1,721,006 research outputs found
Clinical review: Positive end-expiratory pressure and cardiac output.
No full textIn patients with acute lung injury, high levels of positive end-expiratory pressure (PEEP) may be necessary to maintain or restore oxygenation, despite the fact that 'aggressive' mechanical ventilation can markedly affect cardiac function in a complex and often unpredictable fashion. As heart rate usually does not change with PEEP, the entire fall in cardiac output is a consequence of a reduction in left ventricular stroke volume (SV). PEEP-induced changes in cardiac output are analyzed, therefore, in terms of changes in SV and its determinants (preload, afterload, contractility and ventricular compliance). Mechanical ventilation with PEEP, like any other active or passive ventilatory maneuver, primarily affects cardiac function by changing lung volume and intrathoracic pressure. In order to describe the direct cardiocirculatory consequences of respiratory failure necessitating mechanical ventilation and PEEP, this review will focus on the effects of changes in lung volume, factors controlling venous return, the diastolic interactions between the ventricles and the effects of intrathoracic pressure on cardiac function, specifically left ventricular function. Finally, the hemodynamic consequences of PEEP in patients with heart failure, chronic obstructive pulmonary disease and acute respiratory distress syndrome are discussed
Computed tomography scan assessment of lung volume and recruitment during high-frequency oscillatory ventilation
No full textOBJECTIVE:
This review describes how computed tomography has increased our understanding of the pathophysiology of acute respiratory distress syndrome. It summarizes current knowledge about lung volume changes and alveolar recruitment during high-frequency oscillatory ventilation (HFOV) assessed by computed tomography (CT), outlines potential problems when comparing HFOV with conventional ventilation (CV) as a result of the different pressure-time profiles, and describes future research directions.
DATA SOURCE:
CT allows accurate assessment of total lung volumes and differentiation between overinflated, normally aerated, poorly aerated, and nonaerated lung regions. It allows for classification of different patterns of consolidation and may be predictive for the potential for recruitment.
DATA SUMMARY:
Experimental data suggest that HFOV at mean airway pressures (mPaw) set according to a static PV curve leads to effective lung recruitment but results in overall lung volumes that are considerably higher than those predicted from the PV relationship. In saline-lavaged sheep, similar changes in total lung volumes and subvolumes were observed during HFOV and CV. One single study specifically assessed lung volume recruitment during HFOV as compared with CV in eight patients with acute respiratory distress syndrome from pneumonia or sepsis. After 48 hrs on HFOV, total ventilated lung volume was significantly increased, whereas only a minor increase in overinflated lung volume was observed. These changes correlated with a significant improvement in gas exchange.
CONCLUSION:
CT is a valuable tool to quantify recruitment and overinflation during HFOV. Additional studies are needed to better characterize the specific effects of HFOV on lung volume and morphology
Haemodynamic effects of mechanical ventilation
No full textMechanical ventilation and positive end-expiratory pressure (PEEP) are considered to be the cornerstones of therapy for acute lung failure and acute respiratory distress syndrome (ARDS), when high levels of PEEP are applied in order to maintain or restore oxygenation, despite the fact that aggressive mechanical ventilation can markedly affect cardiac function in a complex and often unpredictable fashion. As heart rate usually does not change with PEEP, the entire fall in cardiac output is a consequence of a reduction in left ventricular stroke volume (LVSV). Therefore, changes in cardiac output caused by mechanical ventilation and PEEP are analyzed in terms of changes in SV and its determinants, i.e. preload, afterload, contractility and ventricular compliance. Mechanical ventilation with PEEP, like any other active or passive ventilatory maneuver, primarily affects cardiac function by changing lung volume and intrathoracic pressure (ITP). In order to describe the direct cardiocirculatory consequences of respiratory failure necessitating mechanical ventilation and PEEP, this review will focus on the effects of changes in lung volume, factors controlling venous return, the diastolic interactions between the ventricles and the effects of intrathoracic pressures on right and left ventricular function
Respiratory and haemodynamic changes during decremental open lung positive end-expiratory pressure titration in patients with acute respiratory distress syndrome
No full textINTRODUCTION:
To investigate haemodynamic and respiratory changes during lung recruitment and decremental positive end-expiratory pressure (PEEP) titration for open lung ventilation in patients with acute respiratory distress syndrome (ARDS) a prospective, clinical trial was performed involving 12 adult patients with ARDS treated in the surgical intensive care unit in a university hospital.
METHODS:
A software programme (Open Lung Tool) incorporated into a standard ventilator controlled the recruitment (pressure-controlled ventilation with fixed PEEP at 20 cmH2O and increased driving pressures at 20, 25 and 30 cmH2O for two minutes each) and PEEP titration (PEEP lowered by 2 cmH2O every two minutes, with tidal volume set at 6 ml/kg). The open lung PEEP (OL-PEEP) was defined as the PEEP level yielding maximum dynamic respiratory compliance plus 2 cmH2O. Gas exchange, respiratory mechanics and central haemodynamics using the Pulse Contour Cardiac Output Monitor (PiCCO), as well as transoesophageal echocardiography were measured at the following steps: at baseline (T0); during the final recruitment step with PEEP at 20 cmH2O and driving pressure at 30 cmH2O, (T20/30); at OL-PEEP, following another recruitment manoeuvre (TOLP).
RESULTS:
The ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FiO2) increased from T0 to TOLP (120 +/- 59 versus 146 +/- 64 mmHg, P < 0.005), as did dynamic respiratory compliance (23 +/- 5 versus 27 +/- 6 ml/cmH2O, P < 0.005). At constant PEEP (14 +/- 3 cmH2O) and tidal volumes, peak inspiratory pressure decreased (32 +/- 3 versus 29 +/- 3 cmH2O, P < 0.005), although partial pressure of arterial carbon dioxide (PaCO2) was unchanged (58 +/- 22 versus 53 +/- 18 mmHg). No significant decrease in mean arterial pressure, stroke volume or cardiac output occurred during the recruitment (T20/30). However, left ventricular end-diastolic area decreased at T20/30 due to a decrease in the left ventricular end-diastolic septal-lateral diameter, while right ventricular end-diastolic area increased. Right ventricular function, estimated by the right ventricular Tei-index, deteriorated during the recruitment manoeuvre, but improved at TOLP.
CONCLUSIONS:
A standardised open lung strategy increased oxygenation and improved respiratory system compliance. No major haemodynamic compromise was observed, although the increase in right ventricular Tei-index and right ventricular end-diastolic area and the decrease in left ventricular end-diastolic septal-lateral diameter during the recruitment suggested an increased right ventricular stress and strain. Right ventricular function was significantly improved at TOLP compared with T0, although left ventricular function was unchanged, indicating effective lung volume optimisation
Oleic acid vs saline solution lung lavage-induced acute lung injury: effects on lung morphology, pressure-volume relationships, and response to positive end-expiratory pressure
No full textOBJECTIVE:
To compare two lung injury models (oleic acid [OA] and saline solution washout [SW]) regarding lung morphology, regional inflation, and recruitment during static pressure-volume (PV) curves, and the effects of positive end-expiratory pressure (PEEP) below and above the lower inflection point (Pflex).
METHODS:
Fourteen adult pigs underwent OA or SW lung injury. Lung volumes were measured using CT. PV curves were obtained with simultaneous CT scanning at lung apex and base. Fractional inflation and recruitment were compared to data on PEEP above and below Pflex.
RESULTS:
Severity of lung injury was comparable. At zero PEEP, SW showed an increased amount of edema and poorly aerated lung volume, recruitment during inspiration, and a better oxygenation response with PEEP. Whole-lung PV curves were similar in both models, reflecting changes in alveolar inflation or deflation. On the inspiratory PV limb, recruitment and inflation were on the same line, while there was a substantial difference between deflation and derecruitment on the expiratory limb. PEEP-induced recruitment at lung apex and base was at or above the derecruitment line on the expiratory limb and showed no relationship to the whole-lung expiratory PV curve.
CONCLUSIONS:
The following conclusions were made: (1) OA and SW models are comparable in mechanics but not in lung injury characteristics; (2) neither inspiratory nor expiratory whole-lung PV curves are useful to select PEEP in order to optimize recruitment; and (3) after recruitment, there is no difference in derecruitment between the models at high PEEP, while more collapse occurs at lower PEEP in the basal sections of SW lungs
Assessment of cardiac preload and left ventricular function under increasing levels of positive end-expiratory pressure.
No full textOBJECTIVE:
(1) To assess the impact of high intrathoracic pressure on left ventricular volume and function. (2) To test the hypothesis that right ventricular end-diastolic volume (RVEDV) and intrathoracic blood volume (ITBV) represent cardiac preload and are superior to central venous pressure (CVP) or pulmonary capillary wedge pressure (PCWP). The validity of these parameters was tested by means of correlation with left ventricular end-diastolic volume (LVEDV), the true cardiac preload.
DESIGN:
Prospective animal study.
SUBJECTS:
Fifteen adult sheep.
INTERVENTIONS:
All animals were studied before and after saline washout-induced lung injury, undergoing volume-controlled ventilation with increasing levels of PEEP (0, 7, 14 and 21 cmH2O, respectively).
MEASUREMENTS AND MAIN RESULTS:
Left ventricular ejection fraction (LVEF), stroke volume (LVSV) and LVEDV were measured using computed tomography. ITBV and RVEDV were obtained by the thermal dye dilution technique. At PEEP 21 cmH2O, LVSV significantly decreased compared to baseline, PEEP 0 and PEEP 7 cmH2O. LVEDV was maintained except for the highest level of PEEP, while LVEF remained unchanged. RVEDV and RVEF also remained unchanged. The overall correlation of RVEDV and ITBV with LVEDV was satisfactory ( r=0.56 and r=0.62, respectively) and clearly superior to cardiac filling pressures.
CONCLUSION:
In the present study, (1) ventilation with increasing levels of PEEP did not alter RV function, while LV function was impaired at the highest level of PEEP; (2) unlike cardiac filling pressures, ITBV and RVEDV both provide valid estimates of cardiac preload even at high intrathoracic pressures
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
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