A large population study to assess the magnitude of prenatal programming in dairy cattle

The performance of an adult dairy cow may be influenced by events that occur before her birth. The present study investigated potential effects of 2 prenatal groups of factors, Assisted Reproductive Techniques (ART) and maternal characteristics (e.g., dam parity), on offspring performance during their first lactation, in populations of 2 dairy cow breeds: French Holstein and Montbéliarde. The different ART studied included the type of semen (conventional or X-sorted) used for Artificial Insemination (AI) and the technology of conception used (AI, embryo transfer, or in vitro fertilization). Three maternal characteristics were considered: (1) the dam age at first calving, (2) dam parity number, and (3) indicators of dam udder health during gestation (somatic cell score and events of clinical mastitis). First, we investigated whether heifer survival from 3d to 18 mo old was associated with any of the prenatal factors considered. We then estimated the associations of these prenatal factors with 8 traits of commercial interest: (1) stature, (2-4) milk, fat, and protein yields, (5) somatic cell score, (6) clinical mastitis, and (7-8) heifer and cow conception rate, all measured on genotyped cows. Linear models were used for this study with the prenatal factors as covariates in the model, and for the 8 traits, phenotypes were adjusted for their corresponding genomic estimated breeding value. The results indicated that the survival rate of heifers born from embryo transfer was significantly higher than that of heifers born from AI (probably due to preferential management practices), while the other prenatal factors did not explain differences in heifer survival. Among the Montbéliarde cows born from AI, those born from X-sorted semen showed a lightly but significantly lower milk yield than those born without X-sorting of the semen (-52 kg of milk in the first lactation). Among the Holstein cows, those born from embryo transfer presented significantly lower milk performance than cows born from AI. Regarding the maternal characteristics, none or very weak associations were found between the dam age at first calving and the offspring performance in both breeds. Dam parity, on the other hand, was associated with offspring performance for milk, fat, and protein yield in both breeds, however not in the same direction. In the Holstein breed, an increase in dam parity was favorable for offspring performance for milk, fat, and protein yield, whereas in the Montbéliarde breed, an increase in dam parity was associated with lower milk and protein yield and no association was found for fat yield. The udder health of the dam during gestation was not or only weakly associated with the traits studied in the offspring. Although some significant associations were identified due to the large sample size, the effects were modest, typically less than 1% of the phenotypic mean, and were not consistently observed across the 2 breeds.

Effect of temperature-humidity index on the evolution of trade-offs between fertility and production in dairy cattle

BACKGROUND

In the current context of climate change, livestock production faces many challenges to improve the sustainability of systems. Dairy farming, in particular, must find ways to select animals that will be able to achieve sufficient overall production while maintaining their reproductive ability in environments with increasing temperatures. With future forecasted climate conditions in mind, this study used data from Holstein and Montbeliarde dairy cattle to: (1) estimate the genetic-by-temperature-humidity index (THI) interactions for female fertility, and (2) evaluate the production-fertility trade-off with increasing values of THI.

RESULTS

Two-trait random regression models were fitted for conception rate (fertility) and test-day protein yield (production). For fertility, genetic correlations between different THI values were generally above 0.75, suggesting weak genotype-by-THI interactions for conception rate in both breeds. However, the genetic correlations between the conception rate breeding values at the current average THI (THI = 50, corresponding to a 24-h average temperature of 8 °C at 50% relative humidity) and their slopes (i.e., potential reranking) for heat stress scenarios (THI > 70), were different for each breed. For Montbeliarde, this correlation tended to be positive (i.e., overall the best reproducers are less affected by heat stress), whereas for Holstein it was approximately zero. Finally, our results indicated a weak antagonism between production and fertility, although for Montbeliarde this antagonism intensified with increasing THI.

CONCLUSIONS

Within the range of weather conditions studied, increasing temperatures are not expected to exacerbate the fertility-production trade-off. However, our results indicated that the animals with the best breeding values for production today will be the most affected by temperature increases, both in terms of fertility and production. Nonetheless, these animals should remain among the most productive ones during heat waves. For Montbeliarde, the current selection program for fertility seems to be adequate for ensuring the adaptation of fertility traits to temperature increases, without adverse effects on production. Such a conclusion cannot be drawn for Holstein. In the future, the incorporation of a heat tolerance index into dairy cattle breeding programs would be valuable to promote the selection of animals adapted to future climate conditions.

Short communication: Variability of response to feed restriction in lactating Charolais cows

Involuntary temporary feed restriction on commercial cattle is likely to become more frequent with forage shortages in the context of climate change. If general consequences of feed restriction have been the subject of an abundant scientific literature, focus on the inter-individual variability of response is scarce. Here, we explore the response profile in terms of BW, body condition score, milk production, calf weight and cyclicity resumption of 293 lactations from 169 Charolais cows during a winter feed restriction in early lactation and its subsequent recovery at grazing using a principal component analysis followed by a hierarchical clustering on principal component. Results show a very continuous range of response profiles that was divided into three clusters: one with light animals having an intermediate response in terms of milk production and body maintenance, one with animals prioritising body maintenance and cyclicity resumption over milk production and calf weight, and the last one with animals prioritising milk production and calf weight over the rest. Among the animals performing more than one lactation, 57% remain in the same cluster on two successive lactations. This work highlights that an average group response to feed restriction may hide various resilience individual profiles. Further studies are required to determine the existence of a genetic component as well as the consequences of not taking this phenomenon into consideration with the regular use of feed restriction in commercial farms.

Estimation of genotype by temperature-humidity index interactions on milk production and udder health traits in Montbeliarde cows

BACKGROUND

Heat stress negatively influences cattle welfare, health and productivity. To cope with the forecasted increases in temperature and heat waves frequency, identifying high-producing animals that are tolerant to heat is of capital importance to maintain milk production. This study, based on the joint analysis of on-farm performance and weather data, had two objectives: (1) to determine the response in production performances (milk, fat and protein yields, fat and protein contents) and udder health (somatic cell score) to temperature-humidity index (THI) variations in Montbeliarde cows, and (2) to estimate the interactions between genotype and THI, to enable the identification of the most adapted animals for facing the expected increases in temperature.

RESULTS

Test-day records from first and second lactations from 2016 to 2020 were associated with the average THI during the three days before the test-day record. In total, 446,717 test-day records from 55,650 cows in first lactation and 457,516 test-day records from 58,229 cows in second lactation were analysed. The optimal THI was below 55 (i.e. ~ 12-13 °C) for all traits. Individual responses to THI were estimated by random regression models, which also included individual responses to days in milk. Regardless of the stage of lactation, genetic correlations along the THI gradient were above 0.80, which suggests that genotype-by-THI interactions were weak for production and udder health traits. Nevertheless, a variability in the individual slope of decay could be highlighted at high THI. The genetic correlation between production level at moderate THI and the slope at high THI was negative, while for somatic cell score, it was positive, indicating that heat stress amplifies the susceptibility to mastitis.

CONCLUSIONS

The optimal THI for French Montbeliarde cows is below 55 for production and udder health traits. Genetic-by-THI interactions are weak in French Montbeliarde cows for production and udder health traits, but not all animals react in the same way to high temperatures. Even if there is little room for improvement, using a heat tolerance index in cattle selection would be relevant to anticipate the expected increases in temperature. Further investigations are needed to interpret this variability on production traits. However, the current selection for mastitis resistance seems appropriate to adapt cattle to rising temperatures.

The Blonde d'Aquitaine T3811>G3811 mutation in the myostatin gene: association with growth, carcass, and muscle phenotypes in veal calves

The mutation T3811 → G3811 (TG3811) discovered in the myostatin gene of the Blonde d'Aquitaine breed is suspected of contributing to the outstanding muscularity of this breed. An experiment was designed to estimate the effect of this mutation in an F2 and back-cross Blonde d'Aquitaine × Holstein population. By genotyping all known mutations in the myostatin gene, it was ensured that the TG3811 mutation was indeed the only known mutation segregating in this population. Fifty-six calves (43 F2, 13 back-cross) were intensively fattened and slaughtered at 24.0 ± 1.4 wk of age. The effects of the mutation were estimated by comparing the calves with the [T/T] (n = 18), [T/G] (n = 30), and [G/G] (n = 8) genotypes. Highly significant substitution effects (P < 0.001), above + 1.2 phenotypic SD, were shown on carcass yield and muscularity scores. Birth weight (P < 0.001) was positively affected by the mutation (+0.8 SD) but not growth rate (P = 0.97), while carcass length (P = 0.03), and fatness (P ≤ 0.03) were negatively affected (-0.5 to -0.7 SD). The characteristics of the Triceps brachii muscle were affected by the mutation (P < 0.001), with lower ICDH activity (oxidative) and a higher proportion of myosin type 2X muscle fibers (fast twitch). The effects of the TG3811 mutation were similar to those of other known myostatin mutations, although the Blonde d'Aquitaine animals, which are predominantly [G/G] homozygous, do not exhibit extreme double muscling.

Determination of immunoglobulin concentrations and genetic parameters for colostrum and calf serum in Charolais animals

Colostrum samples from 366 Charolais primiparous cows, as well as serum from their calves at 24 to 48 h of age, were collected to gain an overview of the situation regarding passive immune transfer in beef cattle, from both the phenotypic and genetic points of view. All samples were analyzed to quantify their G₁ immunoglobulins by radial immunodiffusion (RID) and their IgG, IgA, and IgM using ELISA. The average concentrations obtained in colostrum were 84 mg/mL for RID-IgG₁, and 158 mg/mL, 4.5 mg/mL and 10.8 mg/mL for ELISA-IgG, -IgA, and -IgM, respectively. The corresponding values in calf serum were 19.9, 30.6, 1.0, and 1.9 mg/mL. Apart from the general environmental effect (farm-year combination and laboratory conditions), the characteristics of the dams tested did not reveal any influence on colostrum immunoglobulin concentrations. Calving difficulty, as well as the birth weight and sex of calves, were found to be associated with serum concentrations in some cases. Heritability estimates were low to moderate, with the highest being for RID-IgG₁ in colostrum (h² = 0.28, standard error = 0.14) and serum (h² = 0.36, standard error = 0.18). Phenotypic correlations among the different immunoglobulins were generally positive or null, and none of the genetic correlations were significant due to large standard errors. The phenotypic correlation between dam colostrum and calf serum values was 0.2 for RID-IgG₁ and null for the 3 ELISA measurements. The correlation between RID-IgG₁ and ELISA-IgG was, unexpectedly, null for colostrum and 0.4 for serum. Increased RID-IgG₁ levels in calf serum were associated with improved survival, as well as better early growth and fewer health problems. These results thus showed that despite generally higher concentrations in beef than in dairy cattle, passive transfer was unsuccessful in a considerable number of calves. This should be brought to the attention of breeders to avoid negative effects on survival and subsequent performance. The heritability estimates were encouraging; however, obtaining phenotypes on a large scale constitutes a real limitation regarding these traits.

Methane and Carbon Dioxide Emission of Beef Heifers in Relation with Growth and Feed Efficiency

Simple Summary

For sustainable meat production, beef farmers must make the best use of grass and roughage while limiting the carbon footprint of their herds. The genetic improvement in feed efficiency and enteric methane production of replacement heifers is possible if the recorded phenotypes are available. Intuitively, the relationship between the two traits should be negative, i.e., favorable, since the energy lost with the methane is not available for heifer metabolism. The measurement of feed efficiency requires several weeks of feed intake recording. The enteric methane emission rate can also be recorded over several weeks. The two traits of 326 beef heifers from two experimental farms were measured simultaneously for 8 to 12 weeks. The correlations between roughage intake, daily gain, and methane were all positive. The enteric methane emission rate was positively related to body weight, daily gain, and dry matter intake. The relationship with feed efficiency was slightly positive, i.e., unfavorable. Therefore, the two traits should be recorded simultaneously to evidence low-emitting and efficient heifers. This study also showed that replacing the feed intake recording with the carbon dioxide emission rate appeared potentially beneficial for selecting these low-emitting and efficient heifers.

Abstract

Reducing enteric methane production and improving the feed efficiency of heifers on roughage diets are important selection objectives for sustainable beef production. The objective of the current study was to assess the relationship between different methane production and feed efficiency criteria of beef heifers fed ad libitum roughage diets. A total of 326 Charolais heifers aged 22 months were controlled in two farms and fed either a grass silage (n = 252) or a natural meadow hay (n = 74) diet. Methane (CH₄) and carbon dioxide (CO₂) emission rates (g/day) were measured with GreenFeed systems. The dry matter intake (DMI), average daily gain (ADG), CH₄ and CO₂ were measured over 8 to 12 weeks. Positive correlations were observed among body weight, DMI, ADG, CH₄ and CO₂. The residual feed intake (r_wgDMI) was not related to CH₄ or residual methane (r_wiCH₄). It was negatively correlated with methane yield (CH₄/DMI): R_p = −0.87 and −0.83. Residual gain (r_wiADG) and ADG/DMI were weakly and positively related to residual methane (r_wiCH₄): R_p = 0.21 on average. The ratio ADG/CO₂ appeared to be a useful proxy of ADG/DMI (R_p = 0.64 and 0.97) and CH₄/CO₂ a proxy of methane yield (R_p = 0.24 and 0.33) for selecting low-emitting and efficient heifers.

Genetic parameters and genome-wide association study regarding feed efficiency and slaughter traits in Charolais cows

Residual energy intake (REI) on two successive diets (hay and maize based) and slaughter traits, including visceral organs, were phenotyped in 584 adult purebred Charolais cows. To investigate the relationships between these traits and their genetic determinism, we first estimated the genetic parameters, including correlations, using REML modeling under WOMBAT software. The animals were then genotyped on the BovineSNP50 SNPchip before being imputed to the 600K density and genome wide association study was performed with GCTA software. We found low heritability for REI (h2 = 0.12 in each of the diet phases). Although the phenotypic correlation between the two diet phases was moderate (0.36), the genetic correlation was high (0.83), indicating a common genetic determinism for feed efficiency regardless of the diet. Correlations between REI and slaughter traits were negative regarding muscle-related traits and positive for fat-related traits, indicating that efficient animals generally had a more muscular carcass. It was also seen that feed efficiency was genetically and phenotypically correlated with smaller organs when expressed as a proportion of their empty body weight. From the GWAS analysis, seven QTLs were found to be associated with a trait at the genome-wide level of significance and 18 others at the chromosome-wide level. One important QTL was detected in BTA 2, reflecting the essential effect of the myostatin gene on both carcass composition and relative organ weight. Three QTLs were detected for REI during the maize diet phase on BTA 13, 19, and 28, the latter being significant at the genome-wide level. The QTLs on BTA 19 mapped into the TANC2 gene and the QTLs on BTA 28 into the KIF1BP gene, which are both known to interact with the same protein (KIF1A). However, no obvious functional link between these genes and feed efficiency could be made. Among the other QTLs detected, one association on BTA 4 with liver proportion mapped to the candidate gene WASL, which has previously been shown to be differentially expressed in liver cells and linked to feed restriction or cancer development. No QTLs were found to be common between feed efficiency and any slaughter traits.

Genetic analysis of calf health in Charolais beef cattle

The objective of this study was to investigate the factors that influence calf health and survival in Charolais cattle. Data from 2,740 calves, originating from 16 French farms and observed from birth until 30 d of age, were analyzed using models that took account of direct genetic, maternal genetic, and common environmental effects. Both direct and maternal genetic parameters were estimated for birth weight (BW), calving ease (CE), neonatal vitality (NV), survival at 30 d (Surv), and umbilical infection and diarrhea at different ages (0 to 5 d: Umb1 and Diar1; 6 to 20 d: Umb2 and Diar2; and 21 to 30 d: Umb3 and Diar3). The heritability values for direct and maternal genetic effects were, 0.026 (SE = 0.027) and 0.096 (SE = 0.042) for Surv, 0.280 (SE = 0.063) and 0.063 (SE = 0.038) for BW, 0.129 (SE = 0.041) and 0 for CE, 0.073 (SE = 0.035) and 0 for NV, 0.071 (SE = 0.038) and 0.017 (SE = 0.026) for Umb1, 0 and 0.082 (SE = 0.029) for Umb2, 0 and 0.044 (SE = 0.030) for Diar1, 0.016 (SE = 0.022) and 0.012 (SE = 0.026) for Diar2, and 0.016 (SE = 0.028) and 0 for Diar3, respectively. Significant genetic variability in beef cattle was thus revealed for five calf health traits: NV, Surv, Diar1, Umb1, and Umb2. In addition, for three traits (Surv, Diar1, and Umb2), maternal genetic effects clearly contributed more to health performance than direct genetic effects. Estimates of genetic correlation between traits varied markedly (from 0 to 1 in absolute values) depending on the traits in question, the age for a given trait, and the type (direct or maternal) of the genetic effects considered. These results suggest that not all health traits in Charolais cattle can be improved simultaneously, and breeders will therefore have to prioritize certain traits of interest in their breeding objectives. Overall, our results demonstrate the potential utility of collecting and integrating data on calf diseases, NV and survival in future beef cattle breeding programs. To ensure appropriate biological and genetic evaluations of calf health performance, it is important to accurately describe the phenotypes for diarrhea and umbilical infections (in terms of age ranges) and account for maternal genetic and common environmental effects that explain calf health performance traits. Further investigation and improved data collection are now necessary to maximize the efficiency of breeding schemes designed to simultaneously improve production and health traits.

Effects of dietary polyphenols on metabolic syndrome features in humans: a systematic review

Dietary polyphenols constitute a large family of bioactive substances potential beneficial effect on metabolic syndrome (MetS). This review summarizes the results of clinical studies on patients with MetS involving the chronic supplementation of a polyphenol-rich diet, foods, extracts or with single phenolics on the features of MetS (obesity, dyslipidemia, blood pressure and glycaemia) and associated complications (oxidative stress and inflammation). Polyphenols were shown to be efficient, especially at higher doses, and there were no specific foods or extracts able to alleviate all the features of MetS. Green tea, however, significantly reduced body mass index and waist circumference and improved lipid metabolism. Cocoa supplementation reduced blood pressure and blood glucose. Soy isoflavones, citrus products, hesperidin and quercetin improved lipid metabolism, whereas cinnamon reduced blood glucose. In numerous clinical studies, antioxidative and anti-inflammatory effects were not significant after polyphenol supplementation in patients with MetS. However, some trials pointed towards an improvement of endothelial function in patients supplemented with cocoa, anthocyanin-rich berries, hesperidin or resveratrol. Therefore, diets rich in polyphenols, such as the Mediterranean diet, which promote the consumption of diverse polyphenol-rich products could be an effective nutritional strategy to improve the health of patients with MetS. © 2016 The Authors. Obesity Reviews published by John Wiley & Sons Ltd on behalf of World Obesity.

Effect of antioxidant vitamin supplementation on endothelial function in type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials

Controversy exists among trials assessing whether prolonged antioxidant vitamin supplementation improves endothelial function in type 2 diabetes mellitus (T2DM) subjects. The aim of this study was to systematically review and quantify the effect of antioxidant vitamin supplementation on endothelial function in T2DM subjects. MEDLINE, Cochrane, Scopus and Web of Science were searched up to February 2013 for randomized controlled trials assessing the effect of antioxidant vitamin E and/or C supplementation on endothelial function in T2DM subjects. Ten randomized controlled trials comparing antioxidant vitamin-supplemented and control groups (overall n = 296) met the inclusion criteria. Post-intervention standardized mean difference (SMD) in endothelial function did not reach statistical significance between groups (0.35; 95% confidence interval = -0.17, 0.88; P = 0.18). In subgroup analysis, post-intervention endothelial function was significantly improved by antioxidant vitamin supplementation in T2DM subgroups with body mass index (BMI) ≤ 29.45 kg m(-2) (SMD = 1.02; P < 0.05), but not in T2DM subgroups with BMI > 29.45 kg m(-2) (SMD = -0.07; P = 0.70). In meta-regression, an inverse association was found between BMI and post-intervention SMD in endothelial function (B = -0.024, P = 0.02). Prolonged antioxidant vitamin E and/or C supplementation could be effective to improve endothelial function in non-obese T2DM subjects.

Genetic control of multiple births in low ovulating mammalian species

In mammals, litter size is a highly variable trait. Some species such as humans or cattle are monotocous, with one or sometimes two newborns per birth, whereas others, the polytocous species such as mice or pigs, are highly prolific and often produce a dozen newborns at each farrowing. In monotocous species, however, two or three newborns per birth may sometime be unwanted. In more polytocous species such as sheep or pigs, litter size is studied in order to increase livestock prolificacy. By contrast, twinning rates in humans or cattle may increase birth difficulties and health problems in the newborns. In this context, the aim of our review was to provide a clearer understanding of the genetic and physiological factors that control multiple births in low-ovulating mammalian species, with particular focus on three species: sheep, cattle, and humans, where knowledge of the ovulation rate in one may enlighten findings in the others. This article therefore reviews the phenotypic and genetic variability observed with respect to ovulation and twinning rates. It then presents the QTL and major genes that have been identified in each species. Finally, we draw a picture of the diversity of the physiological mechanisms underlying multiple ovulation. Although several major genes have been discovered in sheep, QTL detection methods in humans or cattle have suggested that the determinism of litter size is complex and probably involves several genes in order to explain variations in the number of ovulations.

Endothelial dysfunction, inflammation, and oxidative stress in obese children and adolescents: markers and effect of lifestyle intervention

With an increasing prevalence, pediatric obesity is often a prelude to adulthood obesity, and represents a major public health issue. Comorbidities are very common and severe in obese adults, justifying the search for earlier markers or risk factors for cardiovascular diseases in obese children. Endothelial dysfunction has been found to be present in the early stages of atherosclerosis, and can be non-invasively assessed with widely accepted and well-standardized techniques at the macrocirculation level. Endothelial dysfunction at the microcirculation level is less documented in obese children. Obesity in children has been repeatedly and independently correlated to endothelial dysfunction, inflammation and oxidative stress markers, although the relationship between these factors remains to be investigated. However, this would not only allow substantial improvements in risk stratification, but also provide essential data regarding the evolution of endothelial dysfunction in childhood obesity, especially during puberty when pro-inflammatory and pro-oxidative changes, with relative insulin resistance, occur. Therapeutic strategies such as lifestyle interventions in early childhood obesity appear all the more necessary, optimally including both exercise and diet because of their known effects on inflammatory and oxidative stress markers, potentially reversing endothelial dysfunction.

Automatic detection and classification of human epicardial atrial unipolar electrograms

This paper describes an unsupervised signal processing method applied to three-channel unipolar electrograms recorded from human atria. These were obtained by epicardial wires sutured on the right and left atria after coronary artery bypass surgery. Atrial (A) and ventricular (V) activations had to be detected and identified on each channel, and gathered across the channels when belonging to the same global event. The algorithm was developed and optimized on a training set of 19 recordings of 5 min. It was assessed on twenty-seven 2 h recordings taken just before the onset of a prolonged atrial fibrillation for a total of 1593697 activations that were validated and classified as normal atrial or ventricular activations (A, V) and premature atrial or ventricular activations (PAA, PVA). 99.93% of the activations were detected, and amongst these, 99.89% of the A and 99.75% of the V activations were correctly labelled. In the subset of the 39705 PAA, 99.83% were detected and 99.3% were correctly classified as A. The false positive rate was 0.37%. In conclusion, a reliable fully automatic detection and classification algorithm was developed that can detect and discriminate A and V activations from atrial recordings. It can provide the time series needed to develop a monitoring system aiming to identify dynamic predictors of forthcoming cardiac events such as postoperative atrial fibrillation.

Abnormal vascular reactivity at rest and exercise in obese boys

BACKGROUND

Obese children exhibit vascular disorders at rest depending on their pubertal status, degree of obesity, and level of insulin resistance. However, data regarding their vascular function during exercise remain scarce. The aims of the present study were to evaluate vascular morphology and function at rest, and lower limb blood flow during exercise, in prepubertal boys with mild-to-moderate obesity and in lean controls.

MATERIALS AND METHODS

Twelve moderately obese prepubertal boys [Body Mass Index (BMI: 23.9+/-2.6 kg m(-2))] and thirteen controls (BMI:17.4+/-1.8 kg m(-2)), matched for age (mean age: 11.6+/-0.6 years) were recruited. We measured carotid intima-media thickness (IMT) and wall compliance and incremental elastic modulus, resting brachial flow-mediated dilation (FMD) and nitrate-dependent dilation (NDD), lower limb blood flow during local knee-extensor incremental and maximal exercise, body fat content (DEXA), blood pressure, blood lipids, insulin and glucose.

RESULTS

Compared to lean controls, obese boys had greater IMT (0.47+/-0.06 vs. 0.42+/-0.03 mm, P<0.05) but lower FMD (4.6+/-2.8 vs. 8.8+/-3.2%, P<0.01) in spite of similar maximal shear rate, without NDD differences. Lower limb blood flow (mL min(-1).100 g(-1)) increased significantly from rest to maximal exercise in both groups, although obese children reached lower values than lean counterparts whatever the exercise intensity.

CONCLUSIONS

Mild-to-moderate obesity in prepubertal boys without insulin resistance is associated with impaired endothelial function and blunted muscle perfusion response to local dynamic exercise without alteration of vascular smooth muscle reactivity.

Alternans amplification following a two-stimulus protocol in a one-dimensional cardiac ionic model of reentry: from annihilation to double-wave quasiperiodic reentry

Electrical pacing is a common procedure in both experimental and clinical settings to study and/or annihilate anatomical reentry. A previous study [Comtois and Vinet, Chaos 12, 903 (2002)] has described new ways to terminate reentry in a one-dimensional loop model by a protocol consisting of only two stimulations. Annihilation of the reentrant activity was much more likely with these new scenarios than through a unidirectional block. This paper investigates the sensitivity of these scenarios of annihilation to the length of the pathway. It shows that double-pulse stimulation can stop the reentry if the circuit is shorter than a limiting length. Beyond this upper limit, stimulation rather yields sustained double-wave reentry. The same dynamical mechanism, labeled alternans amplification, is found to be responsible for these two types of post-stimulus dynamics.

Use of structured antedependence models for the genetic analysis of growth curves

Growth curve analysis is an important issue for many agricultural and laboratory species, for both phenotypic and genetic studies. The aim of this paper is to present the use of a novel statistical approach, namely the structured antedependence (SAD) models, to deal with this issue. The basic idea of these models is that an observation at time t can be explained by the previous observations. These models are especially appropriate to deal with cumulative traits such as growth, as BW at age t clearly depends on BW measures at ages (t -1), (t -2), etc. These models were applied on an INRA experimental Charolais herd data set. The data comprised BW records for 560 cows born over an 11-yr period (from 1988 to 1998) from 60 sires and 369 dams. The proposed SAD models were compared with the well-known random regression (RR) models that are already widely used in various areas of longitudinal data analysis. It was found that the SAD models fit the growth process better with far fewer parameters than the RR models (9 instead of 16 covariance parameters for the phenotypic analysis, and 14 instead of 21 for the genetic analysis). Despite this smaller number of covariance parameters, the likelihood value was found to be much higher with the SAD vs. the RR models, with a difference of 262.9 for the phenotypic analysis with a quartic polynomial for the RR and 751.5 for the genetic analysis with a cubic polynomial for both the genetic and environmental parts of the RR model. The SAD models also proved to be better able to interpolate missing values. Heritability, genetic, and environmental correlation coefficients were estimated for weights from birth to adulthood. The structured antedependence models proved, in this study, to be very appropriate to model growth data in a parsimonious and flexible way.

Reproducibility of automated pulse wave velocity measurement during exercise. Running head: pulse wave velocity during exercise

Pulse wave velocity measurement is used as an index of arterial stiffness. The purpose was to evaluate the reproducibility of pulse wave velocity measurement at rest, during exercise and recovery from exercise, using an automated device. Twelve healthy young adults (mean age 22.0 +/- 3.1 yrs) underwent an upright submaximal cycle test on two separate occasions, one week apart. Pulse wave velocity, systolic and diastolic blood pressures and heart rate were assessed at rest, during the last 2 min of exercise and 10 min later. Pulse wave velocity was measured on the upper limb and the forearm by the cross-correlation function of photoplethysmography and Doppler signals. Brachial artery pulse wave velocity was calculated from upper limb and forearm pulse wave velocities. No significant difference was found on duplicate measurements of heart rate, systolic and diastolic blood pressures at rest, during exercise and recovery, showing that pulse wave velocity was measured under similar conditions. Coefficient of variation for upper limb and forearm pulse wave velocities ranged from 2.9 to 5.9% at rest and during recovery, and were respectively 2.9% and 8.3% during exercise. However, coefficient of variation for brachial pulse wave velocity was 7.7 and 10.3% at rest, 15.7% during exercise, and 5.8% during recovery. During exercise, pulse wave velocity measurements were satisfying, but indirect assessment of brachial artery pulse wave velocity showed poor reproducibility. Thus, upper limb and forearm pulse wave velocities may be used during exercise to assess the effect of training or drugs on arterial wall mechanical properties.

Development and implementation of a participative intervention to improve the psychosocial work environment and mental health in an acute care hospital

OBJECTIVES

To describe the development and implementation phases of a participative intervention aimed at reducing four theory grounded and empirically supported adverse psychosocial work factors (high psychological demands, low decision latitude, low social support, and low reward), and their mental health effects.

METHODS

The intervention was realised among 500 care providers in an acute care hospital. A prior risk evaluation was performed, using a quantitative approach, to determine the prevalence of adverse psychosocial work factors and of psychological distress in the hospital compared to an appropriate reference population. In addition, a qualitative approach included observation in the care units, interviews with key informants, and collaborative work with an intervention team (IT) including all stakeholders.

RESULTS

The prior risk evaluation showed a high prevalence of adverse psychosocial factors and psychological distress among care providers compared to a representative sample of workers from the general population. Psychosocial variables at work associated with psychological distress in the prior risk evaluation were high psychological demands (prevalence ratio (PR) = 2.27), low social support from supervisors and co-workers (PR = 1.35), low reward (PR = 2.92), and effort-reward imbalance (PR = 2.65). These results showed the empirical relevance of an intervention on the four selected adverse psychosocial factors among care providers. Qualitative methods permitted the identification of 56 adverse conditions and of their solutions. Targets of intervention were related to team work and team spirit, staffing processes, work organisation, training, communication, and ergonomy.

CONCLUSION

This study adds to the scarce literature describing the development and implementation of preventive intervention aimed at reducing psychosocial factors at work and their health effects. Even if adverse conditions in the psychosocial environment and solutions identified in this study may be specific to the healthcare sector, the intervention process used (participative problem solving) appears highly exportable to other work organisations.

Effectiveness of a participative intervention on psychosocial work factors to prevent mental health problems in a hospital setting

OBJECTIVES

To assess the effectiveness of a workplace intervention aimed at reducing adverse psychosocial work factors (psychological demands, decision latitude, social support, and effort-reward imbalance) and mental health problems among care providers.

METHODS

A quasi-experimental design with a control group was used. Pre-intervention (71% response rate), and one-year post-intervention measures (69% response rate) were collected by telephone interviews.

RESULTS

One year after the intervention, there was a reduction of several adverse psychosocial factors in the experimental group, whereas no such reduction was found in the control group. However, there was a significant deterioration of decision latitude and social support from supervisors in both experimental and control groups. There was also a significant reduction in sleeping problems and work related burnout in the experimental hospital, whereas only sleeping problems decreased in the control group while both client related and personal burnout increased in this hospital. The comparison between the experimental and control groups, after adjusting for pre-intervention measures, showed a significant difference in the means of all psychosocial factors except decision latitude. All other factors were better in the experimental group.

CONCLUSION

Results suggest positive effects of the intervention, even though only 12 months have passed since the beginning of the intervention. Follow up at 36 months is necessary to evaluate whether observed effects are maintained over time. In light of these results, we believe that continuing the participative process in the experimental hospital will foster the achievement of a more important reduction of adverse psychosocial factors at work. It is expected that the intensity of the intervention will be directly related to its beneficial effects. Long term effects will however depend on the willingness of management and of staff to appropriate the process of identifying what contributes to adverse psychosocial factors at work and to adopt means to reduce them.

Effect of intensive training on heart rate variability in prepubertal swimmers

BACKGROUND

In children, there is very limited evidence focusing on the beneficial effect of exercise training on heart rate variability (HRV) during childhood. Despite the fact that more and more children are engaged in intensive training programs, the question arises if such intensive training involves deleterious effects on the cardiac autonomic nervous system during childhood. Thus the aim of the present study was to compare HRV parameters in highly trained swimmer boys and untrained counterparts.

METHODS

Twenty prepubertal boys, aged 11-12 years old, took part in the study. The children were divided into 11 highly trained prepubertal swimmers (training sessions of 8-10 h weekly for at least 4 years) and 9 age-matched active boys. HRV analysis was performed on diurnal recordings in the frequency (short-term recordings 6 min the most 'vagal') and time (long-term recordings 4 h centred on the 6 min most 'vagal') domains.

RESULTS

No significant differences were obtained between groups for all frequency variables whatever the mode of expression (absolute in ms2, relative in Ln or %). All time-domain components were not significantly different in swimmers and untrained boys.

CONCLUSIONS

The results of the present study demonstrate that participating intensively in swimming training does not induce in children changes in HRV indices. Neither time nor domain HRV variables were significantly different between untrained and highly trained prepubertal boys. Thus, intensive training in healthy children does not involve deleterious effects on HRV.

Relationships between Left Ventricular Morphology, Diastolic Function and Oxygen Carrying Capacity and Maximal Oxygen Uptake in Children

Little attention has been paid to children with respect to factors controlling maximal oxygen uptake (V.O (2max)). This study was therefore specifically designed to examine the potential relationships between cardiac size, diastolic function and O (2) carrying capacity with maximal aerobic capacity. Specifically, body size indices (body surface area, lean body mass), resting left ventricular dimensions and filling characteristics, blood haemoglobin concentration as well as V.O (2max) established during a maximal cycle exercise test were assessed in a large cohort (n = 142) of healthy 10 - 11 year old boys and girls. Results were compared between groups of low (< 50, L), moderate (50 - 60, M) and high (> 60, H) V.O (2max) (ml . min (-1) . kg (-1) of lean body mass). Moreover, potential contributors to V.O (2max) variance were investigated using univariate and multivariate regression analyses over the overall population. The major results show no differences between the 3 groups for all diastolic and systolic function indices as well as blood haemoglobin and systemic vascular resistances (used as an index of afterload). None of these variables emerged from regression analyses as potential predictors of V.O (2max.) After accounting for body size variation, heart dimensions, and especially left ventricular internal dimensions, differed between H and M and L and were associated with higher cardiac filling and subsequently stroke volume. Strong relationships between V.O (2max) and heart dimensions were noticed, due primarily but not exclusively to the influence of body size. After adjusting for lean body mass, end-diastolic diameter contributed modestly (8 %) but significantly to V.O (2max) variance, which is biologically meaningful.

Synchronization and symmetry-breaking bifurcations in constructive networks of coupled chaotic oscillators

The spatiotemporal dynamics of networks based on a ring of coupled oscillators with regular shortcuts beyond the nearest-neighbor couplings is studied by using master stability equations and numerical simulations. The generic criterion for dynamic synchronization has been extended to arbitrary network topologies with zero row-sum. The symmetry-breaking oscillation patterns that resulted from the Hopf bifurcation from synchronous states are analyzed by the symmetry group theory.

Cardiovascular responses to endurance training in children: effect of gender

BACKGROUND

The aim of the present study was to determine in healthy children the effect of a well-controlled endurance training programme on cardiac function at maximal exercise and to define whether gender affects the training-induced cardiovascular response. The contribution of factors potentially involved in those adaptations such as cardiac dimensions and diastolic and systolic function was also investigated.

METHODS

Thirty-five l0-11-year-old children took part in this study: 19 children (10 girls and nine boys) were assigned to participate in a 13-week endurance training programme (3 x 1 h week-1, intensity: > 80% HR max), and 16 (seven girls and nine boys) served as a control group. A resting echocardiographic evaluation and a maximal upright cycle test, including measurement of stroke volume (SV), cardiac output (Q) and blood pressure, were performed in all children before and after the study period.

RESULTS

The training programme led to a rise in maximal O2 uptake (VO2max), brought about however, only by an increase in SVmax in both genders. Moreover, the boys increased their VO2max to a greater extent than the girls (boys: +15%; girls: +8%) only because of a higher SVmax improvement (boys: +15%; girls: +11%). No alterations were noticed in the SV pattern from rest to maximal exercise, indicating that the increase in SVrest was a key factor in the improvement of SVmax and thus VO2max. Regarding resting echocardiographic data, an increase in the left ventricular end-diastolic diameter, concomitant with an improvement in diastolic function, was observed after training and constituted an essential element in the rise in VO2max after training in these children. Moreover, during maximal exercise, a decrease in systemic vascular resistances, probably indicating peripheral cardiovascular adaptive changes, might also play an important role in the increase in VO2max.

CONCLUSION

Whatever gender, aerobic training increases VO2max in children, mediated by an improvement in SVmax only. Similar mechanisms, including loading conditions and cardiac morphology, seem to be involved in both genders in order to explain such an improvement.

Prediction of VO(2peak) in wheelchair-dependent athletes from the adapted Léger and Boucher test

PURPOSE

:The purpose of this study was to provide a predictive peak oxygen uptake ([V]O(2) peak) equation in wheelchair-dependent athletes using the Adapted Léger and Boucher test. SUBJECTS AND PROTOCOL: :Fifty-six wheelchair-dependent athletes, 47 males and nine females (30.3+/-4 years), underwent a clinical examination to assess their anthropometric characteristics: height, mass, body mass index (BMI), lean body mass, arm length, and muscular arm volume. They performed a deceleration field test to assess the subject-wheelchair resistance defined as a mechanical variable, and they then performed the Adapted Léger and Boucher test to assess physiological data at maximal exercise ([V]O(2) peak, heart rate max) concomitantly with biomechanical (number of pushes) and performance variables (maximal aerobic velocity Va(max) and maximal distance). The [V]O(2) peak was measured directly using a portable telemetric oxygen analyzer. Subjects were then randomly assigned to an experimental group (n=49) to determine the predictive equation, and a validation group (n=7) to check the external validity of the equation.

RESULTS

A stepwise multiple regression with [V]O(2) peak (l min(-1)) as the dependent variable led to the following equation: [V]O(2) peak=0.22 Va(max) - 0.63 log(age)+0.05 BMI 0.25 level+0.52, with r(2)=0.81 and SEE=0.01. Paraplegic subjects with high and low lesion level spinal injuries were attributed the coefficient of 1 and 0, respectively. The external validity of the equation was positive since the predicted [V]O(2) peak values did not significantly differ from directly measured [V]O(2) peak (P>0.05).

CONCLUSION

We concluded that [V]O(2) peak in wheelchair-dependent athletes was predictable using the equation of the present study and the described incremental test.

Central and peripheral cardiovascular adaptations to exercise in endurance-trained children

Stroke volume (SV) response to exercise depends on changes in cardiac filling, intrinsic myocardial contractility and left ventricular afterload. The aim of the present study was to identify whether these variables are influenced by endurance training in pre-pubertal children during a maximal cycle test. SV, cardiac output (Doppler echocardiography), left ventricular dimensions (time-movement echocardiography) as well as arterial pressure and systemic vascular resistances were assessed in 10 child cyclists (VO2max: 58.5 +/- 4.4 mL min-1 kg-1) and 13 untrained children (UTC) (VO2max: 45.9 +/- 6.7 mL min-1 kg-1). All variables were measured at the end of the resting period, during the final minute of each workload and during the last minute of the progressive maximal aerobic test. At rest and during exercise, stroke index was significantly higher in the child cyclists than in UTC. However, the SV patterns were strictly similar for both groups. Moreover, the patterns of diastolic and systolic left ventricular dimensions, and the pattern of systemic vascular resistance of the child cyclists mimicked those of the UTC. SV patterns, as well as their underlying mechanisms, were not altered by endurance training in children. This result implied that the higher maximal SV obtained in child cyclists depended on factors influencing resting SV, such as cardiac hypertrophy, augmented myocardium relaxation properties or expanded blood volume.

Cardiovascular responses to progressive cycle exercise in healthy children and adults

The aim of this study was to compare resting, relative submaximal (at the same percentage of maximal oxygen uptake) and maximal cardiovascular responses to progressive cycle exercise in pre-pubertal children and young adults with similar aerobic aptitude. Fourteen healthy children (7 girls and 7 boys) with a mean age of 10.8 yr and 16 healthy young adults (8 women and 8 men) with a mean age of 22.4 yr underwent a progressive cycle test until exhaustion with estimation of stroke volume and cardiac output by Doppler echocardiography. Submaximal responses were evaluated at similar exercise intensities (around 40, 60 and 80 % of maximal oxygen uptake). Mean submaximal and maximal oxygen uptake were not significantly different between the children and the adults. As expected, the adults demonstrated larger absolute values of stroke volume and cardiac output at all levels of intensity but when related to body surface area, the differences disappeared. The relationships between cardiac output and oxygen uptake calculated from comparable submaximal intensities were similar (slopes and intercepts) in the children and the adults. According to these results, it seems that the lower cardiovascular responses to exercise in children may be attributed to their smaller heart size.

Effect of a 13-week aerobic training programme on the maximal power developed during a force-velocity test in prepubertal boys and girls

The present study was undertaken in order to evaluate the effect of an aerobic training programme on the maximal power (Pmax) developed during a short-term exercise test in prepubertal children. Thirty-three 10-11 year old boys and girls were investigated: 17 (TG) participated twice a week (1 h per session) in a 13-week running programme and 16 (CG) served as a control group. Pmax was measured during a force-velocity test conducted on a friction-loaded cycle ergometer. The force (Fopt) and velocity (Vopt) at which Pmax was obtained were determined. Lower limb muscle mass (LMM) was evaluated by means of dual X-ray absorptiometry. Following training, Pmax increased even when muscle mass change due to the growth process was taken into account (Pmax W: + 23 %, W x kg(-1) LMM: + 18%, p < 0.001). The increase in Fopt was principally responsible for such an improvement since no alteration was noticed for Vopt after training. As for Pmax, Fopt was still greater following training when LMM was taken into account (p < 0.01). Furthermore, no changes were noticed for CG for all variables evaluated during the anaerobic test after the study period. Differences between TG and CG regarding Pmax and Fopt were obtained after training only. In conclusion this study highlights the effectiveness of an aerobic training programme to improve the maximal power during short-term exercise in prepubertal children.

Reproducibility of cardiac output measurements by Doppler echocardiography in prepubertal children and adults

The aim of this study was to examine reproducibility of stroke volume and cardiac output measurements by Doppler echocardiography during submaximal and maximal exercise in adults and children. Fourteen healthy children (8 girls and 6 boys aged 10.9 +/- 0.9yr) and eleven healthy young adults (1 female and 10 males aged 22.3 +/- 3.8 yr) underwent a progressive maximal upright cycle test until exhaustion with estimation of stroke volume and cardiac output by Doppler echocardiography on two separate occasions (one week apart). Maximal oxygen uptake and maximal heart rate were not significantly different between both tests in the children and adults indicating that similar exhaustive efforts were achieved at each test. No significant differences for mean values of stroke volume and cardiac output were observed at rest in the children and whatever the exercise intensity in the children and adults. No significant differences were observed between values of root mean square (precision and precision of error) in both groups. Thus we demonstrated that stroke volume and cardiac output values obtained by Doppler echocardiography at rest and during submaximal and maximal exercise were reproducible on test-retest measurements in children and adults.

Effect of aerobic training and detraining on left ventricular dimensions and diastolic function in prepubertal boys and girls

PURPOSE

The purpose of this study was to determine the effect of an aerobic training program on the left ventricular (LV) cardiac morphology and function of prepubertal children.

METHODS

Twenty-nine 10-11 year old boys and girls (TG) participated in a 13-week running program (3 x 1 h/week, intensity: > 80% HRmax), 26, of the same age, served as a control group (CG). M-mode, 2-dimensional and pulsed-wave Doppler analyses were performed, during resting conditions, before and after the training period (T) as well as, for TG only, after 2 months of detraining (D).

RESULTS

LV internal chamber dimension increased (+ 4.6 %, p < 0.01) while wall thicknesses concomitantly decreased (-10.7%, p < 0.05) as a result of T. All cardiac morphological parameters returned to pretraining values after D. Doppler-derived measurements of LV diastolic filling performance were also significantly altered by Tand D. A significant enhancement in the early diastolic passive LV filling with a concomitant reduction in the late diastolic active LV filling were in fact obtained after T. The training-induced bradycardia (-7 beats x min(-1), p < 0.01) was probably responsible for the changes in the late characteristics of the diastolic active filling. All diastolic filling indexes returned to pretraining values after D. Systolic function indexes were not modified after either T or D. No changes were obtained for the overall LV morphological and functional variables after 13 weeks of normal life for CG.

CONCLUSION

These findings indicate that cardiac morphological adaptations can occur in prepubertal children after several months of aerobic training. These alterations differ however, in some areas, to those classically reported in adults following endurance training programs where both an increase in LV size and mass exist. Our data likewise demonstrate that endurance training is able to induce favourable LV diastolic filling modifications, directed principally towards an enhancement in the early rapid filling inflow and a corresponding reduction in the atrial contribution to the total diastolic inflow.

[Study of the reproducibility of cardiac output measurement during exercise in pre-pubertal children by doppler echocardiography and CO2 inhalation]

Non-invasive measurement of the cardiac output is essential in investigations of healthy children. However, the data concerning the reproducibility of the measurements are very limited. The aim of this study was to assess the reproducibility of the measurement of cardiac output during exercise by Doppler echocardiography and reinhalation of CO2 (extrapolation method). Fourteen pre-pubertal children underwent two similar tests at increasingly intense levels of exercise. The cardiac output was measured at rest and during the last minute of each stepwise increment of exercise. The results show no difference between the cardiac outputs of the two tests, whichever method was used and at all levels of exercise. They also demonstrate a better reproducibility of cardiac output measurement by Doppler echocardiography (coefficient of variation: 7.5% at rest and 5.2% at maximal effort) compared with reinhalation of CO2 (coefficient of variation: 16.8% at rest and 11.7% at maximal effort). Both methods showed better reproducibility on exercise, resulting from smaller variations in heart rate and stroke volume on effort than at rest. The authors conclude that Doppler echocardiography is very accurate and its simplicity makes it the method of choice in pre-pubertal children for measuring cardiac output during exercise.

Onset dynamics of reentrant tachycardia and rate-dependent conduction changes in canine ventricular muscle: effects of Na+ and Ca2+ channel blockade

To show that cycle-length (CL) prolongation occurring at the onset of reentrant tachycardias may be associated with an increase in conduction time (CT), and to investigate the involvement of Na+ and Ca2+ channel activity, reentrant activity was induced by programmed stimulation in thin ventricular muscle slices with a central cryothermal lesion, as documented with 7 to 12 bipolar recordings. We studied the course of the CL measured in successive tachycardia beats, as well as the course of conduction times after abrupt transition from a pacing CL of 1,000 to 400 ms (pacing paradigm). The majority of the tachycardias displayed a dynamic behavior in which CL increased progressively, with an exponential rate constant of 37 +/- 35 beats (mean +/- SD), stabilizing at 325 +/- 67 ms after a total increase of 17 +/- 17 ms. In the pacing paradigm, CT was prolonged from 68 +/- 21 ms to 79 +/- 24 ms according to a biphasic course consisting of an abrupt increase in the first response to 400 ms, followed up by an exponential increase, stabilizing with a rate constant of 18 +/- 23 beats. Lidocaine 5 x 10(-5) mol/L induced an increase in steady-state CT, which was not further modified by adding verapamil 10(-5) mol/L. However, verapamil prolonged the rate constant of the exponential course by 60 +/- 40 beats. Thus, the onset dynamics of reentrant tachycardias share common features with the dynamic behavior of CT in the pacing paradigm, in which both Na+ channel activity and Ca2+-modulated cellular coupling appear to be involved.

Influence of propafenone on resetting and termination of canine atrial flutter

Previous studies on atrial flutter (AF) presumed that resetting was due to the prematurity effect (PE) in which the stimulated antegrade wavefront travels in the tail of the AF preexisting wavefront. We studied the collision effect (CE) between the AF and the stimulated retrograde wavefronts, its contribution to resetting, and its relationship to AF termination and how they are affected by the Class IC agent propafenone (PPF). A canine model of AF was created using a Y-shaped lesion in the right atrium in 14 dogs (33 +/- 3 kg). Five atrial bipolar electrodes were positioned around the tricuspid valve. In a subsequent set of 11 dogs, we used 16 bipolar electrodes for recording. AF was induced by burst pacing. Single and multiple stimuli were applied to measure conduction time and reset-response curves (RRCs). This was repeated after the administration of PPF (1 mg/kg loading dose for 10 minutes, followed by 1.8 mg/kg/per hour infusion). Three distinct mechanisms were found to contribute to the RRC: the PE, the CE, and heterogeneity. PPF stabilized the RRC, increased significantly the cycle length (CL), the duration of the effective refractory period, as well as the duration of the excitable gap. However, PPF did not alter the duration of the fully excitable portion. We studied 36 annihilations without and 48 with PPF. Transient fibrillation was found in 75% of the episodes without, compared to 22% with PPF. Other types of termination such as conduction block, CL oscillations, and reversal of activation were found for 25% of the episodes without and 78% with PPF. In many cases, conduction block and CL oscillations were associated with a failure of propagation of the stimulated antegrade wavefront in the region of collision. Termination by reversal of activation suggests that propagation was two dimensional and could not be represented by a one dimensional movement. The average coupling interval (in percent of CL), that induced fibrillation was not significantly different from that at which conduction block occurred. This suggests that transient fibrillation is associated with a weak CE rather than with rapid pacing. The CE is amplified by multiple stimuli and PPF. The incidence of transient fibrillation in AF annihilation diminishes with PPF as the CE becomes more important. This suggests that the evaluation of PE and CE in AF may be an indication of the risk of atrial fibrillation.