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Biomedical subjects

L Glass

Publications and source records attributed to L Glass.

At least 91 records · Page 5Linked to original sources
PubMed1983

Phase locking of the respiratory rhythm in cats to a mechanical ventilator.

Mechanical ventilation of paralyzed, pentobarbital-anesthetized adult cats was performed while recording phrenic nerve activity. The periodic changes in lung volume owing to mechanical ventilation affected the rhythm of central respiratory activity, resulting in a variety of regular and irregular patterns of coupling between respiratory system output, monitored by phrenic activity, and the mechanical ventilator. Phase-locked patterns, in which phrenic burst onset occurred at specific and repetitive phase(s) of the mechanical ventilator, with ratios of ventilator frequency: phrenic burst frequency of 1:2, 1:1, 3:2, 2:1, and 3:1 were observed. Regular and irregular patterns occurred over specific ranges of frequency and volume of the mechanical ventilator. A careful study was made of the 1:1 phase locking as the frequency and inflation volume of the mechanical ventilator were changed. The inspiratory time (TI) was defined as the interval between the time when phrenic activity began to rise and the onset of its rapid decline, and the expiratory time (TE) as the time between inspirations. In the 1:1 phase-locking region, as the frequency of the ventilator was increased both TI and TE decreased, and the phase of phrenic onset in the ventilator cycle changed. During ventilation with frequencies higher than the intrinsic phrenic frequency (initial burst frequency of phrenic activity with the ventilator turned off) inspiratory activity was prematurely terminated by lung inflation (Hering-Breuer inspiratory inhibitory reflex). During ventilation with frequencies lower than the intrinsic phrenic frequency, the onset of phrenic activity was delayed (TE was prolonged) by lung inflation (Hering-Breuer expiratory promoting reflex).

Animals↗
PubMed1983

Genetic linkage studies with cleft lip and palate: report of two family studies.

Genetic linkage studies are reported on two families with cleft lip +/- cleft palate. For the first family (LP01) the etiology of the clefting is unknown, and the linkage analyses were done assuming both autosomal dominant and autosomal recessive inheritance. Close linkage is rejected with the Duffy blood group under the dominant model and with four loci (Duffy, Kidd, and ABO blood groups and haptoglobin) under the recessive model. The second family (LP02) is a Mexican-American family segregating the van der Woude syndrome with lip pits. The linkage analyses for this autosomal dominant trait excluded close linkage with seven genetic markers, including three on chromosome one. The maximum lod scores were 0.6 with BF (chromosome 6) and 0.4 with the P blood group, which is not yet mapped.

Cleft Lip↗
PubMed1982

Phase locking, period doubling bifurcations and chaos in a mathematical model of a periodically driven oscillator: a theory for the entrainment of biological oscillators and the generation of cardiac dysrhythmias.

A mathematical model for the perturbation of a biological oscillator by single and periodic impulses is analyzed. In response to a single stimulus the phase of the oscillator is changed. If the new phase following a stimulus is plotted against the old phase the resulting curve is called the phase transition curve or PTC (Pavlidis, 1973). There are two qualitatively different types of phase resetting. Using the terminology of Winfree (1977, 1980), large perturbations give a type 0 PTC (average slope of the PTC equals zero), whereas small perturbations give a type 1 PTC. The effects of periodic inputs can be analyzed by using the PTC to construct the Poincaré or phase advance map. Over a limited range of stimulation frequency and amplitude, the Poincaré map can be reduced to an interval map possessing a single maximum. Over this range there are period doubling bifurcations as well as chaotic dynamics. Numerical and analytical studies of the Poincaré map show that both phase locked and non-phase locked dynamics occur. We propose that cardiac dysrhythmias may arise from desynchronization of two or more spontaneously oscillating regions of the heart. This hypothesis serves to account for the various forms of atrioventricular (AV) block clinically observed. In particular 2:2 and 4:2 AV block can arise by period doubling bifurcations, and intermittent or variable AV block may be due to the complex irregular behavior associated with chaotic dynamics.

Arrhythmias, Cardiac↗
PubMed1982

An interactive computer graphic system for 3-d stereoscopic reconstruction from serial sections: analysis of metastatic growth.

An interactive computer graphic system has been developed for 3-D reconstruction of stained serial sections. The system has been used for 3-D reconstruction of portions of mouse lung containing melanoma nodules. A stereoscopic color picture of a wire model of the reconstructed object is produced. The volume, surface area, and sphericity index of structures such as tumor nodules can be computed.

Animals↗
PubMed1981

Phase locking, period-doubling bifurcations, and irregular dynamics in periodically stimulated cardiac cells.

The spontaneous rhythmic activity of aggregates of embryonic chick heart cells was perturbed by the injection of single current pulses and periodic trains of current pulses. The regular and irregular dynamics produced by periodic stimulation were predicted theoretically from a mathematical analysis of the response to single pulses. Period-doubling bifurcations, in which the period of a regular oscillation doubles, were predicted theoretically and observed experimentally.

Animals↗
PubMed1981

Effect of CSF on bacterial growth.

The growth patterns of five potentially pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, group B beta-hemolytic streptococcus, and Klebsiella pneumoniae) and a commonly encountered, nonpathogenic microorganism (S epidermidis) were compared using CSF, trypticase soy broth (TSB), and a phosphate buffer. Each grew less in CSF than in TSB. Escherichia coli was least affected with a median difference of 2 logarithms between CSF and TSB at 24 hours of growth, whereas S epidermidis was markedly inhibited, with a median difference of 6.85 logarithms. The differences among the remaining four organisms ranged from 3.86 to 5.94 logarithms, all significantly greater than that for E. coli. Similar results were obtained at 48 hours of growth. The non-support of bacterial growth by CSF may constitute a host defense mechanism. The basis of these observations may be the presence of inhibitors or the absence of nutrients required for bacterial growth in the CSF.

Bacteria↗
PubMed1981

Relationship of thyroid hormone levels to the severity of the narcotic withdrawal syndrome.

Serum T3, T4 and thyroid stimulating hormone (TSH) were evaluated in 24 neonates of mothers taking methadone and compared with 16 normal controls using cord serum and serum taken on days 1, 2, 3, 4, 7, and 14. Patients were divided into treated (Rx; n = 14) and not treated (No Rx; n = 10) groups based on withdrawal scores and correlated to thyroid hormone levels. T4 levels were greater in the Rx group when compared to controls on days 2, 4 and 7 (p less than 0.01) and when compared to the No Rx group on days 3 and 7 (p less than 0.005). No Rx patients had higher T4 levels when compared to controls on day 4 (p less than 0.05). In general T3 levels paralleled T4 results. TSH levels were decreased in the Rx group compared to No Rx and controls on day 2 (p less than 0.01). Lipsitz scores correlated with T4 levels on days 3, 4, and 7 in methadone patients (p less than 0.05) but did not correlate with T3 or TSH. These findings suggest a correlation between the severity of withdrawal symptoms and T4 and T3 levels.

Female↗
PubMed1981

Indentikit Model II--a potential tool for judging cosmetic appearance.

The purpose of this paper is to introduce the Identi-kit Model II as a tool for investigation of social reactions to cosmetic variations associated with facial anomalies. In one study, a group of judges rated cosmetic appearance from photographs, while another group rated cosmetic appearance from Identi-Kit constructions. A high correlation was found between ratings obtained from the two sets of stimuli. In a second study, three groups of different judges rated cosmetic appearance of Identi-Kit constructions with three types of facial stigmata associated with facial clefting. Ratings of appearance were found to vary systematically as the number of stigmata were increased. Based on the findings of these studies, the authors suggest that Identi-Kit constructions may be useful for investigating the effects of changing specific facial characteristics while holding others constant.

Adolescent↗
PubMed1981

Three dimensional reconstruction of disseminated cancer modules.

A computer system which can be used to perform three dimensional reconstruction of dispersed cancer growth from serial sections is described. The system was used to reconstruct and analyze melanoma nodules growing in the left upper lobes of the lungs of seven mice following intravenous inoculation of a single cell suspension of melanoma cells. The analysis shows a great variability in the tumor size within a single mouse, and also in different mice. The preponderance of tumors (40 out of 50) were subpleural and extended to the surface of the lung at some point. An analysis of the spatial distribution of the tumors was performed which indicates that the tumors may not be randomly dispersed in the lungs. The mechanisms which could lead to the observed results are discussed.

Animals↗
PubMed1981

Intrauterine exposure to narcotics and cord blood prolactin concentrations.

Umbilical cord serum prolactin concentrations were determined in 17 full-term infants of mothers using narcotic agents during pregnancy and in 18 infants of similar birth weight and gestational age whose mothers did not use narcotics. The median value for the narcotic-exposed group was 266.6 ng/ml (range, 157.5 to 448.7 ng/ml); in the normal group the median was 193.7 ng/ml (range, 69.8 to 693.1 ng/ml). These differences were statistically significant (P less than .05). Although only full-term and borderline premature infants who were not appreciable risk for respiratory distress syndrome (RDS) were studied, it may be speculated that elevated prolactin blood levels in fetuses of addicted mothers may at least in part explain the reported decrease in the incidence of RDS in this group.

Birth Weight↗
PubMed1980

The effects of presentation of noise and dental appliances on speech.

The effects of dental appliances on speech were studied when subjects wore the appliances, both in quiet and in the presence of an intense noise. A group of 24 normal-speaking subjects read lists of syllables, words, and sentences and spoke spontaneously in each of six appliance and noise conditions. Several acoustic and perceptual measurements were made in each condition. In general, speech deteriorated when appliances were placed and when noise was presented. The type and amount of speech disruption varied as a function of speech task and aspect of speech. There was no evidence that the effects of appliances on speech differed in quiet and noise conditions. Inter-subject variability was large.

Adult↗
PubMed1980

Effects of methadone on thyroid function in mother, fetus, and newborn.

The effects of maternal use of methadone during pregnancy on tests of thyroid function were studied in 14 women and their offspring. Twelve normal nonaddicted women and their infants served as a control group. Concentrations of thyrotropin (TSH), thyroxine (T4), and triiodothyronine (T3) were not significantly different in maternal and cord serum, and in infant serum at age 24 hours. There was no significant difference in infants' TSH concentrations at 2, 3, and 7 days of age. At 2 and 7 days, T3 levels were significantly higher in the methadone than in the control group (P = .01 and less than .01, respectively). At 3 days, differences were of borderline significance (P = .08). Increased T4 levels in the methadone group of infants were statistically significant at 2 days (P less than .01) and at 3 and 7 days (P = .05). The mechanisms responsible for the biochemical evidence of hyperthyroidism were not determined, but may have been related to altered autonomic function and/or increased metabolic activity which occurs during neonatal narcotic withdrawal.

Adolescent↗
PubMed1979

Structure and dynamics of neural network oscillators.

Techniques are given to represent oscillating neural networks by asynchronous logical switching networks, and to analyze the oscillating networks using a directed graph called a state transition diagram. Consideration is restricted to network oscillators containing no rhythm determining pacemaker neurons, and no neurons exhibiting self-limiting properties such as post-inhibitory rebound or accumulating refractoriness. In the state transition diagrams, stable oscillations are associated with a particular geometric configuration called a cyclic attractor (the heavy cycle in Fig. 2). We show that given the network connectivity it is possible to predict autonomous dynamic behaviour, as well as behaviour following hyperpolarizing or depolarizing inputs to neurons of the network. Conversely, given information about patterns of firing activity during cycles and transients of neural networks, the network connectivity can be predicted. The theoretical techniques can be used to generate a census of network structures capable of generating stable oscillations. Several representative network oscillators are discussed in the context of previous theoretical and experimental studies of the structure of neural network oscillators. Although the number of theoretically possile network oscillators capable of generating sustained oscillations is very large, the techniques which are given should be useful in the design of experiments capable of distinguishing between equally plausible hypotheses.

Action Potentials↗
PubMed1979

A simple model for phase locking of biological oscillators.

A mathematical model is presented for phase locking of a biological oscillator to a sinusoidal stimulus. Analytical, numerical and topological considerations are used to discuss the patterns of phase locking as a function of amplitude of the sinusoidal stimulus and the relative frequencies of the osillator and the sinusoidal stimulus. The sorts of experimental data which are needed to make comparisons between theory and experiment are discussed.

Biological Clocks↗