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Biomedical subjects

R G Weiss

Publications and source records attributed to R G Weiss.

63 records · Page 4Linked to original sources
PubMed1989

Factors affecting urea clearance during continuous hemodiafiltration in the canine model.

Continuous hemofiltration (CH) for the treatment of hypervolemia and electrolyte abnormalities in critically ill patients with acute renal failure has been shown to be an effective mode of therapy. This technique offers several advantages over peritoneal dialysis or hemodialysis: it is technically less complex, provides efficient ultrafiltration, and produces fewer hemodynamic disturbances. Recently, continuous hemodiafiltration (CHD) using a flow of dialysate fluid into the ultrafiltration chamber has been reported to augment urea clearance. The purpose of this study was to determine the blood flow and dialysate flow characteristics for optimal clearance of urea and creatinine using this technique. Six mongrel dogs (mean weight, 8.0 +/- 1.1 kg) underwent bilateral nephrectomy to induce anuric renal failure. Postoperatively, the animals were fluid resuscitated and fed ad libitum. Twenty-four hours following nephrectomy, venovenous hemofiltration was instituted. Blood flow was regulated via a roller pump, while dialysate flow was regulated using an infusion controller. An Amicon-30S hemofilter was used in the circuit. Blood flow rates of 5, 10, 15, 20, 25, and 30 mL/kg/min were used. Hemodiafiltration using Dianeal 1.5% solution was used in each animal. Net fluid losses via ultrafiltration were replaced using lactated Ringer's solution. Three of six animals survived for the complete five-hour hemofiltration period. No marked disturbances in electrolyte serum concentrations, including hyperkalemia, were observed. BUN concentrations were reduced by 35% and creatinine by 26%. Variation of the dialysate flow rate did not influence clearance of either urea or creatinine. Instead, clearance appeared to be flow dependent, and it was markedly increased at flow rates greater than 15 mL/kg/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed1989

Color flow mapping to document normal pulmonary venous return in neonates with persistent pulmonary hypertension being considered for extracorporeal membrane oxygenation.

This study investigated the value of color flow mapping in documenting normal pulmonary venous return in neonates with persistent pulmonary hypertension who were candidates for extracorporeal membrane oxygenation (ECMO). Forty newborn infants with persistent pulmonary hypertension underwent conventional (two-dimensional and Doppler) echocardiography and color flow mapping. Of 25 candidates for ECMO therapy, 18 subsequently received it. Conventional echocardiography demonstrated normal pulmonary venous return in only 21 of the 40 patients. In all 40, however, color flow mapping demonstrated normal right and left pulmonary venous drainage entering the left atrium. In three other patients with total anomalous pulmonary venous return, conventional echocardiography demonstrated the anomalous pulmonary venous pathways, and color flow mapping did not show jets emanating from the left atrial wall; the left atrium was shown to fill exclusively from right to left shunting through the foramen ovale. We conclude that color flow mapping is superior to conventional echocardiography for verifying normal pulmonary venous return in neonates with persistent pulmonary hypertension.

Color↗
PubMed1989

Comparative 13C and 31P NMR assessment of altered metabolism during graded reductions in coronary flow in intact rat hearts.

13C NMR spectroscopy may offer a unique ability to characterize the metabolic response to graded reduction in coronary flow since it allows repeated, nondestructive identification of products of intermediary metabolism in the same heart. The sensitivity of 13C parameters of glucose metabolism was compared with changes in levels of phosphocreatine, ATP, and pH as determined by 31P NMR in the intact, beating rat heart model during graded reductions in coronary flow. Experiments were performed during 60 min of perfusion with [1-13C]glucose (5 mM) at normal flow (15 ml/min) and at the reduced flow rates of 5 and 2 ml/min. During flow at 5 ml/min, isovolumic developed pressure fell to 51 +/- 4% of control. Although phosphocreatine, ATP, and pH were not changed, [3-13C]lactate was increased (1.46 +/- 0.12 mumol/g of wet weight vs. 0.63 +/- 0.08 during normal flow). In addition, the time to 50% maximum enrichment of [2-13C]glutamate was prolonged (17 +/- 1 min vs. 9 +/- 1 min during normal flow), indicating that glucose-supported flux through the tricarboxylic acid (TCA) cycle was decreased. The relative anaplerotic contribution to citrate synthase-supported TCA flux was increased from 6% to 35%. These 13C metabolic changes could not be reproduced by reduced [1-13C]glucose delivery in the absence of ischemia, although similar reduced TCA flux indices were reproduced in additional hearts when workload was reduced by low calcium (0.7 mM) perfusion. Therefore, the information provided by 13C NMR spectroscopy can be a more sensitive indicator of flow-induced alterations in cardiac metabolism than that provided by the much more commonly used 31P NMR technique.

Adenosine Triphosphate↗
PubMed1989

Brain abnormalities in infants on extracorporeal membrane oxygenation: sonographic and CT findings.

The findings of cranial sonography performed before and during extracorporeal membrane oxygenation (ECMO) in 50 near-term infants and CT findings after ECMO in 18 of those patients are reported. Hemorrhage is uncommon in patients being considered for ECMO: subependymal hemorrhage was seen in one case and subependymal cyst possibly due to in utero hemorrhage was seen in five cases. Hypoxic ischemic ischemic injury is more common: severe cerebral edema was seen in two cases, occipital hemorrhagic infarct in one case, and mild cerebral edema in 17 cases. During ECMO, sonograms showed that the hemorrhage in patients with small subependymal hemorrhage or cyst before ECMO did not extend while on ECMO. Typical germinal matrix/intraventricular hemorrhage was seen uncommonly (three cases). Unusual parenchymal hemorrhage did occur. Hypoxic ischemic brain injury was more common: parenchymal hemorrhage was seen in three cases, severe cerebral edema in three cases, and infarction in three cases. Hypoxic ischemic brain injury probably occurs before ECMO, with a delay in visualization. CT after ECMO detected additional abnormalities, particularly peripheral areas of hemorrhage and infarction not visible on sonograms, and is now being performed on all patients. More emphasis should be placed on better screening of infants being considered for ECMO treatment to identify irreversible anoxic brain injury, not just hemorrhage.

Brain Diseases↗
PubMed1988

Duplications of the alimentary tract. Clinical characteristics, preferred treatment, and associated malformations.

Duplications of the alimentary tract are unusual congenital anomalies that frequently present a diagnostic as well as therapeutic challenge to the surgeon. Because these lesions occur so infrequently, they are often not suspected until encountered intraoperatively. Due to the complicated anatomy and common blood supply shared between the duplication and associated native bowel, appropriate management requires a familiarity with the anatomy and clinical characteristics of this entity. To better define the range of patient characteristics, clinical presentation, and preferred therapy, 20 enteric duplications were reviewed in 17 patients treated at the Children's Hospital Medical Center from 1956 to 1986. Ages of patients ranged from 1 day to 11 years; 60% were less than 2 years of age at initial presentation. Seven duplications in six patients involved alimentary tract structures of foregut derivation (esophagus, stomach, and Parts I and II of duodenum), with a predominance of girls (4 of 6). Most of these patients (67%) presented with moderate to severe acute respiratory distress and a mass present on chest radiograph. In 67% of the patients, the correct diagnosis was established before operation. None required emergency operative intervention. By contrast, 13 duplications in 11 patients were of midgut or hindgut derivation (Parts III and IV of the duodenum, jejunum, ileum, and colon). In this group of patients, 62% of the duplications involved the cecum, 23% involved the ileum, and 16%, the jejunum. Seventy-eight per cent of the patients were boys. The most common symptoms were nausea and vomiting, and the most common sign was a palpable abdominal mass. Emergency operative intervention was required of eight of 11 patients with duplications involving the small bowel and colon. Three patients presented with an intussusception, four with signs and symptoms consistent with acute appendicitis, one with a small bowel obstruction, and two with gastrointestinal hemorrhage due to the presence of ectopic gastric mucosa within the duplication. It was found that two important points must be considered in regard to the management of enteric duplications: (1) the common blood supply shared between the duplication and native bowel must be carefully protected to avoid undue sacrifice of normal bowel, and (2) the presence of heterotopic gastric mucosa in 35% of patients negates internal drainage.(ABSTRACT TRUNCATED AT 400 WORDS)

Abnormalities, Multiple↗
PubMed1982

14C-lactose breath tests during pelvic radiotherapy: the effect of the amount of small bowel irradiated.

Thirty patients who were undergoing pelvic radiotherapy had 14C-lactose breath tests performed in the first and fifth weeks of treatment. In Group I (21 patients), a significant portion of the small intestine was irradiated, and in Group II (9 patients), only a small portion of the small intestine was irradiated. In Group I, the average reductions in the excretion of ingested 14C between the first- and fifth-week tests were 41.5% at 1/2 hour postingestion (p less than 0.05), and 21.8% at 1 hour postingestion (p less than 0.05). In Group II, the percentage reductions were 11.8% and 3.7% at 1/2 and 1 hour, respectively (p greater than 0.05). The data suggest that lactose malabsorption is a factor in the etiology of the nausea, vomiting, and diarrhea experienced by patients who are undergoing pelvic radiotherapy, and that the amount of bowel included in the treatment volume significantly influences the degree of malabsorption.

Breath Tests↗
PubMedDate not supplied

Castleman's disease of the left triceps in a child suspected to be a small round cell tumor of childhood.

Castleman's disease (CD) is histologically characterized by a proliferation of polyclonal small lymphocytes and plasma cells. The clinical presentation varies widely, but most commonly manifests as a solitary mediastinal mass, incidentally found on radiographic examination. We present a case of a 10-year-old girl who exhibited a left arm mass which, preoperatively and on frozen section, was diagnosed as a small round cell tumor of childhood (SRCT). This report emphasizes the unusual location of CD in the soft tissue and as a rare entity to be considered in the differential diagnosis of SRCT.

Arm↗
PubMedDate not supplied

Repeated, transient lactate exposure does not "precondition" rat myocardium.

The precise mechanism of the cardioprotective effect of ischemic preconditioning (IPC) is still unclear, although various mechanisms have been suggested, including activation of ATP-dependent potassium (KATP) channels by adenosine and protein kinase C as well as increased expression of heat shock protein (HSP). Increasing evidence suggests that lactate, which accumulates during IPC periods, can activate several of these "triggers" of preconditioning. We tested whether repeated exposure to lactate, producing tissue lactate concentrations similar to those during brief ischemic periods, could contribute to IPC benefits. Five isolated rat hearts were subjected to a previously reported IPC protocol composed of two 5-min ischemia-reperfusion cycles; another five hearts served as controls; and six hearts underwent a "lactate-preconditioning" protocol, consisting of two 5-min exposures to 15 mM lactate and two 5-min periods of reflow with a lactate-free buffer. Subsequently all hearts underwent 30 min of normothermic, total ischemia followed by 30 min of reflow at a constant perfusion pressure of 80 mmHg (1 mmHg = 133.3 Pa). Lactate exposure resulted in tissue lactate levels similar to those during ischemia in ischemia-preconditioned hearts (10.5 +/- 0.6 versus 10.5 +/- 1.2 mumol/g wet weight, mean +/- SEM). However, the recovery of left ventricular developed pressure (DevP) following 30 min of total ischemia was significantly higher in the IPC hearts than in either the control or lactate-exposed hearts, reaching 56.8 +/- 3.4, 14.2 +/- 6.8, and 9.5 +/- 3.6%, respectively, of the baseline values. There was no significant difference between lactate-preconditioned and control hearts. End-diastolic pressure (EDP) was significantly lower during reperfusion in IPC hearts than in lactate-exposed and control hearts, with no significant differences between the latter two groups (36.2 +/- 3.5, 82.0 +/- 2.9, and 81.2 +/- 8.5 mmHg, respectively). In contrast with the proposed hypothesis, repeated, transient lactate exposure resulting in tissue lactate levels similar to ischemic preconditioning did not improve contractile recovery after a prolonged ischemic period in this model.

Animals↗