Relationships between the antibacterial activity of sodium hypochlorite and treatment time and biofilm age in early Enterococcus faecalis biofilms.

AIM: To determine the relationships between the antibacterial activity of NaOCl and treatment time and biofilm age in early Enterococcus faecalis biofilms using a linear fitting procedure. METHODOLOGY: Enterococcus faecalis biofilms were formed on hydroxyapatite discs. To investigate the relationship between the antibacterial activity of NaOCl and biofilm age, 22-, 46-, 70- and 94-h-old biofilms were exposed to NaOCl (0-3%) for 5 min. To investigate the relationship between the antibacterial activity of NaOCl and treatment time, 70-h-old biofilms were exposed to NaOCl (0-3%) for 1, 3, 5 and 7 min. After treatment, colony-forming units (CFUs) were counted. To determine the relationships between these variables, linear fitting was performed. RESULTS: The change in the minimum biofilm eradication concentration (MBEC) of NaOCl followed a linear pattern of biofilm age (R = 0.941, R(2)  = 0.886) or treatment time dependence (R = -0.948, R(2)  = 0.898). Below the MBEC, the fitting lines for bacterial CFU count versus NaOCl concentration (R ≤ -0.973, R(2)  ≥ 0.948) in the 22-, 46-, 70- and 94-h-old biofilms implied that the antibacterial activity of NaOCl decreased as the biofilm age increased. The fitting lines for bacterial CFU count versus NaOCl concentration (R ≤ -0.970, R(2)  ≥ 0.942) in the 1-, 3-, 5- and 7-min treatments implied that the antibacterial activity of NaOCl increased with treatment time. CONCLUSIONS: These results suggest that the antibacterial activity of NaOCl against early E. faecalis biofilms in root canals may follow a linear pattern depending on biofilm age or treatment time.

Togetherness among Plasmodium falciparum gametocytes: interpretation through simulation and consequences for malaria transmission.

Previous experimental gametocyte infections of Anopheles arabiensis on 3 volunteers naturally infected with Plasmodium falciparum were conducted in Senegal. They showed that gametocyte counts in the mosquitoes are, like macroparasite intakes, heterogeneous (overdispersed). They followed a negative binomial distribution, the overdispersion coefficient seeming constant (k = 3.1). To try to explain this heterogeneity, we used an individual-based model (IBM), simulating the behaviour of gametocytes in the human blood circulation and their ingestion by mosquitoes. The hypothesis was that there exists a clustering of the gametocytes in the capillaries. From a series of simulations, in the case of clustering the following results were obtained: (i) the distribution of the gametocytes ingested by the mosquitoes followed a negative binomial, (ii) the k coefficient significantly increased with the density of circulating gametocytes. To validate this model result, 2 more experiments were conducted in Cameroon. Pooled experiments showed a distinct density dependency of the k-values. The simulation results and the experimental results were thus in agreement and suggested that an aggregation process at the microscopic level might produce the density-dependent overdispersion at the macroscopic level. Simulations also suggested that the clustering of gametocytes might facilitate fertilization of gametes.

Effects of autonomic blockers on linear and nonlinear indexes of blood pressure and heart rate in SHR.

Recent results in normotensive Wistar-Kyoto (WKY) rats show that nonlinear method may be more specific to quantify sympathetic and parasympathetic activities than the low (LF) and high frequencies (HF) spectral powers of blood pressure (BP) and R-R interval (RR). The present study extends this conclusion to spontaneously hypertensive rats (SHR). Blood pressure was recorded for 30 min before and after intravenous injection of saline, hexamethonium, atropine, atenolol, or prazosin. Mean level, standard deviation (SD), spectral LF and HF components, and three nonlinear indexes (percentage of recurrence, percentage of determinism, and length index of the recurrence plot method) were used to analyze the BP and RR signals. In conscious SHR, sympathetic but not parasympathetic blockade reduced BP level and LF-BP, and increased nonlinear indexes of BP. RR increased after beta-sympathetic and ganglionic blockade, decreased after parasympathetic blockade, and remained unchanged after alpha(1)-sympathetic blockade. SD-RR decreased after ganglionic and alpha(1) blockade, whereas HF-RR increased after beta-sympathetic blockade. The effects on nonlinear indexes of RR are clear and consistent: only alpha(1)-blockade increased the indexes. Our nonlinear indexes may be useful to investigate cardiovascular functions in normotension and hypertension.

[Normal and abnormal daily variability of urinary excretion of albumin]. / Variabilité journalière normale et anormale de l'excrétion urinaire d'albumine.

Urinary albumin excretion (UAE) is very variable from day to day. We analyzed day-to-day UAE in 207 elderly (60-75 years) inpatients (134 with and 73 without diabetes mellitus) attending the department of internal medicine of the Angers University hospital. Twenty-four-hour urine was collected 3 times during a 5-10 day hospitalization period. One-hundred-fifty-one patients (73%) displayed normoalbuminuria (UAE < 30 mg/24 h in 2 or 3 measures) while 56 patients (27%) had microalbuminuria (UAE within 30-300 mg/24 h in 2 or 3 measures). As the raw data of UAE was not normally distributed, we transformed UAE into the variable z = log(log(k+ UAE)) where k is an integer. We found that z has a gaussian distribution for k = 2. Mean value and coefficient of variation of z in the 3 measurements were used to define the level and the temporal intra-individual variability of UAE. Expressed in term of z, the day-to-day intra-individual variability of UAE showed a potent change (from large variability to small variability) at the particular level z = 1.25, corresponding to UAE = 30.8 mg/24 h, which is precisely the level currently used to define microalbuminuria in diabetic subjects.

Estimation of the contact rate in a seasonal SEIR model: application to chickenpox incidence in France.

This work was an attempt at analysing the seasonal pattern of varicella epidemics in France by fitting a susceptibles-exposed-infectives-recovered (SEIR) model with a periodic contact rate function to weekly chickenpox incidence data collected over the period 1991 to 1996. The contact rate was assumed to be either a continuous, or a piecewise constant, periodic function. Both assumptions gave a reasonable fit to the data and yielded estimates of the incubation and infectious periods that were consistent with values derived on clinical or serological grounds. Seasonal fluctuation of the estimated contact rate function was likely to reflect the impact of school holidays on chickenpox diffusion among schoolchildren.

Normal and abnormal day-to-day variability of urinary albumin excretion in control and diabetic subjects.

Urinary albumin excretion (UAE) is very variable from day to day. This variability, more or less potent, might by itself have a patho-physiological significance. We analyzed day-to-day UAE in 207 elderly (60-75 years) inpatients (134 with and 73 without diabetes mellitus) attending the department of internal medicine of the Angers University hospital. Twenty-four-hour urine was collected 3 times during a 5-10 day hospitalization period. One-hundred-fifty-one patients (73%) displayed normoalbuminuria (UAE<30 mg/24 h in 2 or 3 measures) while 56 patients (27%) had microalbuminuria (UAE within 30-300 mg/24 h in 2 or 3 measures). As the raw data of UAE was not normally distributed, we transformed UAE into the variable z=log (log (k + UAE)) where k is an integer and looked for a k value for which z might be normally distributed. We found that z was actually normally distributed for k=2. Mean value and coefficient of variation of z in the 3 measurements were used to define the level and the temporal intra-individual variability of UAE. Expressed in term of z, the day-to-day intra-individual variability of UAE showed a potent change (from large variability to small variability) at the particular level z=1.25, corresponding to UAE=30.8 mg/24 h. This value is precisely the level currently used to define microalbuminuria in diabetic subjects. It is remarkable that the day-to-day variability of UAE collapses when UAE crosses the level which has been used to define microalbuminuria.

Evidence for deterministic chaos in aperiodic oscillations of proliferative activity in long-term cultured Fao hepatoma cells.

The proliferative activity of long-term cultured mammalian cells exhibits traits of a complex dynamic system, with a succession of spontaneous rises and falls in proliferation rate. We analyzed three successive series of proliferation data for the Fao hepatoma cell line in long-term cultures. In the three series the proliferation rate displayed apparently disordered oscillations, which each lasted about 3-5 passages, with variable amplitude and were therefore unpredictable. Such non-linear kinetics raises the major issue of whether these fluctuations are random, or determined and coordinated. We used a graphical method of analysis of the data, which demonstrated that all troughs of proliferation were mathematically related to a common value in each series. This common value was itself related to the maximum level of proliferation of the cell line. Non-linear analysis thus confirmed that the fluctuations in proliferation rate of tumoral Fao cells are, at least in part, determined. This pattern evokes chaotic dynamics and is evidence for the flexible coordination of the complex system linking positive and negative growth regulators in long-term cultured cells.

Epidemiology of chickenpox in France (1991-1995).

STUDY OBJECTIVES: To decide whether a mass immunisation against chickenpox should be or should not be organised, it is important to have up to date data on the disease and to have baseline data to further assess a mass immunisation strategy, if any. DESIGN: Recent chickenpox epidemiology (age and sex distribution, seasonal dynamic and complications) in France are reviewed. SETTING: The system works with about 500 Sentinelle general practitioners (SGPs) and has provided surveillance of frequent communicable diseases in continental France since 1984. PARTICIPANTS: The data were collected by the computerised Sentinelle system. The Sentinelle system uses a videotex server that allows information exchange, data entry, and synthetic return of information. Chickenpox was defined as a sudden onset of typical skin eruption with pruritus, leaving scabs and associated with moderate fever. For each reported case, the SGP gave information on the age of the patient, sex, prevailing childcare for the children, contacts and complications (skin superinfections, lower and upper respiratory infections, conjunctivitis and corneal infections, nervous system injuries, stomatitis and others). Spectral analysis was used to detect cyclical patterns. MAIN RESULTS: Between 1991 and 1995, 15,817 cases of chickenpox were reported and provided the basis for the analysis. The yearly national incidence was 1.0-1.35 cases per 100 inhabitants. A pronounced annual periodicity of the incidence was observed and confirmed by spectral analysis. Ninety two per cent of chickenpox cases occurred in children under 14 years of age with about 5% being under one. Complications were reported in 2% of the cases. Common complications reported were skin superinfections, lower and upper respiratory tract infections. However, 21 cases out of 318 complications were nervous system injuries including six encephalitis or cerebellar ataxia. All these cases recovered completely. CONCLUSIONS: Chickenpox is usually a benign childhood disease. This study affords up to date observations on the disease in France. A large panel of complications has been reported. This paper provides the first attempt to describe the epidemiology of chickenpox in France.

Quantification of sympathetic and parasympathetic tones by nonlinear indexes in normotensive rats.

Because the use of spectral powers of blood pressure (BP) and R-R interval (RR) in the low (LF) and high frequencies (HF) to quantify sympathetic and parasympathetic activities is still under debate, we questioned whether nonlinear methods may give better results. The BP signal was recorded for 30 min before and after intravenous injection of hexamethonium (20 mg/kg), atropine (0.5 mg/kg), atenolol (1 mg/kg), and prazosin (1 mg/kg) in conscious, normotensive Wistar-Kyoto rats. Three nonlinear indexes [percentage of recurrence, percentage of determinism, and length index (Lmax)] extracted from the recurrence plot method were used to analyze the BP signal. Sympathetic but not parasympathetic blockade reduced BP level and its LF component. RR increased and decreased after beta- and alpha-blockades, respectively. Hexamethonium increased HF, and atropine reduced LF, of RR. Sympathetic blockade and, in particular, alpha-sympathetic blockade increased nonlinear indexes of BP. In contrast, parasympathetic blockade by atropine increased nonlinear indexes of RR. These results suggest that, compared with spectral indexes, nonlinear indexes may be more specific markers of sympathetic and parasympathetic tones.

Use of nonlinear methods to assess effects of clonidine on blood pressure in spontaneously hypertensive rats.

In spontaneously hypertensive rats (SHR), chronic infusion of clonidine failed to decrease blood pressure and blood pressure variability. We used nonlinear methods to get a deeper insight on the effects of clonidine on blood pressure dynamics. For 24 h and 4 wk, clonidine (0.1 mg . kg-1 . day-1 sc) was infused by minipumps in the conscious SHRs, and, for comparison, a vehicle was infused in SHRs and in Wistar-Kyoto rats. Blood pressure was recorded for 30 min before and after treatments. We used the Lyapunov exponent, approximated by the inverse of the lmax index derived from the recurrence plot method, to characterize nonlinear dynamics. Before treatment, lmax index of blood pressure was lower (P < 0.01) in the SHRs than in the Wistar-Kyoto rats. Clonidine significantly increased lmax (P < 0.01) to the level observed in normotensive rats, at 24 h and up to 4 wk after infusion. We conclude that clonidine has a significant chronic effect on blood pressure dynamics, as evidenced by nonlinear methods. Our study also suggests that the mechanisms governing blood pressure variations are nonlinear.

Pharmacokinetic-pharmacodynamic model relating spiraprilat plasma concentrations to systemic and regional hemodynamic effects in congestive heart failure.

The aim of this study was to investigate the relations between the plasma concentrations of spiraprilat (the active metabolite of the angiotensin-converting enzyme inhibitor spirapril) and its effects on plasma converting enzyme activity (PCEA), pulmonary capillary wedge pressure (PCWP), and brachial blood flow (BBF), after a single oral administration of 6 mg of spirapril in eight patients with severe congestive heart failure (CHF). Concentrations and effects were determined before and repeatedly during 48 h after drug intake. A sigmoid model was fitted to individual observations. Maximal effects, concentrations inducing half-maximal effects, and Hill coefficients were -99 +/- 2%, 3.9 +/- 1.9 ng/ml, and 2.4 +/- 0.7 for PCEA inhibition, -15 +/- 8 mm Hg, 11.8 +/- 9.2 ng/ml, and 2.6 +/- 1.3 for PCWP decrease, and 36 +/- 19 ml/min, 13.8 +/- 7.6 ng/ml, and 3.3 +/- 1.0 for BBF increase. In severe CHF, although a 14 ng/ml plasma concentration of spiraprilat may induce a 95% inhibition of PCEA, a 30 ng/ml plasma concentration is mandatory to normalize PCWP and BBF. This concentration corresponds to the peak achieved after a 6-mg oral dose of spirapril.

Relationship between diabetic autonomic dysfunction and heart rate variability assessed by recurrence plot.

Beat-to-beat heart rate (HR) and blood pressure were measured by the Finapres system in 44 healthy and 64 diabetic subjects in the at-rest condition. Autonomic control in diabetic subjects was assessed by the Ewing test. HR variability was explored by both linear and nonlinear methods. Linear methods used HR standard deviation and power spectrum. The percentage of the spectrum in the low frequencies was used to assess the sympathetic tone of the autonomic control. The nonlinear method used the "recurrence plot." This method explored long parallel subsequences in the HR time series. These sequences characterize the dependence of the HR dynamics on initial values. The HR standard deviation was reduced in the diabetic subjects compared with the healthy subjects (2.80 +/- 1.17 vs. 3.64 +/- 1.45 beats/min; P < 0.001). In the diabetic subjects, the HR standard deviation and the percentage of the spectrum in the low frequencies showed no correlations with the Ewing score (P > 0.10). In contrast, the longest length index was very strongly correlated to the Ewing score (r = -0.60; P < 0.0001). The results suggest that nonlinear methods might be powerful to explore the autonomic dysfunction in diabetic subjects.

Using the Kalman filter and dynamic models to assess the changing HIV/AIDS epidemic.

Many factors, including therapy and behavioral changes, have modified the course of the HIV/AIDS epidemic in recent years. To include these modifications in HIV/AIDS models, in the absence of appropriate external data sources, changes over time in the parameters can be incorporated by a recursive estimation technique such as the Kalman filter. The Kalman filter accounts for stochastic fluctuations in both the model and the data and provides a means to assess any parameter modifications included in new observations. The Kalman filter approach was applied to a simple differential model to describe the observed HIV/AIDS epidemic in the homo/bisexual male community in Paris (France). This approach gave quantitative information on the time-evolution of some parameters of major epidemiological significance (average transmission rate, mean incubation rate, and basic reproduction rate), which appears quite consistent with the recent epidemiological literature.

[Nyctohemeral rhythm of arterial pressure]. / Les variations nycthémérales de la pression artérielle.

It has long been known that blood pressure (BP) varies over time. Several methods for monitoring BP over the 24-hour cycle are available. The Oxford intra-arterial method is the most accurate but is too invasive to be suitable for routine use. Noninvasive monitors that measure BP intermittently have gained acceptance in clinical practice. The Finapress device provides noninvasive beat-by-beat BP recordings that are useful for studying BP variability. The reproducibility of successive recordings remains controversial. BP recordings with measurements at intervals of up to 15 minutes yield acceptable results provided the duration of the recording is at least 8-12 hours. BP decreases at night. Whether or not BP varies according to a circadian rhythm is unsettled; if a circadian BP cycle does exist, it may be dependent on the sympathetic nervous system. The method of expression of ambulatory BP monitoring data is not well-standardized: the 24-hour mean, daytime and nighttime means, histograms, and the BP load (based on values greater than an arbitrary norm) are the most widely used parameters in clinical practice. Mathematical methods have been developed for processing outlying data (ten methods have been proposed), identifying low-BP and high-BP periods (the "cumulative sum" and "square wave" methods), and modeling the 24-hours BP profile (a four-harmonic Fourier model seems to be the most appropriate model). Variability can be divided into short-term and long-term variability. Many factors influence the BP curve, including genetic factors, age, physical activity, and to a lesser extent psychosensory factors (the "office effect"). Apart from the difference in BP levels, the appearance of the BP curve is similar in normotensive subjects and in subjects with borderline or established hypertension. Ambulatory BP data suggest that the WHO definitions for hypertension may not be appropriate, and the normal values obtained in the meta-analysis by Staessen are now widely accepted. Ambulatory BP data provide better prognostic information that office BP measurements. In drug trials, use of ambulatory BP monitoring may abolish the placebo effect reduce required sample sizes, and provide new information on the pharmacology of experimental drugs.

[Circadian variations of blood pressure]. / Variations circadiennes de la pression artérielle.

Blood pressure (BP) exhibit diurnal variations with low level during night time and high level during daytime. There is little evidence of an endogenous mechanism of BP variations whereas a lot of clues show the contribution of external factors such as activity, mood, postures. Different pathophysiological conditions may alter the pattern of BP circadian variations. This is the case of severe hypertension, hypertension in the elderly and some secondary forms of the disease. Other pathological conditions concerned by BP rhythm alterations are dysautonomia, complicated diabetes, Cushing syndrome, organ transplantations. Methods currently in use to handle data are reviewed.

[Evaluation of the degree of diabetic dysautonomy with the analysis of heart rate measured at rest with the FINAPRES system]. / Evaluation du degré de dysautonomie diabétique par l'analyse de la fréquence cardiaque mesurée au repos par le système FINAPRES.

In this work, we developped the ERK (Eckmann, Ruelle and Khamporst) method of recurrent plots to analyse Heart Rate Variability (HRV), measured by the FINAPRES system in diabetic subjects. Our aim was to search some indices that might characterize the degree of dysautonomy detected in diabetic subjects, using the Ewing tests. The idea was to analyze the recurrences of the HR to previously observed values. When a value of HR, xi measured at the j-th beat come back to an already observed value, we compare the distances between the following measures (xi + 1 to xj + 1), (xj + 2 to xj + 2)... If the distances are under a given criteria during k beats, xi is deterministic of order k. Let n1 be the number of recurrent points and nk the number of k-order deterministic points, with k = 2, 3, 4... We defined the index of determinism nk + 1/nk and the Shannon entropy of the Nk = nk-nk + 1. These indices will be correlated to the total score of the 5 Ewing tests, which represent the standard measure to evaluate the diabetic dysautonomy. Blood pressure (BP) and HR were measured during about 30 minutes using the FINAPRES system in 44 healthy subjects and 60 non-hypertensive diabetic subjects. In the diabetic subjects, the age, the body weight and systolic and diastolic BP were 56 +/- 13 years (mean +/- standard-deviation), 79 +/- 14 kg, 80 +/- 10 mmHg and 137 +/- 20 mmHg. HR was weakly correlated to age (r = 0.29; p = 0.02) and the Ewing score (r = 0.31; p = 0.01). Its standard-deviation is also weakly correlated to age (r = 0.32; p = 0.01) and to the Ewing score (r = 0.34; p = 0.01). Using the ERK method, we obtained indices which are much more correlated to the Ewing score. In particular, the ratio n2/n1 and Shannon entropy were correlated to the Ewing score with r = 0.51 and r = 0.53, respectively (p < 0.0001 in both cases). These indices are also correlated to age (r = 0.40; p = 0.003) in both cases. The ERK method give some indices which are easy to obtain (measurement of HR during a rest period) and easy to interpret. These indices are strongly linked to the dysautonomy score which required a good cooperation of the patient and a great vigilance during its execution. This method could be applied to BP to explore BP regulation in hypertensive subjects.

Antihypertensive effect of drugs: statistical distribution of the trough-to-peak ratio.

Explicit formulas for the distribution function, the expectation, and the variance of the ratio X/Y were calculated, where X and Y are dependent variables. We assumed that the pair (X, Log Y) has a bivariate normal distribution. The work was motivated by a recent draft from the American Food and Drug Administration (FDA) on the treatment of high blood pressure (FDA, 1990, Draft of the Proposed Guidelines for the Clinical Evaluation of Antihypertensive Drugs). The effect of antihypertensive drugs on blood pressure usually achieves a peak level and then decreases to a trough level before the next dose. The FDA recommended that the ratio of trough-to-peak effects should be at least 0.5. It is well known that trough and peak effects are correlated.

A simple computer-assisted method to identify schistosome cercariae.

Several methods have been suggested to identify schistosome cercariae. In the present work, a new method is proposed, based on the analysis of the distribution of sensory endings (sensillae) on the body of the cercariae, revealed by an impregnation with silver nitrate. We determined the mutual distances between the sensillae and calculated the mean values, standard deviations, coefficients of asymmetry, and of kurtosis of the distribution of these mutual distances. Applied to two species, Schistosoma mansoni from Brazil and S. intercalatum from Cameroon, these mutual distances had the same mean value and the same standard deviation but quite different coefficients of symmetry (0.34 +/- 0.11 versus 0.73 +/- 0.08; P < 0.0001) and of kurtosis (-0.82 +/- 0.27 versus -0.58 +/- 0.31; P < 0.0001). The latter two indices were therefore very effective for discriminating the two species. The present method can be applied to other species and to hybrids in the field.

[Identification of subjects at high risk of coronary disease in a working population using a prediction model]. / Identification des sujets à risque élevé de morbidité coronairenne dans une population active française à l'aide d'un modèle de prédiction.

Identification of subjects at high risk of coronary morbidity is of major interest in the prevention of cardiovascular disease. This report describes the use of a multifactorial prediction model for the identification of high risk subjects in a French male population. The PCV-METRA study (Prévention Cardiovasculaire en Médecine du Travail) monitors risk factors of cardiovascular morbidity in a population of men and women employed in big companies in the Paris region. A model adapted from a prediction model conceived by K.M. Anderson et al. in the Framingham study was used. The modified model enables an estimation of individual coronary risk based on 7 factors: age, total cholesterol, HDL-cholesterol, systolic blood pressure, smoking, diabetes and presence of left ventricular hypertrophy, taking into account the relatively low prevalence of coronary heart disease in France. The population comprised 4,131 active men aged 30 to 65 years. The average risk at 5 years was estimated to be 1.6%. Subjects at high risk (over the 80th percentile of the risk distribution curve) usually had high blood pressures and cholesterol levels. However, nearly 30% of these subjects were neither hypertensive nor hypercholesteraemic. It is important to note that 3/4 of these smoked. Moreover, they also had low HDL-cholesterol levels. A risk table, derived from the Framingham model, is presented. This table allows estimation of individual risk at 5 years in men aged 30 to 65 years. In each age group, the comparison of individual risk with the percentiles of risk distribution in the PCV-METRA population allows identification of high-risk subjects. This study proposes a tool for identifying subjects at high risk of coronary morbidity in a French male population. This multifactorial model is particularly useful for detecting subjects with several borderline factors none of which overstep the usually accepted limits.