A Fluid Dynamic Analysis Using Flow Visualization of the Baylor/NASA Implantable Axial Flow Blood Pump for Design Improvement

Abstract: The Baylor/NASA Axial Blood Flow Pump has been developed for use as an implantable left ventricular assist device (LVAD). The pump is intended as an assist device for either pulmonary or systemic circulatory support for more than 3-months' duration. To date the pump provides acceptable results in terms of thrombus formation and hemolysis (IH of 0.018 g/100 L). A fluid dynamics analysis using flow visualization was performed to investigate the flow fields and to determine areas within the pump that could be improved. These studies focused upon the inflow area in front of the pump. A prototype axial flow pump assembly was constructed to facilitate the flow visualization studies. Particle image tracking velocimetry techniques were used to measure Amberlite particles suspended in a blood analog fluid composed of 63% water and 37% glycerin. This method used a pulsed (612 Hz) laser light to determine flow velocity profiles, shear stress, Reynolds numbers, and stagnant areas within the axial pump. These studies showed that the flow straightener (a vaned assembly in the pump inflow) reduced Reynolds numbers from 4,640 to 2,540 (at 8.5 L/min) and that the flow straightener exacerbates a discontinuity found between it and the impeller. Within the inflow area, a maximum of 80 N/m² shear stress was measured, which is well below published blood damage thresholds. Design variations were investigated resulting in a smoother flow transition between flow straightener and impeller. These variations must be investigated further to establish a correlation with hemolysis and thrombus formation.     

Autogenous parathyroid grafts for generalized primary parathyroid hyperplasia: contrasting outcome in sporadic hyperplasia versus multiple endocrine neoplasia type I

Sixteen patients with generalized primary parathyroid hyperplasia were treated with attempted total parathyroidectomy and placement of an autogenous parathyroid graft in the forearm musculature; these patients have been followed for up to 79 months. We assessed completeness of parathyroidectomy on the basis of the background immunoreactive parathyroid hormone (iPTH) value 3 to 7 days after surgery, which predicted the chance of a graft-independent recurrence or persistence of hyperparathyroidism (0/8 if undetectable versus 4/5 if normal or high). Total parathyroidectomy was sometimes difficult to achieve because of the presence of supernumerary or ectopic parathyroid glands; to enhance the success rate of total parathyroidectomy, we suggest both the use of preoperative ultrasonography to locate intrathyroidal parathyroids and a routine search for supernumerary parathyroids that includes transcervical thymectomy. Graft function was monitored by measuring the secretory gradient for iPTH (the difference between the two antecubital fossae). Gradients on postoperative days 3 to 7 were barely detectable, but by 3 weeks, larger iPTH gradients were noted in every case. By 4 months, the graft could maintain normal serum calcium levels in all but one case. Autonomous graft function has evolved in four of six evaluable patients with type I multiple endocrine neoplasia (MEN I), but in none of the nine patients with sporadic hyperplasia (p = 0.043). A prospective study is needed to determine whether the use of a smaller number of parathyroid fragments for the autogenous graft in known MEN I patients might delay recurrence.     

HPLC柱切换法对炔诺酮α，β－聚（3－羟丙基）－DL－天冬酰胺在兔体内释放炔诺酮的测定

以柱切换ＨＰＬＣ（ＣＳＨＰＬＣ）技术，对炔诺酮α，β－聚（３－羟丙基）－ＤＬ天冬酰胺在家兔体内释放液中炔诺酮的血药浓度进行了测定，以自制ＯＤＳ预柱，水为流动相联机净化、富集样品；以Ｓｈｉｍ－ｐａｃｋＣＬＣ－ＯＤＳ为分析柱，甲醇－水（７：３）为流动相。结果表明ＣＳＨＰＬＣ对炔诺酮血药浓度有良好的选择性，回收率为８２．６％（ｎ＝５），日内和日间精密度（ＲＳＤ）分别小于４％和６％。在血清０．２２～１．１０μｇ／ｍ１范围内炔诺酮色谱峰面积与浓度有较好的线性关系（ｎ＝５，ｒ＝０．９９８）．     

Aprotinin for Primary Coronary Artery Bypass Grafting: A Multicenter Trial of Three Dose Regimens

Background. High-dose aprotinin reduces transfusion requirements in patients undergoing coronary artery bypass grafting, but the safety and effectiveness of smaller doses is unclear. Furthermore, patient selection criteria for optimal use of the drug are not well defined.

Methods. Seven hundred and four first-time coronary artery bypass grafting patients were randomized to receive one of three doses of aprotinin (high, low, and pump-prime-only) or placebo. The patients were stratified as to risk of excessive bleeding.

Results. All three aprotinin doses were highly effective in reducing bleeding and transfusion requirements. Consistent efficacy was not, however, demonstrated in the subgroup of patients at low risk for bleeding. There were no differences in mortality or the incidences of renal failure, strokes, or definite myocardial infarctions between the groups, although the pump-prime-only dose was associated with a small increase in definite, probable, or possible myocardial infarctions (p = 0.045).

Conclusions. Low-dose and pump-prime-only aprotinin regimens provide reductions in bleeding and transfusion requirements that are similar to those of high-dose regimens. Although safe, aprotinin is not routinely indicated for the first-time coronary artery bypass grafting patient who is at low risk for postoperative bleeding. The pump-prime-only dose is not currently recommended because of a possible association with more frequent myocardial infarctions.     

Infected pancreatic fluid collections: percutaneous catheter drainage

Thirty-eight infected pancreatic fluid collections in 23 patients with acute or chronic pancreatitis were drained percutaneously following initial diagnosis with computed tomography and fine-needle aspiration. Fifteen (65.2%) patients were cured completely without surgery. Eight (34.8%) patients required some type of surgery despite successful treatment of the fluid collection, and in two (6.5%) the collection recurred after catheter removal. Complications occurred in three (13%) patients, but only one complication (4%), empyema, was a direct result of catheter drainage. Catheter drainage time averaged 29 days for 16 patients with isolated collections and 96 days and 104 days for patients with collections with pancreatic duct fistulas (nine patients) or gastrointestinal fistulas (14 patients), respectively. This study confirms that infected pancreatic fluid collections can be safely and effectively treated with percutaneous catheter techniques in most patients.     

Clinical Experience with BioMedicus Centrifugal Ventricular Support in 172 Patients

Abstract: One hundred and seventy-two patients at The Methodist Hospital in Houston, Texas, were placed on BioMedicus centrifugal ventricular support. One hundred thirty-nine patients were male and 33 were female with a mean age of 59.7 years. Reasons for support were post-cardiotomy cardiac failure (129 patients), cardiac allograft failure (17 patients), bridge to transplantation (10 patients), resuscitation (7 patients), postpercutaneous trans-luminal coronary angioplasty emergent (2 patients), and other (7 patients). Support was by left ventricular assist device in 108 patients, right ventricular assist device in 20 patients, and biventricular assist device in 44 patients. Eighty-four patients (48.8%) were weaned from the ventricular assist device, and 88 patients (51.2%) were not weaned. Thirty-four patients (20.0%) were discharged from the hospital. Complications included coagulopathy, renal insufficiency/failure, respiratory insufficiency/ failure, neurological deficits, sepsis, arrhythmias, and device-related complications. Overall causes of death were ventricular failure (55.1%), triage (13.0%), arrhythmias (9.4%), graft failure (5.9%), coagulopathy (4.3%), sepsis syndrome (2.9%), device-related (0.7%), and other (0.7%). BioMedicus centrifugal ventricular support can be implemented rapidly and easily. Device-related complications are few (1.2%), and it is relatively inexpensive when compared with other ventricular assist systems. This series demonstrates that a substantial number of patients may benefit from temporary centrifugal ventricular support.