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Biomedical subjects

L Glass

Publications and source records attributed to L Glass.

At least 37 records · Page 2Linked to original sources
PubMed1993

Selenium status of infants is influenced by supplementation of formula or maternal diets.

Plasma selenium of infants fed proprietary formula was significantly less than that in infants fed human milk. Addition of selenite to the formula (0.253 mumol Se/L) increased plasma selenium and activities of glutathione peroxidase (GPx) and total peroxidase (Px). However, erythrocyte selenium decreased significantly during the 12-wk study in infants receiving human milk or formula with or without supplemental selenite. Infants fed human milk from women receiving 0 or 200 micrograms supplemental selenium as selenomethionine or selenium-enriched yeast had plasma selenium that paralleled changes in their selenium intake. Plasma GPx and Px activities were unrelated to human milk selenium intake. Milk from women given either selenium supplement prevented the decline in infant erythrocyte selenium. Results of these studies suggest that the method of feeding modifies the infant's apparent selenium status and that the molecular form of selenium provided and/or its interaction with other milk constituents are determinants of infant selenium status.

Anthropometry↗
PubMed1993

Selenium status of lactating women is affected by the form of selenium consumed.

The impact of providing selenomethionine (2.7 mumol Se) or selenium-enriched yeast (2.9 mumol Se) on the selenium status of lactating and nonlactating women with customary intakes of approximately 1.3 mumol Se/d was studied. Plasma selenium declined in unsupplemented lactating women but not in nonlactating women. Selenomethionine increased plasma selenium in both lactating and nonlactating women whereas selenium-enriched yeast increased plasma selenium only in nonlactating women. Erythrocyte selenium concentration was not significantly modified by lactation. Plasma glutathione peroxidase (GPx) activity decreased with duration of lactation in unsupplemented women and selenomethionine or selenium-enriched yeast supplementation prevented the decline. Milk selenium declined markedly for 20 wk after parturition in unsupplemented women. Selenomethionine significantly increased milk selenium concentrations whereas selenium-enriched yeast prevented a decline. These results clearly show that the source of selenium provided to lactating women can significantly influence selected indexes of selenium status, including milk selenium concentration.

Adolescent↗
PubMed1993

Mycoplasma hominis and Ureaplasma urealyticum in neonates with suspected infection.

The role of genital mycoplasmas in the pathogenesis of neonatal infection is incompletely understood. We performed nasopharyngeal, blood and cerebrospinal fluid (CSF) cultures for Mycoplasma hominis and Ureaplasma urealyticum in 69 neonates who underwent a diagnostic workup for suspected sepsis. The mean gestational age was 35.9 weeks (range, 25 to 42 weeks) with a mean birth weight of 2386 g (range, 652 to 4420 g). Twenty-seven infants (39.1%) had positive nasopharyngeal cultures; 6 were positive for M. hominis, 10 for U. urealyticum and 11 for both organisms. Seven (26%) of these 27 patients developed chronic lung disease compared with 2 (4.7%) infants in the non-colonized group. Nine infants had positive CSF cultures for M. hominis and one infant had a positive CSF culture for U. urealyticum. All blood cultures were sterile. One of the infants with a positive CSF culture for M. hominis had clinical evidence of systemic infection. All of the infants were treated with antibiotic agents that were not active against mycoplasmas. These data indicate that genital mycoplasmas can be found commonly in the CSF and nasopharynx of infants with suspected sepsis. Their etiologic role in the causation of infection and chronic lung disease, however, remains unclear.

Cerebrospinal Fluid↗
PubMed1993

Time series analysis of complex dynamics in physiology and medicine.

A variety of mathematical methods have been developed to characterize complex rhythms that are observed in physiological systems. These methods include classical techniques such as the mean, standard deviation, and power spectrum, as well as newer methods suggested by nonlinear dynamics including the dimension, Lyapunov number, and entropy. This paper reviews the various ways in which these measures have been applied to analyze physiological dynamics with emphasis on the potential advantages and pitfalls of the various approaches. We conclude that these methods may be useful to help characterize complex time series, but only rarely is it possible to use these methods to establish deterministic chaos in a given time series.

Animals↗
PubMed1992

Phase resetting and fixed-delay stimulation of a simple model of respiratory rhythm generation.

In a previous study (Lewis et al., 1990), the response of the respiratory rhythm to a perturbing stimulus was investigated using two different stimulus protocols: phase resetting and fixed-delay stimulation. The first protocol consists of measuring the effects of perturbing an oscillator at different phases of the cycle on the duration of the perturbed cycle. The resulting phase response curves (PRCs) can be used to characterize the properties of the oscillator (Winfree, 1980). A second protocol, fixed-delay stimulation, involves perturbing an oscillator at a fixed latency from the onset of the cycle, repeated every n-th cycle. If a single stimulus produces an effect that lasts longer than a single cycle, complicated responses can be expected from fixed-delay stimulation (Lewis et al., 1987). A simple three-phase model for respiratory rhythm generation based on a hypothesis by Richter and coworkers (1982, 1983, 1986) was investigated in the context of these experimental studies. Phase resetting and fixed-delay stimulation protocols were simulated in the model. PRCs of the model resemble those obtained experimentally: a phase-dependent prolongation or shortening of the inspiratory phase depending on the stimulus magnitude, and a slight prolongation of the expiratory phase. Stimuli delivered to the model repetitively during successive inspiratory periods at a fixed-delay produced various combinations of shortened and prolonged cycles, similar to those observed in the experiments. However, the marked increases in cycle duration observed in the experiments during, as well as after, stimulation were not evident in the model. These comparisons suggest that (1) PRCs may not be an adequate way to evaluate certain models of rhythmogenesis, and (2) to improve the present simplified formulation of the three-phase model of the respiratory oscillator, time-varying stimulus dependent effects should be incorporated.

Animals↗
PubMed1992

The topology of phase response curves induced by single and paired stimuli in spontaneously oscillating chick heart cell aggregates.

The topological properties of the phase resetting of biological oscillators by an isolated stimulus delivered at various phases of the cycle depend on whether the stimulus is "weak" or "strong." When multiple stimuli are delivered to the oscillator, the response to stimulation also depends on the time between the stimuli, and the rate at which the oscillator returns to an underlying limit cycle attractor. If the time between two consecutive "weak" stimuli is sufficiently short, the effects produced by the pair of stimuli may be characteristic of a single "strong" stimulus. These results are demonstrated in a model experimental system, spontaneously beating aggregates of cells derived from embryonic chick heart, and are illustrated by consideration of a simple theoretical model of nonlinear oscillators, the Poincaré oscillator.

Animals↗
PubMed1992

Possible trazodone potentiation of fluoxetine: a case series.

BACKGROUND: Fluoxetine is an effective serotonin reuptake inhibitor antidepressant that can fail to alleviate either insomnia or major depression in a substantial minority of depressed patients. Trazodone has been reported to be both an effective nonbenzodiazepine hypnotic for antidepressant-associated insomnia and a possible serotonergic antidepressant adjunct. We present a case series of patients with variable responses when trazodone was added to fluoxetine. METHOD: Eight consecutive depressed (DSM-III-R) patients taking fluoxetine were given trazodone either for sleep or as a possible antidepressant potentiator. RESULTS: Three (37.5%) of the eight patients (confidence interval = 4.0%-71.0%) had improvements in both sleep and depression. The remaining five patients either were unaffected by the addition of trazodone to fluoxetine or had intolerable adverse drug reactions. CONCLUSION: Trazodone may be an effective hypnotic and antidepressant potentiator when combined with fluoxetine for some patients, but its use may be limited by adverse effects.

Adult↗
PubMed1992

Predictors of cocaine use in pregnancy.

Several hundred thousand infants are exposed to cocaine in utero every year in the United States. In an attempt to provide services for women abusing drugs, various programs have been proposed for prenatal drug testing. This study was conducted to assess the sensitivity, specificity, and predictive values of screening programs based on a variety of clinical and historical factors. Between October 1988 and March 1989, 1111 parturients who delivered at an inner-city hospital had urine samples and data collected. The urine, linked by code number to the data, which contained no identifiers, was tested anonymously for illicit drugs. We then assessed the associations of a variety of historical and clinical variables with positive toxicologies. An acknowledged history of drug use or a combination of no prenatal care and cigarette use provided the most valid prediction of cocaine use, with a 59.8% sensitivity, 97.5% specificity, 70% positive predictive value, and 94.9% negative predictive value for positive urine toxicologic examinations. The addition of clinical data such as low birth weight did not improve predictive values significantly. Although the use of easily available historical data allowed correct identification of 60% of parturients who used cocaine, no combination of factors could detect all users. If it is considered beneficial to identify all users at a given point, then urine toxicology screening would be more appropriate than sole reliance on patient history.

Cocaine↗
PubMed1991

The biologic and social consequences of perinatal cocaine use in an inner-city population: results of an anonymous cross-sectional study.

Cocaine use among pregnant women and reports of its adverse perinatal consequences have increased substantially over the past 10 years. However, most researchers have studied patients registered at drug treatment centers or have relied on voluntary participation by patients, either of which introduces the possibility of selection bias. To determine the frequency and consequences of prenatal cocaine use among an unselected inner-city obstetric population, we collected urine samples from parturient women at a municipal hospital and anonymously tested these specimens for metabolites of cocaine, marijuana, opiates, and methadone. Urine specimens, with linked obstetric data sheets, were available from a study population of 1111 patients, and pediatric data sheets were available for 846 mother-infant pairs. Cocaine metabolites were found in 11.5% of the urine samples collected, whereas metabolites of marijuana, opiates, and methadone, respectively, were present in 1.1%, 1.2%, and 0.3% of the specimens. Cocaine users were more likely than nonusers to have had no prenatal care (51% vs 8.8%; p less than 0.0001), to be American-born rather than Caribbean-born (71% vs 33%; p less than 0.001), and to have a higher parity (1.83 vs 1.14; p less than 0.0001). Infants of cocaine users had a lower mean gestational age (-0.93 weeks; p less than 0.01), a lower mean birth weight (2560 +/- 788 vs 3151 +/- 699 gm; p less than 0.001), and an increased probability of having an Apgar score of less than 7 at 5 minutes (12.5% vs 3.2%; p less than 0.0001). Multiple linear regression analysis that isolated confounding variables such as the presence or absence of prenatal care, maternal age and parity, and the use of cigarettes and alcohol did not substantially affect the differences described above. The effect of cigarette smoking on reducing fetal size was cumulative. In conclusion, cocaine is the most commonly used illicit drug among parturients in this community and is strongly associated with underutilization of prenatal care services. Infants of cocaine users are more likely to be preterm and depressed at birth and to have a low birth weight. Cocaine use, through the above-noted effects, increases the need for prenatal care while simultaneously decreasing the likelihood that it will be obtained.

Adult↗
PubMed1991

A unified model of atrioventricular nodal conduction predicts dynamic changes in Wenckebach periodicity.

The atrioventricular (AV) node responds in a complex fashion to changes in activation rate. A variety of approaches have been used to explain these dynamic AV nodal responses, but none has been able to account fully for AV nodal behavior. Three specific rate-dependent properties of the AV node have been described: 1) time-dependent recovery after excitation, 2) an effect of short cycles to advance recovery ("facilitation"), and 3) a gradual slowing of conduction in response to sustained, high-frequency activation ("fatigue"). We hypothesized that a model incorporating quantitative descriptors of all three processes might be able to account for a wide variety of AV nodal behaviors. Quantitative descriptors of AV nodal recovery, facilitation, and fatigue were developed based on AV nodal conduction changes during selective pacing protocols in seven autonomically blocked dogs. These descriptors were incorporated into a set of mathematical equations that define AV nodal conduction of any beat based on activation history. The equations were then applied to predict pacing-induced Wenckebach periodicity in each dog. Experimental data were obtained after nine to 19 step decreases in atrial cycle length into the Wenckebach zone in each animal. Observed behaviors included complex patterns of block, a progressive increase in the level of block over 5 minutes of rapid pacing, and periods of alternating patterns of block. The model accurately predicted the onset of AV block at each cycle length, the relation between conduction ratio and cycle length as a function of time, and the changing patterns of Wenckebach periodicity during sustained atrial pacing. All three terms of the model equation (describing recovery, facilitation, and fatigue) were essential to account fully for the observed behaviors. Elimination of AV nodal fatigue from the model resulted in failure to account for time-dependent changes in Wenckebach patterns, whereas exclusion of facilitation led to consistent overestimation of the degree of AV block at each cycle length. We conclude that a mathematical model incorporating terms to describe recovery, facilitation, and fatigue accurately predicts a wide range of Wenckebach-type behavior and that complex conduction patterns of the AV node can be fully accounted for by simple functional AV nodal properties.

Animals↗
PubMed1991

Evolution of rhythms during periodic stimulation of embryonic chick heart cell aggregates.

During periodic stimulation of spontaneously beating chick heart cell aggregates, there is often an evolution of coupling patterns between the stimulator and the aggregate action potential. For example, at rapid stimulation frequencies, a rhythm that is initially 1:1 (stimulus frequency:aggregate frequency) can evolve to other rhythms such as 5:4 and 4:3. Time-dependent effects generated during periodic stimulation are characterized by three types of experiments to determine 1) the effect of periodic stimulation on the intrinsic cardiac beat rate (overdrive suppression), 2) the effect of periodic stimulation on the phase resetting properties of the aggregate, and 3) the time-dependent changes in the coupling patterns between the stimulator and the aggregate during periodic stimulation. The protocols involved variations in the duration and rate of periodic stimulation. A mathematical model is developed in the form of a two-dimensional finite difference equation based on the data from experiments 1 and 2. The model is used to predict the data generated by experiment 3. There is good correspondence with the experiments in that the theory reproduces complex transitions between various rhythms and displays irregular rhythms similar to those observed experimentally. These results have implications for the evolution of cardiac arrhythmias such as atrioventricular heart block and modulated parasystole.

Animals↗
PubMed1990

Chaos in multi-looped negative feedback systems.

Non-linear control systems with multiple negative feedback loops display periodicity, quasiperiodicity and period-doubling bifurcations leading to chaos. The possibility that normal fluctuations in physiological control may result from deterministic chaos in multi-looped negative feedback systems is discussed.

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