Biomedical subjects

Matthew D Johnson

Publications and source records attributed to Matthew D Johnson.

11 recordsLinked to original sources

PubMed2006

Spatiotemporal pH dynamics following insertion of neural microelectrode arrays.

Insertion trauma is a critical issue when assessing intracortical electrophysiological and neurochemical recordings. Previous reports document a wide variety of insertion techniques with speeds ranging from 10 microm/s to 10 m/s. We hypothesize that insertion speed has an effect on tissue trauma induced by implantation of a neural probe. In order to monitor the neural interface during and after probe insertion, we have developed a silicon-substrate array with hydrous iridium oxide microelectrodes for potentiometric recording of extracellular pH (pH(e)), a measure of brain homeostasis. Microelectrode sites were sensitive to pH in the super-Nernstian range (-85.9 mV/pH unit) and selective over other analytes including ascorbic acid, Na(+), K(+), Ca(2+), and Mg(2+). Following insertion, arrays recorded either triphasic or biphasic pH(e) responses, with a greater degree of prolonged acidosis for insertions at 50 microm/s than at 0.5 mm/s or 1.0 mm/s (p<0.05). Spatiotemporal analysis of the recordings also revealed micro-scale variability in the pH(e) response along the array, even when using the same insertion technique. Implants with more intense acidosis were often associated histologically with blood along the probe tract. The potentiometric microsensor array has implications not only as a useful tool to measure extracellular pH, but also as a feedback tool for delivery of pharmacological agents to treat surgical brain trauma.

Acidosis↗

PubMed2006

Treatment for pancreatic abscesses via omentalization with abdominal closure versus open peritoneal drainage in dogs: 15 cases (1994-2004).

OBJECTIVE: To compare survival rate, duration of hospitalization, and complications in dogs with pancreatic abscesses treated with omentalization with abdominal closure versus open peritoneal drainage and evaluate a pancreatitis severity score for potential prognostic value. DESIGN: Retrospective case series. ANIMALS: 15 dogs with pancreatic abscesses. PROCEDURE: Data regarding species, breed, age, initial clinical signs, CBC, serum biochemical abnormalities, pancreatitis severity score, anatomic location of the abscess, intraoperative bacteriologic culture results, treatment modality, postoperative complications, outcome (dismissed alive from the hospital, died in the postoperative period, or euthanized at surgery), and duration of hospitalization were evaluated. RESULTS: 6 dogs survived, 6 dogs died or were euthanized after surgery, and 3 were euthanized during surgery. Five of 8 dogs treated with omentalization and abdominal closure survived, and 1 of 4 dogs treated with open peritoneal drainage survived. In several dogs, treatment required additional surgical procedures, which did not appear to affect outcome. Postoperative complications were similar among survivors and nonsurvivors. Mean duration of hospitalization for dogs treated with omentalization and abdominal closure was less than that of dogs treated with open peritoneal drainage. Neither pancreatitis severity score nor any individual components of the score were associated with outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Omentalization is a viable treatment option for pancreatic abscess in dogs. Furthermore, shorter hospitalization and better survival outcomes may make omentalization preferred over open peritoneal drainage.

Abscess↗

PubMed2006

Recruitment and selection of couples for intervention research: achieving developmental homogeneity at the cost of demographic diversity.

Demographic and relationship quality data were collected from 704 individuals recruited to participate in a randomized study of relationship enhancing interventions. Recruiting at bridal shows produced partners who were more satisfied, earlier in their relationships, and less likely to be parents, with a marginally higher proportion of Latino couples. Radio and television coverage produced more established couples with higher levels of relationship discord. Self-selection effects revealed that couples from demographic groups at greater risk for divorce (those who had not completed high school, those with children at marriage, and African American couples) were more likely to agree to participate. In contrast, imposing a set of common selection criteria served to exclude couples from demographic risk groups and selected for couples with higher marital quality. Implications for recruiting couples to participate in preventive interventions are outlined.

Adult↗

PubMed2006

Voltage pulses change neural interface properties and improve unit recordings with chronically implanted microelectrodes.

Current neuroprosthetic systems based on electro-physiological recording have an extended, yet finite working lifetime. Some posited lifetime-extension solutions involve improving device biocompatibility or suppressing host immune responses. Our objective was to test an alternative solution comprised of applying a voltage pulse to a microelectrode site, herein termed "rejuvenation." Previously, investigators have reported preliminary electrophysiological results by utilizing a similar voltage pulse. In this study we sought to further explore this phenomenon via two methods: 1) electrophysiology; 2) an equivalent circuit model applied to impedance spectroscopy data. The experiments were conducted via chronically implanted silicon-substrate iridium microelectrode arrays in the rat cortex. Rejuvenation voltages resulted in increased unit recording signal-to-noise ratios (10% +/- 2%), with a maximal increase of 195% from 3.74 to 11.02. Rejuvenation also reduced the electrode site impedances at 1 kHz (67% +/- 2%). Neither the impedance nor recording properties of the electrodes changed on neighboring microelectrode sites that were not rejuvenated. In the equivalent circuit model, we found a transient increase in conductivity, the majority of which corresponded to a decrease in the tissue resistance component (44% +/- 7%). These findings suggest that rejuvenation may be an intervention strategy to prolong the functional lifetime of chronically implanted microelectrodes.

Action Potentials↗

PubMed2006

Assessing habitat quality for a migratory songbird wintering in natural and agricultural habitats.

As tropical forests are cleared, a greater proportion of migratory songbirds are forced to winter in agricultural and disturbed habitats, which, if poorer in quality than natural forests, could contribute to population declines. We compared demographic indicators of habitat quality for a focal species, the American Redstart (Setophaga ruticilla), wintering in Jamaican citrus orchards and shade coffee plantations with those in four natural habitats: mangrove, coastal scrub, coastal palm, and dry limestone forests. Demographic measures of habitat quality included density, age and sex ratio, apparent survival, and changes in body mass. Measures of habitat quality for redstarts in citrus and coffee habitats were generally intermediate between the highest (mangrove) and lowest (dry limestone) measurements from natural habitats. The decline in mean body mass over the winter period was a strong predictor of annual survival rate among habitats, and we suggest that measures of body condition coupled with survival data provide the best measures of habitat quality for nonbreeding songbirds. Density, which is far easier to estimate, was correlated with these more labor-intensive measures, particularly in the late winter when food is likely most limiting. Thus, local density may be useful as an approximation of habitat quality for wintering migrant warblers. Our findings bolster those of previous studies based on bird abundance that suggest arboreal agricultural habitats in the tropics can be useful for the conservation of generalist, insectivorous birds, including many migratory passerines such as redstarts.

Agriculture↗

PubMed2006

Porcupine quill injuries in dogs: a retrospective of 296 cases (1998-2002).

The purpose of this retrospective study was to identify factors associated with quill injury in dogs. A second objective was to determine the risk of complications and any factors that would predict the likelihood of complications. Hospital records of 296 porcupine quill injuries in dogs from 1998 to 2002 were studied. There was an increased occurrence of porcupine encounters in the spring and fall months; Siberian huskies, rottweilers, and German shepherd crosses were significantly overrepresented for quill injuries. There was no association between risk of complications and either number of quills or antimicrobial use. Increasing time between quill injury and presentation was associated with an increased risk of complications. Because of the increased frequency of complication with a longer interval until presentation, clients should be strongly encouraged to bring the dog in as soon as the quill injury is discovered. Patients presented after 24 hours should be monitored closely during the first 3 weeks after injury, as most complications occurred during this time.

Animals↗

PubMed2005

Problem-solving skills and affective expressions as predictors of change in marital satisfaction.

Specific skills and affective expressions coded from the problem-solving interactions of 172 newlywed couples were examined in relation to 8-wave, 4-year trajectories of marital satisfaction. Effects varied as a function of whether husbands' versus wives' topics were under discussion and whether husbands' versus wives' satisfaction was predicted, but results indicate that skills, affect, and their statistical interaction account for unique variance in rates of change in marital satisfaction. The interaction between positive affect and negative skills was particularly robust, indicating that (a) low levels of positive affect and high levels of negative skills foreshadowed particularly rapid rates of deterioration and that (b) high levels of positive affect buffered the effects of high levels of negative skills. Findings suggest specific targets for intervention in programs for developing marriages.

Adult↗

PubMed2005

Repeated voltage biasing improves unit recordings by reducing resistive tissue impedances.

Reactive tissue encapsulation of chronically implanted microelectrode probes can preclude long-term recording of extracellular action potentials. We investigated an intervention strategy for functionally encapsulated microelectrode sites. This method, known as "rejuvenation," involved applying a +1.5 V dc bias to an iridium site for 4 s. Previous studies have demonstrated that rejuvenation resulted in higher signal-to-noise ratios (SNRs) by decreasing noise levels, and reduced 1-kHz site impedances by decreasing the tissue interface resistances. In this study, we have investigated: 1) the duration of a single-voltage bias session and 2) the efficacy of multiple sessions. These questions were addressed through electrophysiological recordings, cyclic voltammetry, and modeling the electrode-tissue interface via an equivalent circuit model fit to impedance spectroscopy data. In the six implants studied, we found SNRs improved for 1-7 days with a peak typically occurring within 24 h of the voltage bias. Root-mean square (RMS) noise of the extracellular recordings decreased for 1-2 days, which paralleled a similar decrease in the adsorbed tissue resistance (Ren) from the model. Implants whose SNR effects lasted more than a day showed stabilized reductions in the extracellular tissue resistance (Rex) and cellular membrane area (Am). Subsequent stimulus sessions were found to drop neural tissue parameters consistently to levels observed immediately after surgery. In most cases, these changes did parallel an improvement in SNR. These findings suggest that rejuvenation may be a useful intervention strategy to prolong the lifetime of chronically implanted microelectrodes.

Action Potentials↗

PubMed2004

Individual growth curve analysis illuminates stability and change in personality disorder features: the longitudinal study of personality disorders.

BACKGROUND: The long-term stability of personality pathology remains an open question. Its resolution will come from prospective, multiwave longitudinal studies using blinded assessments of personality disorders (PD). Informative analysis of multiwave data requires the application of statistical procedures, such as individual growth curve modeling, that can detect and describe individual change appropriately over time. The Longitudinal Study of Personality Disorders, which meets contemporary methodological design criteria, provides the data for this investigation of PD stability and change from an individual growth curve perspective. METHODS: Two hundred fifty subjects were examined for PD features at 3 different time points using the International Personality Disorders Examination during a 4-year study. Stability and change in PD features over time were examined using individual growth modeling. RESULTS: Fitting of unconditional growth models indicated that statistically significant variation in PD features existed across time in the elevation and rate of change of the individual PD growth trajectories. Fitting of additional conditional growth models, in which the individual elevation and rate-of-change growth parameters were predicted by subjects' study group membership (no PD vs possible PD), sex, and age at entry into the study, showed that study group membership predicted the elevation and rate of change of the individual growth curves. Comorbid Axis I psychopathology and treatment during the study period were related to elevations of the individual growth trajectories, but not to rates of change. CONCLUSIONS: From the perspective of individual growth curve analysis, PD features show considerable variability across individuals over time. This fine-grained analysis of individual growth trajectories provides compelling evidence of change in PD features over time and does not support the assumption that PD features are traitlike, enduring, and stable over time.

Adolescent↗

PubMed2004

Highly divergent SSU rRNA genes found in the marine ciliates Myrionecta rubra and Mesodinium pulex.

Myrionecta rubra and Mesodinium pulex are among the most commonly encountered planktonic ciliates in coastal marine and estuarine regions throughout the world. Despite their widespread distribution, both ciliates have received little attention by taxonomists. In order to better understand the phylogenetic position of these ciliates, we determined the SSU rRNA gene sequence from cultures of M. rubra and M. pulex. Partial sequence data were also generated from isolated cells of M. rubra from Chesapeake Bay. The M. rubra and M. pulex sequences were very divergent from all other ciliates, but shared a branch with 100% bootstrap support. Both species had numerous deletions and substitutions in their SSU rRNA gene, resulting in a long branch for the clade. This made the sequences prone to spurious phylogenetic affiliations when using simple phylogenetic methods. Maximum likelihood analysis placed M. rubra and M. pulex on the basal ciliate branch, following removal of ambiguously aligned regions. Fluorescent in situ hybridization probes were used with confocal laser scanning microscopy to confirm that these divergent sequences were both expressed in the cytoplasm and nucleolus of M. ruisra and M. pulex. We found that our sequence data matched several recently discovered unidentified eukaryotes in Genbank from diverse marine habitats, all of which had apparently been misattributed to highly divergent amoeboid organisms.

Animals↗

PubMed2002

The observation of specific affect in marital interactions: psychometric properties of a coding system and a rating system.

The Specific Affect Coding System (SPAFF; J. M. Gottman & L. J. Krokoff, 1989) has led to conclusions about which types of dyadic affect predict positive and negative outcomes in marriage, yet the lack of information about collinearity among the codes limits interpretation of SPAFF results. Psychometric properties of SPAFF were examined by assessing the interactions of 172 newlywed couples with SPAFF and with an affect rating system developed for this study. For husbands and wives, factor analysis indicated 4 distinct factors of affect, representing anger/contempt, sadness, anxiety, and humor/affection. Anger/contempt and humor/affection were associated with marital satisfaction, relationship beliefs, and appraisals of the interactions. Correlations were in the expected directions. The strengths, limitations, and implications of the data are discussed.

Adult↗