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Biomedical subjects

L J Myers

Publications and source records attributed to L J Myers.

At least 19 recordsLinked to original sources
PubMed2005

Metabolic setpoint control mechanisms in different physiological systems at rest and during exercise.

Using a number of different homeostatic control mechanisms in the brain and peripheral physiological systems, metabolic activity is continuously regulated at rest and during exercise to prevent catastrophic system failure. Essential for the function of these regulatory processes are baseline "setpoint" levels of metabolic function, which can be used to calculate the level of response required for the maintenance of system homeostasis after system perturbation, and to which the perturbed metabolic activity levels are returned to at the end of the regulatory process. How these setpoint levels of all the different metabolic variables in the different peripheral physiological systems are created and maintained, and why they are similar in different individuals, has not been well explained. In this article, putative system regulators of metabolic setpoint levels are described. These include that: (i) innate setpoint values are stored in a certain region of the central nervous system, such as the hypothalamus; (ii) setpoint values are created and maintained as a response to continuous external perturbations, such as gravity or "zeitgebers", (iii) setpoint values are created and maintained by complex system dynamical activity in the different peripheral systems, where setpoint levels are regulated by the ongoing feedback control activity between different peripheral variables; (iv) human anatomical and biomechanical constraints contribute to the creation and maintenance of metabolic setpoints values; or (v) a combination of all these four different mechanisms occurs. Exercise training and disease processes can affect these metabolic setpoint values, but the setpoint values are returned to pre-training or pre-disease levels if the training stimulus is removed or if the disease process is cured. Further work is required to determine what the ultimate system regulator of metabolic setpoint values is, why some setpoint values are more stringently protected by homeostatic regulatory mechanisms than others, and the role of conscious decision making processes in determining the regulation of metabolic setpoint values.

Adaptation, Physiological↗
PubMed2004

Exponential taper in arteries: an exact solution of its effect on blood flow velocity waveforms and impedance.

The dimensions and wall elasticity commonly taper along the length of mammalian arteries. The effects of taper on flow velocity waveforms can be included by either of two methods; to theoretically divide the artery into short sections wherein the properties are assumed constant (the approximate solution); or to find an exact solution incorporating the effects of taper. In this paper, an exact solution to the resulting, and previously unsolved nonlinear Ricatti equation for the impedance, is obtained by a process of substitutions. This solution is utilised to develop an exact expression for the flow velocity in the artery. The transmission line equations are then combined into a single integral expression for the entire artery and an exact solution to this is evaluated. This is the first solution to simultaneously account for both geometric and elastic taper, and it has been validated by comparing simulations of flow in the aorta of a dog to those using an infinitesimal approximate solution. The Pulsatility Index of the approximate solution requires at least 10 segments to converge to within 5% of that using the exact solution. The exact solution thus accurately accounts for the effects of exponential taper, and may be used to improve existing arterial models, which use the less accurate and more computationally cumbersome approximate solution.

Anatomy, Cross-Sectional↗
PubMed2003

Rectification and non-linear pre-processing of EMG signals for cortico-muscular analysis.

Rectification of the electromyographic (EMG) signal is a commonly used pre-processing procedure that allows detection of significant coherence between EMG and measured cortical signals. However, despite its accepted and wide-spread use, no detailed analysis has been presented to offer insight into the precise function of rectification. We begin this paper with arguments based on single motor unit action potential (AP) trains to demonstrate that rectification effectively enhances the firing rate information of the signal. Enhancement is achieved by shifting the peak of the AP spectrum toward the lower firing rate frequencies, whilst maintaining the firing rate spectra. A similar result is obtained using the analytic envelope of the signal extracted using the Hilbert transform. This argument is extended to simulated EMG signals generated using a published EMG model. Detection of firing rate frequencies is obtained using phase randomised surrogate data, where the original EMG power spectrum exceeds the averaged rectified surrogate spectra at integer multiples of firing rate frequencies. Model simulations demonstrate that this technique accurately determines grouped firing rate frequencies. Extraction of grouped firing rate frequencies prior to coherency analyses may further aid interpretation of significant cortico-muscular coherence findings.

Action Potentials↗
PubMed2002

A transmission line model of the human foetal circulatory system.

A transmission line model of the human foetal circulatory system is presented. The model has been developed in the frequency domain with the cardiac input modeled as a flow rather than as a pressure pulse and is structured upon electrical transmission line analogies. The model is formed by cascading solutions to the two-dimensional Navier-Stokes equations for both oscillatory and steady, laminar viscous fluid flow in isotropic visco-elastic tubes with thick walls, which are constrained by surrounding tissues. Simulations allow for representation of both forward and retrograde travelling flow and pressure waves in all of the main foetal arterial vessels. The solution is verified by a comparison of model generated Doppler indices in the thoracic aorta, abdominal aorta, iliac artery and both ends of the umbilical arteries with previously published indices obtained by clinical measurements in these arteries. For simulations of blood flow in a healthy foetus, the model generated Pulsatility and Resistance indices were on average within 8% of the corresponding clinical measurements. The model results also demonstrates that placental resistance must increase by a factor of three, corresponding to a 60% decrease in flow to the placenta, before umbilical arterial absent end diastolic flow is observed. Differences between indices obtained from simulations at opposite ends of the umbilical arteries increase with increasing placental resistance.

Blood Flow Velocity↗
PubMed2001

Analytical solution for pulsatile axial flow velocity waveforms in curved elastic tubes.

An analytical solution for pulsatile axial flow velocity waveforms in curved elastic tubes is presented. The result is obtained by exact solution of linearized Navier-Stokes and tube motion equations in a torroidal coordinate system. Fourier analysis is used to divide the flow into constant and oscillatory components which are separately considered. The solution is used to investigate the effects of curvature on volumetric axial velocity flow waveforms, as would be measured by Doppler ultrasound techniques. In typical human arteries, the greatest effects of curvature on the volumetric axial flow are exerted on the constant component and at low values of the frequency parameter for the oscillatory components. Here, the magnitude and phase angle of oscillatory flow in the curved tube, relative to that in the straight tube, differ by maximum values of 1.2% and 0.15 rad, respectively. However, constant flow may vary by as much as 60% at high Dean numbers. The solution is presented in a form similar to Womersley's solution for the straight elastic tube and may, thus, be incorporated into a transmission-line analog model. These models are frequently used to investigate axial flow velocity variations in mamillian circulatory systems and this work offers a tool which may extend these models to incorporate the effects of curvature.

Algorithms↗
PubMed1997

An outbreak of foodborne illness caused by Escherichia coli O39:NM, an agent not fitting into the existing scheme for classifying diarrheogenic E. coli.

An outbreak of gastrointestinal illness with clinical and epidemiologic features of enterotoxigenic Escherichia coli (ETEC) occurred among patrons of a restaurant during April 1991. Illnesses among several groups of patrons were characterized by diarrhea (100%) and cramps (79%-88%) lasting a median of 3-5 days. Median incubation periods ranged from 50 to 56 h. A nonmotile strain of E. coli (E. coli O39), which was negative for heat-labile (LT) and heat-stable (STa, STb) ETEC toxins, was isolated only from ill patrons. This organism produced enteroaggregative E. coli heat-stable enterotoxin 1 and contained the enteropathogenic E. coli gene locus for enterocyte effacement; it did not display mannose-resistant adherence, but produced attaching and effacing lesions in the absence of mannose on cultured HEp-2 cells. E. coli that are not part of highly characterized but narrowly defined groups may be important causes of foodborne illness.

Bacterial Adhesion↗
PubMed1996

Black Americans' and White Americans' views of the etiology and treatment of mental health problems.

Black Americans, in contrast to White Americans, use the mental health system in different ways. For example, Blacks tend to terminate treatment earlier than Whites. One explanation for the racial differences is that members of the two groups hold different views about mental health problems and their treatment. To test this explanation, subjects read and responded to questions about vignettes describing individuals encountering personal difficulties that ranged from adjustment challenges to severe psychiatric illness. Black American respondents rated spiritual factors as more important in the etiology and treatment of the difficulties than did Whites. The implications of these findings for theory and practice are discussed.

Adaptation, Psychological↗
PubMed1992

Effects of steroids on the olfactory function of the dog.

Twenty-four (24) mature, mixed breed, healthy dogs weighing from 14.6 kg to 27.6 kg were used to study the effects of various steroids on the olfactory function of the dog using olfactory detection threshold as an index. Two odorants were used, viz; benzaldehyde and eugenol. Of the various steroids used, only dexamethasone produced classical signs of Cushing's syndrome in the dogs. However, all dogs that received either dexamethasone alone or hydrocortisone plus DOCA exhibited a significant elevation in the olfactory detection threshold for both odorants without any observable structural alteration of the olfactory tissue using light microscopy. On the other hand, neither DOCA, hydrocortisone alone, nor any of the vehicles used in the study significantly altered the olfactory function of the dogs. The results show that Cushing's syndrome can be experimentally produced in dogs using exogenous steroids and that this condition diminishes the olfactory capability of the dog without producing classical signs of the disease.

Adrenal Cortex Function Tests↗
PubMed1991

Use of innate behaviors to evaluate sensory function in the dog.

The need to evaluate sensory function in the dog is discussed. A group of techniques that use innate behaviors (species-typical behaviors) and are effective in the evaluation of sensory function of domestic animals are described. Techniques to measure olfactory, gustatory, auditory, and visual function are included.

Animals↗
PubMed1988

Cloning and high level expression of a chimeric antibody with specificity for human carcinoembryonic antigen.

A mouse/human chimeric antibody has been constructed by using variable light and variable heavy regions from a murine hybridoma specific for human carcinoembryonic antigen (CEA) (CEM231.6.7). These V regions were combined with kappa and gamma-1 constant region genes cloned from human lymphocytes. The chimeric constructs were sequentially electroporated into murine non-Ig-producing myeloma (P3.653) and hybridoma (SP2/0) cell. Significant differences were seen in expression levels between the two cell types. High levels of expression (24 to 32 micrograms/ml/10(6) cells) were seen with several of the anti-CEA SP2/0 transfectomas but not with the P3.653 cells. The SP2/0 transfectoma lines were adapted to serum-free, chemically defined media and grown in large scale fermentation cultures where they continued to secrete high levels of antibody. The chimeric antibodies remain reactive against human CEA with affinity constants comparable to that of the parental hybridoma antibody. High level expression will make practical the production of chimeric antibodies for in vivo therapeutic and diagnostic purposes.

Amino Acid Sequence↗
PubMed1988

Newly described muscle attachments to the anterior band of the articular disk of the temporomandibular joint.

The presence of these two muscle attachments will be helpful in treating TM disorders. Why they have not been previously described is a mystery, but it is more understandable when the difficulty of dissection is noted. Freeing the disk while investigating the retrodiskal area, and then performing fiber-by-fiber dissection of the deep masseter muscle are uncommon procedures. Muscle fibers often exist from the deep masseter muscle to the capsule of the TMJ, and these muscles could easily be mistaken for the fibers already known and, therefore, ignored when the masseter was removed in dissection. If the first specimen dissected had not been a well-developed male with strong tendon attachment, the attachments would have been missed in this case as well.

Adult↗
PubMed1988

Dysfunction of sense of smell caused by canine parainfluenza virus infection in dogs.

Olfactory function of 5 dogs that were naturally infected with canine parainfluenza virus and of 4 dogs that were inoculated with the C958 strain of canine parainfluenza virus was evaluated. Except for one dog that was inoculated, the threshold for detection of benzaldehyde and/or eugenol was found to be excessively high during the course of the disease, as determined by electroencephalographic and behavioral olfactometry. In experimentally infected dogs, an increase in threshold developed in the absence of other clinical signs of disease. Changes were not observed in electro-olfactograms recorded throughout the study. Olfactory thresholds returned to normal after the disappearance of clinical signs of disease in the naturally infected dogs. Necropsies and histologic examinations performed during the course of the disease did not reveal abnormalities of the olfactory mucosa.

Animals↗
PubMed1988

Anosmia associated with canine distemper.

The sense of smell in dogs infected with canine distemper virus (CDV) was examined by use of EEG olfactometry, behavioral olfactometry, and electro-olfactography. Infection with CDV was confirmed by a direct immunofluorescence technique in 8 active cases and was suggested by clinical history compatible with canine distemper 10 to 26 weeks earlier in 6 cases. Pathologic alterations of the olfactory mucosa in 3 clinically affected dogs was examined by light microscopy. Infection with CDV was found to be associated with anosmia and lack of recorded responses on electro-olfactogram in 8 of 8 dogs with clinical signs of acute distemper from naturally acquired infections. Anosmia was found in 5 of 6 dogs that had recovered from acute distemper 10 to 26 weeks earlier. The sixth dog had hyposmia, with abnormalities on the electro-olfactogram. Histologic examination was not performed on the 6 dogs that had recovered. Histologic lesions observed at necropsy in 3 dogs that had had clinical signs of acute distemper were those of subacute purulent rhinitis and atrophy of the olfactory epithelium. Altered olfactory function could be explained by mucopurulent exudate blocking odors from olfactory receptors in the acutely affected dogs, but alteration of olfactory function in the dogs that had recovered without clinical evidence of rhinitis could not be explained.

Animals↗
PubMed1988

Preclinical trials using an immunoconjugate of T101 and methotrexate in an athymic mouse/human T-cell tumor model.

We made an immunoconjugate (IC) using the anti-CD5 monoclonal antibody T101 and the chemotherapeutic drug methotrexate. Methotrexate was conjugated to T101 using an active ester intermediate, yielding a drug: antibody molar ratio of 12.4. Although T101 immunoreactivity was not significantly altered by conjugation, the IC did not demonstrate antigen-specific cytotoxicity in vitro. Methotrexate activity, assayed in vitro, decreased approximately 100-fold following conjugation. The IC was tested for in vivo efficacy in athymic mice bearing human T-cell (MOLT 4) xenografts. Experimental arms used in the study included i.p. injections of saline, T101, methotrexate, the IC, and a mixture of T101 and methotrexate. Doses ranged from 500 micrograms T101 (17.5 micrograms methotrexate) to 2 mg T101 (70 micrograms methotrexate). Injections were administered only after palpable tumors were established. In experiments at all doses, totaling 66 animals per arm, injection of the IC significantly inhibited tumor growth, and resulted in more tumor regressions and fewer animal deaths than the other four experimental arms. These data demonstrate that the IC promotes a potential advantage over the use of methotrexate through an increase in the therapeutic index.

Animals↗
PubMed1987

Dysosmia caused by encephalitis in a dog.

A 1- to 2-year-old Beagle was referred for evaluation of a disorder of the sense of smell. The dog had suddenly lost the ability to find rabbits, even though it previously had won field trials. Clinical findings indicated mild encephalitis with some capability to respond to odoriferous stimuli. An unusual test of the sense of smell is described; results indicated some sense of smell, although behavioral response to the odor was inappropriate. It was suspected that canine distemper encephalitis may have been associated with the dysosmia.

Animals↗
PubMed1986

Abnormalities of the brainstem auditory response of the dog associated with equilibrium deficit and seizure.

The brainstem auditory evoked response (BAER) was recorded from 20 dogs, 10 exhibited vestibular deficit, and 10 presented with a history of seizures. Two dogs exhibited both types of signs. Abnormalities of the BAER, prolonged interwave latency, were seen in 8 of the 10 animals with vestibular problems, and in 7 of the 10 animals with seizure history. Several different diagnosis were associated with BAER abnormalities in both groups of animals. In 55.5% of the cases exhibiting abnormalities of the BAER, postmortem evidence of brainstem pathology was not detected. The electroencephalogram (EEG) was normal in three instances of abnormalities of the BAER. The BAER was normal in three dogs with abnormalities of the EEG. The BAER is presented as a useful diagnostic tool for brain lesions in animals with vestibular deficit and seizure history, but appears most useful when used in conjunction with the EEG. Correlations of abnormalities of the BAER and clinical course of disease are discussed.

Animals↗
PubMed1985

Effects of intrajugular hypertonic saline, vaginal distension and vulvar massage on activity of supraoptic neuroendocrine cells.

Activity of 40 single antidromically identified supraoptic neurons was recorded and evaluated in response to a combination of tactile, vulvar massage, vaginal distension, and slow intrajugular 1.2 M sodium chloride infusion in unanesthetized, randomly hydrated ewes. Estradiol-implanted Southdown ewes were prepared according to techniques described by Jennings et al. Only 4 spontaneous firing patterns were observed in the supraoptic nuclei. Analysis of evoked activity indicated that each stimulus evoked alterations in mean firing rates or increased numbers of short interspike intervals in some cells. The resultant activity of units to sequential vulvar massage and 1.2 M sodium chloride infusion suggests a possibility of separate mechanisms of release of oxytocin and vasopressin.

Action Potentials↗