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Biomedical subjects

M Amador

Publications and source records attributed to M Amador.

At least 19 recordsLinked to original sources
PubMed2006

Sample-size requirements for developing strategies, based on the pupal/demographic survey, for the targeted control of dengue.

Several methods to determine the sample size required for a reliable and practical assessment of the number of Aedes aegypti pupae in a community in Puerto Rico have been explored. Because the pupae were highly aggregated, the data were fitted to a negative binomial distribution. Classical statistical-inference methods for sample-size determination demanded the sampling of >3,000 premises for a reliable estimation of the mean number of pupae/person (with a 15% error). This number was reduced to 1,000-1,200 premises after applying a finite-population correction. Database sub-sampling simulations, with increasing sample sizes, showed that the variability in the mean relative abundance of container types and in the mean number of pupae/container substantially decreased after sampling 186 and 310 premises, respectively. Sequential sampling was applied to test the hypotheses that the number of female pupae/person was at least 0.19 (considered the dengue epidemic threshold) or no greater than 0.10 (arbitrarily set as the safe level). After sampling only 25 premises in the first survey and 125 in the second, it was determined that the densities of female pupae were above the epidemic threshold. Thus, sequential sampling provided substantial reductions in the sample size required to determine if vector control was needed. Validation of the Ae. aegypti thresholds required for dengue transmission could confer viability and efficiency to dengue-vector surveillance and control programmes.

Aedes↗
PubMed1999

Absence of impact of aerial malathion treatment on Aedes aegypti during a dengue outbreak in Kingston, Jamaica.

During an outbreak of dengue fever in Jamaica from October to December 1995, a study was carried out to determine the impact of aerial ultra-low volume malathion treatment on adult Aedes aegypti. This was done by monitoring oviposition rates of the vector in three urban communities in Kingston and by exposing caged mosquitoes both directly and indirectly to the aerial malathion treatment. The insecticide was delivered at a rate of 219 mL/ha between 7:10 a.m. and 8:45 a.m. The results of the study clearly showed that the insecticide application was ineffective in interfering with Aedes aegypti oviposition, and adult mosquitoes held in cages inside dwellings were largely unaffected. Consequently, this type of intervention seemed to have little significant impact in arresting or abating dengue transmission.

Aedes↗
PubMed1996

Body mass index at different ages and its association with height at age 14 and with the whole growing process.

The relevance of the association of the body mass index (BMI) at 1,4,6, and 12 years of age with the growing process and its capacity for predicting height at age 14 was investigated in a sample of 354 adolescents (182 boys and 172 girls). Regression analysis showed that body bulk at various ages, as expressed by the BMI is closely related with the height attained at age 14, and longitudinal principal components analysis suggested that it is also associated with the whole growing process. The way in which BMI affects height could be related with the stage of sexual development, which seems to play an intermediate role in the pathway linking body bulk and height.

Adolescent↗
PubMed1996

The relationship of birthweight with height at 14 and with the growing process.

The association of birthweight with length at 12 mo and with height at different ages was assessed in a sample of 260 healthy adolescents (130 boys and 130 girls). The longitudinal study included measures on body weight and height at 4, 6, 12, and 14 yr of age. Birthweight is highly correlated with stature at 14 years, particularly in male adolescents. Longitudinal principal components analysis (LPCA) showed that it is also correlated with the growing process. There is also strong evidence that birthweight can be a good predictor of the onset of the pubertal maturation process.

Adolescent↗
PubMed1995

Discontinuity indices: a tool for epidemiological studies on breastfeeding.

BACKGROUND: The Discontinuity Index (DI), which measures the percentage of infants who were exclusively breastfed (EBF) at the beginning of a given age interval and had abandoned this mode of feeding at its end, and the relative weight of this discontinuation, was introduced and employed in the National Survey on Breast Feeding and Infant Feeding Practices carried out in Cuba in 1990. The aim of this article is to illustrate, through a specific example, the quality of DI as a simple procedure for assessing breastfeeding trends. METHODS: The prevalence of EBF in the 14 provinces of Cuba at discharge from the maternity services and at 30, 60, 120, and 180 days of age, was obtained using data from a national sample of 6661 infants (4820 urban and 1791 rural) which were processed by means of a logistic regression model. Cumulative DI were calculated for the intervals 0-30, 0-60, 0-120 and 0-180 days, and partial DI for the terms 30-60, 60-120 and 120-180 days, for each province and for the whole country. RESULTS: Cumulative DI show the progress of cessation of breastfeeding and are strongly influenced by previous intervals. The Eastern provinces showed the lowest figures at most of the terms. Discontinuation during the first month of life was particularly high in two Western provinces. Partial DI are more specific and allow discrimination of the intervals at which EBF discontinuation is more frequent. The highest values were observed between 4 and 6 months. CONCLUSIONS: Discontinuity indices are useful complements to prevalence rates in epidemiological studies of breastfeeding. The separate analysis of discontinuation in different periods can be highly useful when comparing trends and in the study of the impact of breastfeeding promotion programmes focused on different age intervals.

Age Factors↗
PubMed1995

Mechanism for modulation of nicotinic acetylcholine receptors that can influence synaptic transmission.

Only recently has it been appreciated that neuronal nicotinic ACh receptors (NnAChRs) are highly permeable to Ca2+ and are modulated by Ca2+ in a dose-dependent manner. These findings suggest that Ca2+ could have roles in cholinergic synaptic plasticity. We report a possible mechanism for Ca(2+)-initiated synaptic plasticity that differs from the intracellular Ca2+ cascade associated with plasticity of glutamatergic synapses. Rapid changes in external Ca2+ modulate cholinergic spontaneous synaptic currents in superior cervical ganglionic sympathetic neurons. Inhibition of cholinergic currents by chlorisondamine, which blocks only open channels and becomes trapped in the pore, showed that the modulation is not by a mechanism that activates a previously unresponsive population of NnAChRs. Rather, single-channel recordings with ganglionic NnAChRs from chromaffin cells indicated that Ca2+ directly alters the probability of the channels being open. We hypothesize from the results that activity-dependent decreases in external Ca2+, which occur throughout the nervous system, could directly underlie a rapid negative-feedback mechanism that decreases the responsiveness of NnAChRs at synapses. When external Ca2+ is decreased, presynaptic Ca2+ currents and transmitter release also are diminished. Thus, several mechanisms could combine to potently and rapidly depress synaptic nicotinic receptors until the external Ca2+ concentration recovers.

Animals↗
PubMed1994

Breast-feeding trends in Cuba and the Americas.

In order to analyze breast-feeding trends in the Region of the Americas vis-à-vis trends observed in Cuba, information was culled from a selection of national surveys on the prevalence and duration of breast-feeding conducted in the 1970s and compared with the results of a national survey carried out in Cuba in 1973. Similarly, information from PAHO Document HPN/92.7, which contains reports from countries of the Americas for the period 1986-1991, was compared with the results of the National Survey carried out in Cuba in 1990. A cessation index (CI) was calculated with a view to comparing the relative extent to which the cessation of breast-feeding occurred at different ages in the two time periods. The study revealed a consistent pattern: typically, a relatively high percentage of newborns were initially breast-fed, but the prevalence of exclusive breast-feeding was low and the percentage of breast-fed infants declined quickly. However, the more recent data showed improvements in most of the countries involved with respect to both the prevalence and duration of breast-feeding. Cuba was found to have intermediate values relative to the other countries. Although a slight decline in the initial prevalence of breast-feeding was observed in 1990 (as compared to 1973), notably higher percentages of infants were being breast-fed at 30, 60, 90, and 120 days, and the CI values for the corresponding intervals up to 90 days were lower. These results suggest that positive changes have taken place in factors promoting a longer duration of breast-feeding.

Adult↗
PubMed1994

Percentiles of the waist-hip ratio in Cuban scholars aged 4.5 to 20.5 years.

Values of the waist-hip ratio (WHR), expressed as percentiles and stratified by sex and age, were obtained from a simple judgment sample of 7285 schoolchildren and adolescents (3721 males and 3564 females) aged between 4.5 and 20.5 years. WHR is higher with age in males, and it changes more gradually chronologically also. The graph for males shows three relative maxima at 6, 11-12 and 15-16 years; and for females, two relative maxima at 10 and 13 years. In females, there are two sharp reductions between 10 and 13 and between 13 and 16 years of age. The changes in WHR are associated with age and sexual maturation in both sexes. We conclude that WHR might be useful in assessing body fat distribution in late childhood and adolescence.

Adolescent↗
PubMed1994

[Breast-feeding trends in Cuba and the Americas].

To determine breast-feeding trends in the Region of the Americas and compare them with those observed in Cuba in the last decade, information was complied from a select group of national surveys conducted in the 1970s on the prevalence and duration of breast-feeding and then compared with information from a survey carried out in Cuba in 1973. In addition, data were taken from document HPN/92.7 of the Pan American Health Organization, which contains reports corresponding to the period 1986-1991, and these were compared to the results of the national study carried out in Cuba in 1990. The discontinuation rate (DR) was also calculated. The study found a sustained pattern of initial breast-feeding of a relatively high proportion of babies, with rapid declines in subsequent days and low prevalence of exclusive breast-feeding. In most countries, prevalence and duration showed a tendency to increase. In Cuba intermediate values were observed with a discrete decline in initial prevalence, increases up to 180 days, and lower DR values up to 90 days in 1990 as compared to 1973. This suggests that there have been favorable changes in the factors that help to prolong the duration of breast-feeding. Calculation and analysis of the DR at various intervals proved useful for comparing the trends observed in the different countries.

Adult↗
PubMed1993

[Characteristics of the introduction of foods into the diets of infants in Cuba].

The purpose of this study was to examine the prevailing pattern of introduction of nonmilk foods into the diets of children in Cuba and to assess the degree to which this pattern deviates from internationally accepted recommendations. A cross-sectional study was carried out using a simple random sample of 6,688 children under 1 year of age from all over Cuba. The data were analyzed through logistic regression. The study was carried out in 1990 using the pyramidal structure of the national public health system for the collection of data. Through the status quo method, information was obtained on consumption of four representative foods--juice, vegetables, meat, and fish--and some data were gathered on the child. Consumption prevalence rates were estimated at the beginning and the end of the age ranges (in days) that WHO considers optimum for the introduction of these foods. A marked divergence was found between recommended and actual practice. The recommendations were followed in 3% of the cases for juice, 9% for vegetables, 4% for meat, and 25% for fish. It is noteworthy that noncompliance with the recommendations basically takes the form of early introduction of these foods. The exception is vegetables, which are introduced considerably later than recommended, a fact that seems to reflect a cultural distaste for this food.

Cross-Sectional Studies↗
PubMed1993

[Subscapular/triceps index: percentile values in Cuban children and adolescents].

The percentiles (3,10,25,50,75,90 and 97) of the subscapular/triceps Index (SS/TR), obtained in a sample of 7286 subjects (3721 males and 3765 females) aged 5 to 20 years, were calculated. Median values of SS/TR are generally higher in females up to the age of 13 years approximately, and show a pattern of peripheral distribution of fat during all the period of study. In males, a pattern of central distribution of fat develops starting from age fourteen and becomes more central as age increases. Values obtained were higher than those reported in the literature at all ages and in both sexes. The results reported in this paper show that SS/TR is useful for assessing changes in the pattern of fat distribution during childhood and adolescence.

Adipose Tissue↗
PubMed1992

Calcium modulation and high calcium permeability of neuronal nicotinic acetylcholine receptors.

Two properties were found to distinguish neuronal from muscle nicotinic acetylcholine receptors (nAChRs). First, neuronal nAChRs have a greater Ca2+ permeability. The high Ca2+ flux through neuronal nAChRs activates a Ca(2+)-dependent Cl- conductance, and the Ca2+ to Cs+ permeability ratio (PCa/PCs) is 7 times greater for neuronal than for muscle nAChRs. A second difference between the receptor types is that neuronal nAChRs are potently modulated by physiological levels of external Ca2+. Neuronal nAChR currents are enhanced by external Ca2+ in a dose-dependent manner. The results indicate that changes in extracellular Ca2+ modulate neuronal nAChRs and may modulate cholinergic synapses in the CNS. Also, activation of neuronal nAChRs produces a significant influx of Ca2+ that could be an important intracellular signal.

Adrenal Glands↗
PubMed1992

Nicotinic acetylcholine receptors are directly affected by agents used to study protein phosphorylation.

1. Messenger RNAs for the subunits of the muscle nicotinic acetylcholine receptor (nAChR) were expressed in Xenopus oocytes. A two-electrode voltage clamp was used to measure the acetylcholine (ACh)-induced macroscopic currents. In addition, patch-clamp techniques were used to study nAChR channels in whole cells and in outside-out patches excised from BC3H-1 cells and in patches from oocytes. The single-channel and macroscopic currents were modified by compounds that are usually used to study protein phosphorylation. 2. IBMX (3-isobutyl-1-methylxanthine) is a phosphodiesterase inhibitor. Because it elevates the intracellular concentration of adenosine 3',5'-cyclic monophosphate (cAMP), IBMX is often used to indirectly activate cAMP-dependent protein kinase. H-7 [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine] is mainly used as a rather nonspecific inhibitor of protein kinase activity. Both IBMX and H-7 directly inhibit ACh-induced currents independent of their action on phosphorylation. This direct effect of these compounds is similar to the previously reported inhibition of nAChRs and K+ channels by forskolin, which is commonly used to elevate intracellular cAMP. 3. Macroscopic currents induced in the oocytes by 50 microM ACh had an average peak current of 605 nA, and the currents decayed biexponentially with tau of 15 and 225 s. When 300 microM H-7 was added simultaneously with the ACh, the average peak current was 228 nA and the tau were 1 and 108 s. When 500 microM IBMX was added simultaneously with the ACh, the average peak current was 308 nA and the tau were 9 and 237 s. H-7 and IBMX decreased the peak current induced by ACh, and the compounds increased the decay rate of the current. Under these experimental conditions, the IC50 for reduction of peak amplitude at -30 mV was 160 microM for H-7 and 475 microM for IBMX. 4. H-7 preferentially inhibits the open conformation of the nAChR channel, but there is also some inhibition of the closed channel. The inhibition is voltage dependent: inhibition decreases e-fold per 34 mV depolarization. H-7 does not become trapped within the closed channel and does not significantly alter desensitization under our experimental conditions. 5. H-7 and IBMX interrupt or terminate single-channel openings in membrane patches excised from oocytes or BC3H-1 cells.(ABSTRACT TRUNCATED AT 400 WORDS)

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1992

Adolescent mothers: do they breast-feed less?

Two groups of mothers with infants between sixty and eighty-nine days of age, from the same Health Area of the city of Havana were studied. The first group's age was nineteen years or less and members of the second one were twenty to twenty-five years old. The sociocultural level of the older group was significantly more favourable. The proportion of mothers exclusively breast-feeding was lower among the teenagers, and the frequency of complete weaning by the end of the third month was higher in their group. Duration of breast-feeding, either exclusive or combined with bottle-feeding was also shorter in the group of adolescent mothers, and frequency of diarrheal episodes was higher among their infants; body weight for age and body weight for length showed a shift towards lower percentile channels in these infants. Such differences were evident despite of that both groups of mothers had the same opportunity to receive information about the advantages of breast-feeding and there were no differences in the frequency and quality of prenatal care.

Adolescent↗
PubMed1992

Adiposity and growth: relationship of stature at fourteen years with relative body weight at different ages and several measures of adiposity and body bulk.

A non-probabilistic sample of 354 healthy adolescents (182 boys and 172 girls) with ages ranging from 13.6 to 14.5 years was studied. Measurements of mid-arm muscle, thigh and leg circumferences, triceps and subscapular skinfolds, and records of body weight and height at one, four, six and twelve years of age were available. The sexual maturation stage of all subjects was also determined. Height at fourteen years was found to be significantly associated with relative body weight at different ages in both sexes, and particularly with the relative weight at twelve months. Height is more strongly related with indicators of lean body mass than with indicators of adiposity, especially in boys. The stage of sexual development is also an important determinant of stature at fourteen years of age. The results seem to support the hypothesis that the same factors which increase fat deposition, contribute to increase lean tissues and linear growth.

Adolescent↗
PubMed1991

Protein kinase inhibitor, H-7, directly affects N-methyl-D-aspartate receptor channels.

Compounds commonly used to modify protein phosphorylation have been found to interact directly with K channels, Ca channels, and acetylcholine receptor channels. We report that a general protein kinase inhibitor, H-7, directly affects N-methyl-D-aspartate (NMDA) receptors independent of protein kinase activity. Single-channel records in the presence of H-7 have fewer bursts of activity, and the currents are interrupted in a voltage-dependent manner by brief closures. Hippocampal whole-cell currents induced by NMDA are not decreased by H-7, in part, because the single-channel currents have longer burst lengths that compensate for the brief closures.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗