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Biomedical subjects

J Leach

Publications and source records attributed to J Leach.

At least 55 records · Page 3Linked to original sources
PubMed1990

Fluoride: benefits and risks of exposure.

This summarizes current knowledge of the benefits and risks of fluoride ingestion. The preponderance of evidence indicates that fluoride can reduce the incidence of dental caries and that fluoridation of drinking water can provide such protection. Due to the ubiquitous nature of exposures to fluoride sources other than drinking water, it is currently impossible to draw firm conclusions regarding the independent effect of fluoride in drinking water on caries prevalence using an ecologic study design. Moderate dental fluorosis occurs in 1 to 2% of the population exposed to fluoride at 1 mg/l in drinking water and in about 10% of the population at 2 mg/l; moderate/severe fluorosis occurs in variable percentages ranging up to 33% of the population exposed to fluoride at 2.4 to 4.1 mg/l in drinking water. The issue of whether moderate or severe dental fluorosis represents an adverse health effect is still controversial. There is no evidence of skeletal fluorosis among the general U.S. population exposed to drinking water fluoride concentrations lower than 4 mg/l. Radiographically detected osteosclerosis after chronic exposure to fluoride in drinking water at 8 mg/l was not associated with clinical symptoms. Reports of crippling skeletal fluorosis associated with low concentrations of fluoride in drinking water in tropical countries have been attributed to other dietary factors. The available data suggest that some individuals may experience hypersensitivity to fluoride-containing agents. Further studies on hypersensitivity are required. There is no evidence of increased incidence of renal disease or renal dysfunction in humans exposed to up to 8 mg fluoride per liter in drinking water. Structural changes in kidneys of experimental animals have been detected at doses exceeding 1 to 5 mg fluoride per kilogram per day. Based on four case reports, individuals with renal insufficiency who consume large volumes of naturally fluoridated water at 2 to 8 mg/l are possibly at increased risk of developing skeletal fluorosis. Studies on the effects of fluoride in individuals with renal insufficiency are needed. There is no evidence that chronic exposure to concentrations of fluoride reported to be greater than 2 mg/l in drinking water increases human cancer mortality or incidence. A study of lifetime exposure to fluoride on cancer incidence in rats and mice has been completed, but assessment for cancer has not been completed. There is no evidence that fluoride is genotoxic except in some in vitro assays at cytotoxic concentrations. There is no in vivo evidence that fluoride affects human cellular enzyme activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Survival prediction in amyotrophic lateral sclerosis.

This longitudinal study of 194 patients with sporadic ALS demonstrated that it is possible for physicians to predict the approximate survival time for an individual ALS patient given: (1) the age of the patient, (2) the duration of his weakness and (3) an estimate of his clinical disability (ALS Score). This information is of value in the clinical management of ALS patients, and it should facilitate construction of experimental therapeutic trials in ALS.

Amyotrophic Lateral Sclerosis↗
PubMed1988

Regionally variable pulmonary artery responses to C3a.

Products of the complement (C) cascade may have direct effects on pulmonary vascular tissue and contribute to pulmonary vasoconstriction in states of C activation. We studied the effects of C3a, a C-derived vasoactive peptide, on isolated rabbit hilar (HPA) and main pulmonary arteries (MPA). C3a elicited concentration-dependent constriction of HPA (10(7) M to 5 x 10(7) M) but minimal response in MPA at all concentrations tested. The difference between HPA and MPA responses was significant (P less than 0.05, paired t test). To evaluate HPA desensitization to C3a, the peptide was reapplied at 60 min in some tissues and at 120 min in others. All tissues consistently exhibited less constriction at 60 min than observed with previous exposures. Histamine contribution to the HPA response to C3a was determined by exposing the tissues for 30 min before C3a application to pyrilamine (1 x 10(-5) M), an histamine H1-receptor antagonist. Pyrilamine reduced the HPA response to C3a by 70-85%. We conclude that 1) isolated rabbit PA responses exhibit regional variability to C3a over a range of concentrations; 2) C3a desensitizes HPA for at least 60 min, but the tissue demonstrates variable recovery within 120 min; and 3) HPA responses to C3a are reduced by pyrilamine, an H1-receptor antagonist.

Animals↗
PubMed1987

Recombinant DNA in filamentous fungi: progress and prospects.

Recombinant DNA technology enables the creation of well-defined alterations in the genetic material of an organism. Methods to manipulate recombinant DNA in the filamentous fungi (a group of microorganisms that includes species of academic as well as commercial interest) have recently been developed. This has been the result of adaptation of procedures successfully employed in the manipulation of other microorganisms. There are a number of similarities in the behavior of recombinant DNA in different fungi, but a number of differences have also been observed between the filamentous and the nonfilamentous fungi. Such differences include the ability to identify DNA replication origins and the host range of expression of fungal genes.

Cloning, Molecular↗
PubMed1987

Nonunion following two-level anterior cervical discectomy and fusion.

Nonunion is a potential complication of anterior cervical discectomy and fusion (ACDF). There are reports that cite the prevalence of nonunion for two-level ACDF with various fusion techniques, but they do not recommend treatment alternatives. Pseudarthrosis after a two-level ACDF occurred in a 69-year-old man. Posterior cervical wiring and autograft resulted in a successful fusion anteriorly and posteriorly. Posterior fusion augments stability, enhances the potential for eventual anterior fusion, avoids the risks of an additional anterior procedure, and is an excellent therapeutic alternative to a second anterior attempt at stabilization.

Aged↗
PubMed1986

Foot deformities in infants and children.

Foot deformities may reflect a generalized disorder, especially a neurologic problem; thus, the child should have a brief general examination. Many infantile foot deformities, such as calcaneovalgus, are postural and self-correcting. Metatarsus varus is not referred for treatment until age 2 months and then only if the deformity is moderate or severe. Fixed forefoot equinus and heel varus characterize a clubfoot, which requires immediate treatment. Corrective shoes are not advised as the primary treatment for metatarsus varus or clubfoot but often are prescribed to maintain the corrected position after serial casts. Flexible flatfoot is a manifestation of a constitutional laxity affecting all ligaments and joints. The feet appear abnormal because of weight-bearing stresses. Most children with flatfoot achieve a partial correction spontaneously. Current research does not document that treatment with corrective shoes or inserts produces a result better than the partial correction that occurs naturally.

Clubfoot↗
PubMed1984

Occupational exposure to chlorophenates: toxicology and respiratory effects.

We have identified 71 chlorophenate-exposed sawmill workers as part of a group undergoing an extensive health and environmental evaluation in a pulp mill. We have compared this group with a group (351) with no physical proximity to the area in which chlorophenates were used. We demonstrated a gradient of exposure from 230 ppb in urine and 919 ppb in serum for those directly handling the contaminated wood, to 139 ppb in urine and 354 ppb in serum for those working in the area but not in manual contact as compared with serum levels of 84 ppb in the unexposed group. We noted that the bulk chemical was primarily in the tetrachloro-form but the serum levels contained more pentachlorophenate. The urine proportions were intermediate, approximating the bulk chemical proportions at the lower levels of exposure. We did not find an excess prevalence of respiratory symptoms or spirometric abnormalities which could be explained by the chlorophenate exposure.

Adult↗
PubMed1983

Correlation of scoliosis and pulmonary function in Duchenne muscular dystrophy.

Pulmonary function was correlated with patient age and degree of thoracic scoliosis in 25 patients with Duchenne muscular dystrophy in a retrospective, longitudinal study. The observed forced vital capacity (FVC) was found to peak at approximately the age when standing ceases, then to decline rapidly. Thoracolumbar curves were found to be insignificant in adversely affecting pulmonary function in patients with Duchenne muscular dystrophy. Percent FVC was found to be the parameter of pulmonary function that was most strongly correlated with age and scoliosis measurements. In addition, age and thoracic scoliosis together were better predictors of percent FVC than either one alone. Each 1 year of age had approximately the same negative influence on percent FVC that each 10 degrees of thoracic scoliosis had; both decreased percent FVC by approximately 4%. A regression equation for percent FVC is presented which predicts that the patient who has had scoliosis progression halted by spinal fusion would, subsequent to the surgery, show a slower rate of decline of percent FVC and that this rate is quantifiable, predictable, and dependent solely on the patient's advancing age. Therefore, early spinal instrumentation and fusion is advocated in the patient with Duchenne muscular dystrophy.

Adolescent↗