Breathing variability—implications for anaesthesiology and intensive care

The respiratory system reacts instantaneously to intrinsic and extrinsic inputs. This adaptability results in significant fluctuations in breathing parameters, such as respiratory rate, tidal volume, and inspiratory flow profiles. Breathing variability is influenced by several conditions, including sleep, various pulmonary diseases, hypoxia, and anxiety disorders. Recent studies have suggested that weaning failure during mechanical ventilation may be predicted by low respiratory variability. This review describes methods for quantifying breathing variability, summarises the conditions and comorbidities that affect breathing variability, and discusses the potential implications of breathing variability for anaesthesia and intensive care.

Impairing flow-mediated endothelial remodeling reduces extravasation of tumor cells

Tumor progression and metastatic dissemination are driven by cell-intrinsic and biomechanical cues that favor the growth of life-threatening secondary tumors. We recently identified pro-metastatic vascular regions with blood flow profiles that are permissive for the arrest of circulating tumor cells. We have further established that such flow profiles also control endothelial remodeling, which favors extravasation of arrested CTCs. Yet, how shear forces control endothelial remodeling is unknown. In the present work, we aimed at dissecting the cellular and molecular mechanisms driving blood flow-dependent endothelial remodeling. Transcriptomic analysis of endothelial cells revealed that blood flow enhanced VEGFR signaling, among others. Using a combination of in vitro microfluidics and intravital imaging in zebrafish embryos, we now demonstrate that the early flow-driven endothelial response can be prevented upon specific inhibition of VEGFR tyrosine kinase and subsequent signaling. Inhibitory targeting of VEGFRs reduced endothelial remodeling and subsequent metastatic extravasation. These results confirm the importance of VEGFR-dependent endothelial remodeling as a driving force of CTC extravasation and metastatic dissemination. Furthermore, the present work suggests that therapies targeting endothelial remodeling might be a relevant clinical strategy in order to impede metastatic progression.

The Role of Low-Level Flow Direction on Tropical Cyclone Intensity Changes in a Moderate-Sheared Environment

The impact of low-level flow (LLF) direction on the intensification of intense tropical cyclones under moderate deep-layer shear is investigated based on idealized numerical experiments. The background flow profiles are constructed by varying the LLF direction with the same moderate deep-layer shear. When the maximum surface wind speed of the simulation without background flow reaches 70 knots, the background flow profiles are imposed. After a weakening period in the first 12 h, the members with upshear-left-pointing LLF (fast-intensifying group) intensify faster between 12–24 h than those members (slow-intensifying group) with downshear-right-pointing LLF. The fast-intensifying group experiences earlier development of inner-core structures after 12 h, such as potential vorticity below the mid-troposphere, upper-level warm core, eyewall axisymmmetrization, and moist entropy gradient, while the inner-core features of the slow-intensifying group remain relatively weak and asymmetric. The FI group experiences smaller tilt increase and stronger mid-level PV ring development. The upshear-left convection during 6–12 h is responsible for the earlier development of the inner core by reducing ventilation, providing axisymmetric heating and benefiting the eyewall development. The LLF of the fast-intensifying group enhances surface heat fluxes in the downshear side, resulting in higher energy supply to the upshear-left convection from the boundary layer. In all, this study provides new insights on the impact of LLF direction on intense storms under moderate shear by modulating the surface heat fluxes and eyewall convection.

Multiphase Flow Regime Characterization and Liquid Flow Measurement Using Low-Field Magnetic Resonance Imaging

Multiphase flow metering with operationally robust, low-cost real-time systems that provide accuracy across a broad range of produced volumes and fluid properties, is a requirement across a range of process industries, particularly those concerning petroleum. Especially the wide variety of multiphase flow profiles that can be encountered in the field provides challenges in terms of metering accuracy. Recently, low-field magnetic resonance (MR) measurement technology has been introduced as a feasible solution for the petroleum industry. In this work, we study two phase air-water horizontal flows using MR technology. We show that low-field MR technology applied to multiphase flow has the capability to measure the instantaneous liquid holdup and liquid flow velocity using a constant gradient low flip angle CPMG (LFA-CPMG) pulse sequence. LFA-CPMG allows representative sampling of the correlations between liquid holdup and liquid flow velocity, which allows multiphase flow profiles to be characterized. Flow measurements based on this method allow liquid flow rate determination with an accuracy that is independent of the multiphase flow profile observed in horizontal pipe flow for a wide dynamic range in terms of the average gas and liquid flow rates.

Actuation of Liquid Flow by Guided Acoustic Waves on Punched Steel Tapes with Protruding Loops

In a biomimetic approach the feasibility of liquid flow actuation by vibrating protruding structures excited via guided acoustic waves is investigated. Inspired by periodically beating cilia the loop part of a punched metallic hook-and-loop tape with tilted protruding loops was used as a waveguide for plate waves in water. Such waves were excited in the frequency range of 110 Hz to 220 Hz by directly coupling the tape to a loudspeaker membrane. A flow generated in the tilt direction of the loops with velocities up to 60 mm·s−1 was visualized by ink droplets deposited on the tape. The phenomenon persisted, when the protruding length of the loops was reduced by decreasing the protrusion angle. However, after closing the punch holes near the loops with sticking tape streaming could not be observed any longer. The same happened with open punch holes when the ink was replaced by glycerol. Low-frequency acoustic streaming around vibrating sharp edges is proposed as an explanation for the observed phenomena. Applications are expected with respect to the modification of flow profiles and the enhancement of transport processes along and across liquid-solid boundaries.

Numerical Investigation of MHD Pulsatile Flow of Micropolar Fluid in a Channel with Symmetrically Constricted Walls

This article presented an analysis of the pulsatile flow of non-Newtonian micropolar (MP) fluid under Lorentz force’s effect in a channel with symmetrical constrictions on the walls. The governing equations were first converted into the vorticity–stream function form, and a finite difference-based solver was used to solve it numerically on a Cartesian grid. The impacts of different flow controlling parameters, including the Hartman number, Strouhal number, Reynolds number, and MP parameter on the flow profiles, were studied. The wall shear stress (WSS), axial, and micro-rotation velocity profiles were depicted visually. The streamlines and vorticity patterns of the flow were also sketched. It is evident from the numerical results that the flow separation region near constriction as well as flattening of the axial velocity component is effectively controlled by the Hartmann number. At the maximum flow rate, the WSS attained its peak. The WSS increased in both the Hartmann number and Reynolds number, whereas it declined with the higher values of the MP parameter. The micro-rotation velocity increased in the Reynolds number, and it declined with increment in the MP parameter.

The Range of Jupiter's Flow Structures that Fit the Juno Asymmetric Gravity Measurements

<p>The asymmetric gravity field measured by the Juno spacecraft has allowed the estimation of the depth of Jupiter's zonal jets, showing that the winds extend approximately 3,000 km beneath the cloud level. This estimate was based on an analysis using a combination of all measured odd gravity harmonics, <em>J</em><sub>3</sub>, <em>J</em><sub>5</sub>, <em>J</em><sub>7</sub>, and <em>J</em><sub>9</sub>, but the wind profile's dependence on each of them separately has yet to be investigated. Furthermore, these calculations assumed the meridional profile of the cloud‐level wind extends to depth. However, it is possible that the interior jet profile varies somewhat from that of the cloud level. Here we analyze in detail the possible meridional and vertical structure of Jupiter's deep jet streams that can match the gravity measurements. We find that each odd gravity harmonic constrains the flow at a different depth, with <em>J</em><sub>3</sub> the most dominant at depths below 3,000 km, <em>J</em><sub>5</sub> the most restrictive overall, whereas <em>J</em><sub>9</sub> does not add any constraint on the flow if the other odd harmonics are considered. Interior flow profiles constructed from perturbations to the cloud‐level winds allow a more extensive range of vertical wind profiles, yet when the meridional profiles differ substantially from the cloud level, the ability to match the gravity data significantly diminishes. Overall, we find that while interior wind profiles that do not resemble the cloud level are possible, they are statistically unlikely. Finally, inspired by the Juno microwave radiometer measurements, assuming the brightness temperature is dominated by the ammonia abundance, we find that depth‐dependent flow profiles are still compatible with the gravity measurements.</p>

Shell Crystallization in Granular Hopper Flow

An interesting phenomenon that a layer of crystallized shell formed at the container wall during hopper flow is observed experimentally and is investigated in DEM simulation. Different from shear or vibration driven granular crystallization, our simulation shows during the hopper flow the shell layer is formed spontaneously from the stagnant zone at the base and grows at a constant rate to the top with no external drive. The growth rate of the shell is found linearly proportional to the rate of the hopper flow. This shell is static and served as a new wall, which changes the flow profiles and its stress properties, and in turn guarantees a constant flow rate.