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Biomedical subjects

B D Wigness

Publications and source records attributed to B D Wigness.

29 records · Page 2Linked to original sources
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

Glycerol prevents insulin precipitation and interruption of flow in an implantable insulin infusion pump.

Insulin precipitation is a major obstacle to the use of implantable insulin infusion pumps. In one such pump (Infusaid, Infusaid Corporation, Norwood, Massachusetts), unprotected insulin precipitated and occluded nine pumps implanted in normal dogs within 43 days. In contrast, two similar pumps containing insulin mixed with 80% glycerol functioned normally for more than 250 days. In human studies, a similar mixture allowed insulin to be delivered to nine diabetic subjects for more than 6 mo in each case; total fluid flow rates from the pump were essentially unchanged after 460 patients-weeks of insulin infusion. A possible drawback of the mixture is a time- and temperature-dependent propensity to cause the formation of soluble, higher-molecular-weight insulin polymers, which apparently have lower biologic activity. Formation of such polymers and maintenance of biologic activity were largely prevented by the addition of phosphate buffer at neutral pH.

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

A rabbit model for implanting continuous drug infusion pumps.

This paper describes a surgical technique for implanting a readily available, human-sized drug infusion pump in rabbits. We developed this technique in order to expand uses of implantable infusion pump technology in the laboratory. The dog, which has been the research animal of choice in previous studies using implantable pumps, can now be replaced by smaller, less expensive animals for similar or other laboratory purposes. This technique can be of particular importance in the study of atherosclerosis where the dog is a poor model and the rabbit an excellent one. In 18 rabbits with inferior vena cava cannulations, we were able to obtain 100% survival and constant solution delivery for up to and greater than 6 months. This technique is safe and reproducible. By employing a simple catheter modification and using special pump anchoring precautions, we found that we could successfully use a human-sized device in rabbit studies. Commentary is also made concerning the relative contributions to patency and vein sclerosis of catheter diameter and the infusate media.

Animals↗
PubMedDate not supplied

Portable data acquisition and control apparatus for implanted drug infusion pump interrogation.

Now that implantable drug infusion pumps are well established clinically, methods for diagnosing suspected pump failures are needed. The authors previously constructed a benchtop data acquisition and control apparatus to assist our work in developing new pump technology. Although this device is technically capable of in vivo pump monitoring, it is cumbersome. Thus, they recently created a portable interrogation unit with more limited features. This portable pump interrogation apparatus consists of a 32 bit MS-DOS labtop computer, data acquisition software, an analog/ASCII interface, a pressure transducer, and appropriate fluid conduits. Communication between the device and the implanted pump is via a percutaneous needle puncture of the drug reservoir refill septum. This procedure is identical to that employed in a standard pump refill. Pump performance is evaluated by incrementally filling the pump reservoir while simultaneously measuring reservoir pressure. The resulting data are presented on the computer screen as a plot of pressure versus volume that quickly and simply either eliminates or confirms the reservoir pressure source as a failure mode. Diagnostic runs are saved on file for archival purposes. Their benchtop apparatus has been a valuable and reliable tool over many years of use. The authors believe that their portable apparatus will be equally beneficial.

Data Collection↗