheter tip migrates significantly from the initial position at the time of placement as compared to when the patient assumes the upright position. This knowledge is important in achieving the desired final catheter position.

Adult↗
PubMedDate not supplied

Tissue response to covered Wallstents.

PURPOSE: To evaluate and compare the healing response related to two types of graft-covered Wallstents (WSs) and an uncovered WS in the canine iliac artery. MATERIALS AND METHODS: Eight bare mesh WSs, 10 polyethylene terephthalate interbraided WSs (PET-WSs), and six polytetrafluoroethylene covered WSs (ePTFE-WSs) were placed in the iliac arteries of 12 dogs. Arteriograms were obtained before and after implantation and at explantation. Devices were explanted at 1 month (n = 8), 3 months (n = 6), and 6 months (n = 10) and sent for histologic study. RESULTS: One ePTFE-covered stent-graft was found to be thrombosed at 3 months; the remaining 23 of 24 implants remained patent to the time of explantation. The WS and ePTFE-WS both generated a uniform myointimal cell response without inflammation. The PET-WS induced a fibrous luminal response with substantial foreign body-type inflammatory reaction around the PET fibers. Although neointima associated with the PET-WS appeared thicker than that associated with either the ePTFE-WS or the bare WS, none of the patent implants developed greater than 50% angiographic narrowing. CONCLUSION: The PET-WS induced chronic inflammation, a response not seen with either the WS or ePTFE-WS. This may explain the occurrence of pain and/or fever in human studies of arterial PET endoluminal stent-grafts. Patency for all three implants was excellent in this model.

Animals↗
PubMedDate not supplied

Comparison of preoperative standard angiography with preoperative balloon occlusion femoral angiography of the lower extremity.

The use of saphenous vein in situ bypass for limb salvage has increased the need for adequate visualization of distal lower extremity vessels. Preoperative angiographic techniques are often inadequate, requiring multiple films, extensive patient manipulation, or excessive dye loads. Intraoperative prereconstructive angiography permits adequate distal vessel visualization, but at a significant waste of time and expense if no usable distal vessels are found. There is a need for a reliable means of preoperative angiography in patients being evaluated for saphenous vein in situ bypass. Preoperative balloon occlusion femoral angiography was compared to preoperative standard angiography of the lower extremity in 39 patients referred to the University of Minnesota for limb salvage. Balloon occlusion femoral angiography significantly improved the preoperative ability to visualize lower extremity vessels distal to the superficial femoral artery in this group of patients.

Adult↗
PubMedDate not supplied

Current trends in the management of urinary stones.

The treatment of renal and ureteral stones has undergone rapid and major changes over the past ten years. Extracorporeal shockwave lithotripsy has become the most commonly used modality for the treatment of renal and upper ureteral stones. Lower ureteral stones are more commonly being approached by retrograde techniques. Percutaneous nephrolithotomy, medical therapy, and open surgical nephrolithotomy offer viable alternatives in given situations. Presented here is the current application of each of these techniques, both alone and in combination, for the treatment of urinary stones.

Endoscopy↗