Interlaboratory Study of a Multiresidue Gas Chromatographic Method for Determination of Organochlorine and Pyrethroid Pesticides and Polychlorobiphenyls in Milk, Fish, Eggs, and Beef Fat

An interlaboratory study was conducted to validate a gas chromatographic (GC) method for determination of 21 organochlorine pesticides, 6 pyrethroid pesticides, and 7 polychlorobiphenyl (PCB) congeners in milk, beef fat, fish, and eggs. The method was performed at low contamination levels, which represent relevant contents in food, and is an extension of the European standard (method NF-EN-1528, Parts 1–4). It enlarges the applicable scope of the reference EN method to pyrethroid pesticides and proposes the use of solid-phase extraction (SPE) as a cleanup procedure. Cryogenic extraction was made, and SPE cleanup was performed with 2 successive SPE cartridges: C18 and Florisil®. After injection of the purified extract onto a GC column, residues were measured by electron capture detection. Food samples (liquid milk, beef fat, mixed fish, and mixed eggs) were prepared, tested for homogeneity, and sent to 17 laboratories in France. Test portions were spiked with 27 pesticides and 7 PCBs at levels from 26 to 45, 4 to 27, 31 to 67, and 19 to 127 ng/g into milk, eggs, fish, and fat, respectively. Based on results for spiked samples, the relative standard deviation for repeatability ranged from 1.5 to 6.8% in milk, 3 to 39% in eggs, 4.5 to 12.2% in fish, and 7 to 13% in fat. The relative standard deviation for reproducibility ranged from 33 to 50% in milk, 29 to 59% in eggs, 31 to 57% in fish, and 30 to 62% in fat. This method showed acceptable intra- and interlaboratory precision data, as corroborated by HORRAT values at low levels of pesticide and PCB contamination. The statistical evaluation of the results was performed according to the International Organization for Standardization (ISO; ISO 3534 standard) and 5725-2 Guideline.

[Evaluation of the ExSel® self-questionnaire to screen for an excess salt intake in patients followed in a nephrology consultation]

AIM

To evaluate the reliability of the ExSel® self-questionnaire to detect an excess salt intake (≥12g/24h) in patients consulting for hypertension and/or renal failure.

METHODS

Results of the ExSel® self-questionnaire were compared to 24h sodium excretion using the Cohen's kappa test and a Chi² test. Sensitivity, specificity, VPP and VPN were calculated. A ROC curve was realized to find an accurate cut-off.

RESULTS

Mean characteristics of the 101 patients with reliable results were: age of 67±12 years, Body Mass Index 28.4±5.6kg/m², SBP/DBP 139±23/74±13mmHg (98% were hypertensives. Mean salt intake was 7.5±3.1g/24h and mean creatininuria was 13.9±20.1mmol/24h. An excess salt intake (≥12g/24h) was observed in 8% of the patients. The Kappa test at 0.17 and the Chi² at 0.66 signify that the agreement was very low. Sensitivity was 37%, specificity 90%, PPV 20% and NPV 94%. The AUC under the ROC curve was too low (0.665) to determine a threshold adapted to the renal patients.

CONCLUSIONS

The ExSel® autoquestionnaire is not adapted to outpatients, mainly hypertensives (98%) followed in a nephrology consultation to detect an excess salt consumption.

Study of relationship between volume of distribution and body weight application to amikacin

Amikacin use is difficult because of its narrow therapeutic and its pharmacokinetic variability. This variability of amikacin is not well known. To adapt amikacin the physician assumes that there is a linear and continuous relation between the volume of distribution and the body weight. The objective of our study was to evaluate the relationship between the volume of distribution (Vd) and the body weight (BW) using a non parametric statistical analysis of dependence so called Z method. Retrospective pharmacokinetic population study and statistic analysis. 872 patients receiving intravenous amikacin. The volume of distribution was modelled using the Non Parametric Adaptive Grid algorithm (NPAG) for a two-compartment model with intravenous infusion. Z coefficient was performed to evaluate the relationships between Vd and BW. For the 872 patients (mean age of 73 ± 17 years) dispatched as follow 53 % female and 47 % male, the analysis of the statistical relationships by the non parametric Z analysis showed a scattered linkage between Vd and BW. For the whole population, the relationship between Vd and BW was not linear (regression analysis). Z analysis demonstrated that only for 80 % of patients there is a relationship between Vd and BW. For these patients, regression analysis give a significant adjustment of a linear model (r = 0.47, p < 0.001). In the whole studied population there is not a continuous and linear relationship between Vd estimated by NPAG and the BW. These results underline the difficulties to adapt doses of amikacin with only BW information.

[Practical application of the charter of pharmaceutical sales visit]

BACKGROUND

Visits from pharmaceutical representatives are controlled in France by regulations, but also by a Charter of good practice. The goal of this study was to measure compliance to the conditions of this charter by participating pharmaceutical companies.

MATERIAL AND METHODS

An assessment grid was drafted to determine compliance to interdictions and obligations concerning the information provided during visits from pharmaceutical representatives.

RESULTS

We studied 20 visits from pharmaceutical representatives. All of the documents and obligatory information were only provided in 5% of cases. During 80% of these meetings, the pharmaceutical representatives made a comparison with competitor's drugs, which was associated with negative remarks in 44% of cases. The pharmaceutical representatives promoted cases of use outside those, which had received marketing approval in 35%. Gifts or samples were offered at the end of these meetings in 20% of cases. Prohibited practices were observed in a total of 85% of cases.

DISCUSSION

This study shows that meetings are respected by pharmaceutical representatives in terms of regulations related to donations. In opposite, there is a very low compliance concerning the proper use of the drug, whether to provide official documentation, to give information respectful of other pharmaceutical companies or to promote the proper use.

CONCLUSION

Our results suggest that, at present hospital visits by pharmaceutical representatives do not respect the commitments made by the pharmaceutical industry, and do not make it possible to ensure that honest information is provided to favor the proper use of drugs.

[Relationship between benzodiazepines use and falls in the elderly: a multicenter study in three geriatric centers of a university hospital]

INTRODUCTION

Benzodiazepines are widely used in the elderly, but may induce potentially severe iatrogenic events like falls. The analysis of their use is difficult because of the numerous molecules and dosages available. The aim of the present study is to build a tool to monitor their consumption and to evaluate the relation between this consumption and patient's falls reported in three geriatric institutions.

METHODS

Conversion coefficients found in the literature allowed the expression of benzodiazepine action with a unique comparator: diazepam. Benzodiazepine consumption observed during 20 consecutive months was collected and weighted by hospital activity. A correlation between benzodiazepine consumption and the number of falls reported during the same period was researched.

RESULTS

Benzodiazepine consumption expressed in milligrams of diazepam-equivalent per hospitalization day is significantly linked to the number of falls expressed during the same period (R=0.63; p<0.01). However, no statistical bound was found between monthly falls variations and monthly benzodiazepine consumption variations. These results corroborate others published studies: benzodiazepine consumptions are statistically linked to falls, but the reduction of this consumption is of poor predictive value, maybe because of the multifactorial nature of falls.

DISCUSSION AND CONCLUSION

The expression of benzodiazepine consumption in diazepam-equivalent enables one to estimate the general exposition of patients and to compare the use of each molecule. The statistical link between this indicator and a major iatrogenic event like falls makes it a tool worth interest for both clinicians and pharmacists.

[Interindividual pharmacokinetic variability in long-term antibiotherapy]

OBJECTIVE

The authors wanted to assess intraindividual pharmacokinetic variability, with a case of long-term amikacin therapy.

DESIGN

A 92-year-old female patient, weighing 44kg, with renal failure, was treated by amikacin for 52 days. Her individual pharmacokinetic parameters were assessed 12 times in the course of therapy. The intraindividual variability of key parameters was quantified and compared with published interindividual variability.

RESULTS

Intraindividual volume and clearance variability was measured at about one fourth to one third of the value observed for interindividual variability. Half-life intraindividual variability was almost equivalent to the interindividual variability: 24.5% versus 32%.

CONCLUSIONS

The high pharmacokinetic variability observed has important potential clinical consequences. This case illustrates the need to ensure the effectiveness of treatment, to re-evaluate periodically the patient's status in order to take into account the intraindividual variability of pharmacokinetics parameters.

[Management of hypertension and obesity: the observatory of management of uncontrolled hypertensives with respect to the presence or absence of overweight (PHYSIObs)]

The object of this study was to compare the management of uncontrolled hypertensives (BP > 140/90 mmHg) by general practitioners with respect to the presence or absence of overweight (BMI > or =25 Kg/m2). A 2/1 stratification allowed comparison of 4080 patients who were overweight and 1951 patients with a normal body weight (normal BMI < 25 Kg/m2). The BP of patients who were overweight (> or =25 Kg/m2) was slightly higher than those with a normal BMI (161 +/- 12 mmHg vs. 159 +/- 12 mmHg, p < 0.001). The presence of a metabolic syndrome (43% vs. 7%, ATPIII criteria) was, logically, commoner in the patients overweight. However, the practitioners only recognised the presence of a metabolic syndrome in 65% of the overweight patients (28% true positives and 37% true negatives). The practitioners fixed their target value of systolic BP at 136.5 +/- 5.6 mmHg, in accordance with the recent recommendations of the Health Authorities. The targets were judged to be difficult to obtain in 18% of the overweight group and in 5% of patients with normal body weights. This optimism contrasted with the prescriptions, especially in the overweight patients, 46% of whom were treated by monotherapy and who remained for 44% on monotherapy at the end of the consultation. This descriptive study confirms the lack of awareness of the metabolic syndrome in overweight patients and identifies barriers to effective management of the hypertension of these high risk patients.

[Is the white coat effect an alert reaction?]

Is the white coat effect an alert reaction? In this cross-sectional study we compared the white coat effect on systolic blood pressure with the systolic blood pressure reactivity obtained during a stress test. The influence of the sympathetic system (LF band of systolic BP) and the parasympathetic system (HF band of pulse rate) on white coat systolic blood pressure and stress test systolic blood pressure were analysed. We stratified 174 subjects into two groups, according to their blood pressure: hypertensives (HT, n=44, BP>140/90 mmHg) and normotensives (NT, n=130). The BP was recorded during an occupational health consultation, over 24 hours, and beat to beat during a stress test (Finapress). White coat systolic BP was calculated as the difference between the consultation BP and the average systolic BP over 24 hours. The white coat systolic BP was not related with an increase in pulse rate. In contrast, during the stress test the increases in systolic BP and pulse rate were correlated (r=0.44; p<0.001). The white coat systolic BP was lower than the stress test systolic BP in the NT (6.6 +/- 7.2 vs 23 +/- 12 mmHg; p<0.001) and in the HT (16 +/- 11 vs 29 +/- 17 mmHg; p<0.001). The HT had a lower parasympathetic index than the NT (0.45 +/- 0.43 vs 0.92 +/- 0.83 bpm2; p<0.001). In the HT the white coat systolic BP was positively correlated with the stress test systolic BP (r=0.47: p<0.01) and negatively with the parasympathetic activity index. In conclusion, for recently diagnosed and untreated HT an early alteration of the parasympathetic system reveals that the white coat effect is a low amplitude alert reaction.

[Risk profiles of hypertension in normotensive subjects]

The aim of this study was to evaluate the influence of 10 factors suspected to be involved in hypertension genesis (age, body mass index, alcohol consumption, sodium to potassium urinary excretion ratio, systolic BP and heart rate response to mental stress, baroreflex sensitivity (BRS), job demand, job latitude (Karasec's questionnaire), and personality (Bortner's score). A cohort of 213 normotensive healthy subjects was followed during five years. Using K-means clustering technique we have defined 7 homogeneous groups of subjects. Four groups with different combinations of these factors had a significantly higher 5-year systolic BP increase. The common characteristic of these groups was a low BRS. In conclusion, cluster analysis is well suited to analyse combined effect of factors on hypertension genesis. Only low BRS seems to be the common factor involved in hypertension development.

[Target organ effects in untreated hypertension]

The parallel investigation of the renal and cardiac complications of recent and never treated systemic hypertension has only rarely been undertaken. The aim of this study was to define the renal function of never treated hypertensive subjects, separated into white coat hypertensives (HTbb: n = 19, BP at consultation 153/97 mmHg) or permanent hypertensives (HT: n = 49, BP at consultation 169/104 mmHg) as a function of their 24 hour BP. Their renal functions were then compared with those of normotensive subjects (NT: n = 10). The 68 hypertensive subjects seen consecutively underwent renal function investigation (DFG: glomerular filtration rate, DPR: renal plasmatic debit, and muAlb: microalbuminuria over 24 hours), and myocardial echography (measurement of the left ventricular mass index, IMVG). The white coat hypertensives had a normal renal function, while the permanent hypertensives had a significant decrease in DPR and a significantly higher muAlb compared to the normotensives. Compared to the white coat hypertensives, the permanent hypertensives had a significantly lower DFG and DPR, as well as a higher muAlb and IMVG. In all the hypertensives (white coat and permanent) the 24 hour systolic BP was significantly correlated with muAlb (r = 0.51, p < 0.001), filtration fraction (r = 0.30, p < 0.05), and IMVG (r = 0.52, p < 0.001). The renal and myocardial parameters were not significantly correlated. In conclusion, there seems to be a continuum between the level of ambulatory BP and the effect on target organs without a parallel progression of the renal and myocardial effects. From a practical point of view, only ambulatory BP measurement allows differentiation of permanent hypertensives who have a very early renal and/or myocardial effect, while white coat hypertensives are spared.

[PK/PD modeling of aminoglycoside nephrotoxicity]

Aminoglycosides are bactericidial antibiotics with a serum concentration-dependent activity. They are mainly eliminated by the kidneys and the main difficulty arising in clinical use is their uptake by the renal cortex which leads to nephrotoxicity. An ototoxicity is also reported. We propose a PK/PD modelling of aminoglycoside nephrotoxicity which unifies more fourty years of physiological knowledge. This deterministic model successively describes the pharmacokinetics of aminoglycosides, their storage into renal cortex, their effect on renal cells, their consequences on the renal function through tubuloglomerular feedback and the changes in the serum concentrations of creatinine that is considered as a toxicity marker. The simulation of the model displays the leading effect of the shape and daily-time of administration schedule on the search for minimizing toxicity.

[Efficacy and toxicity of aminoglycoside therapy in the elderly: combined effect of both once-daily regimen and therapeutic drug monitoring]

This study was aimed to compare with previous results (Grillot et al., 1994), the efficacy of amikacin adaptive optimal control in a geriatric hospital.

PATIENTS

During six months, 32 patients (aged of 82 +/- 8 years) were included versus 51 during two years (aged of 80 +/- 5). The mean age was not different between the two populations (NS, Student test). They received amikacin initial dosage of 17.7 +/- 5.1 mg/kg/d (vs 13.3 +/- 3.5 for the reference study) and maintenance dosage of 15.1 +/- 4.8 mg/kg/d (vs 11.8 +/- 5.1 for the reference study).

METHOD

Two efficacy outcomes (E1 and E2) and 1 toxicity outcome (T) were taken into account: E1 estimated the effect of adaptive control on maximal drug level, E2: overall recovery. Toxicity outcome was used: T the nephrotoxicity (increasing creatininémia over 44 mumol/l).

RESULTS

All the results are given versus the reference study. 57.6% versus 29.4% of adaptive strategy were once-a-day. E1: Chi square test show that initial dosage and maintenance dosage are greater our study than the previous one (p < 0.05: 78.8% versus 5.9% for initial dosage, 84.4% versus 13.8% for maintenance dosage). E2: 73.6% overall of recovery versus 77% (NS, Chi square test). T: 94% versus 85% (p < 0.05, Chi square test) of creatininemia variation are lower than 44 mumol/l. Duration of treatment is 9.8 +/- 4.8 versus 15 +/- 9 days (p < 0.5, Student test).

CONCLUSIONS

Once-a-day strategy in amikacin therapeutic regimen is no more efficient but decreases toxicity and duration treatment.

Renal elimination of amikacin and the aging process

OBJECTIVE

Although amikacin is primarily eliminated via glomerular filtration, drug concentrations are not consistently predicted in all patients. To better describe the relationship between amikacin clearance and both age and renal function, we used a new heuristic approach involving statistical analysis of dependence.

DESIGN AND SETTING

Retrospective pharmacokinetic study using data from seven centres in France.

PARTICIPANTS

634 patients with sepsis aged between 18 and 98 years of age who received intravenous amikacin.

METHODS

Clearance of amikacin was modelled using the NonParametric EM algorithm for a two-compartment model (NPEM2) with intravenous infusion.

RESULTS

A total of 2499 serum amikacin determinations was available for analysis. The relationship between the clearance of amikacin and age was weak. Interestingly, the Z method, which filters data based on dependence criteria, selected data that were best fitted by a polynomial function (r = 0.90; p < 0.001). This representation of the polynomial function was similar to a previously proposed theoretical model describing covariations between the clearance of amikacin and age. However, the polynomial function applied to only 33% of the patients that were selected by the Z method. The correlation between the clearance of amikacin and renal function was also relatively low (r = 0.39). The Z method exhibited a continuous and strong dependence pattern between the clearance of amikacin and age for 49% of the patients.

CONCLUSIONS

The Z methodology, which filters data using dependence criteria, confirms that age, renal function and amikacin clearance are strongly related, but only in less than half of a large sample of patients with sepsis without renal pathology. These results suggest that other variables should be taken into account in order to improve the description of the behaviour of amikacin. The Z methodology improved the classical description of relationships between variables, and should be applied to better select pertinent variables in pharmacokinetic studies.

Limits of clinical tests to screen autonomic function in diabetes type 1

OBJECTIVES

A precocious detection of cardiac autonomic dysfunction is of major clinical interest that could lead to a more intensive supervision of diabetic patients. However, classical clinical exploration of cardiac autonomic function is not easy to undertake in a reproducible way. Thus, respective interests of autonomic nervous parameters provided by both clinical tests and computerized analysis of resting blood pressure were checked in type 1 diabetic patients without orthostatic hypotension and microalbuminuria.

MATERIAL AND METHODS

Thirteen diabetic subjects matched for age and gender to thirteen healthy subjects volunteered to participate to the study. From clinical tests (standing up, deep breathing, Valsalva maneuver, handgrip test), autonomic function was scored according to Ewing's methodology. Analysis of resting beat to beat blood pressure provided autonomic indices of the cardiac function (spectral analysis or Z analysis).

RESULTS

5 of the 13 diabetic patients exhibited a pathological score (more than one pathological response) suggesting the presence of cardiovascular autonomic dysfunction. The most discriminative test was the deep breathing test. However, spectral indices of BP recordings and baro-reflex sensitivity (BRS) of these 5 subjects were similar to those of healthy subjects and of remaining diabetic subjects.

CONCLUSION

Alteration in Ewing's score given by clinical tests may not reflect an alteration of cardiac autonomic function in asymptomatic type 1 diabetic patients, because spectral indices of sympathetic and parasympathetic (including BRS) function were within normal range. Our results strongly suggest to confront results provided by both methodologies before concluding to an autonomic cardiac impairment in asymptomatic diabetic patients.

Perceived job stress but not individual cardiovascular reactivity to stress is related to higher blood pressure at work

Psychological stress has been reported to be related to higher blood pressure (BP) and unfavorable cardiovascular profile. However, because of the complexity of personal stress management, a multilevel stress measurement strategy is needed. The aim of this cross-sectional study was to analyze the respective influences of the subjective perception of professional strain (high demand and low latitude) and cardiovascular reactivity to a stress test (Stroop stress test) on BP. Worksite BP was measured in 303 healthy normotensive subjects, 18 to 55 years of age, who worked in the same chemical company. In a subset of 70 randomly selected subjects, 24-hour ambulatory BP was performed to assess BP during working hours. The 20% of subjects who reported the highest job strain (high-strain group) or the highest BP stress reactivity (high-responder group) were compared with the remaining subjects (80%) (non-high-strain or low-responder groups). Subjects who submitted to the highest job strain had significantly higher ambulatory diastolic BP (4.5 mm Hg, P=0.015) during only working hours, whereas BP was similar during the remaining hours. Worksite BP and stress cardiovascular reactivity were similar between job strain groups. BP stress reactivity did not influence worksite and ambulatory BP. Spontaneous BP variability assessed by standard deviation and spectral analysis was equivalent between complementary groups. Prevalence of microalbuminuria was significantly higher in the high-responder group (8.2% versus 2.5% in low responders) and only slightly higher in the high-strain group (6.2% versus 3.2% in non-high strain). Potential confounding factors, such as age, gender, alcohol consumption, salt intake, body mass index, and occupation, which were equivalent between groups, did not interfere with our results. Our study quantifies high-professional strain effects on BP levels that appear to be higher only during the working period and to be independent from spontaneous BP variability and stress BP reactivity.

Mental stress-induced increase in blood pressure is not related to baroreflex sensitivity in middle-aged healthy men

The baroreflex that acts to blunt blood pressure (BP) variations through opposite variations in heart rate should limit the BP increase produced by an emotional challenge. However, relations between baroreflex sensitivity and BP reactivity induced by a psychological stress in a large group of adults have never been firmly established. In 280 healthy men, rest (10 minutes) and stress (5 minutes) BP and heart rate were recorded beat to beat by a blood pressure monitor. The mental stress was elicited by a well-standardized computerized version of a word color conflict stress test (Stroop Color Test). Rest and stress baroreflex sensitivity was assessed by the cross-spectral analysis of BP and heart rate and by the sequence method. The stress-induced increase in systolic BP (22.4+/-0.1 mm Hg) was not correlated with resting baroreflex sensitivity but was slightly correlated (r=0.2, P<0.001) with BP variability assessed either by standard deviation or by mid-frequency band spectral power. Our results suggested that a centrally mediated sympathetic stimulation overcame cardiac autonomic regulation and emphasized the role of the sympathetic vasoconstriction in the pressure response at the onset of the stressing stimulation. During the sustained sympathoexcitatory phase, the cardiac baroreflex blunts BP variations but at a lower sensitivity.

Effects of rilmenidine on stress-induced peak blood pressure and renal function

Rilmenidine is an imidazoline I1-receptor agonist that centrally acts by reducing the sympathetic tone. There is strong experimental evidence that natriuresis could be evoked by proximal tubular I1-receptors that have also been isolated in human kidneys. However, in humans, the natriuretic effects of proximal tubular I1-receptors have never been demonstrated. Because stress tests elicited a sympathetically mediated increase in blood pressure and in sodium reabsorption, this study examined whether a short-term infusion of rilmenidine (1 mg) may interfere with stress-induced cardiovascular response and renal sodium handling in normotensive men, in a double-blind, crossover, placebo-controlled study. The stress test used is an efficient and reproducible computerized version of the Stroop's stress test. During the experimental sessions, both basal and stress renal functional parameters were determined: glomerular filtration rate, renal plasma flow, filtration fraction, sodium excretion, and segmental sodium tubular reabsorption (lithium clearance). During the placebo phase, stress induced a significant increase in systolic blood pressure (SBP; 22.2+/-10.1 mm Hg) and diastolic blood pressure (DBP; 11.0+/-5.0 mm Hg). During stress, glomerular filtration rate and renal plasma flow tended to decrease, resulting in a nonsignificant increase in filtration fraction. Despite the increase in BP, stress induced a significant decrease in sodium excretion that was due mainly to a nonsignificant increase in sodium reabsorption in the proximal parts of the tubules. Rilmenidine significantly reduced rest and stress BP, but the cardiovascular reactivity to stress was not altered. The treatment slightly decreased basal glomerular filtration rate and increased renal plasma flow, so that the filtration fraction significantly decreased. The treatment-related decrease in BP was associated with a significant increase in basal sodium reabsorption. Stress-induced modifications in renal function and sodium handling were not altered by the treatment. In conclusion, rilmenidine reduced rest BP and preserved stress-induced reactivity in BP and heart rate. Renal effects of rilmenidine are characterized by a decrease in glomerular filtration rate and in filtration fraction and an increase in sodium reabsorption. The study failed to demonstrate any effect of rilmenidine on stress-induced increase in sodium reabsorption.

Noninvasive exploration of cardiac autonomic neuropathy. Four reliable methods for diabetes?

OBJECTIVE

The purpose of this work was to assess relevant information that could be provided by various mathematical analyses of spontaneous blood pressure (BP) and heart rate (HR) variabilities in diabetic cardiovascular neuropathy.

RESEARCH DESIGN AND METHODS

There were 10 healthy volunteers and 11 diabetic subjects included in the study. Diabetic patients were selected for nonsymptomatic orthostatic hypotension in an assessment of their cardiovascular autonomic impairment. Cardiac autonomic function was scored according to Ewing's methodology adapted to the use of a Finapres device. The spontaneous beat-to-beat BP and HR variabilities were then analyzed on a 1-h recording in supine subjects. The global variabilities were assessed by standard deviation, fractal dimension, and spectral power. The cardiac baroreflex function was estimated by cross-spectral sequences and Z analyses.

RESULTS

In diabetic patients, Ewing's scores ranged from 1 to 4.5, confirming cardiovascular autonomic dysfunction. In these diabetic patients, global indices of variabilities were consistently lower than in healthy subjects. Furthermore, some of them (standard deviation and fractal dimension of HR, spectral power of systolic blood pressure and HR) were significantly correlated with the Ewing's scores. The Z methods and the spectral analysis found that the cardiac baroreflex was less effective in diabetic subjects. However, the baroreflex sensitivity could not be reliably assessed in all the patients. The sequence method pointed out a decreased number of baroreflex sequences in diabetic subjects that was correlated to the Ewing's score.

CONCLUSIONS

Indices of HR spontaneous beat-to-beat variability are consistently related to the degree of cardiac autonomic dysfunction, according to Ewing's methodology. The Z method and spectral analysis confirmed that the cardiac baroreflex was impaired in diabetic patients. These methods might be clinically relevant for use in detecting incipient neuropathy in diabetic patients.

Mechanisms of spontaneous baroreflex impairment in lyon hypertensive rats

This experiment aimed at 1) comparing the spontaneous baroreflex sensitivity (SBRS) in Lyon genetically hypertensive (LH), normotensive (LN), and low blood pressure (LL) rats and 2) assessing some aspects of the mechanisms of its impairment in LH rats. Baroreflex was studied in control animals after an early chronic converting enzyme inhibition with perindopril and after a 4-wk infusion of ANG II in perindopril-treated rats. The SBRS was determined with a previously validated method, using statistical dependence between blood pressure (BP) and heart rate values recorded in freely moving animals. LH rats exhibited high BP, cardiac hypertrophy, and decreased SBRS (LH, 1.3 +/- 0.2; LN, 2.5 +/- 0.4; LL, 2.2 +/- 0.4 beats . min-1 . mmHg-1). Perindopril prevented the development of hypertension and cardiac hypertrophy and normalized SBRS. BP rose in LH and LL rats after ANG II infusion, but only LH rats, which developed a cardiac hypertrophy, had an impaired SBRS (LH, 1.1 +/- 0.2; LN, 2.5 +/- 0.2; LL, 2.8 +/- 0.3 beats . min-1 . mmHg-1). This impairment was partially reversed by an acute ANG II blockade with losartan. These results demonstrate that high BP does not account for the decreased SBRS in LH rats. SBRS impairment could result either from cardiac hypertrophy or from the direct effect of ANG II on the baroreflex loop.

Spontaneous cardiac baroreceptor reflex and regional circulations in conscious rats

OBJECTIVE

To determine the relationships between the activity of the spontaneous cardiac baroreceptor reflex (BRX) and regional vascular dynamics in conscious unrestrained rats.

DESIGN

Simultaneous beat-to-beat recordings of blood pressure and measurements of indices of mesenteric and hindquarters blood flows were performed in seven male normotensive conscious rats under baseline conditions during 1 h.

METHODS

The relationships between systolic blood pressure (SBP) and heart rate were examined using a computerized method, giving the degree of statistical dependence between values of the two parameters with the Z coefficient. This analysis permitted detection of cardiac beats related to cardiac BRX activity. Z analysis was also applied to SBP and to mesenteric or hindquarters blood flow or vascular resistance. Time-series representations were used to describe the chronological patterns corresponding to BRX spontaneous activity.

RESULTS

In these rats, which presented spontaneous BRX-like patterns manifested by the Z analysis, BRX was active during approximately 15% of the time. For 80% of these patterns, cardiac BRX acted to buffer falls in SBP. These depressor events were preceded by muscular vasodilations whereas vasodilations in the mesentery were delayed. Z analysis of these spontaneous haemodynamic patterns confirmed that muscular vasodilations were strongly associated with falls in SBP, whereas vasodilations lagged behind SBP by about seven beats and were not dependent on simultaneous SBP values.

CONCLUSIONS

The Z method showed that spontaneous hindquarters vasodilations were associated with cardiac BRX patterns and that mesenteric vasodilations were not concomitant with falls in SBP and may be the consequence either of a delayed central response or of a local mechanism such as myogenic autoregulation.

[Comparison of three methods for the estimation of spontaneous cardiac baroreflex sensitivity in normotensive and hypertensive subjects]

This study aimed at comparing estimations of spontaneous cardiac baroreflex sensitivity (BRS) obtained with 3 different methods from continuous non-invasive blood pressure recordings in humans. A new method, allowing the quantification of the statistical dependence between values of 2 parameters (Z coefficient), was applied to beat-to-beat systolic blood pressure (SBP) and heart period (HP) values. SBP and HP values with positive Z coefficient and corresponding to baroreflex activity (SBP and HP values both lower or higher than the modal values) were submitted to a linear regression and the regression coefficient (Zgain) was taken as an index of BRS. Second, cross-spectral analysis of SBP and HP gave a BRS value (Csgain) computed as the average value of transfer function moduli for frequencies between 0.07 and 0.14 Hz, with coherence between SBP and HP greater than 0.5. The third method relies on the analysis of linear sequences (r > 0.97) containing at least 3 values of SBP and HP varying in the same direction. The average regression coefficient obtained from all selected SBP and HP sequences is the index of BRS (Seqgain). SBP and HR were recorded during 1 hour with a Finapres in 10 healthy male volunteers (NT), 23 to 32 year-old (SBP: 123 +/- 2 mmHg) and 10 recent and untreated hypertensive subjects (HT) (SBP: 152 +/- 6 mmHg). [table: see text] These results show that, in both groups, Zgain and Seqgain correlated with Csgain. No correlation was found between Zgain and Seqgain in healthy volunteers whereas the correlation was strong in hypertensives probably due to more heterogeneous SBP levels and BRS values in these subjects. This suggests that these methods are sensitive to different ways of response of the baroreflex.

A new non-invasive statistical method to assess the spontaneous cardiac baroreflex in humans

1. A new method was developed to evaluate cardiac baroreflex sensitivity. The association of a high systolic blood pressure with a low heart rate or the converse is considered to be under the influence of cardiac baroreflex activity. This method is based on the determination of the statistical dependence between systolic blood pressure and heart rate values obtained non-invasively by a Finapres device. Our computerized analysis selects the associations with the highest statistical dependence. A 'Z-coefficient' quantifies the strength of the statistical dependence. The slope of the linear regression, computed on these selected associations, is used to estimate baroreflex sensitivity. 2. The present study was carried out in 11 healthy resting male subjects. The results obtained by the 'Z-coefficient' method were compared with those obtained by cross-spectrum analysis, which has already been validated in humans. Furthermore, the reproducibility of both methods was checked after 1 week. 3. The results obtained by the two methods were significantly correlated (r = 0.78 for the first and r = 0.76 for the second experiment, P < 0.01). When repeated after 1 week, the average results were not significantly different. Considering individual results, test-retest correlation coefficients were higher with the Z-analysis (r = 0.79, P < 0.01) than with the cross-spectrum analysis (r = 0.61, P < 0.05). 4. In conclusion, as the Z-method gives results similar to but more reproducible than the cross-spectrum method, it might be a powerful and reliable tool to assess baroreflex sensitivity in humans.

Assessment of spontaneous baroreflex sensitivity in rats a new method using the concept of statistical dependence

A new method was developed to evaluate the cardiac baroreflex sensitivity (BRS) from spontaneous mean arterial pressure (MAP) and heart rate (HR) changes in conscious rats. It relies on the determination of the statistical dependence between MAP and HR values. In 13 control rats, 12 rats with a pharmacologically induced hypertension, and 7 rats with a chronic sinoaortic denervation (SAD), dependent (MAP, HR) couples related to the baroreflex activity were selected to determine the spontaneous BRS (Sp-BRS). In control and hypertensive rats, pharmacological BRS (Ph-BRS) was estimated using graded bolus intravenous doses of vasoactive drugs. Ph-BRS was significantly lower in hypertensive than in control rats. Sp-BRS was determined in 10 control and 10 hypertensive rats and was strongly correlated with Ph-BRS (r = 0.83, n = 20, P < 0.0001). Sp-BRS could be evaluated in six SAD rats and was profoundly decreased (-86%, P < 0.001) compared with control rats. In conclusion, this work validates the estimation of the cardiac BRS from spontaneous MAP and HR variations with use of (MAP, HR) couples of values that are statistically dependent.

Renal denervation does not prevent hypertension in Lyon hypertensive rats

The effects on blood pressure (BP) of a single and repeated renal denervations (RD) were compared in genetically hypertensive (LH) and normotensive (LN) rats of the Lyon strain. Indirect BP was measured by the tail-cuff method, and direct BP was measured through an aortic catheter in conscious quiet rats receiving a normal-sodium diet. Single RD (10 wk of age) did not reduce BP in both LN and LH rats. Repeated RD (4, 7, and 10 wk of age) partly prevented the age-related increase in tail-cuff BP but did not affect the directly recorded BP in 11-wk-old LH rats. Single and repeated RD reduced the renal norepinephrine content by greater than 90%. Both procedures did not alter the BP lowering effects of angiotensin-converting enzyme inhibition and of ganglionic blockade. It is concluded that renal nerves are not necessary for the development and the maintenance of hypertension in LH rats.