Biomedical subjects

T C Smith

Publications and source records attributed to T C Smith.

At least 19 recordsLinked to original sources

PubMed2006

Distribution of novel and previously investigated virulence genes in colonizing and invasive isolates of Streptococcus agalactiae.

Although Streptococcus agalactiae has emerged as an important cause of invasive disease, relatively little is known regarding the genetic basis of virulence of this organism. Three novel genes with characteristics suggesting a role in virulence were identified via comparison of sequenced genomes of S. agalactiae. The presence of these genes and of the previously identified genes bac, bca, rib, and spb1 was determined, and isolates were assigned a binary genetic signature. It was found that isolates containing spb1, previously suggested to be limited to serotype III-3, were represented by 18 different genetic signatures and several serotypes, and that the presence of both sbp1 and rib was more predictive of invasive disease than spb1 alone. Additionally, bac-positive isolates, reported to be genetically homogeneous, were represented by 14 different genetic signatures. Finally, the majority of serotype V isolates examined contained zero or only one of the genes tested, suggesting that much remains undiscovered regarding important virulence factors in isolates of this serotype.

Aged↗

PubMed2004

Acute effects of adrenergic agents on post-defibrillation arrest time in a cultured heart model.

Possible drug interactions with electrical defibrillation were examined. We tested the hypothesis that adrenergic agents (epinephrine, norepinephrine, isoproterenol) and a calcium channel blocker (verapamil), when applied acutely, alter the duration of arrest following a defibrillator shock. A secondary hypothesis (based on observations) was that the drugs alter the occurrence of changes to normal rhythms following the shock. Dissociated heart cells from 10-day chicken embryos were cultured to form spherical aggregates and plated in petri dishes. In the experiments, the spheres were paced at 0.75 V/cm above contraction threshold, and a biphasic defibrillator shock was applied for 1 ms at 46 V/cm. The arrest time and occurrence of rhythm changes were recorded. The adrenergic agents shortened the duration of arrest following a defibrillator shock, while the calcium channel blocker lengthened the arrest time. Comparisons with the control proportion of double beats showed no significant change with the adrenergic agents and a decrease with verapamil.

Adrenergic Agents↗

PubMed2003

Occurrence of amyotrophic lateral sclerosis among Gulf War veterans.

BACKGROUND: In response to Gulf War veterans' concerns of high rates of ALS, this investigation sought to determine if Gulf War veterans have an elevated rate of ALS. METHODS: A nationwide epidemiologic case ascertainment study design was used to ascertain all occurrences of ALS for the 10-year period since August 1990 among active duty military and mobilized Reserves, including National Guard, who served during the Gulf War (August 2, 1990, through July 31, 1991). The diagnosis of ALS was confirmed by medical record review. Risk was assessed by the age-adjusted, average, annual 10-year cumulative incidence rate. RESULTS: Among approximately 2.5 million eligible military personnel, 107 confirmed cases of ALS were identified for an overall occurrence of 0.43 per 100,000 persons per year. A significant elevated risk of ALS occurred among all deployed personnel (RR = 1.92; 95% CL = 1.29, 2.84), deployed active duty military (RR = 2.15, 95% CL = 1.38, 3.36), deployed Air Force (RR = 2.68, 95% CL = 1.24, 5.78), and deployed Army (RR = 2.04; 95% CL = 1.10, 3.77) personnel. Elevated, but nonsignificant, risks were observed for deployed Reserves and National Guard (RR = 2.50; 95% CL = 0.88, 7.07), deployed Navy (RR = 1.48, 95% CL = 0.62, 3.57), and deployed Marine Corps (RR = 1.13; 95% CL = 0.27, 4.79) personnel. Overall, the attributable risk associated with deployment was 18% (95% CL = 4.9%, 29.4%). CONCLUSIONS: Military personnel who were deployed to the Gulf Region during the Gulf War period experienced a greater post-war risk of ALS than those who were not deployed to the Gulf.

Adult↗

PubMed2003

The sit-up: complex kinematics and muscle activity in voluntary axial movement.

This paper describes the kinematics and muscle activity associated with the standard sit-up, as a first step in the investigation of complex motor coordination. Eight normal human subjects lay on a force table and performed at least 15 sit-ups, with the arms across the chest and the legs straight and unconstrained. Several subjects also performed sit-ups with an additional weight added to the head. Support surface forces were recorded to calculate the location of the center of pressure and center of gravity; conventional motion analysis was used to measure segmental positions; and surface EMG was recorded from eight muscles. While the sit-up consists of two serial components, 'trunk curling' and 'footward pelvic rotation', it can be further subdivided into five phases, based on the kinematics. Phases I and II comprise trunk curling. Phase I consists of neck and upper trunk flexion, and phase II consists of lumbar trunk lifting. Phase II corresponds to the point of peak muscle contraction and maximum postural instability, the 'critical point' of the sit-up. Phases III-V comprise footward pelvic rotation. Phase III begins with pelvic rotation towards the feet, phase IV with leg lowering, and phase V with contact between the legs and the support surface. The overall pattern of muscle activity was complex with times of EMG onset, peak activity, offset, and duration differing for different muscles. This complex pattern changed qualitatively from one phase to the next, suggesting that the roles of different muscles and, as a consequence, the overall form of coordination, change during the sit-up.

Adolescent↗

PubMed2002

Coexistence of stability and mobility in postural control: evidence from postural compensation for respiration.

This study evaluated the extent to which movement of the lower limbs and pelvis may compensate for the disturbance to posture that results from respiratory movement of the thorax and abdomen. Motion of the neck, pelvis, leg and centre of pressure (COP) were recorded with high resolution in conjunction with electromyographic activity (EMG) of flexor and extensor muscles of the trunk and hip. Respiration was measured from ribcage motion. Subjects breathed quietly, and with increased volume due to hypercapnoea (as a result of breathing with increased dead-space) and a voluntary increase in respiration. Additional recordings were made during apnoea. The relationship between respiration and other parameters was measured from the correlation between data in the frequency domain (i.e. coherence) and from time-locked averages triggered from respiration. In quiet standing, small angular displacements ( approximately 0.5 degrees ) of the trunk and leg were identified in raw data. Correspondingly, there were peaks in the power spectra of the angular movements and EMG. While body movement and EMG were coherent with respiration (>0.5), the coherence between respiration and COP displacement was low (<0.2). The amplitude of movement and coherence was increased when respiration was increased. The present data suggest that the postural disturbance that results from respiratory movement is matched, at least partly, and counteracted by small angular displacements of the lower trunk and lower limbs. Thus, stability in quiet stance is dependent on movement of multiple body segments and control of equilibrium cannot be reduced to control of a single joint.

Abdomen↗

PubMed2001

Randomized, placebo-controlled clinical trial of oral azithromycin prophylaxis against respiratory infections in a high-risk, young adult population.

Military Special Forces trainees undergo intense psychological and physical stressors that often lead to respiratory infection. During 1998-2000, 477 Navy Special Forces trainees were enrolled in a double-blind trial of oral azithromycin (1 g given weekly) plus a placebo injection, compared with benzathine penicillin G (1.2 million U) plus azithromycin placebo tablets. Among the 464 subjects with complete data, 44 developed acute respiratory infection (20 with pneumonia) during the 2 weeks of most intense training; of these subjects, 12 (27.3%) had evidence of Chlamydia pneumoniae infection and 7 (15.9%) had evidence of Mycoplasma pneumoniae infection. Trainees who received azithromycin were less likely than were trainees who received benzathine penicillin G to develop acute respiratory infection (risk ratio, 0.50; 95% confidence interval [CI], 0.28-0.92) and less likely at the end of training to report episodes of breathing difficulty (odds ratio [OR], 0.59; 95% CI, 0.34-1.01) or sore throat (OR, 0.66; 95% CI, 0.41-1.05). Compared with benzathine penicillin G prophylaxis, weekly oral azithromycin was superior in preventing respiratory infection in this population at transient high risk.

Adult↗

PubMed2001

National Department of Defense Surveillance for Invasive Streptococcus pneumoniae: antibiotic resistance, serotype distribution, and arbitrarily primed polymerase chain reaction analyses.

To provide surveillance among US military personnel and their beneficiaries, 157 invasive Streptococcus pneumoniae clinical isolates were collected systematically from 7 large military hospitals between August 1997 and August 1999. The isolates were studied for antibiotic resistance, and 120 were serotyped and subjected to arbitrarily primed polymerase chain reaction (AP-PCR). Fifty (31.9%) of 157 isolates had intermediate or high-level resistance to penicillin, and 15.9% had multidrug resistance. The most common serotypes were 4, 6B, 9V, 14, 19F, and 23F. Those serotypes associated with penicillin resistance were 6B, 9V, 19A, and 19F. Most invasive disease cases were caused by serotypes included in the currently available 23- and 7-valent pneumococcal vaccines. By use of AP-PCR, 4 DNA groups were correlated with health care site (P< or =.0001). These results are valuable in assessing appropriate use of antibiotics and vaccines against S. pneumoniae in both military personnel and their families.

Adolescent↗

PubMed2001

The Department of Defense Birth Defects Registry: overview of a new surveillance system.

BACKGROUND: The U.S. Department of Defense (DoD) is challenged with monitoring and protecting the health and wellbeing of its service members. The growing number of women on active duty and the diverse hazardous exposures associated with military service make reproductive health issues a special concern of DoD. To address this concern, the DoD Birth Defects Registry was established at the DoD Center for Deployment Health Research located at the Naval Health Research Center, San Diego, California. METHODS: The registry captures comprehensive data on healthcare utilization to calculate the prevalence of birth defects in the children of military beneficiaries. Population-based electronic surveillance is supplemented by active case validation efforts. RESULTS: Since its establishment in 1998, the registry has captured data on more than 90,000 births that occur in military families each year. Detailed analyses, to include linking registry data with military occupational exposure data (e.g., anthrax vaccination), are underway. CONCLUSIONS: The DoD Birth Defects Registry provides important reproductive health information on the geographically dispersed military population. This program is expected to complement civilian public health programs and be especially valuable to military members and their families.

Congenital Abnormalities↗

PubMed2001

Active surveillance of birth defects among U.S. Department of Defense beneficiaries: a feasibility study.

Since the Vietnam War, concern regarding the association of military exposures and birth defects has grown. The possibility of such associations remains a source of unease. To determine if such an association exists, birth defects surveillance among military families must be conducted. This project compared health record abstraction (active surveillance) with screening of Department of Defense electronic medical data (passive surveillance) to detect birth defects among San Diego County military families during the period January 1, 1997, through June 30, 1998. A total of 171 of 5,351 infants (3.2%) were identified as having a major defect, consistent with national civilian rates. There was approximately 80% concurrence between passive and active surveillance birth defect data, suggesting that a hybrid system of electronic data, supplemented with active surveillance in a specific region, represents a feasible and cost-effective surveillance program for the geographically dispersed military population.

Abstracting and Indexing↗

PubMed2001

Viral hepatitis in the U.S. military: a study of hospitalization records from 1974 to 1999.

Viral hepatitis remains a health threat for military forces. Most recently, there has been concern about hepatitis C virus transmission during military service because a high prevalence of hepatitis C virus infection has been found in some U.S. veteran populations. In this study, hospitalizations of active duty U.S. military personnel for hepatitis were evaluated using standardized computer records. Only the first hospitalization was assessed during the period January 1, 1989, to December 31, 1999. Among active duty forces, the rate of hospitalization for all types of acute hepatitis declined from 13 to 1.1 per 100,000 personnel from 1989 to 1999. Males, nonwhite racial/ethnic groups, and older troops were more likely to be hospitalized for acute hepatitis. This study's finding of declining rates of acute hepatitis is a continuation of a trend observed since 1974. The decreasing risk of viral hepatitis in the U.S. military is attributable to several factors, including reduced levels of injection drug use because of routine, randomized drug testing.

Acute Disease↗

PubMed2000

Factor analysis of self-reported symptoms: does it identify a Gulf War syndrome?

Active duty US Naval mobile construction battalion personnel (Seabees) were surveyed in 1994 for the presence of a variety of symptoms. Questions were drawn from the Hopkins Symptom Checklist and from a collection of symptoms either defining clinical depression or commonly reported by Persian Gulf War veterans. Of those surveyed, 524 were Gulf War veterans and 935 were nondeployed Gulf War-era veterans. Factor analysis applied to Gulf War veterans yielded five factors, three deriving from the Hopkins Symptom Checklist, one suggesting clinical depression, and one containing symptoms commonly reported by Gulf War veterans. Factor analysis applied to nondeployed veterans yielded five similar factors. Three of the factors yielded statistically significantly greater standardized factor scores for Gulf War veterans than for nondeployed veterans. Four of the factors resembled factors resulting from a previous analysis on a sample of similar Gulf War veterans. Gulf War veterans and nondeployed era veterans reported similar clusters of symptoms and illnesses. However, Gulf War veterans reported these same clusters with greater frequencies than did nondeployed veterans. The authors conclude that, in contrast to a previous report, factor analysis did not identify a unique Gulf War syndrome.

Adult↗

PubMed2000

Is systemic lupus erythematosus, amyotrophic lateral sclerosis, or fibromyalgia associated with Persian Gulf War service? An examination of Department of Defense hospitalization data.

Since the Persian Gulf War ended in 1991, veterans have reported diverse, unexplained symptoms. Some have wondered if their development of systemic lupus erythematosus, amyotrophic lateral sclerosis, or fibromyalgia might be related to Gulf War service. The authors used Cox proportional hazard modeling to determine whether regular, active-duty service personnel deployed to the Persian Gulf War (n = 551,841) were at increased risk of postwar hospitalization with the three conditions compared with nondeployed Gulf War era service personnel (n = 1,478,704). All hospitalizations in Department of Defense facilities from October 1, 1988, through July 31, 1997, were examined. With removal of personnel diagnosed with any of the three diseases before August 1, 1991, and adjustment for multiple covariates, Gulf War veterans were not at increased risk of postwar hospitalization due to systemic lupus erythematosus (risk ratio (RR) = 0.94, 95% confidence interval (CI): 0.65, 1.35). Because of the small number of cases and wide confidence limits, the data regarding amyotrophic lateral sclerosis were inconclusive. Gulf War veterans were slightly at risk of postwar hospitalization for fibromyalgia (RR = 1.23, 95% Cl: 1.05, 1.43); however, this risk difference was probably due to the Gulf War veteran clinical evaluation program beginning in 1994. These data do not support Gulf War service and disease associations.

Adult↗

PubMed2000

Heterogeneous conductance levels of native AMPA receptors.

The single-channel properties of AMPA receptors can affect information processing in neurons by influencing the amplitude and kinetics of synaptic currents, yet little is known about the unitary properties of native AMPA receptors in situ. Using whole-cell and outside-out patch-clamp recordings from granule cells in acute cerebellar slices, we found that migrating granule cells begin to express AMPA receptors before they arrive in the internal granule cell layer and receive synaptic input. At saturating agonist concentrations, the open probability of channels in outside-out patches from migrating cells was very high, allowing us to identify patches that contained only one or two active channels. Analysis of the single-channel activity in these patches showed that individual AMPA receptors exhibit as many as four distinguishable conductance levels. The conductance levels observed varied substantially for different channels, although on average the values fell within the range of unitary conductances estimated previously for synaptic AMPA receptors. In contrast to patches from migrating granule cells, we rarely observed directly resolvable single-channel currents in patches excised from the somata of granule cells in the internal granular layer, even though these cells gave large AMPA receptor whole-cell currents. We did, however, detect AMPA receptors with apparent unitary conductances of <1 pS in patches from both migrating and mature granule cells. Our results suggest that granule cells express a heterogeneous population of AMPA receptors, a subset of which are segregated to postsynaptic sites after synaptogenesis.

Animals↗

PubMed2000

Are Gulf War veterans suffering war-related illnesses? Federal and civilian hospitalizations examined, June 1991 to December 1994.

A previous epidemiologic study demonstrated no unexplained increase in risk for postwar hospitalization among Gulf War veterans who had remained on active duty. The authors sought to expand this study to include Reserve and separated military personnel. They examined hospitalization data from the Department of Defense, the Department of Veterans Affairs (VA), and the California Office of Statewide Health Planning and Development hospital systems for the years 1991-1994. Since denominator data were not available, the authors compared the proportional morbidity ratios (PMRs) of hospitalization discharge diagnoses (both large categories and specific diagnoses) between Gulf War veterans and other veterans of the same era. There were no indications that Gulf War veterans were suffering increased PMRs for infectious diseases; neoplasms; endocrine diseases; blood diseases; skin conditions; or diseases of the nervous system, circulatory system, or musculoskeletal system. However, these veterans did experience proportionally more hospitalizations for various specific diagnoses, namely, fractures and bone and soft-tissue injuries (Department of Defense and California Office of Statewide Health Planning and Development), various diseases of the respiratory (including asthma) and digestive systems (VA), and diverse symptom diagnoses (VA). While these findings may be influenced by chance or by a number of potential confounders, including health registry participation, they merit further examination using other study designs.

Adolescent↗

PubMed2000

Concentration-dependent substate behavior of native AMPA receptors.

AMPA-type glutamate receptors mediate most excitatory postsynaptic currents (EPSCs) at central synapses, and their conductance determines in part the size of EPSCs. The conductance of a recombinant AMPA receptor depends on the number of agonist molecules bound to the channel. Here we tested whether native AMPA and kainate receptors show this behavior in outside-out patches from neurons in situ by measuring conductance levels of single channels over a wide range of agonist concentrations. We found that the conductance of AMPA, but not kainate, receptors depended strongly on agonist concentration. Our results suggest that alterations in the glutamate concentration in the synaptic cleft may change the apparent unitary conductance of postsynaptic AMPA receptors.

Animals↗

PubMed1999

The postwar hospitalization experience of Gulf War Veterans possibly exposed to chemical munitions destruction at Khamisiyah, Iraq.

Using Department of Defense hospital data, the authors examined the postwar hospitalization experience from March 1991 through September 1995 of US Gulf War veterans who were near Khamisiyah, Iraq, during nerve agent munition destruction in March 1991. Multiple sources of meteorologic, munition, and toxicology data were used to circumscribe geographic areas of low level, vaporized nerve agent for 4 days after the destruction. Plume estimates were overlaid on military unit positions, and exposure was estimated for the 349,291 US Army Gulf War veterans. Exposure was classified as not exposed (n = 224,804), uncertain low dose exposure (n = 75,717), and specific estimated subclinical exposure (n = 48,770) categorized into three groups for dose-response evaluation. Using Cox proportional hazard modeling, the authors compared the postwar experiences of these exposure groups for hospitalization due to any cause, for diagnoses in 15 unique categories, and for specific diagnoses an expert panel proposed as most likely to reflect latent disease from such subclinical exposure. There was little evidence that veterans possibly exposed to the nerve agent plumes experienced unusual postwar morbidity. While there were several differences in hospitalization risk, none of the models suggested a dose-response relation or neurologic sequelae. These data, having a number of limitations, do not support the hypothesis that Gulf War veterans are suffering postwar morbidity from subclinical nerve agent exposure.

Adolescent↗

PubMed1999

Distinct kainate receptor phenotypes in immature and mature mouse cerebellar granule cells.

1. Although glutamate receptors have been shown to be involved in neuronal maturation, a developmental role for kainate-type receptors has not been described. In addition, the single-channel properties of native kainate receptors have not been studied in situ. We have characterized the electrophysiological properties of native kainate receptors of granule cell neurons at two distinct stages in postnatal development, using whole-cell and outside-out patch-clamp recordings in acute cerebellar slices. 2. Kainate-type currents were detected in both immature and mature granule cells. However, noise analysis showed that the apparent unitary conductance of kainate-type channels is significantly higher in proliferating than post-migratory granule cells. The conductance and rectification behaviour of the channels in immature granule cells indicate that they contain unedited GluR5 and GluR6 subunits and are likely to be calcium permeable. 3. Single-channel kainate-type currents were observed in outside-out patches from proliferating granule cells in the external germinal layer. The kinetic behaviour of kainate receptors in immature cells was complex. Openings to multiple conductance levels were observed, although our analysis indicates that the channels spend most of their open time in a 4 pS state.

Animals↗

PubMed1999

Acute eosinophilic pneumonia associated with shock.

OBJECTIVE: To describe an unusual case of acute eosinophilic pneumonia (AEP) associated with hemodynamic instability. DESIGN: Case report, clinical. SETTINGS: Tertiary care intensive care unit (ICU). PATIENT: A single patient admitted to the ICU. INTERVENTIONS: Intravenous corticosteroids. MEASUREMENTS AND MAIN RESULTS: Resolution of distributive shock and respiratory failure. CONCLUSIONS: AEP with respiratory failure was first reported in 1989 as a distinct clinical entity. Patients with this variant of eosinophilic lung disease develop acute hypoxemic respiratory failure with a rapid response to treatment with corticosteroids, The characteristic feature of this syndrome is a predominance of eosinophils found in bronchoalveolar lavage fluid and lung biopsy. Despite the increasing number of reported cases, to our knowledge, distributive shock has not been reported as a feature of AEP. We report a unique case of AEP associated with shock and review the pertinent literature.

Acute Disease↗