Draft genome sequence of the purple photosynthetic bacterium Phaeospirillum molischianum DSM120, a particularly versatile bacterium.

Here we present the draft genome sequence of the versatile and adaptable purple photosynthetic bacterium Phaeospirillum molischianum DSM120. This study advances the understanding of the adaptability of this bacterium, as well as the differences between the Phaeospirillum and Rhodospirillum genera.

PlaScope: a targeted approach to assess the plasmidome from genome assemblies at the species level.

Plasmid prediction may be of great interest when studying bacteria of medical importance such as Enterobacteriaceae as well as Staphylococcus aureus or Enterococcus. Indeed, many resistance and virulence genes are located on such replicons with major impact in terms of pathogenicity and spreading capacities. Beyond strain outbreak, plasmid outbreaks have been reported in particular for some extended-spectrum beta-lactamase- or carbapenemase-producing Enterobacteriaceae. Several tools are now available to explore the 'plasmidome' from whole-genome sequences with various approaches, but none of them are able to combine high sensitivity and specificity. With this in mind, we developed PlaScope, a targeted approach to recover plasmidic sequences in genome assemblies at the species or genus level. Based on Centrifuge, a metagenomic classifier, and a custom database containing complete sequences of chromosomes and plasmids from various curated databases, PlaScope classifies contigs from an assembly according to their predicted location. Compared to other plasmid classifiers, PlasFlow and cBar, it achieves better recall (0.87), specificity (0.99), precision (0.96) and accuracy (0.98) on a dataset of 70 genomes of Escherichia coli containing plasmids. In a second part, we identified 20 of the 21 chromosomal integrations of the extended-spectrum beta-lactamase coding gene in a clinical dataset of E. coli strains. In addition, we predicted virulence gene and operon locations in agreement with the literature. We also built a database for Klebsiella and correctly assigned the location for the majority of resistance genes from a collection of 12 Klebsiella pneumoniae strains. Similar approaches could also be developed for other well-characterized bacteria.

The Odyssey of the Ancestral Escherich Strain through Culture Collections: an Example of Allopatric Diversification.

More than a century ago, Theodor Escherich isolated the bacterium that was to become Escherichia coli, one of the most studied organisms. Not long after, the strain began an odyssey and landed in many laboratories across the world. As laboratory culture conditions could be responsible for major changes in bacterial strains, we conducted a genome analysis of isolates of this emblematic strain from different culture collections (England, France, the United States, Germany). Strikingly, many discrepancies between the isolates were observed, as revealed by multilocus sequence typing (MLST), the presence of virulence-associated genes, core genome MLST, and single nucleotide polymorphism/indel analyses. These differences are correlated with the phylogeographic history of the strain and were due to an unprecedented number of mutations in coding DNA repair functions such as mismatch repair (MutL) and oxidized guanine nucleotide pool cleaning (MutT), conferring a specific mutational spectrum and leading to a mutator phenotype. The mutator phenotype was probably acquired during subculturing and corresponded to second-order selection. Furthermore, all of the isolates exhibited hypersusceptibility to antibiotics due to mutations in efflux pump- and porin-encoding genes, as well as a specific mutation in the sigma factor-encoding gene rpoS. These defects reflect a self-preservation and nutritional competence tradeoff allowing survival under the starvation conditions imposed by storage. From a clinical point of view, dealing with such mutator strains can lead microbiologists to draw false conclusions about isolate relatedness and may impact therapeutic effectiveness. IMPORTANCE Mutator phenotypes have been described in laboratory-evolved bacteria, as well as in natural isolates. Several genes can be impacted, each of them being associated with a typical mutational spectrum. By studying one of the oldest strains available, the ancestral Escherich strain, we were able to identify its mutator status leading to tremendous genetic diversity among the isolates from various collections and allowing us to reconstruct the phylogeographic history of the strain. This mutator phenotype was probably acquired during the storage of the strain, promoting adaptation to a specific environment. Other mutations in rpoS and efflux pump- and porin-encoding genes highlight the acclimatization of the strain through self-preservation and nutritional competence regulation. This strain history can be viewed as unintentional experimental evolution in culture collections all over the word since 1885, mimicking the long-term experimental evolution of E. coli of Lenski et al. (O. Tenaillon, J. E. Barrick, N. Ribeck, D. E. Deatherage, J. L. Blanchard, A. Dasgupta, G. C. Wu, S. Wielgoss, S. Cruveiller, C. Médigue, D. Schneider, and R. E. Lenski, Nature 536:165-170, 2016, https://doi.org/10.1038/nature18959) that shares numerous molecular features.

Escherichia coli molecular genetic map (1000Kbp):update.

The sequenced genes from Escherichia coli that are available in the EMBL library (release 21) have been localized on an updated and corrected version of the restriction map of the chromosome generated by kohara et al. (1987). One thousand kbp of sequenced DNA are incorporated in this update; this is equivalent to 23% of the total genome. The accuracy of the map is assessed, and it is corrected and updated where appropriate, A significant number of sites were missing from the original map, mainly involving two of the eight enzymes used by Kohara et al. (1987), ie. Pvull and EcoRV, The nucleotide environment of such missing sites was examined and, using an Artificial intelligence approach, it appears that the site for these enzymes is sensitive to context effects. Several genes of known position on the E. coli chromosome could not be placed on the restriction map; this suggests that additional gaps are likely to exists on the restriction map, in addition to the original seven identified by Kohara et al. We have also obtained information about the probable direction of transcription of chromosomal genes with respect to the map. Most genes are transcribed in the same direction as the replication forks, particularly around oriC at 84 min.

Evidence for horizontal gene transfer in Escherichia coli speciation.

After extracting more than 780 identified Escherichia coli genes from available data libraries, we investigated the codon usage of the corresponding coding sequences and extended the study of gene classes, thus obtained, to the nature and intensity of short nucleotide sequence selection, related to constraints operating at the nucleotide level. Using Factorial Correspondence Analysis we found that three classes ought to be included in order to match all data now available. The first two classes, as known, encompass genes expressed either continuously at a high level, or at a low level and/or rarely; the third class consists of genes corresponding to surface elements of the cell, genes coming from mobile elements as well as genes resulting in a high fidelity of DNA replication. This suggests that bacterial strains cultivated in the laboratory have been fixed by specific use of antimutator genes that are horizontally exchanged.

Myocardial determinants in regulation of the heart rate.

Heart rate is a function of at least three factors located in the sinus node, including the pacemaker and the activity of the sympathetic and vagal pathways. Heart rate varies during breathing and exercising. The is far from being a purely academic question because, after myocardial infarction or in cardiac insufficiency, reduced heart rate variability (HRV) represents the most valuable prognostic factor. HRV is usually considered index of the sympathovagal balance and is explored using time domain analysis, such as spectral analysis. Nevertheless, methods such as the Fast Fourier Transformation are not applicable to small rodents which have an unstable heart rate with asymmetric oscillations. Nonlinear methods show chaotic behavior under some conditions. A time and frequency domain method of analysis, the Wigner-Villé Transform, has been proposed for the study of HRV in both humans and small rodents, as a compromise between linear and nonlinear methods. We developed a method to quantify both arrhythmias and HRV in unanesthetized rodents. Such a method allows study of the relationship between the physiological parameters and the myocardial phenotype. Ventricular premature beats are more frequent in 16-month-old spontaneously hypertensive rats than in age-matched controls. In addition, HRV is attenuated in spontaneously hypertensive rats, as in compensatory cardiac hypertrophy in humans, and such attenuation is considered a prognostic index. Converting enzyme inhibition reduces in parallel arterial hypertension, cardiac hypertrophy, and ventricular fibrosis; it prevents ventricular premature beats and normalizes heart rate variability. It can be demonstrated that the incidence of ventricular premature beats is linked to the myocardial phenotype in terms of both cardiac hypertrophy and fibrosis. The two factors act as independent variables. HRV is correlated with the incidence of arrhythmias, suggesting that the beneficial effects of converting enzyme inhibition are related to prevention of arrhythmias.

Linear and non-linear analyses of heart rate variability: a minireview.

To complete traditional time- and frequency-domain analyses, new methods derived from non-linear systems analysis have recently been developed for time series studies. A panel of the most widely used methods of heart rate analysis is given with computations on mouse data, before and after a single atropine injection.

Analysis of a Bacillus subtilis genome fragment using a co-operative computer system prototype.

Analysis of the huge volume of data generated by large scale sequencing projects requires the construction of new, sophisticated computer systems. These systems should be able to manage the biological data as well as the results of their analysis. They should also help the user to choose the most appropriate methods, and to string them together in order to solve a global analysis task. In this paper we present the prototype of a software system providing an environment for the analysis of large-scale sequence data. As a first step toward this end, this environment has been put to the test within the Bacillus subtilis genome sequencing project. This system integrates both the descriptive knowledge of the entities involved (genes, regulatory signals and the like) and the methodological knowledge comprising an extensible set of analytical methods. A knowledge representation based on two existing object-oriented models is used to implement this integrated system. In addition, the present prototype provides a suitable user interface both for displaying simultaneously the results generated by several methods and for interacting with the objects. We present in this paper the analysis of a B. subtilis genome fragment, present in data libraries but not annotated. Annotation of the genes present in the fragment allowed us to combine the results of several methods used for predicting coding sequences, and to characterize it as comprising a cryptic phage, the skin element. Comparison between the annotation of the skin element and a standard region of the chromosome indicated that local features of the nucleotide sequence could discriminate between phage and non-phage DNA sequence.

From data banks to data bases.

The information collected in national and international libraries on nucleotide and protein sequences cannot be directly treated for proper handling by existing software. Therefore we evaluated the feasibility of constructing a data base for Escherichia coli using the data present in the banks. The knowhow thus acquired was applied to Bacillus subtilis. Specific examples of the general procedure are given.

Cardiorespiratory system dynamics in chronic heart failure.

AIMS: With the complex demodulation (CDM) method, we assessed the instantaneous amplitude and frequency of cardiovascular (CV) and respiratory oscillations, and the instant phase (IP) between the CV and respiratory signals using respiration as a periodic forced stimulation. We hypothesised a possible lack of synchronisation between CV and respiratory signals under regular breathing at different frequencies. METHODS: RR interval (ECG), blood pressure (SBP/DBP, Finapress), respiration (Respitrace) were monitored during two random-order periods of voluntary paced-breathing (0.15 Hz/0.25 Hz) in 10 moderate CHF patients and 10 age-matched controls. The CDM method provides the amplitude and frequency of a particular spectral component as a function of time in both LF and HF bands. IP between CV and respiratory oscillations was assessed using the real modulating breathing rate. RESULTS: (i) Continuous phase variations between CV oscillations and the respiratory signal were evidenced in CHF patients, the slower the breathing rate, the greater the phase variation (RR/Resp; 0.25 Hz, 23+/-17 degrees; 0.15 Hz, 46+/-57 degrees, P<0.01; RR/Resp at 0.15 Hz 6+/-3 vs. 46+/-57 P<0.01 controls vs. CHF). Phase was constant in controls. (ii) In patients, the instant amplitude of the cardiovascular oscillations in the high frequency domain is more markedly altered when the breathing rate was slowed down as compared to controls. CONCLUSION: The lack of synchronisation between physiological signals during voluntary breathing in CHF patients highlights a central uncoupling between CV and respiratory neuronal activities.

Altered baroreflex gain during voluntary breathing in chronic heart failure.

BACKGROUND: We assessed the behavior of the baroreflex (BR) gain in chronic heart failure (CHF) patients using the spectral analysis method during application of a forcing stimulus, i.e. respiration. METHODS: Simultaneous RR interval and arterial pressure fluctuation recordings were obtained during two random-order periods of voluntary paced-breathing (0.15 Hz and 0.25 Hz) in seven patients with moderate CHF (NYHA class II/III; EF, 30+/-9%; peak VO(2), 18+/-5 ml kg(-1) min(-1)) and six age-matched controls. BR gain was assessed in the time (sequential method) and frequency (cross-spectral gain in the low and high frequency) domains. RESULTS: Slower breathing was associated with a BR gain decrease in CHF patients whereas a BR gain increase was evidenced in controls (BR gain: 6+/-5 ms mmHg(-1) at 0.25 Hz vs. 4+/-3 ms mmHg(-1) at 0.15 Hz, P<0.05 in CHF; BR gain: 12+/-7 ms mmHg(-1) at 0.25 Hz vs. 15+/-7 ms mmHg(-1) at 0.15 Hz, P<0.05 in controls). CONCLUSIONS: Voluntary breathing, which involves cortical centers in the brain, had major effects on cardiovascular system controller gain in CHF patients, indicating an impairment of the central neural regulation of the autonomic outflow.

Heart rate variability in normal sleeping full-term and preterm neonates.

To assess maturation of the Autonomic Nervous System (ANS) and sleep states, Heart Rate Variability (HRV) was studied in 24 healthy sleeping newborns, aged from 31 to 41 weeks, conceptional age (CA). Spectral analysis of the interbeat interval (RR) signal, was performed by Short-Time Fourier Transform, in three frequency bands: high (HF), of purely vagal origin, mid (MF), and low (LF), vagal and sympathetic, thus allowing evaluation of both branches of the ANS, observed in Active Sleep (AS = REM Sleep) and in Quiet Sleep (QS = nREM Sleep). Principal Component Analysis, Discriminant Analysis, and hypothesis tests were used to investigate the evolution of spectral variables and their relation with sleep states. HF, MF, LF, and mean RR all increased with age; the differences from the premature to the full-term group, were more marked, as a whole, in AS than in QS. HF showed the highest increase from the premature (31-36 weeks CA) to the intermediate (37-38) group, whereas LF showed equal differences from the premature to the intermediate, and from the intermediate to the full-term (39-41) groups. These results suggest a steep increase in vagal tone at 37-38 weeks CA, with stability afterwards, and a more regular increase in sympathetic tone from 31 to 41 weeks CA.

Heart-rate variability in low-risk prematurely born infants reaching normal term: a comparison with full-term newborns.

To investigate the influence of prematurity and postnatal age on the maturation of the autonomic nervous system function, we analysed heart-rate and heart-rate variability in twelve prematurely born infants (< 37 weeks gestational age) reaching the conceptional age of 37-41 weeks. These neonates were compared with sixteen 37-41 week conceptional age newborns (< 10 days postnatal age). Heart-rate variability was analysed by spectral analysis of interbeat intervals using Short-Time Fourier Transform. We found that during both active and quiet sleep, the durations of RR-intervals were shorter and the amplitude of heart-rate variability in different frequency bands was lower in prematures reaching term than in newborns of the same conceptional age (P < 0.001). Between-state comparison showed differences in both groups. In both groups, low-frequency heart-rate variability was higher in active sleep than in quiet sleep. Between-state differences of RR-intervals and high-frequency heart-rate variability were present only in newborns (P < 0.01). Discrimination between newborns and prematures reaching term, based on RR-intervals and heart-rate variability, was correct in both sleep states with errors between 7 to 16%. However, in both newborns and prematures reaching term, between-state discrimination showed less reliable results, especially for quiet sleep discrimination with 24% (in PRT) and 20% (in NB) of errors. Our results, especially information given by factor analysis, suggest that the differences between newborns and prematures reaching term, concerning RR-interval and heart-rate variability, may be related to a changed balance between the sympathetic and parasympathetic nervous systems with a diminished parasympathetic component of heart rate control in prematures reaching term, as compared to newborns.

[Obstructive sleep apnea syndrome and heart failure]. / Syndrome d'apnées obstructives du sommeil et insuffisance cardiaque.

Heart failure has an increasing prevalence in middle age adults. The prognosis is very poor even with improved medical therapy and heart transplants. The outcome is related to the neurohumoral disease resulting from heart failure which leads to sympathetic activation that in turns worsens the prognosis. About half of the patients have sleep breathing disorders with variable proportions of central and obstructive apneas. Obstructive apneas are acutely deleterious to ventricular function. On the long run, they may be responsible for a worsening of the disease due to the permanent sympathetic activation seen in obstructive sleep apnea. It is therefore important to detect sleep apnea in patients and to apply a treatment. The best therapeutic procedure in obstructive events appears to be CPAP, provided hemodynamic status is closely monitored.

[Anti-Müllerian hormone, an endocrine predictor of the response to ovarian stimulation in the bovine species]. / L'hormone antimüllérienne, prédicteur endocrinien de la réponse à une stimulation ovarienne chez les bovins.

The strong between-animal variability in the number of ovulations and embryos produced after ovarian stimulation by gonadotropins is a major limit to the development of embryo biotechnologies in cattle. In reproductive medicine, anti-mullerian hormone (AMH) is now widely used as an endocrine marker of the ovarian follicular reserve. In the cow, as in the woman, AMH is secreted by the granulosa cells of growing follicles. We have shown recently that in the cow, AMH is a very good endocrine marker of the population of small antral follicles that constitute the direct target of ovarian stimulatory treatments. AMH concentration measured in plasma before treatment varies between animals and is positively correlated to the number of ovulations and transferable embryos produced after an ovarian stimulatory treatment. Interestingly, AMH concentrations can remain stable over several months for each animal. Moreover, the number of embryos produced after ovarian stimulation is highly repeatable and has a relatively good heritability. From these observations, we propose the determination of AMH concentration in the plasma of a potential donor cow as a simple predictive method to evaluate both its level of ovarian activity and its capacity to produce high or low numbers of embryos. Optimal conditions for implementing this diagnostic test in cattle remain to be defined considering the age, the breed, the physiological status and the environmental factors related to breeding conditions for each animal.

MicroScope: a platform for microbial genome annotation and comparative genomics.

The initial outcome of genome sequencing is the creation of long text strings written in a four letter alphabet. The role of in silico sequence analysis is to assist biologists in the act of associating biological knowledge with these sequences, allowing investigators to make inferences and predictions that can be tested experimentally. A wide variety of software is available to the scientific community, and can be used to identify genomic objects, before predicting their biological functions. However, only a limited number of biologically interesting features can be revealed from an isolated sequence. Comparative genomics tools, on the other hand, by bringing together the information contained in numerous genomes simultaneously, allow annotators to make inferences based on the idea that evolution and natural selection are central to the definition of all biological processes. We have developed the MicroScope platform in order to offer a web-based framework for the systematic and efficient revision of microbial genome annotation and comparative analysis (http://www.genoscope.cns.fr/agc/microscope). Starting with the description of the flow chart of the annotation processes implemented in the MicroScope pipeline, and the development of traditional and novel microbial annotation and comparative analysis tools, this article emphasizes the essential role of expert annotation as a complement of automatic annotation. Several examples illustrate the use of implemented tools for the review and curation of annotations of both new and publicly available microbial genomes within MicroScope's rich integrated genome framework. The platform is used as a viewer in order to browse updated annotation information of available microbial genomes (more than 440 organisms to date), and in the context of new annotation projects (117 bacterial genomes). The human expertise gathered in the MicroScope database (about 280,000 independent annotations) contributes to improve the quality of microbial genome annotation, especially for genomes initially analyzed by automatic procedures alone.Database URLs: http://www.genoscope.cns.fr/agc/mage and http://www.genoscope.cns.fr/agc/microcyc.

Ventilatory thresholds assessment from heart rate variability during an incremental exhaustive running test.

The present study examined whether the ventilatory thresholds during an incremental exhaustive running test could be determined using heart rate variability (HRV) analysis. Beat-to-beat RR interval, V(.-)O (2), V(.-)CO (2) and V(.-) (E) of twelve professional soccer players were collected during an incremental test performed on a track until exhaustion. The "smoothed pseudo Wigner-Ville distribution" (SPWVD) time-frequency analysis method was applied to the RR time series to compute the usual HRV components vs. running speed stages. The ventilatory equivalent method was used to assess the ventilatory thresholds (VT1 and VT2) from respiratory components. In addition, ventilatory thresholds were assessed from the instantaneous components of respiratory sinus arrhythmia (RSA) by two different methods: 1) from the high frequency peak of HRV ( FHF), and 2) from the product of the spectral power contained within the high frequency band (0.15 Hz to fmax) by FHF (HF x FHF) giving two thresholds: HFT1 and HFT2. Since the relationship between FHF and running speed was linear for all subjects, the VTs could not be determined from FHF. No significant differences were found between respective running speeds at VT1 vs. HFT1 (9.83 +/- 1.12 vs. 10.08 +/- 1.29 km x h (-1), n.s.) nor between the respective running speeds at VT2 vs. HFT2 (12.55 +/- 1.31 vs. 12.58 +/- 1.33 km x h (-1), n.s.). Linear regression analysis showed a strong correlation between VT1 vs. HFT1 (R (2) = 0.94, p < 0.001) and VT2 vs. HFT2 (R (2) = 0.96, p < 0.001). The Bland-Altman plot analysis reveals that the assessment from RSA gives an accurate estimation of the VTs, with HF x FHF providing a reliable index for the ventilatory thresholds detection. This study has shown that VTs could be assessed during an incremental running test performed on a track using a simple beat-to-beat heart rate monitor, which is less expensive and complex than the classical respiratory measurement devices.

Assessment of ventilatory thresholds from heart rate variability in well-trained subjects during cycling.

The purpose of this study was to implement a new method for assessing the ventilatory thresholds from heart rate variability (HRV) analysis. ECG, VO2, VCO2, and VE were collected from eleven well-trained subjects during an incremental exhaustive test performed on a cycle ergometer. The "Short-Term Fourier Transform" analysis was applied to RR time series to compute the high frequency HRV energy (HF, frequency range: 0.15 - 2 Hz) and HF frequency peak (fHF) vs. power stages. For all subjects, visual examination of ventilatory equivalents, fHF, and instantaneous HF energy multiplied by fHF (HF.fHF) showed two nonlinear increases. The first nonlinear increase corresponded to the first ventilatory threshold (VT1) and was associated with the first HF threshold (T(RSA1) from fHF and HFT1 from HF.fHF detection). The second nonlinear increase represented the second ventilatory threshold (VT2) and was associated with the second HF threshold (T(RSA2) from fHF and HFT2 from HF.fHF detection). HFT1 , T(RSA1), HFT2, and T(RSA2) were, respectively, not significantly different from VT1 (VT1 = 219 +/- 45 vs. HFT1 = 220 +/- 48 W, p = 0.975; VT1 vs. T(RSA1) = 213 +/- 56 W, p = 0.662) and VT2 (VT2 = 293 +/- 45 vs. HFT2 = 294 +/- - 48 W, p = 0.956; vs. T(RSA2) = 300 +/- 58 W, p = 0.445). In addition, when expressed as a function of power, HFT1, T(RSA1), HFT2, and T(RSA2) were respectively correlated with VT1 (with HFT1 r2 = 0.94, p < 0.001; with T(RSA1) r2 = 0.48, p < 0.05) and VT2 (with HFT2 r2 = 0.97, p < 0.001; with T(RSA2 )r2 = 0.79, p < 0.001). This study confirms that ventilatory thresholds can be determined from RR time series using HRV time-frequency analysis in healthy well-trained subjects. In addition it shows that HF.fHF provides a more reliable and accurate index than fHF alone for this assessment.

Comparative and functional genomic analyses of iron transport and regulation in Leptospira spp.

The spirochetes of the Leptospira genus contain saprophytic and pathogenic members, the latter being responsible for leptospirosis. Despite the recent sequencing of the genome of the pathogen L. interrogans, the slow growth of these bacteria, their virulence in humans, and a lack of genetic tools make it difficult to work with these pathogens. In contrast, the development of numerous genetic tools for the saprophyte L. biflexa enables its use as a model bacterium. Leptospira spp. require iron for growth. In this work, we show that Leptospira spp. can acquire iron from different sources, including siderophores. A comparative genome analysis of iron uptake systems and their regulation in the saprophyte L. biflexa and the pathogen L. interrogans is presented in this study. Our data indicated that, for instance, L. biflexa and L. interrogans contain 8 and 12 genes, respectively, whose products share homology with proteins that have been shown to be TonB-dependent receptors. We show that some genes involved in iron uptake were differentially expressed in response to iron. In addition, we were able to disrupt several putative genes involved in iron acquisition systems or iron regulation in L. biflexa. Comparative genomics, in combination with gene inactivation, gives us significant functional information on iron homeostasis in Leptospira spp.

Effect of exercise intensity and repetition on heart rate variability during training in elite trotting horse.

RR intervals of ten elite trotting horses were recorded during an interval training session performed on track. This study examined two hypotheses. Firstly, like in humans, the hyperpnea combined with a decrease in cardiac autonomic control on heart rate during heavy exercise could result in a prevalence of high frequency heart rate variability. Secondly, this prevalence could increase with the heavy exercise repetition. Two exercise intensities were compared: moderate (ME) and heavy (HE). Furthermore, heavy exercise repetitions were compared between the beginning and the end of the interval training session. When comparing ME and HE periods: heart rate was significantly lower (155 +/- 12 vs. 210 +/- 9 ms, p < 0.001), LF spectral energy (0.04 - 0.2 Hz) was significantly higher (ME: 6.94 +/- 4.80 and HE: 0.24 +/- 0.14 ms(2) . Hz (-1), p < 0.001) whereas HF (0.2 - 2 Hz) was significantly lower (ME: 7.09 +/- 2.24 and HE: 10.60 +/- 3.64 ms(2) . Hz (-1), p < 0.05). In relative terms, ME showed similar results in both LFn (LF/LF+HF) and HFn (HF/LF+HF) whereas HE showed a large prevalence of HFn energy compared to LFn (p < 0.001). The difference in LF/HF ratio between the two exercise conditions was significant (1.14 +/- 0.92 vs. 0.09 +/- 0.12, p < 0.001). Exercise repetition induced a significant increase in heart rate between the beginning and the end of the interval training session (207 +/- 10 beats . min (-1) vs. 212 +/- 9 beats . min (-1), p < 0.001) whereas LF energy decreases (1.54 +/- 1.65 vs. 0.32 +/- 0.24 ms(2) . Hz (-1), p < 0.01) and HF energy remained constant (10.79 +/- 4.10 vs. 10.40 +/- 3.35 ms(2) . Hz (-1), NS). This study confirmed the results observed in humans during heavy exercise conditions with a large prevalence of HF in contrast to LF, this prevalence increasing with exercise repetitions. The observed decrease in LF/HF ratio could provide an index of hyperpnea in horses during interval training.