The velocity of the arterial pulse wave: a viscous-fluid shock wave in an elastic tube

<p>Abstract</p> <p>Background</p> <p>The arterial pulse is a viscous-fluid shock wave that is initiated by blood ejected from the heart. This wave travels away from the heart at a speed termed the pulse wave velocity (PWV). The PWV increases during the course of a number of diseases, and this increase is often attributed to arterial stiffness. As the pulse wave approaches a point in an artery, the pressure rises as does the pressure gradient. This pressure gradient increases the rate of blood flow ahead of the wave. The rate of blood flow ahead of the wave decreases with distance because the pressure gradient also decreases with distance ahead of the wave. Consequently, the amount of blood per unit length in a segment of an artery increases ahead of the wave, and this increase stretches the wall of the artery. As a result, the tension in the wall increases, and this results in an increase in the pressure of blood in the artery.</p> <p>Methods</p> <p>An expression for the PWV is derived from an equation describing the flow-pressure coupling (FPC) for a pulse wave in an incompressible, viscous fluid in an elastic tube. The initial increase in force of the fluid in the tube is described by an increasing exponential function of time. The relationship between force gradient and fluid flow is approximated by an expression known to hold for a rigid tube.</p> <p>Results</p> <p>For large arteries, the PWV derived by this method agrees with the Korteweg-Moens equation for the PWV in a non-viscous fluid. For small arteries, the PWV is approximately proportional to the Korteweg-Moens velocity divided by the radius of the artery. The PWV in small arteries is also predicted to increase when the specific rate of increase in pressure as a function of time decreases. This rate decreases with increasing myocardial ischemia, suggesting an explanation for the observation that an increase in the PWV is a predictor of future myocardial infarction. The derivation of the equation for the PWV that has been used for more than fifty years is analyzed and shown to yield predictions that do not appear to be correct.</p> <p>Conclusion</p> <p>Contrary to the theory used for more than fifty years to predict the PWV, it speeds up as arteries become smaller and smaller. Furthermore, an increase in the PWV in some cases may be due to decreasing force of myocardial contraction rather than arterial stiffness.</p

The effectiveness of mindfulness-based interventions in the perinatal period: a systematic review and meta-analysis

Perinatal mental health difficulties are associated with adverse consequences for parents and infants. However, the potential risks associated with the use of psychotropic medication for pregnant and breastfeeding women and the preferences expressed by women for non-pharmacological interventions mean it is important to ensure that effective psychological interventions are available. It has been argued that mindfulness-based interventions may offer a novel approach to treating perinatal mental health difficulties, but relatively little is known about their effectiveness with perinatal populations. This paper therefore presents a systematic review and meta-analysis of the effectiveness of mindfulness-based interventions for reducing depression, anxiety and stress and improving mindfulness skills in the perinatal period. A systematic review identified seventeen studies of mindfulness-based interventions in the perinatal period, including both controlled trials (n = 9) and pre-post uncontrolled studies (n = 8). Eight of these studies also included qualitative data. Hedge’s g was used to assess uncontrolled and controlled effect sizes in separate meta-analyses, and a narrative synthesis of qualitative data was produced. Pre- to post-analyses showed significant reductions in depression, anxiety and stress and significant increases in mindfulness skills post intervention, each with small to medium effect sizes. Completion of the mindfulness-based interventions was reasonable with around three quarters of participants meeting study-defined criteria for engagement or completion where this was recorded. Qualitative data suggested that participants viewed mindfulness interventions positively. However, between-group analyses failed to find any significant post-intervention benefits for depression, anxiety or stress of mindfulness-based interventions in comparison to control conditions: effect sizes were negligible and it was conspicuous that intervention group participants did not appear to improve significantly more than controls in their mindfulness skills. The interventions offered often deviated from traditional mindfulness-based cognitive therapy or mindfulness-based stress reduction programmes, and there was also a tendency for studies to focus on healthy rather than clinical populations, and on antenatal rather than postnatal populations. It is argued that these and other limitations with the included studies and their interventions may have been partly responsible for the lack of significant between-group effects. The implications of the findings and recommendations for future research are discussed

The Nature of Knowledge in Composition and Literary Understanding: The Question of Specificity

↵PETER SMAGORINSKY is Assistant Professor, College of Education, University of Oklahoma, 820 Van Vleet Oval, Norman, OK 73019-0. He specializes in classroom literacy.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Anthropometric characterization of spleen in children

Benjamin Coquet, Baptiste Sandoz, Pierre-Henri Savoie, Lionel Thollon, Thierry Serre, Christian Brune

Effectiveness and safety of early medication abortion provided in pharmacies by auxiliary nurse-midwives: A non-inferiority study in Nepal

Expanding access to medication abortion through pharmacies is a promising avenue to reach women with safe and convenient care, yet no pharmacy provision interventions have been evaluated. This observational non-inferiority study investigated the effectiveness and safety of mifepristone-misoprostol medication abortion provided at pharmacies, compared to government-certified public health facilities, by trained auxiliary nurse-midwives in Nepal.Auxiliary nurse-midwives were trained to provide medication abortion through twelve pharmacies and public facilities as part of a demonstration project in two districts. Eligible women were ≤63 days pregnant, aged 16-45, and had no medical contraindications. Between 2014-2015, participants (n = 605) obtained 200 mg mifepristone orally and 800 μg misoprostol sublingually or intravaginally 24 hours later, and followed-up 14-21 days later. The primary outcome was complete abortion without manual vacuum aspiration; the secondary outcome was complication requiring treatment. We assessed risk differences by facility type with multivariable logistic mixed-effects regression.Over 99% of enrolled women completed follow-up (n = 600). Complete abortions occurred in 588 (98·0%) cases, with ten incomplete abortions and two continuing pregnancies. 293/297 (98·7%) pharmacy participants and 295/303 (97·4%) public facility participants had complete abortions, with an adjusted risk difference falling within the pre-specified 5 percentage-point non-inferiority margin (1·5% [-0·8%, 3·8%]). No serious adverse events occurred. Five (1.7%) pharmacy and two (0.7%) public facility participants experienced a complication warranting treatment (aRD, 0.8% [-1.0%-2.7%]).Early mifepristone-misoprostol abortion was as effective and safe when provided by trained auxiliary nurse-midwives at pharmacies as at government-certified health facilities. Findings support policy expanding provision through registered pharmacies by trained auxiliary nurse-midwives to improve access to safe care