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Biomedical subjects

J Lehman

Publications and source records attributed to J Lehman.

At least 19 recordsLinked to original sources
PubMed2006

Evaluation of a pyroelectric detector with a carbon multiwalled nanotube black coating in the infrared.

The performance of a pyroelectric detector with a carbon multiwalled nanotube coating was evaluated in the 0.9-14 microm wavelength range. The relative spectral responsivity of this detector was shown to be flat over most of the wavelength range examined, and the spectral flatness was shown to be comparable to the best infrared black coatings currently available. This finding is promising because black coatings with spectrally flat absorbance profiles are usually associated with the highest absorbance values. The performance of the detector (in terms of noise equivalent power and specific detectivity) was limited by the very thick (250 microm thick) LiNbO3 pyroelectric crystal onto which the coating was deposited. The responsivity of this detector was shown to be linear in the 0.06-2.8 mW radiant power range, and its spatial uniformity was comparable to that of other pyroelectric detectors that use different types of black coating. The carbon nanotube coatings were reported to be much more durable than other infrared black coatings, such as metal blacks, that are commonly used to coat thermal detectors in the infrared. This, in combination with their excellent spectral flatness, suggests that carbon nanotube coatings appear extremely promising for thermal detection applications in the infrared.

Journal Article↗
PubMed2002

Characterisation of atovaquone resistance in Leishmania infantum promastigotes.

Atovaquone, an antiparasitic agent, could possibly represent an alternative therapy after relapse following classical treatment for visceral leishmaniasis. Atovaquone-resistant strains were selected in vitro by stepwise drug pressure to study the mechanism of resistance in Leishmania. Characteristics of a promastigote strain resistant to 250 microg/ml of atovaquone were compared with those of the wild type (WT) strain. Resistant strains were shown to have a high level of resistance (45 times). They were stable in drug-free medium for 6 months, and showed no cross-resistance with other antileishmanial drugs. Rhodamine uptake and efflux were studied. They were not modified in the resistant strain, indicating the absence of P-glycoprotein overexpession. The effect of atovaquone on membrane lipidic composition was determined in both WT and atovaquone-resistant promastigotes. Analysis of lipid composition of the atovaquone-resistant strain showed that sterol biosynthesis was decreased in atovaquone-resistant parasites. Cholesterol was found to be the major membrane sterol as opposed to the WT strain. Cholesterol, due to its ordering effect, could decrease membrane fluidity and subsequently block the passage of atovaquone through the membrane. Increased membrane cholesterol content and altered drug membrane fluidity resulted from possible decrease of ergosterol biosynthesis by atovaquone, incorporation of cholesterol by promastigotes in the culture medium, solubilisation of atovaquone by cholesterol and co-passage of the two compounds or influence of dimethylsulfoxide. These results indicate that different cellular alterations may participate in the resistant phenotype, by altering drug membrane permeability.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Laryngostroboscopic, acoustic, and environmental characteristics of high-risk vocal performers.

Vocal performance often requires excessively high vocal demand. In particular "high-risk" performers, a group of individuals who use their voices at their maximum effort level, are often exposed to unique vocal abuse characteristics which include high environmental and performance demands and inconsistencies of cast performance. Three categories of high-risk performers were studied: musical theater, choral ensemble, and street theater. Musical theater performers produce a Broadway, West End "belting" style voice. Street theater performers use a high-energy pitch varying dialogue in order to imitate a desired character voice. Choral ensemble performance requires group cohesion and blending of four-part harmony. The melodies require sustained vocal durations within each of the respective registers. For each of these studied groups vocal tasks of sustained production of /i/ and /a/ were subjected to analysis. Acoustic measures included fundamental frequency, standard deviation of fundamental frequency, jitter percent, shimmer percent, and noise-to-harmonic ratio. Laryngostroboscopic parameters were assessed during sustained /i/. Environmental acoustic sound field measurements were made using an A weighting and linear weighting sound pressure level. These weightings were used to describe noise levels and vocal output, respectively, within the performance environments. Results of the analysis suggest that high-risk performers are a unique performance type defined by distinctive, acoustic, laryngostroboscopic, and environmental characteristics.

Adolescent↗
PubMed2001

Ex vivo purging by adenoviral p53 gene therapy does not affect NOD-SCID repopulating activity of human CD34+ cells.

Co-incubation of a replication-deficient, recombinant adenovirus carrying the wild-type p53 gene (rAd-p53) and hematopoietic stem cell (HSC) products from patients with breast cancer can significantly reduce tumor cell contamination. Whereas this approach provides a powerful tumor cell purging strategy, potential detrimental effects on the HSC population have not been investigated. The ability of human HSC to reconstitute hematopoiesis in severe combined immunodeficient (SCID) mice and to undergo secondary transplantation provides the only nonclinical measure of self-renewing, stem cell function. The objective of this study was to investigate whether co-incubation with rAd-p53 compromised the SCID repopulating activity (SRA) of HSC. Granulocyte colony-stimulating factor-mobilized human CD34+ cells were co-cultured with rAd-p53 at our targeted clinical dose, and the ability of these cells to establish multilineage hematopoiesis in sublethally irradiated, nonobese diabetic (NOD)-SCID mice was investigated. The persistence of human cells in the mice was investigated by flow cytometry, granulocyte-macrophage colony-forming unit assay, and polymerase chain reaction of human Alu sequences. Further, limiting dilution analysis provided a quantitative comparison between the SRA of CD34+ cells co-incubated with rAd-p53 and control CD34+ cells (no rAd-p53 co-incubation). We conclude that co-incubation with rAd-p53 has little effect on the SRA of HSC.

Adenoviridae↗
PubMed2001

Penetrance and expressivity of genes involved in the development of epilepsy in the genetically epilepsy-prone rat (GEPR).

In order to understand the level of complexity of the epileptic phenotype in the two strains of Genetically Epilepsy-Prone Rats (GEPRs), we determined two important measures of genetic complexity, penetrance and expressivity. Penetrance is the percentage of animals of a specific genotype who express the phenotype associated with that underlying genotype. Expressivity refers to the degree that a particular genotype is expressed as a phenotype within an individual. Incomplete penetrance and variable expressivity are caused by genetic and environmental variation. In this paper we have studied the epileptic phenotype for 20,373 rats. Animals were tested on three occasions for audiogenic seizure and given an audiogenic response score (on a scale of 0-9, 0 being no seizure and 9 being the most severe). The GEPR-3 and GEPR-9 animals both show incomplete penetrance and variable expressivity of the underlying genetic predisposition. The GEPR-9 strain has more animals that have variable levels of seizure predisposition (as measured by a scoring system that denotes the severity of generalized tonic/clonic seizures) and a greater percentage of animals that exhibit no susceptibility to such seizures induced by sound. Both strains have a number of animals that are not susceptible to sound-induced GTCSs and that exhibit some variability in seizure severity. The GEPR-9 males show greater differences in expressivity and penetrance compared to GEPR-9 females. The GEPR-3 animals also show sex-associated variable penetrance and expressivity of the epileptic phenotype, although the differences are much smaller. These findings are the first step toward the mapping of the underlying quantitative trait loci (QTL) for seizure in these animals.

Animals↗
PubMed2000

Crc is involved in catabolite repression control of the bkd operons of Pseudomonas putida and Pseudomonas aeruginosa.

Crc (catabolite repression control) protein of Pseudomonas aeruginosa has shown to be involved in carbon regulation of several pathways. In this study, the role of Crc in catabolite repression control has been studied in Pseudomonas putida. The bkd operons of P. putida and P. aeruginosa encode the inducible multienzyme complex branched-chain keto acid dehydrogenase, which is regulated in both species by catabolite repression. We report here that this effect is mediated in both species by Crc. A 13-kb cloned DNA fragment containing the P. putida crc gene region was sequenced. Crc regulates the expression of branched-chain keto acid dehydrogenase, glucose-6-phosphate dehydrogenase, and amidase in both species but not urocanase, although the carbon sources responsible for catabolite repression in the two species differ. Transposon mutants affected in their expression of BkdR, the transcriptional activator of the bkd operon, were isolated and identified as crc and vacB (rnr) mutants. These mutants suggested that catabolite repression in pseudomonads might, in part, involve control of BkdR levels.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1998

The increased need for a permanent pacemaker after reoperative cardiac surgery.

OBJECTIVE: The requirement for permanent pacemaker implantation after most initial cardiac surgical procedures generally is less than 3%. To identify the incidence and factors related to permanent pacemaker need after repeat cardiac surgery, we retrospectively studied 558 consecutive patients undergoing at least one repeat cardiac operation. METHOD: Univariable and multivariable analyses of comorbidity, preoperative catheterization values, and operative data were performed to identify factors related to pacemaker implantation. RESULTS: In this group, 54 patients (9.7%) required a permanent pacemaker. A multivariable model showed a relationship between a permanent pacemaker and tricuspid valve replacement/annuloplasty associated with aortic/mitral valve replacement, preoperative endocarditis, increasing number of reoperations, the degree of hypothermia during cardiopulmonary bypass, and advanced age. Additional univariable predictors of pacemaker need included multiple valve replacement, increased cardiopulmonary bypass and aortic crossclamp times, and aortic valve replacement. Over 90% of patients who have or have not received permanent pacemaker implantation were in New York Heart Association class I to II, with a mean follow-up time of 6 years. Kaplan-Meier survival curves were statistically similar for both groups at 5 and 10 years after the operation. CONCLUSION: Permanent pacemaker implantation was required in 9.7% of patients undergoing repeat cardiac surgery. This represented approximately a fourfold increase compared with similar primary operations reported in other series. Factors strongly related to this need included valve replacement, preoperative endocarditis, number of reoperations, advanced age, and degree of hypothermia during cardiopulmonary bypass. The need for a permanent pacemaker after reoperations did not result in significant long-term impairment of functional status or longevity compared with those who did not require a permanent pacemaker.

Adolescent↗
PubMed1995

Internal jugular vein patency after functional neck dissection: venous duplex imaging.

We present a retrospective study performed to determine jugular patency after functional neck dissection (FND). Twenty-six patients, 16 females and 10 males, ranging in age from 16 to 78 were examined. These patients underwent either unilateral FND or bilateral FND for cervical lymph node metastases. Cervical duplex and pulsed Doppler imaging were chosen to determine internal jugular vein (IJV) patency. The examination was performed after a minimum postoperative period of 2 months and a maximum one of 22 years. Thirty-one IJVs were examined. All but 4 IJVs examined were found patent postoperatively. The preservation rate of patency of the IJV in FND was found to be high (27 of 31 or 87%). These results favor the use of FND for IJV preservation, particularly in bilateral neck dissection.

Adolescent↗
PubMed1989

[Spontaneous external biliary fistula].

Spontaneous biliary cutaneous fistula is a rare complication of inflammatory perforation of the gallbladder. We describe a 70-year-old woman who developed a fistula between the gallbladder and the skin following drainage of an abdominal wall abscess. In such cases primary drainage of the abscess alone is advisable. Only after the active infection has subsided should definitive cholecystectomy and excision of the fistulous tract be carried out.

Abdominal Muscles↗
PubMed1983

Characterization of phi 6 mutants that are temperature sensitive in the morphogenetic protein P12.

P12 is a morphogenetic protein necessary for the envelopment of the bacteriophage phi 6 nucleocapsid with the viral membrane. Gene 12 is located along with three other genes on the smallest chromosome of the virion. ts mutants in P12 were obtained by first characterizing the isoelectric focusing behavior of phi 6 proteins and then screening ts mutants of phi 6 that had previously been assigned to chromosome C for changes in the behavior of P12. In this manner, three independently isolated mutants were identified and were found to have morphogenetic consequences at restrictive temperatures similar to gene 12 nonsense mutants in nonsuppressor cells in that only unenveloped nucleocapsids were formed. When infected cells were labeled at restrictive temperature, 27 degrees, and then shifted to 21 degrees, normal phage particles were formed; however, the hydrophobic membrane proteins in the particles were not labeled, indicating that functional P12 must be present at the time of synthesis of the membrane proteins for them to assemble into virions or that the defective P12 leads the membrane proteins into a nonfunctional pathway.

Capsid↗