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Biomedical subjects

L Navarrete

Publications and source records attributed to L Navarrete.

17 recordsLinked to original sources
PubMed2006

Population cycles produced by delayed density dependence in an annual plant.

In contrast to insect and animal populations, little attention has been directed to the study of cycles in plant populations. It has been argued on theoretical grounds that plants present stable dynamics. Nevertheless, there are examples where plant populations appear to exhibit oscillatory dynamics, but the oscillatory signal is variable and comes from very short time series data. Using a combination of time series, models, and empirical results, we present evidence of population cycles for Descurania sophia in a 16-year field experiment. Endogenous and exogenous causal mechanisms were studied to identify processes underlying this temporal dynamic. Our results show a 4-year cycle produced by delayed density dependence. We suggest that high nutrient levels might be responsible for the observed dynamics of D. sophia. Our results suggest that although plant population dynamics may be stabilized by direct density dependence, delayed density dependence could destabilize dynamics.

Brassicaceae↗
PubMed1997

Reclassification after delivery of diabetes in pregnancy.

Gestational diabetes mellitus (GDM) constitutes a risk factor for the development of non insulin-dependent diabetes mellitus (NIDDM). The search for parameters to provide discrimination between a high risk and a low risk for future development of NIDDM is today the aim of many investigations. The absence or presence of several factors such as glycemia during pregnancy and post partum, the need for insulin treatment, disorders of the pancreatic insulin secretion, the number of pregnancies, maternal obesity, the early diagnosis of GDM, the family history of diabetes mellitus, the race and immune disorders give rise to a very high relative risk (RR) of developing NIDDM. To know the degree of risk will allow a future appropriate clinical intervention to reduce the incidence of NIDDM and its economic cost.

Adult↗
PubMed1997

Autoimmune thyroid disease and insulin-dependent diabetes mellitus during pregnancy and post partum.

The aim of this study was to assess thyroid dysfunction and autoimmunity in pregnant insulin-dependent diabetes mellitus (IDDM) women during pregnancy and early post partum. Fifteen pregnant IDDM women and 77 healthy pregnant women were studied. Free T4, TSH, TPO-Ab and Tg-Ab were assayed during the first and third trimester of pregnancy and 3 months post partum. In IDDM women FT4 levels significantly decreased (p < 0.05) during third trimester and 3 months post partum and also TPO-Ab during third trimester (p < .01). 26% of IDDM and 4% of the controls presented post partum thyroid dysfunction. We recommend that prepregnant IDDM be screened for TPO-Ab. Those with a positive result would be followed with serial monitoring of free T4 and TSH levels during each trimester as well as during the post partum period.

Adolescent↗
PubMed1993

Thyroid function parameters and TSH-receptor antibodies in healthy subjects and Graves' disease patients: a sequential study before, during and after pregnancy.

The changes in thyroid function and in TSH receptor antibody titers were analyzed in a prospective sequential study before, during and after pregnancy in a group of 15 healthy women and 45 patients with Graves' disease. Twenty-five patients with Graves' disease were untreated before pregnancy (Group A) and twenty treated with carbimazole throughout pregnancy (Group B). In healthy pregnant women serum FT4 levels were slightly but significantly elevated early in pregnancy (p < 0.05) and lower during the third trimester (p < 0.01), compared to pregestational values (although within the reference range of nonpregnant subjects). During postpartum, serum FT4 reverted to values similar to those found before pregnancy. Serum TSH levels showed a slight increment during gestation with a significant decrease (p < 0.01) in the early postpartum period. There was a significant increase in serum thyroglobulin (Tg) during the first trimester (p < 0.01); Tg levels remaining markedly elevated throughout gestation. After delivery, Tg progressively decreased, but were still above normal, six months later in 27% of subjects. TSH-receptor antibody titers were normal but tended to decrease during late gestation; a significant rebound was observed in late postpartum, even though most individual values remained in the normal range. When we compared "active" and "remission" Graves' disease patients, the concentration of FT4 was significantly higher in group B ("active") than in group A ("remission" (p < 0.01) during early gestation. Serum Tg was also significantly higher in Group B than in Group A before pregnancy (p < 0.01), and during late gestation and postpartum (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Reverse use-dependent effects of sotalol demonstrated by recording monophasic action potentials of the right ventricle.

In 22 patients referred for electrophysiologic study, monophasic action potentials (MAP) were recorded from the right ventricular aspect of the ventricular septum. The duration of MAP at 90% (MAP90) and 30% (MAP30) repolarization was measured in sinus rhythm, at a constant atrial paced cycle length of 600 ms for 3 minutes and at constant ventricular paced cycle lengths of 600, 500, 400 and 300 ms for 20 beats. Programmed ventricular stimulation from the apex of the right ventricle was performed at a basic drive cycle length of 400 ms and MAP90 and MAP30 of premature beats was determined. Changes of MAP duration were assessed 20 minutes after administration of intravenous sotalol 1.5 mg/kg. Sotalol significantly increased MAP90 and MAP30 in sinus rhythm. This was independent from sinus cycle length prolongation as evidenced by a significant prolongation of MAP90 and MAP30 with constant atrial pacing after sotalol. With slow ventricular stimulation frequencies and with long coupling intervals at programmed ventricular stimulation, sotalol significantly prolonged MAP90 and MAP30; with high stimulation frequencies and at short coupling intervals the action potential-prolonging effect of sotalol was diminished, indicating a reverse use-dependent effect of sotalol on repolarization of the right ventricle in humans.

Action Potentials↗