Biomedical subjects
H Buchwald
Publications and source records attributed to H Buchwald.
Implantable pumps and other devices for chronic infusion. Choices and issues.
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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.
Implantable pumps. Recent progress and anticipated future advances.
The implantable pump field is now more than 20 years old. The original goal of developing a totally artificial beta-cell remains unrealized, but programmable insulin pumps that contain all of the elements of the artificial beta-cell except the glucose sensor are involved in clinical trials in the United States and are commercially available in Europe. Currently, both single-rate and programmable implantable pumps are in general clinical use in the United States for the treatment of pain and spasticity, cancer, and osteomyelitis. Only a few of the potential applications of implantable pumps have been developed to the stage of commercial availability. This is, in part, because drug companies have traditionally developed parenteral drug applications only as a last resort and, in part, because of the complexity of the regulatory process for implantable pumps, often requiring review by both the drug and device branches of the Food and Drug Administration.
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.
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.
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.
Alberta's new look for occupational health and safety.
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A novel device for measuring the effect of cholesterol on the release of oxygen from red blood cells into myocardial tissue.
A novel method has been devised to measure the effect of cholesterol on the release of oxygen (O2) from the red blood cell (RBC) into a tailored environment, which can be made to mimic myocardial tissue. Cholesterol affects the cell membrane of the RBC and thus the release of O2 into tissue. While this is true of all tissue, the myocardium is especially sensitive because of its critical nature, its high O2 requirements, and the shortness of time that arterial blood spends in the muscle. Calculations are presented that show that the release time for O2 from RBCs is close to the residence time of the RBC in the coronary system. Sequential measurements of blood oxygen saturation (SO2) are made when oxygenated blood is subjected to conditions similar to those in the myocardium. The natural logarithm of the relative value of the SO2 at time t compared with the initial value of the SO2 can be fitted to a straight line whose slope is proportional to the parameters of the RBC membrane, the sample size, the hematocrit, and the diffusion parameters of the apparatus. This value is used to estimate the effects of cholesterol-lowering treatments on O2 release. This test will serve as a valuable adjunct to or replacement for stress tests in the evaluation of coronary artery disease, especially in patients whose physical conditions make standard stress testing painful or risky.
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.
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.
Insulin delivery by implanted pump. A chronic treatment for diabetes.
In the eight years that have elapsed since the first implantation of an insulin pump in a human subject, insulin delivered by implantable pump has been shown to improve metabolic control while reducing total and LDL cholesterol, serum amyloid A, and serum anti-insulin antibody titres. Both single-rate and programmable insulin pumps are now being evaluated in human trials with generally favorable results. Current clinical trial results indicate that the problem of insulin aggregation in pumps that inhibited initiation and expansion of clinical trials for several years has now been largely solved. Patients with implantable pumps are generally well-satisfied with this form of therapy, would choose it again, and recommend it to friends and relatives. Though currently more costly than subcutaneous insulin injections, the convenience of implantable pump therapy and the potential for reduction of diabetic complications through improved metabolic control may make it the treatment of choice in the future.
Chemotherapy via implanted infusion pump: new perspectives for delivery of long-term continuous treatment.
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Nursing and cardiovascular clinical trial research: collaborating for successful outcomes.
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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.
Normalization of lipoproteins following partial ileal bypass in individual WHO lipoprotein phenotypes.
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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.
An improved glycerol/insulin formulation for use in implantable pumps.
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