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Biomedical subjects

R C Hermida

Publications and source records attributed to R C Hermida.

At least 55 records · Page 3Linked to original sources
PubMed1996

Circadian variation of growth hormone secretion in normal prepubertal children. Comparison to constitutional growth delay and growth hormone deficiency.

When studying short slowly growing children, several investigators have found differences in spontaneous circulating growth hormone (GH) levels in some short children as compared with children of normal stature. The circadian and ultradian characteristics of GH secretion have not been considered in most of those studies. With the aim to study possible differences in rhythm characteristics of plasma GH with stature, we analyzed data from a total of 141 prepubertal children: 1) 13 GH-deficient children; 2) 36 children with short stature (up to 2 standard deviations below their peer group mean); 3) 61 children with very short stature (up to 4 standard deviations below their peer group mean); and 4) a reference group of 31 children with standard stature. Subjects were living at the hospital setting on a diurnal waking (07:30 a.m. to 10:30 p.m.), nocturnal resting routine during sampling, consuming the usual hospital diet at fixed times. GH concentrations were determined by immunoradiometric assay in plasma obtained at about 2-3 hour intervals during most of the day and at about half-hour intervals between 9:00 p.m. and 3:00 a.m. Circadian rhythm characteristics obtained by least-squares estimation were compared between groups divided according to gender and stature with a parameter test. Results show a statistically significant circadian rhythm in GH secretion for all groups studied (p<0.001 for standard, short and very short children; p=0.013 for GH-deficient children). A comparison of circadian parameters indicates similar characteristics between subjects of short, very short and standard stature. The difference in rhythm-adjusted mean and amplitude is, however, of borderline statistical [correction of statistically] significance when comparing non-deficient with GH-deficient children.

Body Height↗
PubMed1996

Circadian occurrence of variceal bleeding in patients with liver cirrhosis.

Several clinical events have a rhythmicity over the 24 h period. We assessed the presence of periodic rhythm in the occurrence of haematemesis in patients with liver cirrhosis under different daylight regimens, namely during standard time and during daylight savings. Over a 48 month period there were 212 consecutive admissions of 118 cirrhotics with variceal bleeding. Complete data were available for 181 episodes of bleeding: 121 (66.9%) started with haematemesis and 60 (33.1%) started with melaena. One hundred and two (56%) episodes occurred during daylight savings and 79 (44%) occurred during standard time. The cosinor test showed a 24 h biphasic peak for the occurrence of haematemesis (09.45 and 21.45 h). Moreover, a biphasic diurnal asymmetric frequency was also found by multiple component rhythmometry. The time peaks of onset of variceal haemorrhage did not change significantly during standard time and daylight savings. Patients with more than one haematemesis episode significantly bled over the same time interval. The present study confirms that over the 24 h period variceal bleeding in cirrhotic patients occurs with a predictable rhythmicity that does not seem to be under the control of the light-dark cycle. The finding of a chronorisk for variceal haemorrhage addresses specific questions for pathophysiological studies as well as for new treatment strategies.

Aged↗
PubMed1996

Reproducible and predictable yearly pattern in the incidence of uterine cervical cancer.

A yearly pattern in the occurrence of uterine cervical cancer (UCC), obtained from cytological examinations reported as type V (cases concluding a malignant alteration), has been previously shown for data obtained in the Monterrey Metropolitan Area (state of Nuevo Leon, Mexico) for a span of 10 years (1978-1987), with a peak of relative incidence in the month of February being high stable for consecutive years. With the aim of extending and validating those results, we analyzed the monthly totals of positive detected cases of UCC in the states of Nuevo Leon, Chihuahua, Coahuila, and Tamaulipas (covering most of Northern Mexico) during the same period. To eliminate bias due to the seasonal variation in the number of screening smears, data were first expressed in relation to the number of cytological examinations done the same month. The least-squares fit of a 1-year cosine curve to the data of relative incidence in the four states reveals a statistically significant yearly pattern (p = .008), with a maximum of relative incidence in February almost double that during the rest of the year. Results indicate that the relative incidence of UCC is higher than the yearly average during the winter, with secondary peaks in May and October. In view of the nonsinusoidal waveform in the incidence of UCC, we undertook a multiple-component analysis, allowing several cosine functions to be simultaneously fitted to the data. Results indicate that the yearly pattern in the relative incidence of UCC can be represented by a model that includes two components with periods of 12 and 4 months (p = .004). The same model can be documented as statistically significant independently for each of the four states. These results, summarizing over 2200 positive cases of UCC detected in more than 1,100,000 screening smears, are in full agreement with those found previously for part of the state of Nuevo Leon and reveal a highly stable and predictable yearly pattern of variation in the relative incidence of UCC in Northern Mexico.

Chlamydia Infections↗
PubMed1995

Ultradian rhythms in gross motor activity of adult humans.

During waking h, the existence of ultradian rhythms in gross motor activity has been described in nonprimates, nonhuman primates and newborn humans, but not in adult humans. Some of the previous studies suggested that the appearance of these rhythms could be favored by conditions of isolation and low environmental demands. To confirm the existence of ultradian rhythmicity in the gross motor activity of adult humans and to describe their characteristics, an actimeter was used to record the mobility of 13 adults who remained alone and isolated for 5 h (15:00-20:00) in a monotonous environment with nothing to do. Least squares rhythmometry analysis showed that the gross motor activity of 12 out of 13 subjects had significant rhythms (p < 0.05) within the ultradian band, with periods of between 0.5 and 2.5 h. There were important individual differences between the dominant periods and the same subject might show more than one significant period. These rhythms were stable and they tended to appear immediately the experiment began. The results suggest that a philogenetically old mechanism that organizes gross motor activity in ultradian rhythms exists in adult humans.

Activity Cycles↗
PubMed1995

Temporal (circadian) and functional relationship between atrial natriuretic peptides and blood pressure.

Long-acting natriuretic peptide, vessel dilator, and atrial natriuretic factor consisting of amino acids (a.a.) 1 to 30, 31 to 67, and 99 to 126 of the 126-a.a. atrial natriuretic factor (ANF) prohormone, respectively, circulate in humans and have potent vasodilatory properties. To determine if these atrial natriuretic peptides are directly related to blood pressure in clinically healthy normotensive humans, we obtained 24-h profiles of vessel dilator, long-acting natriuretic peptide, ANF, and blood pressure in 10 men in 1988 and 11 men in 1993 (seven men were studied twice) to compare circulating concentrations of atrial natriuretic peptides with naturally occurring changes in blood pressure. Overall, vessel dilator, long-acting natriuretic peptide, and ANF each had significant (p<0.001) circadian rhythms, with peak concentrations late during sleep (at 04:00 h) being nearly twice their concentrations in the afternoon and evening. This high-amplitude circadian change allowed for the refinement of normal limits for ANF peptides by computing 3-hourly tolerance intervals (chronodesms) against which to compare time-specified single samples for normality. Systolic, diastolic, and mean arterial blood pressure also had significant circadian rhythms (p<0.001) with peaks and troughs that were exactly opposite those of the ANF peptides. In addition to this inverse temporal relationship, there was a significant inverse correlation between absolute values for blood pressure and each ANF peptide (p<0.001), implying a functional relationship. These data suggest that in addition to other well-established neurochemical factors, the ANF peptides (vessel dilator, long-acting natriuretic peptide, and ANF) are important for the maintenance of blood pressure and modulation of its circadian rhythm.

Adult↗
PubMed1994

Circadian variations of portal pressure and variceal hemorrhage in patients with cirrhosis.

This study was aimed at investigating whether portal pressure, which is usually measured in the morning, is subject to circadian variations in patients with cirrhosis. Furthermore, a possible circadian variation for the occurrence of variceal bleeding was also investigated. Ten patients with alcoholic cirrhosis and portal hypertension had serial measurements of portal pressure, evaluated by the hepatic venous pressure gradient (the difference between wedged and free hepatic venous pressures), during a 24-hr period. In addition, a survey of the hour of occurrence of variceal hemorrhage was performed in 101 consecutive cirrhotic patients with hematemesis, in whom the precise moment of onset of bleeding could be determined, and the origin of bleeding was confirmed by emergency endoscopy. Statistical evaluation with the population-mean cosinor method allowed detection of a circadian variation in portal pressure. Portal pressure progressively declined during the afternoon and evening (from 17.9 +/- 5.3 mm Hg at 12 PM to a nadir of 16.8 +/- 4.9 mm Hg at 7 PM (p < 0.05). Thereafter, portal pressure increased during the night, returning to baseline values at 9 AM (18.1 +/- 5.1 mm Hg). The acrophase was at 8:32 AM (+/- 100 min) with an amplitude of 3.45 +/- 1.1 (% of mean +/- S.E.) (rhythm detection: p < 0.03). Similarly, the analysis of the time of occurrence of variceal hemorrhage with the use of a multiple-components rhythmometry test disclosed two peaks in the prevalence of esophageal bleeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Assessment of hypertension based on chronoengineering.

For the study of blood pressure, the use of automatic fully ambulatory recording systems greatly facilitates data collection and, in combination with proper software, the interpretation of results. Hardware for automatic long-term measurement is here wedded to a set of software modules to assess the circadian variability of human blood pressure. To evaluate changes in blood pressure within a day, the authors analyzed 303 series of systolic and diastolic blood pressures and heart rates automatically monitored every 30 minutes for at least 48 hours. Subjects were clinically healthy men and women, 19-23 years of age. Individual circadian rhythm parameters computed for each time series by least-squares rhythmometry were used, first, to assess rhythm characteristics of all subjects and for each gender separately, and, second, to compute a so-called paradesm, a (here 90%) time-specified prediction region for the amplitude-acrophase pair. The limits thus obtained for the circadian amplitude (an index of within-day variability) of blood pressure are exceeded in cases of amplitude-hypertension. Additionally, the original data were also used to compute time-specified tolerance limits for blood pressure and heart rate in clinical health. By the use of these reference standards many false positive and false negative diagnoses can be eliminated. Such reference limits may serve for an objective and positive definition of health, for the screening and diagnosis of disease, and for gauging a subject's response to treatment. The combined hardware-software method for the establishment of time-qualified tolerance limits presented allows the assessment of the extent and timing of rhythmic change and can be used for the interpretation of single values obtained at specified times.

Adult↗
PubMed1993

Circadian time structure of cardiovascular characteristics in human pregnancy.

Conventional time-unspecified single measurements of blood pressure and heart rate may be misleading because they may be influenced, among other factors, by the patient's emotional state, position, diet, and external stimuli. All of these effects depend on the stages of a (mathematical) spectrum of rhythms and trends with age. The evaluation of predictable variability in blood pressure and heart rate by (a) the use of fully ambulatory devices, and (b) chronobiologic data processing, assesses early cardiovascular disease risk, e.g., in pregnancy. We have used this approach to quantify changes in 24-h synchronized (circadian) characteristics of cardiovascular variables in two consecutive pregnancies of a clinically healthy woman. Blood pressure and heart rate were automatically monitored, with few interruptions, at 1-h intervals, each time for at least 48 consecutive h, and for a total of 76 days of monitoring in each pregnancy. Circadian parameters of those circulatory variables were computed for each single day of measurement by the least-squares fit of a 24-h cosine curve. Regression analysis of parameters thus obtained revealed patterns of variation of circadian-rhythm-adjusted means and amplitudes with gestational age. In both pregnancies, the predictable variability of the circadian-rhythm-adjusted mean of blood pressure can be approximated by a second-order polynomial model on gestational age: a steady linear decrease in systolic, diastolic, and mean arterial blood pressure up to the 22nd week of pregnancy is followed by an increase in blood pressure up to the day of delivery. This longitudinal study confirms and extends to ambulatory everyday life conditions the predictable pregnancy-associated variability in blood pressure and heart rate and also allows the establishment of prediction and confidence limits for cardiovascular parameters in a healthy pregnancy.

Blood Pressure↗
PubMed1993

Circannual variation in the incidence of uterine cervix cancer.

The impact of uterine cervix cancer (UCC) can be greatly reduced by regular vaginal examination and other preventive measures. With this aim, UCC screening programs had been developed and applied for several years in Mexico and elsewhere. One point still to be considered in such preventive programs is the possible circannual pattern in the morbidity or mortality of UCC. With the aim of identifying a possible circannual pattern of variation in the incidence of UCC, we analyzed the monthly totals of positive detected cases of UCC in the state of Nuevo León (Mexico) between 1978 and 1987. For eliminating bias due to the seasonal variation in the number of preventive check-ups, data were first expressed in percentage of tests done in the same month. The least-squares fit of a 1-year cosine curve to the data reveals a statistically significant circannual pattern (p = 0.013), with a maximum of relative incidence detected in February. Results indicate UCC incidence higher than the yearly average during the winter, with secondary peaks in August and November. This pattern of variation is similar if one considers separately for analysis the relative incidence of type III, IV, or V UCC (relating to cases suggesting, highly suggesting, or concluding a malignant alteration, respectively). For evaluating the cost-effectiveness of the UCC screening campaign providing these data, the monthly totals of screening check-ups done over the same period were also analyzed. Results reveal a statistically significant circannual rhythm (p < 0.001), with a maximum detected in June.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronobiology Phenomena↗
PubMed1993

Neonatal cardiovascular dynamics in relation to matroclinous and patroclinous history of high blood pressure.

Genetic risk is a primary contributing factor to the predisposition of a newborn child to elevated blood pressure later in life. An index of this factor is needed to assess in the neonate the success or failure of preventive interventions instituted for the pregnant women. This index could be based on characteristics of blood pressure and heart rate variability measured during the first 2 days after birth. In the search for such an index, the systolic and diastolic blood pressures and heart rates of 127 newborn babies were automatically monitored at about 30-min intervals for 48 h with a Nippon Colin device, starting early after birth. Circadian parameters (obtained by the linear least-squares fit of a 24-h cosine curve to each individual series) and descriptive statistics for the three circulatory variables were used in a multiple regression analysis to compute a linear prediction function for the cardiovascular risk score. This score was obtained for each neonate on the basis of the presence or absence of overt cardiovascular disease, elevated blood pressure, or obesity across two generations, those of the newborn's parents and grandparents. Results from regression indicate that the best model includes the circadian amplitudes of systolic and diastolic blood pressure and the circadian ranges of systolic blood pressure and heart rate. The contributions from patroclinous versus matroclinous family history were then compared. Results show that linear prediction models include the same variables for both paternal and maternal cardiovascular risk score. These results provide a neonatal index of cardiovascular risk, to be used later for the evaluation of the effects on the newborn of intervention for the pregnant women.

Blood Pressure↗
PubMed1992

Chronolab: an interactive software package for chronobiologic time series analysis written for the Macintosh computer.

Methods based on periodic regression have been designed for the detection of periodic components in short, noisy, and nonequidistant time series (as they are usually present in medicine and biology). The procedure consists of fitting a set of (cosine) curves to the data, with the analyst choosing the domain of trial periods to be analyzed and the distance between consecutive trial periods. We here describe an interactive program for least-squares rhythmometry written in C language for the Macintosh computer. For any given number of time series to be analyzed at once, the program is able to perform two different kinds of analyses: (a) linear in time, for the sequential fit of trial periods; and (b) linear in frequency, for the sequential fit of harmonic components from an initial fundamental period. For each series and for each trial period fitted to the data, the program gives the following information: fitted period; percent rhythm; p value from testing the assumption of zero amplitude; rhythm-adjusted mean or mesor, amplitude, and acrophase, each with corresponding standard errors and 95% confidence intervals when the component is statistically significant; and (when required by the analyst) p values from tests of sinusoidality, normality of residuals, and homogeneity of variance. Additionally, the program provides a summary report for each time series analyzed, including descriptive statistics such as the number of data analyzed for that series, minimum, maximum, arithmetic mean, standard deviation, standard error, 90% range, and 50% range. The analyst is also able to transform the data before doing any rhythmometric analysis. Transformations already integrated in the program include square root, logarithm, inverse, data as percentage of mean, data as percentage of mesor, and elimination of values outside +/- 3 SD from the mean. When several periods are suspected to be statistically significant, a multiple-component analysis can be also used by the concomitant least-squares fit of several harmonics. The program allows the simultaneous analysis of several periods in several variables from several individuals, with limitations depending solely on internal memory availability and speed requirements from the user. When series from different subjects or different variables in the same subject are available for analysis, a parameter test also included in the program can be used for comparison of rhythm characteristics at any given period. All information required in a single analysis is given by the analyst in the form of self-explanatory commands grouped in different "menus."(ABSTRACT TRUNCATED AT 400 WORDS)

Biometry↗
PubMed1990

Multiple component analysis of plasma growth hormone in children with standard and short stature.

Growth hormone (GH) concentrations (in ng/ml) were determined by radioimmunoassay, in plasma obtained at about 3-hr intervals during a 24-hr sampling span, from 42 boys and 12 girls of short stature (2-4 standard deviations below their peer group mean), and 13 boys and 9 girls of standard stature. Subjects had 11.20 +/- 0.37 years of age at the time of study, and were living on a diurnal waking (approximately 07:30 to approximately 22:30), nocturnal resting routine during sampling. Analysis of these data by single and population-mean cosinor methods as well as by analysis of variance revealed circadian and ultradian prominent components characterizing most groups. Accordingly, a multiple component analysis was undertaken for data of each group separately, as well as for all subjects. A comparison of circadian parameters indicates similar characteristics between short and standard children, whether one compares boys [P = 0.674, 0.371 and 0.749 for comparison of rhythm adjusted means (M), amplitudes (A) and acrophases (phi), respectively], girls (P = 0.993, 0.914 and 0.397), or all children (P = 0.859, 0.712 and 0.865). Differences are found, however, in circasemidian characteristics as well as in the prominent 8-hr ultradian component documented for the short but not for the standard children. These ultradian components should be taken into consideration in the design and later evaluation of a time-specified treatment of children of short stature.

Activity Cycles↗
PubMed1990

Circadian characteristics of plasma cortisol in children with standard and short stature.

Cortisol (CT) concentrations (in micrograms/dl) were determined by radioimmunoassay in plasma obtained at about 3-hr intervals during a 24-hr sampling span from 42 boys and 13 girls of short stature (2-4 standard deviations below their peer group mean), and from a reference group of 11 boys and 10 girls with standard stature, before any treatment were administered to the former. Subjects were 11.20 +/- 0.37 years of age at the time of study, and were living on a diurnal waking (approximately 07:30 to approximately 22:30), nocturnal resting routine during sampling, consuming the usual hospital diet. Circadian rhythm parameters were computed separately for each group by the single and population-mean cosinor fits of a 24-hr cosine curve. A comparison of circadian parameters indicates a statistically significant difference in acrophase (phi; P = 0.033) between short and standard children, as well as added differences in rhythm-adjusted mean (M; P = 0.011) and phi (P = 0.035) between boys and girls of short stature. These differences, as well as any other added information from relevant marker rhythms, should be taken into account for the time-specification of therapy before treatment starts in children of short stature.

Child↗
PubMed1990

Circannual incidence of Giardia lamblia in Mexico.

Giardia lamblia, once considered a harmless commensal organism, has become one of the most common pathogenic intestinal parasites. Evidence for various methods of transmission has accumulated and serious physiological and nutritional disturbances as a result of infestation with this parasite have been clinically documented. Giardia lamblia has now been identified as a causative agent of waterborne, foodborne and sexually transmitted infectious diarrhea. Preventive interventions by health education (especially in personal hygiene) are indicated to reduce its spread in the community. The timing of such educational endeavours may be adjusted to the changes in the incidence of giardiasis if such should be predictable insofar as they are rhythmic. Accordingly, monthly totals of positive detected cases of giardiasis reported in Mexico between 1977 and 1985 were first fitted by linear least-squares with a 1-yr cosine curve. Results indicate a predictable circannual variability of Giardia incidence (P less than 0.001), with a crest time situated on the third week of July and monthly means of detected cases above the yearly average incidence between May and September. The validity of this circannual rhythm was further checked by nonlinear least-squares. Results show a presumably 1-yr synchronized estimated period of 8715.1 hr, with a total predictable change (double amplitude of 1788 cases per month) of 43% the average monthly incidence. Moreover, circannual rhythm parameters computed separately for each consecutive year are similar in terms of acrophase (P = 0.771). Awareness of the thus detected circannual predictable variability in the incidence of giardiasis may be important in the prevention, diagnosis and treatment of this infectious disorder. According to the results here found, the timing of prevention interventions by health education should be a readily exploitable factor.

Animals↗
PubMed1990

Nonparametric testing of melatonin characteristics as potential markers of breast cancer risk.

On the average, the circadian A of ML is larger in clinically healthy women at high vs. low RDBC. The original finding was made without numerical sampling on data from a relatively small group of women sampled systematically around the clock and the year. It was hence of further interest to see whether the risk-related difference can be corroborated by numerical resampling, i.e., by BS, a fairly general, usually computerintensive technique used for estimating the sampling distribution of an estimator or statistic (i.e., a quantity computed from the data). For BS of circannual parameters, one here assumes that 1) circadian As (obtained by the fit of a 24-hour cosine curve by linear least squares) are correlated for any given subject from season to season; and 2) deviations of each circadian A from the average are random. The method then estimates the characteristics of harmonic components, ordered by P-values obtained by linear least-squares analysis involving a test of the assumption of zero A for each special component. Results from BS validate differences in circadian A of ML between the low and high RDBC groups throughout the year. The use of BS serves to introduce inferential considerations into discriminant analysis and to test results obtained with very limited samples sizes, before embarking upon the actual labor-intensive, costly resampling required in circannual and circadian work. BS is a procedure recommended for broad routine use in non-parametric hypothesis testing and biomedical signal simulation. The re-evaluation of ML data by BS provides further inferential statistical validation of the finding as a first complement, not substitute, for additional sampling in order to assess a possibly important component of a test battery for breast cancer risk.

Biomarkers↗