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F D Dorman

Publications and source records attributed to F D Dorman.

At least 37 records · Page 2Linked to original sources
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The Minnesota shunt.

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Ascites↗
PubMedDate not supplied

The spring-driven implantable pump. A low-cost alternative.

In the current era of cost containment in medicine, manufacturing economics have become increasingly important. The authors devised an implantable pump powered by spring force from an elastomeric Belleville washer, which is also the outer flexible wall of the drug reservoir. Use of formed and injection molded parts provides for low-cost manufacturing, in contrast to the precision welded alternative designs. Additional advantages include insensitivity to changes in ambient temperature and pressure. Finite element modeling of the elastomer spring allows prediction of the effects of parameter changes on performance, so that expansions and reductions of scale can be made without compromising the uniform spring rate of the device. A concern that subcutaneous fibrous encapsulation might markedly alter reservoir pressure was not supported by experimental data. In a unit implanted subcutaneously in a dog, reservoir pressures measured over a 4 year period were stable. This new, simple, implantable infusion pump can serve as an economical vehicle for prolonged parenteral drug treatment of ambulatory subjects in circumstances where continuous single-rate infusion is appropriate.

Animals↗
PubMedDate not supplied

A peritoneovenous shunt with an access port enables non surgical reversal of intraperitoneal catheter occlusion.

Management of chronic peritoneal ascites by transfer of the fluid to the right atrium via peritoneovenous shunt (PVS) is often complicated by occlusion of the peritoneal catheter by one, or a combination, of the following: 1) omental plugging of drain holes, 2) fibrin obstruction of the lumen, and 3) encapsulation of the peritoneal segment by a cocoon. A PVS design that includes an access port facilitates the reversal of fibrin obstruction by urokinase. Eight dogs with implanted PVS were tested weekly for patency (indicated by the flow rate of saline into the peritoneum via the access port) and performance (indicated by the percent transfer of saline from the peritoneum to the vasculature). In 256 test sessions performed to date, 15 catheter occlusions occurred. Nine of these were reversed by one or two flushes with 5,000 units of urokinase via the access port. The remaining six were found to be occluded by cocoons (two), omentum (three), and fibrin (one). Although it is an effective treatment for ascites, the PVS is not in common use, because it has a relatively high occlusion rate. The access port and other features of the authors' PVS are designed to reduce the incidence of PVS occlusion.

Animals↗
PubMedDate not supplied

A totally implantable drug infusion defice: laboratory and clinical experience using a model with single flow rate and new design for modulated insulin infusion.

The Infusaid implantable infusion pump with a single delivery rate has maintained chronic intravenous heparin infusion in man for greater than 35 mo and for greater than 5 yr in the dog. Intra-arterial infuson of fluorodeoxyuridine has been maintained for greater than 8 mo in man. In a pilot study using a commercially available, transcutaneously controllable, magnetically activated valve for baseline superimposed bolus insulin infusion, the feasibility of maintaining near normal serum glucose in diabetic dogs was demonstrated. The effect of long-term intravenous cannulation was investigated; it was found that the intimal tissues of the vena cava surrounding the cannulae were largely unaltered and microemboli could not be detected in the lungs of the animals studied. Cannula plugging, which occurred on several occasions due to thrombus formation in the final centimeter of the cannula, has been solved by changes in pump design and refilling procedures. The problem of insulin precipitation in flow passages of the pump remains unsolved, but there are indications that substances entering the cannula from the blood may be involved. A new pump design for modulated insulin infusion is described.

Animals↗
PubMedDate not supplied

Catheter with an anchoring tip for chronic joint capsule perfusion.

An orthopedic catheter for long-term access to the synovial joint is anchored by a hollow threaded tap that penetrates the capsule through a hole drilled in the surrounding bone. The proximal end of the catheter is connected to either an implantable drug infusion pump or an implantable access port for continuous or intermittent perfusion or sampling. Four catheters were evaluated in dogs. Three were attached to ports, the fourth to a pump. Water (one trial, 22 weeks) and hyaluronic acid (HA) (5 mg/ml; two trials of 8 weeks each) were administered through ports twice weekly in 1.5 ml boluses; 5 mg/ml HA was delivered by pump (1 trial of 33 weeks) at 0.31 ml/day.

Animals↗
PubMedDate not supplied

In vitro and in vivo testing of a new valved intravascular catheter design.

Long-term intravascular catheterization carries a finite risk of catheter occlusion. A catheter tip valve design is presented (Buchwald-Wigness, Strato Medical Corporation, Beverly, MA) which incorporates features designed to decrease the risk of thromboembolism and reduce the need for maintenance procedures. Aspiration and infusion are controlled by separate valves, making it possible to engineer optimized inlet and outlet parameters. The outlet valve is an elastic sleeve expanded around the sidewall outlet ports which opens under injection pressure. The inlet valve is a tubular elastic element compressed against the inlet port from within the lumen, opening under aspiration pressure. A series of valves were prototyped with outlet pressures ranging from 2 to 100" H2O, and inlet pressures ranging from -40-70" H2O, and flowrates at 36" H2O of greater than 1,400 ml/hr. Dog implants of two prototypes with outlet valve pressures of 10" H2O, and inlet pressures of -40" H2O, demonstrated that dormant periods of up to 7.5 weeks could be achieved without detectable blood cell entry into the lumen. No significant hemolysis was observed in blood samples aspirated with a 6 cc syringe (8% scored "slightly hemolyzed" vs. 44% with the nonvalved controls) indicating that a hemodialysis application is likely.

Animals↗
PubMedDate not supplied

Advances and new concepts in the designing of peritoneovenous shunts for the treatment of refractory ascites.

From August 1984 to December 1987, 10 patients received the Minnesota peritoneovenous shunt at our institution. Four of these patients previously had received seven Denver catheters with clinical and/or radiologic evidence of malfunction. Eight patients had the diagnosis of benign intractable ascites and two malignant ascites. In two hypercoagulable patients re-exploration of the intravascular limbs was necessary for fibrin plugging, but in no case have we seen catheter tip blood clot thrombosis. One shunt failed to work properly because of adhesions. At present, six of these patients are alive with a functioning shunt and four have died of nonshunt-related complications. The longest period of continuous function with a Minnesota shunt was 100 weeks. Data from this trial are compared retrospectively with data from patients who received LeVeen (n = 8) or Denver shunts (n = 7) at the University of Minnesota Hospitals during the same time period. Performance of the Minnesota shunt was comparable to the commercially available LeVeen and Denver shunts in most respects and appeared to offer advantages in longer functional life and reduction of intensive care unit admissions.

Ascites↗
PubMedDate not supplied

Restoration and maintenance of intravenous insulin infusion in the vapor-pressure powered implantable infusion device.

Of the reasons to discontinue continuous implantable insulin pump therapy, flow rate reduction is the most common, occurring in 27 of 42 pumps in the University of Minnesota series. Thrombosis at the catheter tip appears to be a major reason for flow reduction. Six different procedures to restore flow in pumps were performed. Two of the procedures involve the infusion of an alkaline solution through the device, replacing the insulin/glycerol solution normally infused; the other four procedures are surgical ones involving manipulation of the catheter. In restoring flow the non-operative procedures achieved a success rate of 50%, having taken as long as 3 months to restore flow, and having allowed up to 1 year of further insulin pump therapy; flow in all the pumps so treated eventually decreased again. The operative procedures were nearly 100% successful, restored flow immediately, and allowed longer periods of adequate flow, but flow rate did again decrease. When flow rate reduction occurs further flow improvement procedures may be attempted without difficulty and are well tolerated. In implantable pumps the biocompatibility of the blood-catheter tip interface needs to be improved to deal with the recurrent problems of insulin infusion device flow rate decrease.

Bicarbonates↗
PubMedDate not supplied

An implantable pump for long-term intravascular drug infusion.

A totally implantable infusion pump has been developed that can provide chronic, continuous, low-rate drug infusions in ambulatory patients. The device relies on vapor pressure for its power source, and thus needs no recharging other than periodic drug refills. It is implanted surgically under the skin of the chest or abdomen, with the delivery cannula placed in an appropriate blood vessel. Pumps implanted in this way have delivered heparin, 5-fluorodeoxyuridine, or other drugs in patients; some outpatients have received continuous intravenous heparin infusions for more than 4 years.

Animals↗