The cardiovascular and intracranial effects of laryngoscopy and endotracheal intubation in hypercarbic neonatal piglets

Laryngoscopy and endotracheal intubation is a potent sympathetic stimulus in adults. Neonates are frequendy intubated, but few data exist on the cerebral effects of this intervention. The cardiovascular and intracranial effects of laryngoscopy and endotracheal intubation were studied in 17 hypercarbic neonatal piglets. The mean arterial pressure in the study group (11 piglets) increased significandy within 2 minutes of the stimulus, and remained elevated for almost 14 minutes. The intubated animals showed significantly more haemorrhage in the basal area of the brain than the 6 control animals. The distribution suggests bleeding in the choroid plexus of the 4th ventricle. The significance of such bleeds is not immediately apparent, since none of the animals was grossly neurologically affected by the intervention. However, subtle long-term neurological deficits cannot be excluded and this aspect requires further study. Laryngoscopy and endotracheal intubation may cause non-lethal haemorrhage in the choroid plexus and central canal of the hindbrain  in hypercarbic, neonatal piglets

Validation of a Single-Nucleotide Polymorphism-Based Non-Invasive Prenatal Test in Twin Gestations : Determination of Zygosity, Individual Fetal Sex, and Fetal Aneuploidy

We analyzed maternal plasma cell-free DNA samples from twin pregnancies in a prospective blinded study to validate a single-nucleotide polymorphism (SNP)-based non-invasive prenatal test (NIPT) for zygosity, fetal sex, and aneuploidy. Zygosity was evaluated by looking for either one or two fetal genome complements, fetal sex was evaluated by evaluating Y-chromosome loci, and aneuploidy was assessed through SNP ratios. Zygosity was correctly predicted in 100% of cases (93/93; 95% confidence interval (CI) 96.1%-100%). Individual fetal sex for both twins was also called with 100% accuracy (102/102; 95% weighted CI 95.2%-100%). All cases with copy number truth were also correctly identified. The dizygotic aneuploidy sensitivity was 100% (10/10; 95% CI 69.2%-100%), and overall specificity was 100% (96/96; 95% weighted CI, 94.8%-100%). The mean fetal fraction (FF) of monozygotic twins (n = 43) was 13.0% (standard deviation (SD), 4.5%); for dizygotic twins (n = 79), the mean lower FF was 6.5% (SD, 3.1%) and the mean higher FF was 8.1% (SD, 3.5%). We conclude SNP-based NIPT for zygosity is of value when chorionicity is uncertain or anomalies are identified. Zygosity, fetal sex, and aneuploidy are complementary evaluations that can be carried out on the same specimen as early as 9 weeks' gestation

Essays on the term structure of equity returns

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Economics, September, 2020Cataloged from student-submitted PDF of thesis.Includes bibliographical references.This dissertation contains three essays on the term structure of equity returns. In the first chapter I document substantial variation in the cross-section of the term premium of US stocks between 1996 and 2019. I introduce a model with multiple stocks and an SDF with two priced sources of risk - dividend volatility risk and discount rate risk - which generates an economy with both upward and downward sloping equity term structures. The model creates two hypotheses: (1) dividend strips of stocks with more volatile dividends should earn higher returns, and (2) controlling for dividend volatility, cash flow duration should increase a stock's term premium. I use the Fama-French factors to empirically validate the model, with factor regressions explaining the majority of variation in term premia. The second chapter studies the relationship between the low volatility anomaly and the equity term structure. I show that dividend strip returns are positively related to measures of risk and volatility, while term premium returns are negatively related to risk and volatility. This generates a puzzle for explanations of the low volatility anomaly based on general preference for volatility, such as leverage constraints, that cannot distinguish across the term structure. The results support market specific explanations such as behavioral models of utility over realized gains (as opposed to unrealized paper gains) from investments. The third chapter studies the effect of buybacks on the equity term premium. First, I show that firms that conduct a buyback for the first time see an immediate drop in the returns to their dividend strips (due to unfulfilled dividend expectations), and a concurrent increase in their term premia. This confirms that buybacks do indeed substitute for dividends. Second, I show that firms that have repurchased shares earn a "buyback premium" due to the fact that cash flows may be returned as repurchases instead of dividends.by Layne David Kirshon.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Economic