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Biomedical subjects

R Lee

Publications and source records attributed to R Lee.

At least 271 records · Page 15Linked to original sources
PubMed1990

Dental and skeletal contributions to occlusal correction in patients treated with the high-pull headgear-activator combination.

The purpose of this study was to examine dental and skeletal changes in patients treated with the high-pull headgear-activator combination. A group of 40 consecutively treated subjects with a Class II molar relationship and a minimum of 5 mm overjet was used for this study. The results showed that Class II correction often was achieved by distal repositioning of the maxillary teeth (mean, 0.07 mm) and mesial repositioning of the mandibular teeth (mean, 3.3 mm) with a wide range of variation. Correlation of maxillary molar repositioning with total interarch occlusal change showed a positive relationship; however, a weak correlation suggested that other variables were contributing factors, in addition to distal upper molar positioning. The change in mandibular molar position compared with the movement of pogonion strongly suggests that forward growth of the mandible is important to the correction of the Class II malocclusion. When total molar repositioning in the upper jaw was correlated with total molar repositioning in the lower jaw, a strong inverse correlation was found, indicating that upper molar movement parallels lower molar movement.

Activator Appliances↗
PubMed1990

Tourniquet-induced limb ischemia: a neurophysiologic animal model.

A rat model of tourniquet-induced ischemia was created to observe the changes in sciatic afferent neuronal activity associated with prolonged tourniquet inflation on the hind leg. The sciatic nerve was divided in the proximal thigh and a two-electrode microfilament recording technique and signal averaging computer were used to survey afferent neuronal activity prior to and after tourniquet inflation. This method was able to determine both firing rate and conduction velocity of spontaneously active or mechanically sensitive nerve fibers. In 14 rats observed prior to tourniquet inflation there was much spontaneous activity. These fibers all had rapid conduction velocities (30 +/- 6.9 m/s) (mean +/- SD) and firing rates (16.3 +/- 1.9 H). All fibers could be stimulated by movement of distal joints or by probing the skin of the leg. After tourniquet inflation, a pressure-induced conduction block occurred stopping all spontaneous and mechanically induced activity. After a short interval, (55 +/- 16 min) a different group of spontaneously active fibers were observed that had both slow conduction (2.04 +/- 0.77 m/s) firing rates (0.54 +/- 0.9 H). These fibers did not respond to mechanical stimulation of the limb distal to the tourniquet, or local anesthetic or cold block of the nerve distal to the tourniquet. Blockade of the sciatic nerve just proximal to the tourniquet and deflation of the tourniquet did abolish activity in these fibers. In ten separate rats in which tourniquets were placed but no surgical incision made, mean arterial blood pressure rose significantly after tourniquet inflation. With tourniquet deflation, blood pressure fell significantly from levels observed during tourniquet inflation.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1990

Clinical evaluation of a diameter sensing Doppler cardiac output meter.

A concentric beam Doppler ultrasonic flowmeter has been developed. This instrument has capacity for independent assessment of volumetric flow, as it determines flow cross-section area, stroke length, and pulse rate from the Doppler signals alone. The method is practically independent of the angle of interrogation. We used this device and obtained noninvasive estimates of cardiac output in 54 patients undergoing invasive assessment of cardiac output by thermodilution, Fick, or indicator dye methods (x). Correlations against pooled cardiac output reference standards ranged from r = .86 (y = .86x + 1.03) in 26 studies of high confidence to r = .45 (y = .30x + 2.62) in 17 studies under difficult conditions. The overall correlation was r = .68 (y = .63x + 1.49, n = 87). Noninvasive results of experienced and inexperienced operators were similar (r = .87). The instrument returned accurate assessments of heart rate (r = .83), but underestimated stroke length (r = .72) and appeared to be limited in the assessment of aortic diameters less than 28 or greater than 31 mm (r = .23). We conclude that stand-alone Doppler assessment of cardiac output is appealing and feasible, but difficult or impossible in many ICU scenarios. Further evolution of the concentric beam Doppler approach is needed and anticipated.

Aorta↗
PubMed1990

Predicted normocapnea in infants and children using the Bain circuit with controlled ventilation.

We have constructed a nomogram for fresh gas flow (VFG) and minute ventilation (VE) for paediatric anaesthesia during controlled ventilation using the Bain coaxial Mapleson D circuit. VFG was based upon the assumption of a high fresh gas utilization because of a low VFG/VE ratio (0.67) and known figures of carbon dioxide elimination. The formulas VFG = 27.8 x VCO2 and VE = 1.5 x VFG were used to calculate the necessary flows to generate normocapnea. The nomogram was evaluated in 59 children (6-62 kg, age 5 months-14 years). PaCO2 (mean +/- s.d.) was 5.0 +/- 0.5 kPa (38 +/- 4 mmHg) with a total range of 3.9-6.3 kPa (29-47 mmHg). Ninety percent of the children had a PaCO2 of 5.7 kPa (43 mmHg) or lower. There was no correlation between body weight and PaCO2. Hence, there was no difference in mean values between children below or above a body weight of 20 kg.

Adolescent↗
PubMed1990

Update on ventricular assist devices.

Ventricular assist devices serve as a valuable adjunct to therapy in the setting of profound heart failure. The two largest patient groups--postcardiotomy and those being bridged to transplant--show an average 40-50% survival rate after ventricular assist. Several devices exist including centrifugal, pneumatic, and electrical pumps. Options for ventricular assist include right (RVAD), left (LVAD), and biventricular (BiVAD) support. Knowledge regarding the devices and the pathophysiology of severe heart failure is crucial for the critical care nurse caring for these patients. Critical care nursing interventions for bleeding, renal failure, infection, and other complications will be outlined.

Cardiac Output, Low↗
PubMed1990

Identification and chromosomal mapping of new human tyrosine kinase genes.

To identify novel protein tyrosine kinase (PTK) genes expressed in human lymphoid cells, we have screened B- and T-cell cDNA libraries at low stringency using a c-fms tyrosine kinase domain probe. Three new PTK genes were identified, based on the presence of conserved amino acid sequence motifs characteristic of the catalytic domain of tyrosine kinases. Of these three genes, one (tyk1) appears to be the human homologue of a previously cloned murine gene (ltk), which has been reported to encode a tyrosine kinase with a unique structure; while the second gene, tyk2 cannot be clearly assigned to any of the known PTK subfamilies, and therefore may be the prototype of a new PTK gene subfamily. The third gene (tyk3/fer) has been very recently cloned by others; we present additional characterization in this report. We have performed Northern blots to establish the size of the mRNA encoded for by these genes, and to confirm their expression in lymphoid cells. Finally, we have determined the chromosomal location of all three genes by analyzing human-mouse somatic cell hybrids.

Amino Acid Sequence↗
PubMed1990

Hemodynamic effects and oxygen transport properties of a new blood substitute in a model of massive blood replacement.

Recent concerns regarding the safety of the national blood supply have rekindled interest in the development of blood substitutes. Clinical studies have dampened the initial enthusiasm for fluorocarbon solutions as blood substitutes. The potential of hemoglobin solutions as blood substitutes has continued to stimulate investigations. However, the development of an ideal hemoglobin-derived blood substitute has eluded investigators for the past century. A persistent problem has been the inability to develop hemoglobin solutions that provide adequate oxygen and carbon dioxide exchange, while avoiding toxicity that precludes clinical safety and long-term survival. Traditionally, investigators have focused on human hemoglobin solutions. The use of outdated banked blood or pedigree human donor blood as a hemoglobin source poses continued disease transmission risks and a prohibitively limited supply. We evaluated the hemodynamic and gas transport effects of a new purified, polymerized bovine hemoglobin preparation. Bovine hemoglobin oxygen affinity is regulated by chloride ion. The concentration of chloride ions in human plasma results in excellent oxygen transport properties in a stroma-free environment. In addition, unlike human blood, bovine blood is a more disease-free hemoglobin source that is available in large supply. We exchange-transfused eight conscious sheep with this new polymerized bovine hemoglobin solution. All animals tolerated greater than or equal to 95% exchange transfusion to reach a final ovine hematocrit of 2.4 +/- 0.5% with stable hemodynamics and no clinical evidence of distress. The exchange transfusion with bovine hemoglobin polymer resulted in a final plasma hemoglobin concentration of 6.1 +/- 1.6 gm/dl, which supported oxygen consumption at baseline levels. All animals that were exchange transfused with this preparation survived long term with rapid resynthesis of ovine erythrocytes.

Animals↗
PubMed1989

Monoclonal antibody targeting of liposomes to mouse lung in vivo.

A monoclonal antibody (MoAb), 273-34A, specifically binds to an epitope expressed almost exclusively on capillary endothelial cells of the lung. Within 15 min after i.v. injection, approximately 80 to 85% of the injected radioiodinated MoAb 273-34A accumulates in the lung. Approximately 90 to 95% of the recovered dose is found in the lung for up to 1 week postinjection. Ratios of MoAb 273-34A to a nonspecific, irrelevant MoAb 135-14 are 250 to 285 times higher in the lung than in the serum. When 273-34A was coupled with palmitic acid and incorporated into liposomes, the amount of 125I-labeled liposomes recovered per g of tissue was 12 times higher in the lung than in the liver at 15 min postinjection, and 22 times higher at 5 h postinjection. At 24 h postinjection the amount of liposomes per gram of lung tissue was still 6.0 times the amount per gram of liver tissue. Liposomes conjugated to MoAb 273-34A locate in the lung 20 and 15 times better than do liposomes conjugated to the nonspecific MoAb 135-14 at 15 min and 24 h postinjection, respectively. The results indicate that this immunoliposome system could be used as a model for enhanced drug delivery to the lung. The potential use for delivering anticancer drugs for therapy of lung tumors is discussed.

Animals↗
PubMed1989

Cloning and expression of a smooth muscle caldesmon.

Caldesmon is a smooth muscle and nonmuscle regulatory protein that interacts with actin, myosin, tropomyosin, and calmodulin. Two overlapping clones, isolated from a chicken oviduct cDNA plasmid library and a chicken gizzard cDNA lambda NM1149 library, were used to generate a 4108-base pair sequence coding for one caldesmon. Expression of the coding sequence confirms this is one of the large smooth muscle caldesmons. The deduced protein molecular weight is 86.974, significantly less than the molecular weights estimated by sodium dodecyl sulfate gel electrophoresis. The protein has a high content of Gly, Lys, Arg, and Ala; there are two cysteine residues, one at either end of the molecule. Comparison with the Protein Identification Resource database demonstrates a similarity with a tropomyosin binding domain of troponin T, but none with any calmodulin or actin binding proteins. The center of the protein has an 8-fold repeat of a 13 amino acid sequence whose general motif is -Glu3-(Lys/Arg)2-Ala2-Glu2-(Lys/Arg)1-X-(Lys/Arg)1-Ala1-, where X is Glu, Gln, or Ala. Comparison with peptide sequences from a chymotryptic fragment that binds actin and calmodulin places this domain on the C terminus of caldesmon adjacent to the troponin T similarity. A tentative map of the major binding domains is proposed on the basis of available data.

Amino Acid Sequence↗
PubMed1989

Efficient coupling of glycopeptides to proteins with a heterobifunctional reagent.

A heterobifunctional linking reagent containing a masked aldehydo group and acyl hydrazide was synthesized for coupling of glycopeptides and other amino-containing compounds to proteins. After conversion to acyl azide, the reagent reacts with the amino group of a glycopeptide, and the modified glycopeptide is deacetalized with a weak acid to unmask the aldehydo group, which is then conjugated to bovine serum albumin (BSA) by reductive alkylation with pyridine-borane. The overall reaction scheme proceeds under relatively mild conditions. When the protein amino group was in a large excess (greater than 6-fold) of the aldehyde reagent, the efficiency of conjugation was as high as 88% even at submicromole levels. As a test case for application of this reagent, 6-aminohexyl beta-D-galactopyranoside (Gal-AH) was attached to the linking reagent and conjugated to BSA at various aldehyde-to-protein molar ratios ranging from 25 to 200. The level of O-galactosyl residue incorporated into BSA by this reagent far exceeded that observed in a similar reductive alkylation involving S-galactoside reagents [Lee, R. T., & Lee, Y. C. (1980) Biochemistry 19, 156-163]. By use of the present conjugating procedure, as many as 112 mol of Gal-AH residues were incorporated per mole of BSA, which represents near total modification of the amino groups. Some binding characteristics of the new BSA derivatives were studied in the mammalian hepatic galactose/N-acetylgalactosamine specific lectin system along with other types of BSA derivatives (containing S-galactosyl residues). In general, the behavior of the new derivatives was similar to that of other types. For instance, the affinity increased exponentially at low sugar substitution levels (up to 30 mol of galactosyl residues/mol of BSA), and the slope of exponential increase and affinity at a given sugar substitution level was similar to those of other types.

Amides↗
PubMed1989

Injectable cross-linked collagen with improved flow properties.

Aqueous suspensions of glutaraldehyde cross-linked fibrillar collagen and non-cross-linked fibrillar collagen were examined by rheometry, particle size analysis, and microscopic techniques. Although cross-linked collagen suspensions were similar to non-cross-linked suspensions by microscopic and size analyses, they differed in rheometric properties. Concentric cylinder Couette flow, shear creep, uniaxial creep, and porous bed flow all revealed that cross-linked collagen was more resistant to deformation and flow than non-cross-linked collagen. These results were in agreement with in vivo dermal implantation studies, both in pig and human; i.e., compared to non-cross-linked collagen, the cross-linked formulation was more difficult to inject into tissue and did not spread uniformly, sometimes giving rise to palpable lumps or large masses evident in histological sections. When hyaluronic acid was blended with cross-linked collagen to achieve a final hyaluronate concentration of 5 mg/mL, there was a significant improvement in ease of injection into tissue. Rheometry on blends of hyaluronate and cross-linked collagen demonstrated that the blend required lower forces to achieve deformation and flow, compared to cross-linked collagen alone. Particle size analysis on the blend showed a reduction in fiber aggregate dimensions, compared to cross-linked collagen alone.

Animals↗
PubMed1989

Thyroid function and immune reactivity during metamorphosis in Xenopus laevis, the South African clawed toad.

High plasma titers of thyroid and adrenocorticoid hormones are present during the metamorphosis of Xenopus laevis. Here we examine the influence of thyroid hormones on several features of immune reactivity during this period, e.g., the capacity of thymus-derived immunocytes to reduce (immune suppression) or amplify (helper function) antibody production. Further, we test whether thyroid hormone is able to modulate the expression of putative interleukin 2 (IL-2) receptors on lectin-activated adult Xenopus splenocytes, an aspect of helper function. Finally, we have tested the ability of thyroid hormones to affect larval antibody-producing cells directly. Our data suggest that all three functions (suppressor, helper, and antibody producing) are independent of thyroid function during metamorphosis. However, the anatomical distribution of two features of immune suppression, as well as the numbers of lectin-activated splenocytes able to bind anti-IL-2 receptor antibody, were changed by thyroid function. In vivo thyroid blockade by thiourea prevented the transition from the premetamorphic to the adult pattern of distribution of the two suppressor functions; triiodothyronine in vitro stimulated an increase in the numbers of cells able to bind an IL-2 receptor antibody.

Adrenal Cortex Hormones↗
PubMed1989

Ultrapure, stroma-free, polymerized bovine hemoglobin solution: evaluation of renal toxicity.

Because of recent concern about the safety of our national blood supply, there is increased interest in finding safe and effective blood substitutes. One option is the use of stroma-free hemoglobin (SFH) solutions. Recently, a SFH solution based on ultrapure, polymerized bovine hemoglobin (UPPBHg) has been shown to be effective in oxygen transport. We examined the potential renal toxicity of this material. Sprague-Dawley rats were infused with UPPBHg at doses of 25, 50, 75, and 100 ml/kg. Additional groups of rats were infused with UPPBHg at these doses with the addition of bicarbonate at a dose adequate to alkalinize the urine. Further groups of rats received UPPBHg intentionally contaminated with raw bovine blood lysate. Renal function was examined by subsequent determination of serum creatinine. UPPBHg infusion up to 50 ml/kg caused no significant change in serum creatinine; at higher doses, there was a reversible rise in creatinine at 24 hr following infusion. Addition of bicarbonate diminished the amount of reversible toxicity seen, even at doses of 100 ml/kg. In contrast, with hemolysate-contaminated UPPBHg, there were sharp increases in creatinine 24 hr after infusion of all doses tested, even at 25 ml/kg; these did not decrease significantly by 48 hr following infusion. At the higher doses tested, death occurred. These observations were not affected by simultaneous bicarbonate infusion. This study shows that UPPBHg may be administered in very large doses with only mild, reversible renal toxicity. The observation that urine alkalinization ameliorates this toxicity suggests that this may occur by hemoglobin precipitation or by a toxic effect in the renal tubules.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Expression of lymphokine genes in splenic lymphocytes of autoimmune mice.

Lymphocytes of autoimmune mice have been reported to have defective IL-2 production and proliferation in response to the mitogen concanavalin A. We have examined transcription of lymphokine genes in Con A stimulated spleen cells from both autoimmune and normal mice and found that IL-2, IL-4 and gamma-interferon (IFN gamma) were induced in all mice tested. Spleen cells were taken from young (pre-disease) or old (clinically active) MRL/lpr (lpr) and male BXSB autoimmune mice and from their normal counterparts (MRL/n, BXSB females, BALB/c and DBA/2) and stimulated with Con A. Con A induced production of IL-2, IL-4 and IFN gamma message and protein, and kinetics of induction did not vary significantly among the strains. However, in old lpr mice, levels of IL-2 protein and mRNA were about 10-fold lower than in other strains; IL-4 protein and mRNA were decreased approximately three-fold; and IFN gamma mRNA was readily detected in unstimulated cells and low but detectable levels of protein were produced constitutively. In contrast, little or no defect in IL-2 or IL-4 transcription or secretion were seen in male BXSB mice and no constitutive IFN gamma transcription was seen in this strain. These data indicate that all three lymphokine genes are activated by Con A in autoimmune mice, even though Con A-induced proliferation is defective in these mice. Furthermore, autoimmune mouse strains vary in terms of lymphokine expression: male BXSB mice display a normal lymphokine profile, whereas lpr mice show a marked imbalance of lymphokines compared to normal controls.

Animals↗
PubMed1989

Collagen tube containers in alveolar ridge augmentation.

This article reports the use of collagen tube containers with implants of particulate hydroxyapatite. Tubes were used to aid in the particle placement and to prevent particle migration. Implant success was judged by the patient and the prosthodontist. Results were favorable.

Adult↗