1,720,965 research outputs found
Pulmonary mechanical dysfunction in the critically ill
No full textModern ventilators employed in intensive care units (ICUs) display in real time and breath by breath flow (V̇), volume (V), and pressure (Paw) curves, both as a function of time and as a loop. Data obtained from curve analysis can help the physician to understand the interactions between the patient and the ventilator. The right interpretation of information provided from modern ventilators allows real time monitoring of the actual needs of the patient, ensuring a custom ventilatory support and reducing the risk of complications that can increase the mortality and prolong the ICU length of stay. In patients undergoing mechanical ventilation, measurements of respiratory mechanics can be performed at the bedside in dynamic (no flow interruption) or static (occlusion techniques) conditions. From these, it’s also possible to derive the values of pulmonary compliance and airway resistance
Dead space in acute respiratory distress syndrome
No full textDead space is the portion of each tidal volume that does not take part in gas exchange and represents a good global index of the efficiency of the lung function. Dead space is not routinely measured in critical care practice, because the difficulties in in interpreting capnograms and the different methods of calculations. Different dead space indices can provide useful information in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) patients, where changes in microvasculature are the main determinants for the increase in dead space and consequently a worsening of the outcome. Lung recruitment is a dynamic process that combines recruitment manoeuvres (RMs) with positive end expiratory pressure (PEEP) and low Vt to recruit collapsed alveoli. Dead space guided recruitment allows avoiding regional overdistension or reduction in cardiac output in critical care patients with ALI or ARDS. Different patterns of ventilation affect also CO2 elimination; in fact, end-inspiratory pause prolongation reduces dead space, increasing respiratory system compliance; plateau pressure and consequently driving pressure increase accordingly. Dead space measurement is a reliable method that provides important clinical and prognostic information. Different capnographic indices can be useful to evaluate therapeutic interventions or setting mechanical ventilation
Closing, opening and reopening: the difficult coexistence
No full textVolume-controlled ventilation (VCV) has always been considered as protective ventilation, in particular during spontaneous breathing, being able to avoid the administration of injurious tidal volumes (Vt) to the patient. In fact, spontaneous efforts increase transpulmonary pressure (Pl) only during pressure-regulated ventilations (1). Despite this difference in terms of Pl, the conditions of lung parenchyma determine the damage to the lung tissue and
the onset of ventilator induced lung injury (VILI). In normal lung the pressures applied to a local region of the pleura are homogeneous and distributed over the whole lung (fluid-like behavior), whereas negative pleural pressures (Ppl) generated by diaphragmatic contraction are rather concentrated in dorsal parts (solid-like), once lung has been injured (2). Furthermore, when Pl is applied to the lung, a counterforce of equal intensity is developed (lung
stress), whereas the associated lung deformation is called strain. These two forces are directly correlated by the specific elastance (Elsp), which reflects the intrinsic mechanical characteristics of the lung parenchyma (3). This concept is a recent introduction, but it has an important clinical relevance right away; in fact, Elsp is peculiar in each species: in pigs is about half that in human and consequently a plateau pressure (Pplat) of 30 cmH2O in pigs would approximately correspond to 60 cmH2O in humans
In vitro estimation of pressure drop across tracheal tubes during high-frequency percussive ventilation
No full textTracheal tubes (TT) are used in clinical practice to connect an artificial ventilator to the patient's airways. It is important to know the pressure used to overcome tube impedance to avoid lung injury. Although high-frequency percussive ventilation (HFPV) has been increasingly used, the mechanical behavior of TT under HFPV has not yet been described. Thus, we aimed at characterizing in vitro the pressure drop across TT (ΔPTT) by identifying the model that best fits the measured pressure-flow (P-V̇) relationships during HFPV under different working pressures (PWork), percussive frequencies and mechanical loads. Three simple models relating ΔPTT and flow (V̇) were tested. Model 1 is characterized by linear resistive [Rtube ⋅ V̇(t)] and inertial [I · V̈(t)] terms. Model 2 takes into consideration Rohrer's approach [K1· V̇(t) + K2 ⋅V̇(t)] and inertance [I ·V̈(t)]. In model 3 the pressure drop caused by friction is represented by the non-linear Blasius component [Kb· V̇(1.75)(t)] and the inertial term [I· V̈(t)]. Model 1 presented a significantly higher root mean square error of approximation than models 2 and 3, which were similar. Thus, model 1 was not as accurate as the latter, possibly due to turbulence. Model 3 presented the most robust resistance-related coefficient. Estimated inertances did not vary among the models using the same tube. In conclusion, in HFPV ΔPTT can be easily calculated by the physician using model 3
In vitro measurement of respiratory mechanics during HFPV using a mechanical lung model
No full textHigh-frequency percussive ventilation (HFPV) may be defined as flow-regulated time-cycled ventilation that creates controlled pressure and delivers a series of high-frequency subtidal volumes in combination with low-frequency breathing cycles. In recent years, the usefulness of HFPV has been clinically assessed as an alternative to conventional mechanical ventilation. In the clinical practice, HFPV is not an intuitive ventilatory modality and the absence of real-time delivered volume monitoring produces disaffection among the physicians. For this purpose, it would be useful to develop a monitor able to realize a complete online characterization of high-frequency percussive ventilators and to identify the best combination of their parameters according to the specific pathological situation. This paper describes an innovative acquisition and elaboration system based on the use of new generation pressure transducers presenting high sensitivity and fast response. Such a system is compact and inexpensive, and it allows the user to carry out a more correct online characterization of high-frequency percussive ventilators. This output allowed best real-time ventilatory setting, minimizing the potential baro-volutrauma hazard
Uncommon Occurrences of Air Embolism: Description of Cases and Review of the Literature
Full text linkMany different risk factors have been associated with the occurrence of gas embolism making this potentially lethal complication easily avoidable. However, this condition can occur in circumstances not commonly reported. Three different and extremely uncommon cases of gas embolism are presented and discussed: the first was caused by the voluntary ingestion of hydrogen peroxide, the second occurred during a retrograde cholangiopancreatography, and the last followed the intrapleural injection of Urokinase. Whereas in the first patient the gas embolism was associated with only relatively mild digestive symptoms, in the remaining two it caused a massive cerebral ischemia and an extended myocardial infarction, respectively. Despite a hyperbaric oxygen therapy performed timely in each case, only the first patient survived. The classical risk factors associated with gas embolism like indwelling central venous catheters, diving accidents, etc. are rather well known and thus somewhat preventable; however, a number of less common and difficult-to-recognize causes can determine this condition, making the correct diagnosis elusive and delaying the hyperbaric oxygen therapy, whose window of opportunity is rather narrow. Thus, a gas embolism should be suspected in the presence of not otherwise explainable sudden neurologic and/or cardiovascular symptoms also in circumstances not typically considered at risk
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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