A Model Analysis of Arterial Oxygen Desaturation during Apnea in Preterm Infants

Rapid arterial O2 desaturation during apnea in the preterm infant has obvious clinical implications but to date no adequate explanation for why it exists. Understanding the factors influencing the rate of arterial O2 desaturation during apnea () is complicated by the non-linear O2 dissociation curve, falling pulmonary O2 uptake, and by the fact that O2 desaturation is biphasic, exhibiting a rapid phase (stage 1) followed by a slower phase when severe desaturation develops (stage 2). Using a mathematical model incorporating pulmonary uptake dynamics, we found that elevated metabolic O2 consumption accelerates throughout the entire desaturation process. By contrast, the remaining factors have a restricted temporal influence: low pre-apneic alveolar causes an early onset of desaturation, but thereafter has little impact; reduced lung volume, hemoglobin content or cardiac output, accelerates during stage 1, and finally, total blood O2 capacity (blood volume and hemoglobin content) alone determines during stage 2. Preterm infants with elevated metabolic rate, respiratory depression, low lung volume, impaired cardiac reserve, anemia, or hypovolemia, are at risk for rapid and profound apneic hypoxemia. Our insights provide a basic physiological framework that may guide clinical interpretation and design of interventions for preventing sudden apneic hypoxemia

Early Gnathostome Phylogeny Revisited: Multiple Method Consensus

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.A series of recent studies recovered consistent phylogenetic scenarios of jawed vertebrates, such as the paraphyly of placoderms with respect to crown gnathostomes, and antiarchs as the sister group of all other jawed vertebrates. However, some of the hylogenetic relationships within the group have remained controversial, such as the positions of Entelognathus, ptyctodontids, and the Guiyu-lineage that comprises Guiyu, Psarolepis and Achoania. The revision of the dataset in a recent study reveals a modified phylogenetic hypothesis, which shows that some of these phylogenetic conflicts were sourced from a few inadvertent miscodings. The interrelationships of early gnathostomes are addressed based on a combined new dataset with 103 taxa and 335 characters, which is the most comprehensive morphological dataset constructed to date. This dataset is investigated in a phylogenetic context using maximum parsimony (MP), Bayesian inference (BI) and maximum likelihood (ML) approaches in an attempt to explore the consensus and incongruence between the hypotheses of early gnathostome interrelationships recovered from different methods. Our findings consistently corroborate the paraphyly of placoderms, all `acanthodians' as a paraphyletic stem group of chondrichthyans, Entelognathus as a stem gnathostome, and the Guiyu-lineage as stem sarcopterygians. The incongruence using different methods is less significant than the consensus, and mainly relates to the positions of the placoderm Wuttagoonaspis, the stem chondrichthyan Ramirosuarezia, and the stem osteichthyan LophosteusÐthe taxa that are either poorly known or highly specialized in character complement. Given that the different performances of each phylogenetic approach, our study provides an empirical case that the multiple phylogenetic analyses of morphological data are mutually complementary rather than redundant

Révision de l'ichthyostratigraphie du Silurien supérieur-Dévonien inférieur du nord de la France et du sud de la Belgique (Artois-Ardenne)

Le Silurien supérieur-Dévonien inférieur de la région Ardenne-Artois a livré 39 localités fossilifères à Vertébrés que l&#39;on peut corréler au moins aux séquences à Vertébrés de la Bordure Galloise (Angleterre) et du Spitsberg. Les invertébrés et palynomorphes présents autorisent des corrélations avec les faciès marins, ailleurs en Europe. La mise en relation de l&#39;échelle biostratigraphique fondée sur les Vertébrés avec celle qui est fondée sur les Conodontes-Graptolites-Dacryoconarides n&#39;est pas résolue. Cependant l&#39;acmé des faunes de Vertébrés dans la partie inférieure de la zone à crouchi en Artois pourrait être liée au haut niveau marin de la zone à eurekaensis. A l&#39;inverse, l&#39;appauvrissement des faunes des zones à leachi supérieure et à dunensis inférieure serait lié au bas niveau marin du Lochkovien supérieur-Praguien.39 localities within the Upper Silurian-Lower Devonian sequence of the Ardenne-Artois area yield vertebrate species which allow correlation with at least the vertebrate succession of the Welsh Borderland, England, and of Spitsbergen. Invertebrate fossils and palynomorphs suggest a correlation with the marine facies elsewhere in Europe. Relating the vertebrate biostratigraphy to that of conodont-graptolite-dacryoconarids is problematic but the postulated acme of the local vertebrate faunas in the lower crouchi zone of Artois may be related to the high sea level of the eurekaensis zone, and the impoverishment of the upper leachi and lower dunensis zones to the low sea level of the upper Lochkovian-Pragian.</p

Pr\ue9sence de sables helv\ue9tiens d\u27origine fluviatile sous les faluns du bassin de Noyant-sous-Le-Lude (Maine-et-Loire)

Volume: 42Start Page: 435End Page: 43

Recent Advances in the (Molecular) Phylogeny of Vertebrates

The analysis of molecular phylogenetic data has advanced the knowledge of the relationships among the major groups of living vertebrates. Whereas the molecular hypotheses generally agree with traditional morphology-based systematics, they sometimes contradict them.We reviewthe major controversies in vertebrate phylogenetics and the contribution of molecular phylogenetic data to their resolution: (a) the mono-paraphyly of cyclostomes, (b) the relationships among the major groups of rayfinned fish, (c) the identity of the living sistergroup of tetrapods, (d ) the relationships among the living orders of amphibians, (e) the phylogeny of amniotes with particular emphasis on the position of turtles as diapsids, (f ) ordinal relationships among birds, and (g) the radiation of mammals with specific attention to the phylogenetic relationships among the monotremes, marsupial, and placental mammals. We present a discussion of limitations of currently used molecular markers and phylogenetic methods as well as make recommendations for future approaches and sets of marker genes