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Biomedical subjects

R R White

Publications and source records attributed to R R White.

At least 19 recordsLinked to original sources
PubMed2006

Energy input and response from prompt and early optical afterglow emission in gamma-ray bursts.

The taxonomy of optical emission detected during the critical first few minutes after the onset of a gamma-ray burst (GRB) defines two broad classes: prompt optical emission correlated with prompt gamma-ray emission, and early optical afterglow emission uncorrelated with the gamma-ray emission. The standard theoretical interpretation attributes prompt emission to internal shocks in the ultra-relativistic outflow generated by the internal engine; early afterglow emission is attributed to shocks generated by interaction with the surrounding medium. Here we report on observations of a bright GRB that, for the first time, clearly show the temporal relationship and relative strength of the two optical components. The observations indicate that early afterglow emission can be understood as reverberation of the energy input measured by prompt emission. Measurements of the early afterglow reverberations therefore probe the structure of the environment around the burst, whereas the subsequent response to late-time impulsive energy releases reveals how earlier flaring episodes have altered the jet and environment parameters. Many GRBs are generated by the death of massive stars that were born and died before the Universe was ten per cent of its current age, so GRB afterglow reverberations provide clues about the environments around some of the first stars.

Journal Article↗
PubMed2006

Fixation of Vancouver B1 peri-prosthetic fractures by broad metal plates without the application of strut allografts.

The use of allograft struts and cerclage wire, possibly augmented by plate fixation, for the treatment of Vancouver type-B1 peri-prosthetic fractures around a total hip replacement has been strongly advocated. We examined our results using plate fixation without allograft struts and compared them with the results of the use of struts alone or when combined with plate fixation. Of 20 consecutive patients with type-B1 fractures treated by open reduction and plate fixation, 19 were available for follow-up. The fractures healed in 18 patients with a mean time to weight-bearing of ten weeks (4 to 19). There were no cases of infection or malunion. Nonunion occurred in one patient and required a second plate fixation to achieve union. Safe, cost-effective treatment of Vancouver type-B1 fractures can be performed by plate fixation without the addition of cortical struts. This procedure may allow earlier weight-bearing than allograft strut fixation alone.

Aged↗
PubMed2005

A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts.

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium.

Journal Article↗
PubMed2005

Modeling the environmental fate of manganese from methylcyclopentadienyl manganese tricarbonyl in urban landscapes.

The environmental impacts of gasoline additives such as lead (Pb) and Methyl Tertiary Butyl Ether (MTBE) are well documented, leading to the phasing out of these additives. In contrast, little is known about the health and environmental impacts of potential replacement chemicals such as Methylcyclopentadienyl Manganese Tricarbonyl (MMT). The combustion of MMT in gasoline leads to the formation of MnPO4 and MnSO4 and MMT is considered a recent source of inorganic Mn in urban landscapes particularly in high traffic areas. The main objective of this study is to estimate the automotive deposition of Mn from MMT relative to the traffic volume at sites near a major highway in the Greater Toronto Area of Canada, where MMT is currently being used. Manganese emission levels were estimated for two sites that varied according to Annual Average Daily Traffic (AADT) density, fuel consumption, distance traveled by automobiles, and Mn concentration (mg l(-1)) in gasoline. Multiple regression analysis was used to predict the AADT volume from year 2002-2010. Comparison of the mass balance between the ANOVA means of 15% Mn emitted from the automobile tailpipes at 10, and 18 mg of Mn l(-1) in gasoline was conducted for both study sites. The percentage difference between the Mn input at the selected concentrations of Mn in gasoline and output into surface soil were found to be 99% significant for both sites. Thus the predicted 15% tailpipe emission levels for 10 mg of Mn l(-1) of gasoline used in automobiles, which represented 1290.03 g/year for site 1 and 555.94 g/year for site 2, will add 5.73 and 2.47 mg/kg of Mn annually, respectively. These input levels are considered negligible when compared to the natural abundance of Mn in soil. Based on these data, it could take more than 95-256 years of continuous MMT usage in the region to double the content of Mn in surface soils at the respective sites.

Canada↗
PubMed2002

The effect of reverberation on the damping of bubbles.

The measurement of an acoustic emission, or scatter, from a bubble is not difficult. However, an accurate interpretation of that signal in terms of the bubble dynamics may require careful consideration. The study presented here is at first sight relatively simple: comparison of the predicted and measured quality factors of injected bubbles. While the measurement is normally done by monitoring the decay of passive emissions from a bubble, this technique becomes difficult with smaller bubbles. Therefore an active technique is introduced, which removes all the frequency-dependent effects on the measurement (such as transducer response) bar one. That, critically, is the effect of the change in the bubble resonance (frequency and damping) which results from the loading on the bubble due to the reverberant field. The vast majority of theoretical treatments of bubble acoustics assume free field conditions, yet the environmental conditions rarely if ever match these. Therefore measurements of bubble damping are compared both with the established free field theory, and with a new theory relevant to the prevailing reverberant conditions (whether caused by tank surfaces, monochromatic neighboring bubbles, or both).

Journal Article↗
PubMed2001

Neoadjuvant chemoradiation for localized adenocarcinoma of the pancreas.

BACKGROUND: The use of neoadjuvant (preoperative) chemoradiotherapy (CRT) for pancreatic cancer has been advocated for its potential ability to optimize patient selection for surgical resection and to downstage locally advanced tumors. This article reports our experience with neoadjuvant CRT for localized pancreatic cancer. METHODS: Since 1995, 111 patients with radiographically localized, pathologically confirmed pancreatic adenocarcinoma have received neoadjuvant external beam radiation therapy (EBRT; median, 4500 cGy) with 5-flourouracil-based chemotherapy. Tumors were defined as potentially resectable (PR, n = 53) in the absence of arterial involvement and venous occlusion and locally advanced (LA, n = 58) with arterial involvement or venous occlusion by CT. RESULTS: Five patients (4.5%) were not restaged due to death (n = 3) or intolerance of therapy (n = 2). Twenty-one patients (19%) manifested distant metastatic disease on restaging CT. Twenty-eight patients with initially PR tumors (53%) and 11 patients with initially LA tumors (19%) were resected after CRT. Histologic examination revealed significant fibrosis in all resected specimens and two complete responses. Surgical margins were negative in 72%, and lymph nodes were negative in 70% of resected patients. Median survival in resected patients has not been reached at a median follow-up of 16 months. CONCLUSIONS: Neoadjuvant CRT provided an opportunity for patients with occult metastatic disease to avoid the morbidity of resection and resulted in tumor downstaging in a minority of patients with LA tumors. Survival after neoadjuvant CRT and resection appears to be at least comparable to survival after resection and adjuvant (postoperative) CRT.

Adenocarcinoma↗
PubMed2001

Impact of core-needle breast biopsy on the surgical management of mammographic abnormalities.

OBJECTIVE: To evaluate the accuracy of percutaneous, image-guided core-needle breast biopsy (CNBx) and to compare the surgical management of patients with breast cancer diagnosed by CNBx with patients diagnosed by surgical needle-localization biopsy (SNLBx). SUMMARY BACKGROUND DATA: Percutaneous, image-guided CNBx is a less invasive alternative to SNLBx for the diagnosis of nonpalpable mammographic abnormalities. CNBx potentially spares patients with benign lesions from unnecessary surgery, although false-negative results can occur. For patients with malignant lesions, preoperative diagnosis by CNBx allows definitive treatment decisions to be made before surgery and may affect surgical outcomes. METHODS: Between 1992 and 1999, 939 patients with 1,042 mammographically detected lesions underwent biopsy by stereotactic CNBx or ultrasound-guided CNBx. Results were categorized pathologically as benign or malignant and, further, as invasive or noninvasive malignancies. Only biopsy results confirmed by excision or 1-year-minimum mammographic follow-up were included in the analysis. Patients with breast cancer diagnosed by CNBx were compared with a matched control group of patients with breast cancer diagnosed by SNLBx. RESULTS: Benign results were obtained in 802 lesions (77%), 520 of which were in patients with adequate follow-up. Ninety-five of the 520 evaluable lesions (18%) were subsequently excised because of atypical hyperplasia, mammographic-histologic discordance, or other clinical indications. There were 17 false-negative CNBx results in this group; 15 of these lesions were correctly diagnosed by excisional biopsy within 4 months of CNBx. In two patients (0.9%), delayed diagnoses of ductal carcinoma in situ were made at 15 and 19 months after CNBx. Malignant results were obtained in 240 lesions (23%), 220 of which were surgically excised from 202 patients at our institution. Two lesions diagnosed as ductal carcinoma in situ were reclassified as atypical ductal hyperplasia and considered false-positive results (0.4%). For malignant lesions, the sensitivity and specificity of CNBx for the detection of invasion were 89% and 96%, respectively. During the first surgical procedure, 115 of 199 patients (58%) diagnosed by CNBx underwent local excision; 194 of 199 patients (97%) evaluated by SNLBx underwent local excision. For patients whose initial surgery was local excision, those diagnosed before surgery by CNBx had larger excision specimens and were more likely to have negative surgical margins than were patients initially evaluated by SNLBx. Overall, patients diagnosed by CNBx required fewer surgical procedures for definitive treatment than did patients diagnosed by SNLBx. CONCLUSIONS: Diagnosis by CNBx spares most patients with benign mammographic abnormalities from unnecessary surgery. With the selective use of SNLBx to confirm discordant results, missed diagnoses are rare. When compared with SNLBx, preoperative diagnosis of breast cancer by CNBx facilitates wider initial margins of excision, fewer positive margins, and fewer surgical procedures to accomplish definitive treatment than diagnosis by SNLBx.

Biopsy, Needle↗
PubMed2000

Management of node-positive melanoma in the era of sentinel node biopsy.

Regional lymph node metastasis is a powerful predictor of decreased overall survival from malignant melanoma. However, the therapeutic value of elective node dissections and the role of adjuvant therapy for node-positive disease have been highly controversial. Sentinel lymph node biopsy has reshaped the debate by allowing for staging of the regional lymph nodes with less morbidity and greater accuracy. This review summarizes the current consensus on the management of node-positive melanoma in the era of sentinel lymph node biopsy.

Algorithms↗
PubMed2000

Bacteria of asymptomatic periradicular endodontic lesions identified by DNA-DNA hybridization.

Possible inclusion of contaminant bacteria during surgery has been problematic in studies of periradicular lesions of endodontic origin. Therefore, in this study, two different surgical techniques were compared. A second problem is that some difficult to cultivate species may not be detected using bacteriological methods. Molecular techniques may resolve this problem. DNA-DNA hybridization technology has the additional advantage that DNA is not amplified. The purpose of this investigation was to determine if bacteria from periradicular endodontic lesions could be identified using DNA-DNA hybridization. A full thickness intrasulcular mucoperiosteal (IS) flap (n = 20) or a submarginal (SM) flap (n = 16) was reflected in patients with asymptomatic apical periodontitis. DNA was extracted and incubated with 40 digoxigenin-labeled whole genomic probes. Bacterial DNA was detected in all 36 lesions. Seven probes were negative for all lesions. In patients with sinus tract communication, in teeth lacking intact full coverage crowns, and in patients with a history of trauma 4-13 probes provided positive signals. Seven probes were positive in lesions obtained by the IS, but not the SM technique. Two probes were in samples obtained with the SM technique, but not the IS. Only Bacteroides forsythus and Actinomyces naeslundii genospecies 2 were present in large numbers using either the IS or the SM technique. The SM flap technique, in combination with DNA-DNA hybridization, appeared to provide excellent data pertaining to periradicular bacteria. These results supported other studies that provide evidence of a bacterial presence and persistence in periradicular lesions.

Actinomyces↗
PubMed2000

The reproducibility of sputum gram film interpretation.

OBJECTIVES: To evaluate the reproducibility with which microbiologists interpret Gram-stained sputa and examine the effect of the smear preparation method. METHODS: Two hundred and ten coded slides prepared directly from a purulent portion of sputum (DS) and 140 slides prepared after homogenization of the same sputum (HS) were examined by three experienced microbiologists. A proportion of the slides prepared by each method were recorded and represented to the raters. Intraobserver and interobserver variation was assessed using the kappa statistic (kappa). RESULTS: Evaluation of the smear as being infected and predicting Streptococcus pneumoniae as the infecting organism showed the greatest intraobserver agreement (kappa=0.74-0.82) and interobserver agreement (kappa=0.50-0.82). The agreement concerning the number of cells and infection with Haemophilus influenzae was only fair to moderate. Differences in the interpretation of smears prepared by the two methods could be explained by the intrinsic disagreement that occurs when the same smear is examined twice. The positive predictive value of a positive S. pneumoniae smear for a positive culture ([10(6)/ml) was 81% with the DS and 97% with the HS. CONCLUSION: In this laboratory, a sputum Gram film interpretation suggesting infection with S. pneumoniae was reproducible and predictive of a significant positive culture.

Adolescent↗
PubMed1999

Development of a clindamycin-impregnated fiber as an intracanal medication in endodontic therapy.

The effectiveness of traditional endodontic intracanal medications in reducing bacterial numbers and preventing acute flare-ups and pain continues to be questioned. In the present study, a new local delivery device was developed that releases a substantive dose of clindamycin into root canals. Clindamycin-impregnated ethylene vinyl acetate (EVA) fibers were produced, and the sensitivity of common endodontic microbes to the fibers were established. An in vitro model was developed to persistently infect 32 extracted human teeth with endodontic pathogens to test the efficacy of the clindamycin/EVA fibers in reducing the number of colony-forming units. The clindamycin/EVA fibers were shown to be effective in reducing growth of common endodontic microbes on blood agar plates, and in significantly reducing growth of Prevotella intermedia, Fusobacterium nucleatum, and Streptococcus intermedius in extracted human teeth, thus indicating merit in further exploring the potential of these fibers as intracanal medications.

Anti-Bacterial Agents↗
PubMed1999

Eosinophil-derived transforming growth factors (TGF-alpha and TGF-beta 1) in human periradicular lesions.

Inflammatory mediators of periradicular lesions are poorly understood. Transforming growth factors-alpha and -beta 1 (TGF-alpha and TGF-beta 1) have been linked with the cellular processes for both soft and hard tissue wound healing. The purpose of this study is to demonstrate the cellular sources of TGF-alpha and TGF-beta 1 mRNA and protein in periapical lesions by in situ hybridization and immunohistochemistry. Nine periapical granulomas and nine periapical cysts were examined. TGF-alpha mRNA and protein were not detectable in the granulomas examined. However, eosinophils surrounding the periapical cysts demonstrated both TGF-alpha mRNA and protein. The vast majority of eosinophils present in the periapical granulomas and cysts also demonstrated TGF-beta 1 mRNA and protein. Other cells producing TGF-beta 1 were lymphocytes, fibroblasts, and monocytes. The presence of wound repair cytokines, such as TGF-alpha and TGF-beta 1, suggests a mechanism by which the host inflammatory response may participate in the repair and remodeling of periapical tissues.

Adult↗
PubMed1999

Residual antimicrobial activity associated with a chlorhexidine endodontic irrigant used with sodium hypochlorite.

PURPOSE: To evaluate the in vitro efficacy of 2.0% chlorhexidine gluconate (CH) as an endodontic irrigant combined with the traditional irrigant, sodium hypochlorite (SH). MATERIALS AND METHODS: Extracted single-rooted human teeth were instrumented using one of three regimens: CH alone; SH alone until instrumentation with the last file, at which time CH was used as the filing irrigant; or SH alone followed by a single rinse with CH. After instrumentation, each root canal was dried with endodontic paper points, filled with sterile water, and maintained in a water-saturated environment. At 6, 12, 24, 48 and 72 hours after instrumentation, the root canal fluid was absorbed with an endodontic paper point, and the canal was irrigated and refilled with sterile water. The paper points containing root canal fluids were assayed for antimicrobial activity by placing them on agar plates inoculated with Streptococcus mutans, and measuring zones of inhibition after incubation. RESULTS: Comparisons of the results obtained from the three treatment regimens indicated there were no significant differences (P > 0.5) in the relative in vitro antimicrobial activity remaining in the three groups of teeth.

Anti-Infective Agents, Local↗
PubMed1998

Definition of optimal substrate recognition motifs of Ca2+-calmodulin-dependent protein kinases IV and II reveals shared and distinctive features.

The substrate recognition determinants of Ca2+-calmodulin-dependent protein kinase (CaMK) IV and CaMKIIalpha were investigated using peptide substrates modeled on the amino acid sequence encompassing Ser-9 of synapsin I. For both kinases, hydrophobic residues (Leu or Phe) at the -5 position, are well tolerated, whereas non-hydrophobic residues (Arg, Ala, or Asp) decrease Vmax/Km by 55- to >4000-fold. At the -3 position, substitution of Ala for Arg leads to decreases of 99- and 343- fold in Vmax/Km for CaMKIV and CaMKIIalpha, respectively. For both kinases, the nature of the residues occupying the -4, -1, and + 4 positions exerts relatively little influence on phosphorylation kinetics. CaMKIV and CaMKIIalpha respond differently to substitutions at the -2 and +1 positions. Substitution of Arg at the -2 position with non-basic residues (Gln or Ala) leads to 6-fold decreases in Vmax/Km for CaMKIV, but 17-28-fold increases for CaMKIIalpha. Additionally, peptides containing Leu, Asp, or Ala at the +1 position are phosphorylated with similar efficiencies by CaMKIV, whereas the Leu-substituted peptide is preferred by CaMKIIalpha (by a factor of 5.8-9.7-fold). Thus, CaMKIV and CaMKIIalpha preferentially phosphorylate substrates with the motifs: Hyd-X-Arg-X-X-Ser*/Thr*, and Hyd-X-Arg-NB-X-Ser*/Thr*-Hyd, respectively, where Hyd represents a hydrophobic, X any, and NB a non-basic amino acid residue. The different specificities of the two kinases may contribute to their targeting to distinct physiological substrates during Ca2+-dependent cellular events.

Amino Acid Sequence↗
PubMed1998

Molecules involved in mammalian sperm-egg interaction.

To achieve fertilization, sperm and egg are equipped with specific molecules which mediate the steps of gamete interaction. In mammals, the first interaction between sperm and egg occurs at an egg-specific extracellular matrix, the zona pellucida (zp). The three glycoproteins, ZP1, ZP2, and ZP3, that comprise the zp have been characterized from many species and assigned different roles in gamete interaction. A large number of candidate-binding partners for the zp proteins have been described; a subset of these have been characterized structurally and functionally. Galactosyltransferase, sp56, zona receptor kinase, and spermadhesins are thought to participate in the primary binding between sperm and zp and may initiate the exocytotic release of hydrolytic enzymes in the sperm head, the acrosome reaction. Digestion of the zp by these enzymes enables sperm to traverse the zp, at which time the proteins PH20, proacrosin, sp38, and Sp17 are thought to participate in secondary binding between the acrosome-reacted sperm and zp. Once through the zp, sperm and egg plasma membranes meet and fuse in a process reported to involve the egg integrin alpha 6 beta 1 and the sperm proteins DE and fertilin. These molecules and the processes involved in gamete interaction are reviewed in this chapter within a physiological context.

Animals↗