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Biomedical subjects

D D Lee

Publications and source records attributed to D D Lee.

64 records · Page 4Linked to original sources
PubMed1985

Some physico-chemical properties of deciduous enamel of children with and without pre-natal fluoride supplementation (PNF).

Physico-chemical investigations of enamel from deciduous teeth of a small number of children with and without pre-natal fluoride supplementation (PNF) exhibited the following differences between the PNF and non-PNF enamel, with the former showing: (a) more homogeneous and less extensive patterns of acid-etching; (b) denser crystal populations in intra-prismatic regions; (c) larger prism dimensions; (d) greater total mineral density (wt%ash); (e) higher degree of crystallinity; (f) smaller a-axis dimensions; and (g) more fluoride and less carbonate contents. On the basis of these preliminary findings, further studies with larger numbers of samples would seem appropriate.

Carbonates↗
PubMed1982

Bacteriophage T7 defective in the gene 6 exonuclease promotes site-specific cleavages of T7 DNA in vivo and in vitro.

Site-specific cleavages of intracellular DNA were demonstrated in bacteriophage T7 6am-infected cells. The sites of the cleavages were located at 46.8 and 68.7% (1% of the T7 DNA length = 400 base pairs) from the left end of the T7 genome. These cleavages required the products of genes 3 (endonuclease), 4 (DNA primase), and 5 (DNA polymerase). However, the product of gene 6 (exonuclease) must be absent. Site-specific cleavage was also shown to occur in vitro in extracts of T7 6am-infected cells, although at a different site: 82.8% from the left end of the T7 genome.

DNA Primase↗
PubMed1980

Effect of pore diffusion limitation on dextrin hydrolysis by immobilized glucoamylase.

Data reported here and previously indicate that when dextrin is hydrolyzed in the presence of immobilized glucoamylase, use of a larger average molecular weight substrate leads to lower overall rates of hydrolysis, while the maltose concentration during the bulk of the reaction and the maximum glucose concentration are lower than when the soluble form of the enzyme is employed under the same conditions. Computer simulation of the system demonstrated that all three observations were caused by pore diffusion limitation: the first by slow diffusion of substrate, the second by slow diffusion of intermediates, and the third by slow diffusion of glucose. Follow-up experiments with glucoamylase immobilized to particles of different sizes confirmed this finding, as results with the smallest beads were identical to those with soluble glucoamylase.

Dextrins↗
PubMed1976

Pilot plant production of glucose with glucoamylase immobilized to porous silica.

Glucoamylase was immobilized to porous silica and its kinetics and stability were observed with acid- and alpha-amylase-hydrolyzed dextrin as feed. The enzyme was found to be extremely stable in both laboratory and pilot plant operations. When the feed had been previously only lightly hydrolyzed, pore diffusion limitation caused appreciable decreases in glucose production rate. The severity of starch hydrolysis to dextrin markedly affected ultimate glucose yields. The diffusional gradients present in the carrier pores caused the immobilized enzyme to yield lower glucose concentrations than the free enzyme at similar feed conditions.

Glucose↗
PubMedDate not supplied

The autapse: a simple illustration of short-term analog memory storage by tuned synaptic feedback.

According to a popular hypothesis, short-term memories are stored as persistent neural activity maintained by synaptic feedback loops. This hypothesis has been formulated mathematically in a number of recurrent network models. Here we study an abstraction of these models, a single neuron with a synapse onto itself, or autapse. This abstraction cannot simulate the way in which persistent activity patterns are distributed over neural populations in the brain. However, with proper tuning of parameters, it does reproduce the continuously graded, or analog, nature of many examples of persistent activity. The conditions for tuning are derived for the dynamics of a conductance-based model neuron with a slow excitatory autapse. The derivation uses the method of averaging to approximate the spiking model with a nonspiking, reduced model. Short-term analog memory storage is possible if the reduced model is approximately linear and if its feedforward bias and autapse strength are precisely tuned.

Action Potentials↗
PubMedDate not supplied

Complications of osteotomies in severe cerebral palsy.

Seventy-nine consecutive children with cerebral palsy who underwent osteotomies about the hip for subluxation or dislocation were studied retrospectively to determine risk factors that would correlate with postoperative complications of death, fracture, or decubitus ulcer. Except for the three patients who died, all of the children had > or = 1 year of follow-up. Twenty (25%) patients had at least one complication. Three children died; one at 1 week, one at 2 weeks, and one at 5 months after surgery. Sixteen patients sustained 25 fractures. All were managed with cast or splint immobilization in the clinic. Five patients developed decubitus ulcers requiring > or = 2 weeks of local care, but none required skin grafts or flaps. Complications occurred in 13 (68%) of 19 children with gastrostomies or tracheostomies but in only seven (12%) of the remaining 60 children. Only one (8%) of 13 ambulatory patients had a complication compared with 19 (29%) of 66 nonambulatory patients. In conclusion, ambulatory function correlates well with the risk of complications after osteotomies. A nonambulatory patient with a gastrostomy or tracheostomy is at even greater risk. Fortunately the fractures and ulcers observed in this series healed uneventfully with no operative intervention.

Adolescent↗
PubMedDate not supplied

Respiratory depressant and skeletal muscle relaxant effects of low-dose pancuronium bromide in spontaneously breathing, isoflurane-anesthetized dogs.

OBJECTIVE: To assess and compare the respiratory depressant and skeletal muscle relaxant effects of two low doses of a nondepolarizing neuromuscular blocker, pancuronium bromide. To determine if a "low dose" of pancuronium bromide can produce selective skeletal muscle relaxation in extraocular muscles sufficient to perform intraocular surgery while sparing or minimizing depression of muscles of ventilation. STUDY DESIGN: Blinded, randomized crossover, placebo controlled study. ANIMALS: Six healthy, adult mongrel dogs weighing 20.8 +/- 1.9 kg. METHODS: Spontaneously breathing, isoflurane-anesthetized dogs received 0.02 mg/kg pancuronium bromide, intravenously (i.v.), (high dose [HD]), 0.01 mg/kg pancuronium bromide, i.v., (low dose [LD]), or saline placebo i.v. in a blinded, randomized crossover study. Indices of patient ventilation including tidal volume (Vt), respiratory rate (RR), and minute ventilation (VE) were recorded throughout the study period. Serial arterial blood gas analyses were performed at timed intervals. Neuromuscular blockade of skeletal muscle was assessed at timed intervals with train-of-four stimulus/response ratios. Eye position scores, based on the degree of ocular rotation from a neutral gaze axis, were assigned by an ophthalmologist who was blinded to the treatment given. RESULTS: VT and VE in HD dogs decreased by 82% from baseline after administration of pancuronium bromide. Similarly, Vt and VE in LD dogs decreased 40% and 55%, respectively. Decreased ventilation in HD dogs corresponded with significant (P< .05) neuromuscular blockade, as indicated by train-of-four ratio less than 75% between 0 and 60 minutes. Eye position scores in HD and LD dogs were suitable for intraocular surgery between 0 and 60 minutes. Eye position scores in five of six control dogs were unsuitable for intraocular surgery at any time period. CONCLUSIONS: LD dogs experienced only transient, mild to moderate respiratory depression compared with HD dogs, which experienced prolonged, moderate to severe respiratory depression. Both LD and HD dogs acquired and maintained eye position scores suitable for intraocular surgery between 0 to 60 minutes. A "low dose" of pancuronium bromide, which would provide adequate extraocular muscle relaxation while minimizing ventilatory depression, was not identified. CLINICAL RELEVANCE: All patients receiving any dose of neuromuscular blocking agents should be closely monitored and receive ventilatory assistance as needed.

Anesthesia, Inhalation↗