[Reference ranges for M-mode echocardiographic measurements within seven days after birth in preterm infants]

Objective: To establish reference ranges for M-mode echocardiography in preterm infants within 7 days after birth based on different gestational age (GA) and birth weight. Methods: This retrospective study analyzed M-mode echocardiographic values of 489 premature infants, who were admitted to the neonatal intensive care unit of Department of Pediatrics, Peking University Third Hospital from March 2017 to February 2020. These infants were divided into four groups according to GA:<28 weeks, 28-31⁺⁶weeks, 32-33⁺⁶weeks and 34-36⁺⁶weeks; and five groups according to birth weight:<1 000 g, 1 000-1 499 g, 1 500-1 999 g, 2 000-2 499 g and ≥2 500 g. The M-mode values among groups were compared by independent sample K-W test, and based on which, the 95% confidence interval (CI) and the Z-value reference ranges were established. Results: The gestational age of these infants was 32.0 (24.0-36.7) weeks, and the birth weight was 1 700 (650-3 180) g. The interventricular septum end-diastolic thickness (IVSd), left ventricular posterior wall end-diastolic thickness (LVPWd), left atrial diameter (LAD), left ventricular end-diastolic diameter (LVED), left ventricular end-systolic diameter (LVES), right ventricular outflow tract (RVOT) and the right ventricular end-diastolic diameter (RVED), were all correlated with GA and birth weight (r = 0.209, 0.216, 0.430, 0.608, 0.495, 0.464, 0.447; r = 0.275, 0.288, 0.445, 0.609, 0.496, 0.499, 0.464;all P<0.01). While the left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) had no correlation with GA or birth weight (all P<0.05). Within the first 7 days after birth, the greater the GA and birth weight, the greater the inner diameters of the heart chambers, and the thicker the ventricular wall. The LVEF and LVFS maintained a high and stable level within the first week of life (95%CI: 67%-69%, 34%-36%). Conclusions: According to different GA and birth weight, the reference ranges for chamber diameters, interventricular septal thickness and left ventricular wall thickness within 7 days were established. The 95% CI and Z score ranges for M-mode echocardiographic measurements established based on gestational age and birth weight can provide a reliable reference for preterm infants aged 0-7 days.

Iron-Catalyzed Direct Olefin Diazidation via Peroxyester Activation Promoted by Nitrogen-Based Ligands

We herein report an iron-catalyzed direct diazidation method via activation of bench-stable peroxyesters promoted by nitrogen-based ligands. This method is effective for a broad range of olefins and N-heterocycles, including those that are difficult substrates for the existing olefin diamination and diazidation methods. Notably, nearly a stoichiometric amount of oxidant and TMSN₃ are sufficient for high-yielding diazidation for most substrates. Preliminary mechanistic studies elucidated the similarities and differences between this method and the benziodoxole-based olefin diazidation method previously developed by us. This method effectively addresses the limitations of the existing olefin diazidation methods. Most notably, previously problematic nonproductive oxidant decomposition can be minimized. Furthermore, X-ray crystallographic studies suggest that an iron-azide-ligand complex can be generated in situ from an iron acetate precatalyst and that it may facilitate peroxyester activation and the rate-determining C-N₃ bond formation during diazidation of unstrained olefins.

Practical Synthetic Procedures for the Iron-Catalyzed Intermolecular Olefin Aminohydroxylation Using Functionalized Hydroxylamines

A set of practical synthetic procedures for the iron-catalyzed intermolecular olefin aminohydroxylation reactions in gram scale is reported. In these transformations, a bench-stable functionalized hydroxylamine is applied as the amination reagent. This method is compatible with a broad range of synthetically valuable olefins including those that are incompatible with the existing aminohydroxylation methods. It also provides valuable amino alcohol building blocks with regio- and stereo-chemical arrays that are complementary to known methods.

Iron(II)-Catalyzed Intermolecular Aminofluorination of Unfunctionalized Olefins Using Fluoride Ion

We herein report a new catalytic method for intermolecular olefin aminofluorination using earth-abundant iron catalysts and nucleophilic fluoride ion. This method tolerates a broad range of unfunctionalized olefins, especially nonstyrenyl olefins that are incompatible with existing olefin aminofluorination methods. This new iron-catalyzed process directly converts readily available olefins to internal vicinal fluoro carbamates with high regioselectivity (N vs F), many of which are difficult to prepare using known methods. Preliminary mechanistic studies demonstrate that it is possible to exert asymmetric induction using chiral iron catalysts and that both an iron-nitrenoid and carbocation species may be reactive intermediates.

Iron-Catalyzed Direct Diazidation for a Broad Range of Olefins

Reported herein is a new iron-catalyzed diastereoselective olefin diazidation reaction which occurs at room temperature (1-5 mol% of catalysts and d.r. values of up to >20:1). This method tolerates a broad range of both unfunctionalized and highly functionalized olefins, including those that are incompatible with existing methods. It also provides a convenient approach to vicinal primary diamines as well as other synthetically valuable nitrogen-containing building blocks which are difficult to obtain with alternative methods. Preliminary mechanistic studies suggest that the reaction may proceed through a new mechanistic pathway in which both Lewis acid activation and iron-enabled redox-catalysis are crucial for selective azido-group transfer.

Iron(II)-catalyzed intermolecular amino-oxygenation of olefins through the N-O bond cleavage of functionalized hydroxylamines

An iron-catalyzed diastereoselective intermolecular olefin amino-oxygenation reaction is reported, which proceeds via an iron-nitrenoid generated by the N-O bond cleavage of a functionalized hydroxylamine. In this reaction, a bench-stable hydroxylamine derivative is used as the amination reagent and oxidant. This method tolerates a range of synthetically valuable substrates that have been all incompatible with existing amino-oxygenation methods. It can also provide amino alcohol derivatives with regio- and stereochemical arrays complementary to known amino-oxygenation methods.

A technique of double-resonant operation of 19F and 1H quadrature birdcage coils

A technique was developed to change the resonant frequency of a rotating field birdcage coil from 19F resonance (76.14 MHz) to 1H resonance (80.92 MHz). This was done by inserting an additional shield with a smaller radius on the coil which resonates at 19F. It was shown that the inhomogeneity introduced by reducing the shield radius is not significant. A working coil built with this technique produced both 19F and 1H images satisfactorily.

A mathematical description of pressures in alveolar pores of Kohn

Small interalveolar holes within the lung are called pores of Kohn. Some researchers have correlated enlarged pore size with diseases, e.g. emphysema, that are characterized by tissue destruction. Mathematical models of the pressures generated in closed, fluid-filled and open, fluid-lined pores demonstrate that pressures capable of rupturing lung tissue can be developed in a pore due to the surface tension and shape of the air-liquid interface. Pore enlargement accompanied by tissue destruction is presented as a possible mechanism for the disease process observed during aging and the development of emphysema in the lung.

The evaluation of quantitative autoradiogram processing systems for cerebrovascular research

The development of an image processing system for quantitative autoradiography (QAR) is described, with emphasis on the evaluation of image digitization systems independent of hardware or software design. Each step of converting the autoradiographic image to a functional image of a physiological variable such as local cerebral blood flow (LCBF) or local cerebral glucose utilization rate (LCGU) is evaluated. The autoradiograms are digitized, aligned, transformed to a tissue tracer concentrations image based on the gray value (GV) of calibrated 14C standards, subtracted from each other as required in double tracer QAR, and converted to an LCBF or LCGU image using the proper tracer kinetic model. Geometric size, mean and standard deviation of the LCBF, LCGU, and tracer concentration can be measured in regions of interest. These steps are evaluated separately for their contribution to the accuracy and precision of the final, functional image. The qualities important in the final image are spatial resolution, intensity linearity, and intensity sensitivity, as well as the noise level. Techniques for evaluating the LCBF image include: (1) optimization of the input linearity and dynamic range of the video camera to maximize relative intensity sensitivity of the final functional image; (2) visual inspection of the curves used to fit various functions that are important in the conversion of the GV image to an image of physiological interest; (3) consideration of the noise introduced by the input devices and during the image conversion; and (4) above all, the integration of the various parts of the system to produce an accurate image useful in cerebrovascular research.