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Biomedical subjects

R Ragnarsson

Publications and source records attributed to R Ragnarsson.

11 recordsLinked to original sources
PubMed2001

Alternating tip splitting in directional solidification.

We report experimental results on the tip splitting dynamics of seaweed growth in directional solidification of succinonitrile alloys. Despite the random appearance of the growth, a tip splitting morphology was observed in which the tip alternately splits to the left and to the right. The tip splitting frequency f was found to be related to the growth velocity V as a power law f~V1.5. This finding is consistent with the predictions of a tip splitting model that is also presented. Small anisotropies are shown to lead to different kinds of seaweed morphologies.

Journal Article↗
PubMed1993

Clinical experience with the Unilink/3M Precise microvascular anastomotic device.

The Unilink/3M Precise anastomotic device for microvascular anastomoses has been evaluated in 38 critical anastomoses in 26 selected patients. The microvascular anastomosis was usually completed within three minutes by a single surgeon. There was only one failure, when an arterial anastomosis clotted because of a technical error. In all patients tissue survival was dependent on patent mechanical anastomoses (critical anastomoses) and the follow-up period was more than three years.

Anastomosis, Surgical↗
PubMed1992

Long term evaluation of the unilink anastomotic system. A study with light and scanning electron microscopy.

The long term effects of the Unilink mechanical microvascular anastomosis in terms of anastomotic patency and histological changes in the vessel wall were evaluated in 10 rabbits. Both carotid arteries and facial veins were divided and reanastomosed with the Unilink device. At death two years later all 40 anastomoses were fully patent, with histological changes similar to those described previously after 16 weeks, that is, normal endothelial lining, but almost total atrophy of the media at the anastomotic site. The thinning of the vessel wall at the anastomosis caused neither occlusions nor aneurysms during the observation period.

Anastomosis, Surgical↗
PubMed1990

Microvascular anastomoses in irradiated vessels: a comparison between the Unilink system and sutures.

A new mechanical device (the Unilink system) was compared to conventional suture anastomoses in irradiated microvessels. Twenty rabbits received a single radiation dose of 20 Gy from a 7-MeV electron source through an anterior neck field. One and 6 months following irradiation, the carotid arteries and facial veins were divided and anastomosed on one side with the Unilink system and on the other side with suture technique. At sacrifice 4 weeks postoperatively, all vessels were evaluated for patency and histologic changes associated with radiation and anastomotic trauma. Histology disclosed severe radiation changes. Also, intimal hyperplasia was consistently found at the anastomotic sites in the arteries, while it was totally absent in the venous anastomoses. Occlusive thrombosis was found in two arteries, one anastomosed with the Unilink system and one sutured. Two other arteries, one from each group, had subtotal occlusions at the anastomotic site. No occlusions occurred in any of the venous anastomoses. The overall patency in this study was 97.5 percent, with no difference between the two techniques.

Anastomosis, Surgical↗
PubMed1989

Microvenous grafts to arterial defects. The use of mechanical or suture anastomoses.

A mechanical microvascular anastomotic device, the Unilink system, was compared with sutures in terms of patency, anastomotic time, and histologic changes when a microvenous graft is placed in an arterial defect. Twenty rabbits underwent grafting of a 1.0-cm defect in both carotid arteries with a 1.5-cm reversed femoral vein graft. Anastomoses were performed with the Unilink system on one side and sutures on the other. Animals were killed at 2 weeks (10 animals) and 16 weeks (10 animals) with the vein grafts being assessed with clinical patency tests and then fixated for histologic evaluation. All 20 grafts (100%) interposed with the Unilink system were fully patent while 17 (85%) of the 20 grafts interposed with sutures were fully patent. The grafting procedure with the Unilink anastomoses averaged 12.5 minutes while the sutured anastomoses averaged 41.9 minutes. No differences in the histologic appearance of the vein grafts were noted between the two types of anastomoses. All grafts showed endothelialization at 2 weeks with intimal hyperplasia or "arterialization" being a constant finding.

Anastomosis, Surgical↗
PubMed1989

Strength of microvascular anastomoses: comparison between the unilink anastomotic system and sutures.

The Unilink system, a mechanical anastomotic device, was compared with standard suture techniques in terms of anastomotic strength under conditions of uniaxial loading. Twenty-five rabbits underwent Unilink and suture anastomosis of both carotid arteries and facial veins. Animals were sacrificed at 1 hour (five animals), 2 weeks (10 animals), and 16 weeks (10 animals), and all vessels were tested by constant loading in a material testing machine. The maximum load required to disrupt the anastomosis as well as the site of vessel failure were recorded. All 100 anastomoses were fully patent as evaluated by clinical testing. At 1 hour and 2 weeks, the Unilink arterial anastomoses were consistently and significantly stronger than the sutured anastomoses. At 16 weeks the sutured arterial anastomoses were significantly stronger than Unilink. The Unilink anastomoses, however, remained approximately 50% stronger than unoperated normal vessels. No statistical differences were observed in the strength of venous anastomoses at any of the intervals tested. There were no statistical differences in the sites of failure of the vessels under loading (i.e., at the anastomosis or proximal or distal to it) between the two techniques.

Anastomosis, Surgical↗
PubMed1989

The UNILINK system for mechanical microvascular anastomosis in hand surgery.

A new mechanical anastomotic device--the UNILINK system--for small vessels, designed for work under the operating microscope was used in four patients for microvascular, hand surgical operations. All procedures were successful with regard to tissue survival and wound healing. Basal skin temperature and systolic blood pressure distal to the mechanical anastomoses were normal 12 to 26 months after the operation. Doppler investigation also confirmed that all mechanical anastomoses were patent. At the time of this report, 32 to 45 months after the operations, no adverse effects of the method have been found. The device offers increased safety and speed in microvascular operations.

Adolescent↗
PubMed1989

Microvenous end-to-side anastomosis: an experimental study comparing the Unilink system and sutures.

A method for mechanical microvascular end-to-side anastomosis is presented and compared to conventional suture technique. Twenty rabbits had their facial veins divided from the jugular veins and reanastomosed end-to-side to the jugular veins, 2 cm cranially to the original bifurcation. The anastomoses were performed on one side of the neck with the Unilink system and on the other side with sutures. At sacrifice at two weeks (10 animals) and at 16 weeks (10 animals), all anastomoses were tested for patency and histologically evaluated. All 40 anastomoses were fully patent. The time required for completion of a mechanical anastomosis was on the average one-fourth the time required for suture anastomosis. No thrombus formation was noted in any of the specimens, but a slight narrowing because of intimal hyperplasia was noted in the recipient vessels in two mechanical anastomoses. It was demonstrated that mechanical anastomoses of small veins end-to-side can be performed in a rapid and safe manner with the Unilink system.

Anastomosis, Surgical↗
PubMed1989

Arterial end-to-side anastomosis with the UNILINK system.

A new technique for mechanical end-to-side anastomoses using the UNILINK anastomotic system is presented. The technique, based on the concept of vessel wall eversion over paired ring pins, is described as is a new device for vessel expansion. To evaluate the technique of end-to-side anastomosis, we detached the left renal artery in 18 rabbits and then reanastomosed them end-to-side to the aorta using the UNILINK anastomotic system. Renal blood flow was evaluated before and after anastomoses with a laser Doppler flowmeter. Animals were separated into three groups of 6 and were killed at 24 hours, 2 weeks, and 16 weeks, respectively. To evaluate the acute effects of vessel expansion, 7 additional rabbits underwent expansion of the aorta without subsequent anastomosis. All vessels were evaluated with light and scanning electron microscopy. A patency rate of 100% was achieved in the 18 animals; histological changes at the anastomotic site were comparable to those described previously for this mechanical anastomotic system. The animal model demonstrates that it is both technically possible and efficacious to perform end-to-side anastomoses of arteries with the UNILINK anastomotic system.

Anastomosis, Surgical↗
PubMed1989

Microvascular anastomosis of interpositional vein grafts with the UNILINK system. A comparative experimental study.

Vein segments from the posterior facial vein of the rabbit were surgically isolated and re-anastomosed, either by manual suture technique or by the use of a new mechanical anastomotic device, the UNILINK apparatus. The purpose of the study was to compare anastomotic patency and time required for an orthotopic vein grafting procedure, when the two techniques were used. In the grafts anastomosed with the UNILINK technique, both clinical and histological evaluation showed 100% patency, while 20% of the sutured grafts showed impaired flow as a result of occlusive thrombosis. When the mechanical device was used, the full procedure was completed within one third of the time, as compared to suture anastomoses.

Anastomosis, Surgical↗