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Biomedical subjects

R G Lee

Publications and source records attributed to R G Lee.

At least 91 records · Page 5Linked to original sources
PubMed1991

Bacterial nutrients in drinking water.

Regrowth of coliform bacteria in distribution systems has been a problem for a number of water utilities. Efforts to solve the regrowth problem have not been totally successful. The current project, which was conducted at the New Jersey American Water Co.-Swimming River Treatment Plant, showed that the occurrence of coliform bacteria in the distribution system could be associated with rainfall, water temperatures greater than 15 degrees C, total organic carbon levels greater than 2.4 mg/liter, and assimilable organic carbon levels greater than 50 micrograms of acetate carbon equivalents per liter. A multiple linear regression model based on free chlorine residuals present in dead-end sections of the distribution system and temperature predicted 83.8% of the heterotrophic plate count bacterial variation. To limit the growth of coliform bacteria in drinking water, the study concludes that assimilable organic carbon levels should be reduced to less than 50 micrograms/liter.

Carbon↗
PubMed1991

Occurrence of Giardia and Cryptosporidium spp. in surface water supplies.

Giardia and Cryptosporidium levels were determined by using a combined immunofluorescence test for source waters of 66 surface water treatment plants in 14 states and 1 Canadian province. The results showed that cysts and oocysts were widely dispersed in the aquatic environment. Giardia spp. were detected in 81% of the raw water samples. Cryptosporidium spp. were found in 87% of the raw water locations. Overall, Giardia or Cryptosporidium spp. were detected in 97% of the raw water samples. Higher cyst and oocyst densities were associated with source waters receiving industrial or sewage effluents. Significant correlations were found between Giardia and Cryptosporidium densities and raw water quality parameters such as turbidity and total and fecal coliform levels. Statistical modeling suggests that cyst and oocyst densities could be predicted on the basis of watershed and water quality characteristics. The occurrence of high levels of Giardia cysts in raw water samples may require water utilities to apply treatment beyond that outlined in the Surface Water Treatment Rule of the U.S. Environmental Protection Agency.

Animals↗
PubMed1991

Giardia and Cryptosporidium spp. in filtered drinking water supplies.

Giardia and Cryptosporidium levels were determined by using a combined immunofluorescence test for filtered drinking water samples collected from 66 surface water treatment plants in 14 states and 1 Canadian province. Giardia cysts were detected in 17% of the 83 filtered water effluents. Cryptosporidium oocysts, were observed in 27% of the drinking water samples. Overall, cysts or oocysts were found in 39% of the treated effluent samples. Despite the frequent detection of parasites in drinking water, microscopic observations of the cysts and oocysts suggested that most of the organisms were nonviable. Compliance with the filtration criteria outlined by the Surface Water Treatment Rule of the U.S. Environmental Protection Agency did not ensure that treated water was free of cysts and oocysts. The average plant effluent turbidity for sites which were parasite positive was 0.19 nephelometric turbidity units. Of sites that were positive for Giardia or Cryptosporidium spp., 78% would have been able to meet the turbidity regulations of the Surface Water Temperature Rule. Evaluation of the data by using a risk assessment model developed for Giardia spp. showed that 24% of the utilities examined would not meet a 1/10,000 annual risk of Giardia infection. For cold water conditions (0.5 degree C), 46% of the plants would not achieve the 1/10,000 risk level.

Animals↗
PubMed1990

Effects of unexpected perturbations on trajectories and EMG patterns of rapid wrist flexion movements in humans.

To investigate how motor programs can be modified by sensory inputs we recorded kinematic and EMG patterns from normal human subjects performing well-practised wrist flexion movements in response to an auditory tone. On random trials unexpected wrist perturbations were introduced at varying times after the signal to move had been given. Extension perturbations delivered before agonist EMG onset resulted in an increased maximum velocity (MV) during the wrist flexion movement and in an increased target overshoot even though the wrist was further from the target than expected by the subject at the onset of the movement. The first agonist EMG burst and the antagonist burst were both increased in magnitude in these perturbed trials. Flexion perturbations delivered before the agonist EMG onset moved the hand nearer to the target just prior to movement onset. These resulted in a reduced MV, but the expected increased target overshoot did not occur. The first agonist burst was reduced in magnitude, and the antagonist burst was increased in magnitude. Perturbations delivered after agonist EMG onset produced less change in the first agonist and antagonist EMG burst, and less compensation for the perturbation was evident in wrist position and velocity recordings. These results indicate that, at least in some situations, motor programs for rapid voluntary movements can be modified by afferent inputs. This interaction between central motor commands and sensory feedback might occur at the cortical or spinal level, depending on when perturbations occur relative to onset of EMG and movement. The timing of the EMG changes suggest that both reflex mechanisms and longer latency 'voluntary' adjustments contribute to the compensatory changes in movement trajectory.

Adult↗
PubMed1990

Manual tracking performance in patients with cerebellar incoordination: effects of mechanical loading.

Manual tracking performance was studied in five patients with cerebellar incoordination due to unilateral cerebellar hemisphere lesions. The subjects were required to track a target on an oscilloscope screen by moving a cursor controlled by flexion-extension movements of the wrist. In comparison to normal subjects, the cerebellar patients, using their clinically affected arm, demonstrated irregular tracking patterns with inappropriate accelerations and decelerations, numerous high velocity peaks of movement, and an increased time lag between the cursor and the target. The addition of a viscous load provided by feeding back wrist velocity to a torque motor coupled to the apparatus resulted in significant improvement in tracking performance and suppression of the high velocity peaks. Increasing elastic stiffness by feeding back wrist position or inertial load by adding weights to the hand did not improve performance on this task. It is proposed that a hypotonic cerebellar limb behaves like an underdamped mechanical system. The addition of viscous loads helps restore more normal damping during voluntary movements of the arm.

Adolescent↗
PubMed1990

Gastrointestinal involvement in Langerhans cell histiocytosis (histiocytosis X): diagnosis by rectal biopsy.

We report two patients with biopsy-proven involvement of the gastrointestinal tract by Langerhans cell histiocytosis (LCH). The two patients were infants with congenital cutaneous lesions and bloody diarrhea beginning at 1 or 2 wk of age. Rectal biopsy specimens showed a mucosal infiltrate of typical Langerhans cells that focally invaded and destroyed the crypt epithelium. Gastrointestinal involvement by LCH is unusual and only rarely has represented a prominent clinical manifestation. In most cases, such involvement has been an indicator of widespread multisystemic disease. Its distinctive morphologic and immunohistochemical features allow LCH to be distinguished from other histiocytic infiltrations found in mucosal biopsy specimens.

Biopsy↗
PubMed1989

Liver histology in rheumatoid arthritis patients receiving long-term methotrexate therapy. A prospective study with baseline and sequential biopsy samples.

Twenty-nine patients with active rheumatoid arthritis receiving long-term oral weekly methotrexate (MTX) therapy were studied to determine the extent of their hepatic architectural changes. Liver biopsies (n = 101) were performed in all patients before the initiation of MTX therapy, after 2 years, and annually thereafter (mean duration of therapy 53 months). The hepatic histologic grade (5-point scale) in 25 patients increased (worsened) (mean +/- SEM change 0.84 +/- 1.02; P = 0.001). Fibrosis, confirmed by trichrome staining, developed in 14 of 27 patients (52%). A history of alcohol consumption prior to starting MTX correlated significantly with subsequent worsening of the liver biopsy grade (r = 0.55, P = 0.0054). Alcohol intake prior to study entry, elevated weight at MTX initiation, and dose and duration of MTX were significantly associated with the development of fibrosis. Elevations in serum aspartate aminotransferase levels at 29-53 months of therapy correlated with the increase in hepatic histologic grade at the 3-year biopsy (r = 0.50, P = 0.04) and 4-year biopsy (r = 0.58, P = 0.03). We conclude that long-term MTX therapy in rheumatoid arthritis patients results in a statistically significant worsening in hepatic histologic grade, with common development of mild fibrosis. We do not consider these changes to be clinically significant at present.

Administration, Oral↗
PubMed1989

Anterior lesser curvature laser seromyotomy with posterior truncal vagotomy: a potential treatment of peptic ulcer disease.

Anterior lesser curvature seromyotomy combined with posterior truncal vagotomy has been suggested as an alternative to proximal gastric vagotomy in the treatment of peptic ulcer. The argon laser may be an ideal instrument for performing seromyotomy. This study compares anterior lesser curvature argon laser seromyotomy/posterior or truncal vagotomy with anterior proximal gastric vagotomy/posterior truncal vagotomy in a canine preparation. Six dogs underwent anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy and six others underwent anterior proximal gastric vagotomy/posterior truncal vagotomy. Gastric emptying and acid secretion studies were performed preoperatively and at 1 and 6 months postoperatively. Operating time and blood loss were determined. Anterior lesser curvature argon laser seromyotomy was performed with the argon laser at 10 W, continuous, delivered through a 600 micron unsheathed quartz fibre. Anterior proximal gastric vagotomy and posterior truncal vagotomy were performed in the standard fashion. Solid phase gastric emptying was slowed with both operations (P less than 0.05) but this was not manifest clinically. Blood loss (millilitres) was less following anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy than following anterior proximal gastric vagotomy/posterior truncal vagotomy (21(6.8) versus 95(28.1), mean (s.e.m.), P less than 0.05) but operating time was not significantly different between the groups. Mean basal acid secretion was reduced by 64 per cent 6 months after anterior lesser, curvature argon laser seromyotomy/posterior truncal vagotomy (P less than 0.05) and by 53 per cent after anterior proximal gastric vagotomy/posterior truncal vagotomy (not significant). Mean stimulated acid secretion was reduced by 41 per cent 6 months after anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy (P less than 0.05) and by 24 per cent after anterior proximal gastric vagotomy/posterior truncal vagotomy (not significant). We conclude that anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy is an acceptable alternative to anterior proximal gastric vagotomy/posterior truncal vagotomy and may provide superior parietal cell denervation with less operative blood loss.

Animals↗
PubMed1989

High prevalence of adenomatous polyps of the duodenal papilla in familial adenomatous polyposis.

Eighteen consecutive asymptomatic patients with familial adenomatous polyposis (both familial polyposis coli and Gardener's syndrome) were studied over a 12-month period; side-viewing upper endoscopy and biopsy were used to assess the frequency of adenomatous polyps of the duodenal papilla. Nine of the 18 patients demonstrated adenomatous polyps of the papilla, varying in size and appearance from microadenomas in normal-appearing duodenal papillae (two) to a sessile polyp 3 cm in diameter. Two were tubulovillous adenomas (0.5 cm and 2 cm in diameter) and the remainder were tubular adenomas. Severe atypia and malignancy were not encountered. These findings reveal that adenomas of the duodenal papilla are common in individuals with familial adenomatous polyposis. Because of these findings and because of the known risk of periampullary adenocarcinomas and nonmalignant complications of polyps of the duodenal papilla in patients with familial adenomatous polyposis, upper gastrointestinal screening of such patients should include examination of the duodenal papilla with a side-viewing endoscope.

Adenomatous Polyposis Coli↗
PubMed1989

Sclerosing peritonitis.

An unusual case of widespread peritoneal fibrosis of unknown cause ("sclerosing peritonitis") is described. The patient presented with ascites and bowel obstruction and was found to have numerous fibrous plaques involving primarily the serosa of the small bowel. The plaques were composed of bland spindle cells, ultrastructurally characterized as myofibroblasts, set within a collagenous stroma. Progressive involvement led to the patient's death 17 months after onset of symptoms. A literature review shows similar cases reported with a variety of names and a number of associated clinical conditions, none of which was present in this patient. The pathologic features seen in this case suggest that sclerosing peritonitis represents a nonspecific reaction of the peritoneal surface to a variety of insults and is characterized by florid reactive hyperplasia of submesothelial mesenchymal cells.

Humans↗
PubMed1989

Nonalcoholic steatohepatitis: a study of 49 patients.

Nonalcoholic steatohepatitis (NASH) refers to an alcoholic hepatitis-like histologic pattern found in nonalcoholic patients. A review of 543 liver biopsies diagnosed as alcoholic hepatitis yielded 49 cases of NASH. The patients were commonly middle-aged women who were obese and often diabetic. NASH was usually discovered because of abnormal liver function tests or hepatomegaly noted during evaluation of other medical problems. Histologic examination revealed the same spectrum of changes found in alcoholic hepatitis, including cirrhosis in eight patients. Follow-up information was available for 39 patients after an average length of 3.8 years. Only one patient developed hepatic decompensation or died with liver failure or portal hypertension. Repeat histologic material was available for 13 patients after a mean 3.5 years of follow-up. Five patients showed progression of fibrosis, with cirrhosis developing in two, but the other eight patients demonstrated little morphologic change. These findings indicate that NASH is, in general, a clinically mild and biologically low-grade condition, but with the potential to progress and evolve into cirrhosis in some patients. The factors promoting progression are unclear.

Adult↗
PubMed1989

Backward masking, information processing, and schizophrenia.

Many researchers have used backward masking to examine information-processing speed in schizophrenic subjects. The validity of this approach rests upon two main assumptions. One is that the mask effectively limits the time a previously presented stimulus is available for processing. The other is that the components of the masking mechanism in schizophrenic subjects are comparable to those in control groups. It is argued that the masking procedures used in these studies fail to meet either assumption. Alternative interpretations of these investigations, however, suggest important hypotheses for further research in our quest to understand information-processing deficits associated with schizophrenia.

Humans↗
PubMed1989

Carbon isotope fractionation by thermophilic phototrophic sulfur bacteria: evidence for autotrophic growth in natural populations.

Purple phototrophic bacteria of the genus Chromatium can grow as either photoautotrophs or photoheterotrophs. To determine the growth mode of the thermophilic Chromatium species, Chromatium tepidum, under in situ conditions, we have examined the carbon isotope fractionation patterns in laboratory cultures of this organism and in mats of C. tepidum which develop in sulfide thermal springs in Yellowstone National Park. Isotopic analysis (13C/12C) of total carbon, carotenoid pigments, and bacteriochlorophyll from photoautotrophically grown cultures of C. tepidum yielded 13C fractionation factors near -20%. Cells of C. tepidum grown on excess acetate, wherein synthesis of the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase ribulose bisphosphate carboxylase) was greatly repressed, were isotopically heavier, fractionation factors of ca. -7% being observed. Fractionation factors determined by isotopic analyses of cells and pigment fractions of natural populations of C. tepidum growing in three different sulfide thermal springs in Yellowstone National Park were approximately -20%, indicating that this purple sulfur bacterium grows as a photoautotroph in nature.

Bacteria↗
PubMed1989

Pathophysiology of rigidity and akinesia in Parkinson's disease.

Although rigidity and akinesia are two of the cardinal features of Parkinson's disease, their exact pathophysiology remains uncertain. Mechanisms which may contribute to rigidity include accentuation of the long-latency component of the stretch reflex and enhanced fusimotor drive causing increased sensitivity of muscle spindles. Current evidence concerning the role of these factors in rigidity is reviewed. The relationship between akinesia, prolonged reaction times, and delay in initiation of internally generated movements in parkinsonian patients is discussed.

Humans↗
PubMed1989

High-altitude mountaineering and brain function: neuropsychological testing of members of a Mount Everest expedition.

Concern has been raised regarding the possibility that hypoxic conditions encountered during high-altitude mountaineering may have lasting harmful effects on the human brain. Members of an expedition to Mount Everest completed a series of neuropsychological tests before and after the expedition. Exposure to altitudes above 7,200 m was limited to a maximum of four consecutive nights, separated by rest periods at lower altitudes. No significant decline in performance was observed on any test. The subjects also completed a short series of tests at different altitudes during the expedition. No significant deterioration was observed at altitudes up to 7,500 m. There do not appear to be lasting harmful effects on brain function under these conditions.

Altitude↗
PubMed1988

Common inheritance of susceptibility to colonic adenomatous polyps and associated colorectal cancers.

We studied 670 persons in 34 kindreds by flexible proctosigmoidoscopic examination (60 cm) to determine how frequently colorectal adenomas and cancers result from an inherited susceptibility. Kindreds were selected through either a single person with an adenomatous polyp or a cluster of relatives with colonic cancer. The kindreds all had common colorectal cancers, not the rare inherited conditions familial polyposis coli and nonpolyposis inherited colorectal cancer. Likelihood analysis strongly supported the dominant inheritance of a susceptibility to colorectal adenomas and cancers, with a gene frequency of 19 percent. According to the most likely genetic model, adenomatous polyps and colorectal cancers occur only in genetically susceptible persons; however, the 95 percent confidence interval for this proportion was 53 to 100 percent. These results suggest that an inherited susceptibility to colonic adenomatous polyps and colorectal cancer is common and that it is responsible for the majority of colonic neoplasms observed clinically. The results also reinforce suggestions that first-degree relatives of patients with colorectal cancer should be screened for colonic tumors. This evidence of an inherited susceptibility to a cancer with well-recognized environmental risk factors supports the hypothesis that genetic and environmental factors interact in the formation and transformation of polyps.

Adenomatous Polyposis Coli↗
PubMed1988

Hepatic ultrastructure after methotrexate therapy for rheumatoid arthritis.

Twenty-six patients receiving long-term oral methotrexate (MTX) therapy for rheumatoid arthritis (24 patients) or psoriasis (2 patients) were prospectively evaluated for alterations in liver morphology by light microscopy, electron microscopy, and immunofluorescence microscopy. Although only 4 MTX-treated patients had light microscopic evidence of mild fibrosis, all had evidence of collagen deposition in the space of Disse near Ito cells and changes in hepatocyte lysosomes on electron microscopy. These findings were absent from control livers. Fibrinogen, fibronectin, and type IV collagen were identified by immunofluorescence in both MTX-treated patients and controls. We conclude that long-term MTX therapy for rheumatoid arthritis is associated with alterations in hepatic ultrastructure, including collagen deposition in the space of Disse and changes in hepatocyte lysosomes.

Adult↗