This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Charloux, A. Articles by Brandenberger, G. Search for Related Content PubMed PubMed Citation Articles by Charloux, A. Articles by Brandenberger, G. Pubmed/NCBI databases Substance via MeSH

Oscillations in Sympatho-Vagal Balance Oppose Variations in -Wave Activity and the Associated Renin Release

Laboratoire des Régulations Physiologiques et des Rythmes Biologiques chez l’Homme, Institut de Physiologie, 67085 Strasbourg Cedex, France

Address all correspondence and requests for reprints to: Dr. Anne Charloux, Laboratoire des Régulations Physiologiques et des Rythmes Biologiques, Institut de Physiologie, 4 rue Kirschleger, 67085 Strasbourg Cedex, France.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
To determine the potential role of the sympathetic nervous system in the generation of the oscillations in PRA over the 24-h period, we used the autocorrelation coefficient of RR interval (rRR), a new tool to evaluate the sympatho-vagal balance continuously. We determined the influence of the sympathetic nervous system both on the nocturnal PRA oscillations associated to increases in -wave activity and on the daytime oscillations that occur randomly in awake subjects.

PRA and rRR were determined every 10 min during 24 h in nine healthy subjects under continuous bed rest. Electroencephalographic spectral analysis was used to establish the variations in -wave activity during sleep, from 2300–0700 h. The overnight profiles in PRA, rRR, and -wave activity were analyzed using a modified version of the pulse detection program ULTRA. The temporal link among the profiles of rRR, PRA, and -wave activity was quantified using cross-correlation analysis.

During sleep, large oscillations in PRA were strongly linked to variations in -wave activity. They were preceded by opposite oscillations in rRR, decreases in rRR reflecting predominant vagal activity, and increases in rRR reflecting sympathetic dominance. During the waking periods, the levels of rRR were higher, with smaller variations. The daytime PRA oscillations were not associated with any significant changes in rRR, and conversely, significant oscillations in rRR were not followed by any significant changes in PRA.

In conclusion, the sympathetic nervous system is not directly involved in the generation of renin oscillations observed under basal conditions. During sleep, the oscillations in sympatho-vagal balance are inversely related to the variations in -wave activity and the associated renin release. The processes that give the intermittent signal for concomitant increases in slow wave activity and renin release from the kidney remain to be identified.

	Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
DURING sleep, PRA displays large oscillations that are strongly linked to sleep stage alternation; PRA increases during nonrapid eye movement (NREM) sleep and decreases during REM sleep (1). Drugs such as converting enzyme inhibitors, ß-blockers, and diuretics or a low sodium diet modulate the amplitude of these oscillations, but do not abolish the relationship between PRA and sleep structure (2). In patients with sleep disorders, PRA variations reflect the disorganization in the internal sleep structure quite precisely (3, 4, 5). More recently, we demonstrated by spectral analysis of the sleep electroencephalogram (EEG) that PRA oscillations are correlated with variations in relative power that reflect sleep deepness; PRA increases are associated with increases in slow waves, and PRA decreases are associated with decreases in slow waves (6).

It is well known that renin release by the juxtaglomerular apparatus is induced peripherally by a fall of perfusion pressure in the afferent arterioles of the kidney, a decrease in sodium chloride concentration at the macula densa, or the stimulation of ß-adrenoceptors on the juxtaglomerular cells (7). Numerous animal experiments have described the stimulatory effect of sympathetic activation on renin secretion either by direct electrical renal nerve stimulation or indirectly by compression of the carotid artery sinus or ß-agonist infusion (8, 9, 10, 11). However, the relationship between spontaneous variations in autonomic nervous system activity and renin release has not been studied.

Heart rate variability, based on analysis of the time interval between two electrocardiographic R waves (RR interval), results mostly from the interaction between the sympathetic and the parasympathetic system activities. The Poincaré plot is a nonlinear procedure based on a scatterplot of the current RR interval against the previous RR interval. It provides a qualitative picture of beat to beat interval behavior (12). Using autonomic blocking agents, it has been demonstrated that the Poincaré plots have distinctive and characteristic patterns according to the degree of activity of the sympathetic and parasympathetic systems (13). Quantitative measures of the Poincaré plots based on statistical evaluation of the RR interval variance or RR histogram have been accepted as indexes of either sympathetic or parasympathetic activity (12). In a previous study, we calculated, every minute, the interbeat autocorrelation coefficients of RR interval (rRR) derived from the Poincaré plot and reported that their overnight profiles are highly related to the variations in EEG mean frequency, which reflect deepness of sleep (14). More recently, we demonstrated that the overnight profiles of rRR are closely cross-correlated with the profile of low- to high-frequency power ratio. The power in the two main frequency peaks, the high frequency and low frequency peaks, detected by spectral analysis of RR intervals is widely used as a quantitative measure of autonomic nervous system activity. Therefore, rRR can be regarded as a tool to evaluate the sympatho-vagal balance continuously in man, with an increase in rRR reflecting an increase in sympathetic tone.

In the present study, we used this new index to establish the potential role of the sympathetic nervous system in the generation of PRA oscillations over the 24-h period. PRA and rRR were determined concomitantly every 10 min in subjects under continuous bed rest. EEG spectral analysis was used to establish the concomitant variations in -wave activity during sleep. We determined the influence of the autonomic nervous system on both the nocturnal PRA oscillations associated with increases in -wave activity and the daytime peaks occurring randomly in awake subjects.

	Subjects and Methods

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Subjects

Nine healthy male volunteers, aged 21–28 yr, gave their written informed consent to participate in this study. They had regular sleep-wake habits and did not take any medication. During the experiment, they did not take alcohol or caffeine-containing beverages and were not allowed to smoke or participate in sports. This study was approved by the local ethic committee.

Procedures

The measurements were performed in a sleep room equipped for polysomnographic recordings and blood sampling. After a habituation night, a catheter was inserted into an antecubital vein 4 h before the beginning of recordings and was kept patent by a heparinized solution. Heart rate was recorded from 1800–1800 h, and sleep recording was carried out from 2300–0700 h. When awake, the subjects read, listened to music, watched television, and conversed with an experimentor to prevent daytime sleep. To avoid the influence of repeated meal intake, the subjects received continuous enteral nutrition through a nasogastric feeding tube that began 4 h before blood sampling (Sondalis, ISO, Sopharga, Puteaux, France; 50% carbohydrate, 35% fat, and 15% protein; 378 kJ/h).

Sleep recording

Sleep recordings were based on two EEG derivations (C3-A2 and C4-A1), one chin electromyogram and one horizontal electrooculogram (upper canthus of one eye vs. lower canthus of the other eye). The EEG signal was converted from analog to digital with a sampling frequency of 128 Hz. Subsequently, spectra were computed for consecutive 2-s periods using a Fast Fourier Transformation algorithm (15). To yield 10-min power density values, the median was calculated for 300 consecutive 2-s periods. The spectral parameter considered was absolute power (0.5–3.5 Hz).

Blood sampling and PRA assessment

Blood was collected from 1800–1800 h in an adjoining room. Blood was removed continuously using a peristaltic pump and was sampled at 10-min intervals in tubes containing ethylenediamine tetraacetate-K₂ salt. A maximum of 200 mL was removed during the 24 h. The samples were collected in a refrigerated container and centrifuged at 4 C within the subsequent 20 min. The plasma was immediately stored at -25 C. PRA was measured by a RIA of angiotensin I generated after incubation of the plasma (commercial kits, Sorin Biomedica, Saluggia, Italy). The intraassay coefficient of variation for duplicate samples was 4% for levels between 10–20 ng/mL·h, 6% for levels between 2–10 ng/mL·h, 10% for levels between 1–2 ng/mL·h, and 30% for levels below 1 ng/mL·h. The detection limit was 0.18 ng/mL·h. All samples from one subject were measured in the same assay to avoid interassay variations.

Heart rate analysis

The electrocardiogram signal was fed into a generator that produces a pulse at the rising phase of each R wave. The trigger event times were recorded with an accuracy of ±1 ms, and the RR intervals were calculated on a computer equipped with a data acquisition control board including a timer. Each RR interval was plotted against the previous RR interval to produce a cardiac Poincaré plot (RR_n+1 vs. RR_n) for each minute. The rRR values (i.e. Pearson’s correlation coefficients between the RR_n and RR_n+1) were calculated for each minute and averaged over a 10-min period.

Data analysis

The pulse analysis program ULTRA (16) was used for quantitative detection and characterization of PRA oscillations with a threshold of 3 times the coefficient of variation. This program takes into account the limit of detection of the analytical procedure and the precision of the assay for various ranges of concentrations. To identify the main oscillations in absolute power and rRR, the individual profiles were analyzed using a modified pulse analysis algorithm. Taking into account the large interindividual variability, identification of the main oscillations was achieved using a subject-adapted threshold for detection. This threshold was set at 20% of the maximum increment in absolute power or in rRR observed for each subject. During sleep, mean PRA oscillations were obtained by averaging point by point the levels of the significant oscillations aligned by their maximum. To calculate a mean oscillation for the group of nine subjects, all individual pulses were averaged for each subject, giving the subjects the same weight. Corresponding -wave activity and rRR levels were considered, and their variations were analyzed using an ANOVA with repeated measures (BMDP Statistical Software, Los Angeles, CA). Similar analyses were performed during the day. Firstly, mean significant PRA oscillations were calculated and aligned by their maximum, and corresponding rRR levels were plotted with regard to PRA oscillations. Secondly, the mean significant rRR oscillations were calculated, and the corresponding PRA levels were considered. For all of these analyses, two periods were considered: the sleep period (2300–0700 h) and the subsequent waking period (0700–1500 h). Mann-Whitney test was used to assess the statistical differences among the mean values, the number of oscillations, their amplitude, and the SD for the series of data obtained during these two periods.

The temporal relationship between rRR and PRA or EEG -wave activity was quantified using cross-correlation analysis between two chronological series for lags -3 to +3, each lag corresponding to 10-min interval (Box Jenkins Time Series Analysis, BMDP Statistical Software). For PRA, a least squared polynome was adjusted to the night and day PRA profiles, and the polynomial values were subtracted point by point from the series of PRA levels. The residual data were then used for cross-correlation analysis. The level of significance for each cross-correlation coefficient was assessed by estimating the SE. The SE was given by (N - k)^-1/2, where N denotes the number of samples in the series, and k is the particular lag. The cross-correlation coefficient is considered significant (P < 0.05) when it exceeds zero by more than 2 times the SE.

	Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
24-h PRA and rRR profiles

Figure 1 illustrates a 24-h profile for PRA with regard to the profile for rRR in one representative subject. As previously described (1), large oscillations in PRA occurred during the sleep period. Variations in PRA were also observed during the waking periods, but they were usually small, more irregularly distributed, and variable according to individuals. The rRR coefficient decreased 15–35 min before sleep onset and then had a series of large falls during the sleep period before returning to high initial levels during the subsequent waking period, thus indicating sympathetic activation. Table 1 summarizes the results obtained in the nine subjects. Mean PRA levels were significantly higher during sleep than during the waking period. In contrast, the rRR levels were significantly lower during the sleep period. However, for both PRA and rRR, the amplitude, number of oscillations, and SD of the data were higher during the 8-h sleep period than during the subsequent 8-h waking period. In the nine subjects studied, the overnight profiles of rRR showed coordinate variations with the low/high frequency power ratio, a customary measure of sympatho-vagal balance. The cross-correlation coefficients ranged between 0.468–0.805 (P < 0.001).

View larger version (24K): [in this window] [in a new window]   Figure 1. Twenty-four-hour profiles of PRA and rRR in a representative subject.

Figure 2 illustrates the concomitant profiles of PRA, absolute power, and rRR in a representative subject during sleep. absolute power and PRA oscillations were positively correlated with cross-correlation coefficients ranging between 0.29–0.65 (P < 0.05). Oscillations in -wave activity were concomitant with or preceded PRA oscillations by 10 min. rRR was inversely correlated with absolute power and the associated renin release, with cross-correlation coefficients ranging respectively between -0.30 and -0.65 (P < 0.001 in all subjects but one) and between -0.29 and -0.65 (P < 0.05). rRR variations preceded PRA oscillations with a 10-min lag in most subjects (Table 2). During the sleep periods, in the 9 subjects, 29 significant oscillations of PRA were detected using the ULTRA program. Figure 3 shows the mean values of PRA oscillations aligned by their maximum together with the oscillations in absolute power and the inverse oscillations in rRR.

View larger version (22K): [in this window] [in a new window]   Figure 2. Concomitant overnight profiles of PRA, absolute power, and rRR, after z-score transformation, in a representative subject. Ascending phases of absolute power indicate sleep deepening. Ascending phases of rRR indicate increased sympathetic activity.

View larger version (12K): [in this window] [in a new window]   Figure 3. Mean ± SE PRA and absolute power together with the opposite variations in rRR during the sleep period in nine subjects. Significant PRA oscillations were aligned by their maximum.

During the 8-h waking period, pulse analysis of the residual profiles revealed the existence of 16 significant PRA oscillations in the 9 subjects. These oscillations in PRA were not associated with any systematic changes in rRR (see example in Fig. 1). The cross-correlation coefficients between PRA and rRR ranged between -0.39 and +0.31, with a lag between -30 and +20 min (Table 2). The mean curves are given in Fig. 4, which illustrates the absence of a temporal association between the daytime PRA oscillations aligned by their maximum and concomitant rRR time courses. Similarly, the 15 significant daytime oscillations of rRR aligned by their maximum were not associated with any significant variation in PRA (Fig. 5).

View larger version (14K): [in this window] [in a new window]   Figure 4. Mean ± SE PRA and the concomitant values of rRR during the waking period in nine subjects. Significant PRA oscillations were aligned by their maximum.

View larger version (16K): [in this window] [in a new window]   Figure 5. Mean ± SE rRR and of the concomitant values of PRA during the waking period in nine subjects. Significant rRR oscillations were aligned by their maximum.

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

The role of the sympathetic nervous system in renin secretion has been defined thanks to animal experiments that focused on the effect of one particular stimulus, i.e. electrical stimulation of renal nerves, compression of the carotid artery sinus, or intraarterial administration of ß-adrenergic agonists to rat kidney and incubation of rat kidney slices in catecholamine-containing medium (7, 8, 9, 10). In these experiments, renin release followed a dose-response pattern and could be prevented by ß-blockers (7, 10, 17). However, these experimental conditions cannot be compared to the physiological stimuli of the sympathetic system observed in daily life. Moreover, the physiological implications of these experiments are limited by the fact that in conscious subjects, all stimuli responsible for renin secretion are acting simultaneously.

In the present experiment, oscillations of PRA in awake subjects were not preceded by a rise of rRR, and a significant increase in rRR was not followed by a rise in PRA. It is likely that sympathetic stimulation in continuously recumbent subjects is too low to produce increases in renin release. Moreover, it has been demonstrated that isoproterenol, a ß-adrenergic agonist, only has a significant effect on renin release at low blood pressure levels (11). In our healthy subjects, who have intact renal autoregulation and normal blood pressure, light sympathetic stimulation is not able to increase renin release.

During sleep, an inverse cross-correlation between rRR and PRA was observed; the rises in PRA and slow wave activity were preceded by a decrease in sympathetic activity, as reflected by a decrease in rRR. Assessment of rRR offers a precise characterization of moment to moment changes in sympatho-vagal activity in relation to changes in brain activity and renin release. Using microneurography (18, 19) or spectral analysis of RR intervals (13, 20, 21), it has been previously reported that rapid eye movement (REM) sleep is associated with profound sympathetic activation, and NREM sleep is associated with a predominance of parasympathetic activity. The Poincaré plots, generally based on 5- to 20-min sleep recording, give different patterns according to sleep stages, as demonstrated by pharmacological tests, reflecting reciprocal sympathetic and vagal influences (13). However, the precise time courses of PRA variations and EEG mean frequency with regard to variations in sympatho-vagal activity have not been reported yet.

In experiments performed on isolated or in situ perfused rat kidney, the delay between arterial isoproterenol infusion and renin release was very short, i.e. less than 5 min (9, 17). According to these studies, the rise in PRA observed during increments in slow waves cannot be attributed to the increase in sympathetic activity observed concomitantly to decreases in slow waves. Therefore, it can be concluded that the oscillations in sympatho-vagal balance are not directly involved in generation of the nocturnal oscillations in PRA.

Thus, the nocturnal oscillations in PRA may be generated by peripheral feedback mechanisms or by sleep-related processes. Scarcely any data have been published on variations in renal arterial pressure and sodium chloride concentration at the macula densa during sleep. In man, studies reported a fall in systemic arterial pressure during slow wave sleep and a large variability in blood pressure during REM sleep (18, 22). It is possible that the oscillations in PRA reflect oscillations in blood pressure, with low perfusion pressure of the juxtaglomerular apparatus eliciting a release of renin during NREM sleep. If this hypothesis is correct, then the sympathetic nervous system is indirectly responsible for renin release during sleep by the mechanism of low blood pressure. However, the precise temporal relationship between peripheral factors and PRA oscillations has not yet been described, and the potential roles of these peripheral factors in generating PRA oscillations have yet to be evaluated.

The hypothesis according to which central processes related to sleep may play an essential role is supported by previous studies that demonstrated that the association between sleep stage alternation and PRA cannot be broken (2, 3, 4, 5). This argues in favor of a central control of renin, coupled with or regulated by sleep control processes. Experiments performed in the rat support this hypothesis. The administration of a serotonin releaser produces a dose-dependent increase in renin secretion (23). Discrete cell-selective lesions have shown that this increase in PRA is mediated by neurons in the paraventricular nucleus of the hypothalamus (24). A renin-releasing factor, which is probably a peptide, has been partially characterized from rat plasma and hypothalamus (25). The role of the serotoninergic system in renin secretion during sleep has not yet been confirmed in humans.

In summary, there is a positive relationship between -wave activity and PRA oscillations, whereas -wave activity and PRA oscillations are inversely related to variations in sympatho-vagal activity, continuously evaluated by rRR. These temporal links argue in favor of a central generator synchronizing renin release and autonomic and sleep processes. The inverse temporal relationship between sympathetic activity and renin release, which is normally stimulated by sympathetic nerve activity, raises the question of how the common processes for concomitant increases in slow waves and renin release function.

	Acknowledgments

 
We are indebted to Béatrice Reinhardt and Michèle Siméoni for PRA measurements, and to Daniel Joly for sleep recording. We also thank Dr. Eve Van Cauter for providing the ULTRA program.

Received October 7, 1997.

Revised December 31, 1997.

Accepted January 14, 1998.

	References

Top Abstract Introduction Subjects and Methods Results Discussion References

 

1. Brandenberger G, Follenius M, Muzet A, Ehrhart J, Schieber JP. 1985 Ultradian oscillations in plasma renin activity: their relationships to meals and sleep stages. J Clin Endocrinol Metab. 61:280–284.[Abstract/Free Full Text]
2. Brandenberger G, Krauth MO, Ehrhart J, Libert JP, Simon C, Follenius M. 1990 Modulation of episodic renin release during sleep in humans. Hypertension. 15:370–375.[Abstract/Free Full Text]
3. Follenius M, Krieger J, Krauth MO, Sforza F, Brandenberger G. 1991 Obstructive sleep apnea treatment: peripheral and central effects on renin activity and aldosterone. Sleep. 14:211–217.[Medline]
4. Brandenberger G, Buguet A, Spiegel K, Stanghellini A, Muanga G, Bogui P, Dumas M. 1996 Disruption of endocrine rhythms in sleeping sickness with preserved relationship between hormonal pulsatility and the REM-NREM sleep cycle. J Biol Rhythms. 11:258–267.[Abstract/Free Full Text]
5. Schultz H, Brandenberger G, Gudewill S, et al. 1992 Plasma renin activity and sleep-wake structure of narcoleptic patients and control subjects under continuous bedrest. Sleep. 15:423–429.[Medline]
6. Luthringer R, Brandenberger G, Schaltenbrand N, et al. 1995 Slow wave electroencephalic activity parallels renin oscillations during sleep in humans. Electroencephalogr Clin Neurophysiol. 95:318–322.[CrossRef][Medline]
7. Skott O, Jensen L. 1993 Cellular and intrarenal control of renin secretion. Clin Sci. 84:1–10.[Medline]
8. Bunag RD, Page IH, McCubbin JW. 1966 Neural stimulation of renin release. Circ Res. 19:851–858.[Abstract/Free Full Text]
9. Vandongen R, Peart GW. 1973 Adrenergic stimulation of renin secretion in the isolated perfused rat kidney. Circ Res. 32:290–295.[Abstract/Free Full Text]
10. Taher MS, McLain LG, McDonald KM, Schrier RW. 1976 Effect of ß-adrenergic blockade on renin response to renal nerve stimulation. J Clin Invest. 57:459–465.
11. Holdaas H, Langaard O, Eide I, Kiil F. 1982 Conditions for enhancement of renin release by isoproterenol, dopamine and glucagon. Am J Physiol. 242:F267–F273.
12. Kamen PW, Krum H, Tonkin AM. 1996 Poincaré plot of heart rate variability allows quantitative display of parasympathetic nervous activity in humans. Clin Sci. 91:201–208.[Medline]
13. Zemaityte D, Varoneckas G. 1984 Heart rhythm control during sleep. Psychophysiology. 21:279–289.[Medline]
14. Otzenberger H, Simon C, Gronfier C, Brandenberger G. 1997 Temporal relationship between dynamic heart rate variability and electroencephalographic activity during sleep in man. Neurosci Lett. 229:173–176.[CrossRef][Medline]
15. Cooley JW, Tuckey JW. 1965 An algorithm for machine calculation of complex Fourier series. Math Comput. 19:297–301.[CrossRef]
16. Van Cauter E. 1988 Estimating false-positive and false-negative errors in analyses of hormonal pulsatility. Am J Physiol. 17:E113–E119.
17. Sinaiko AR, Mirkin BL. 1977 Isoproterenol-evoked renin release from the in situ perfused kidney. Dose response characteristics in spontaneously hypertensive and normotensive Wistar rats. Circ Res. 42:381–385.[Free Full Text]
18. Somers VK, Dyken ME, Mark AL, Abboud FM. 1993 Sympathetic nerve activity during sleep in normal subjects. N Engl J Med. 328:303–307.[Abstract/Free Full Text]
19. Okada H, Iwase S, Mano T, Sugiyama Y, Watanabe T. 1991 Changes in muscle sympathetic nerve activity during sleep in humans. Neurology. 41:1961–1966.[Abstract/Free Full Text]
20. Akselrod S, Gordon D, Ubel FA, Shannon DC, Barger AC, Cohen RJ. 1981 Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control. Science. 213:220–222.[Abstract/Free Full Text]
21. Vaughn BV, Quint SR, Messnheimer JA, Robertson KR. 1995 Heart period variability in sleep. Electroencephalogr Clin Neurophysiol. 94:155–162.[CrossRef][Medline]
22. Khatri IM, Freis AD. 1966 Hemodynamics changes during sleep. J Appl Physiol. 22:867–873.
23. Van de Kar L, Wilkinson CW, Ganong WF. 1981 Pharmacological evidence for a role of brain serotonin in the maintenance of plasma renin activity in unanesthetized rats. J Pharmacol Exp Ther. 219:85–90.[Abstract/Free Full Text]
24. Rittenhouse PA, Li Q, Levy AD, Van de Kar LD. 1992 Neurons in the hypothalamic paraventricular nucleus mediate the serotonergic stimulation of renin secretion. Brain Res. 593:105–113.[CrossRef][Medline]
25. Van de Kar L, Urban JH, Brownfield MS, Simmons WH. 1987 Partial characterization of a renin-releasing factor from plasma and hypothalamus. Hypertension. 9:598–606.[Abstract/Free Full Text]

This Article Abstract Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Charloux, A. Articles by Brandenberger, G. Search for Related Content PubMed PubMed Citation Articles by Charloux, A. Articles by Brandenberger, G. Pubmed/NCBI databases Substance via MeSH