The European respiratory journal : official journal of the European Society for Clinical Respiratory Physiology
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The aim of this study was to evaluate whether pressure support ventilation (PSV) requires different diaphragmatic efforts and patient-ventilator matching, according to the underlying disease. Four groups of patients requiring PSV were studied: Group A, recovering from an episode of acute respiratory failure due to adult respiratory distress syndrome (ARDS); Group B, with postsurgical complications; and two subsets of chronic obstructive pulmonary disease (COPD) patients, with "normal" static compliance of the respiratory system (Cst,rs) (Group C) or elevated Cst,rs (Group D). Ventilatory pattern, transdiaphragmatic pressure (Pdi), the pressure-time product of the diaphragm (PTPdi), static (PEEPi,stat) and dynamic intrinsic positive end-expiratory pressure (PEEPi,dyn), Cst,rs and resistance of the total respiratory system (Rrs) were recorded. ⋯ Tidal volume and the spontaneous inspiratory efforts were similar in the four groups, but the number of breaths delivered by the ventilator was significantly higher in Groups A and B. The application of different levels of pressure support ventilation in patients with acute respiratory failure due to different pathologies, led them to breathe with comparable pressure time product of the diaphragm. The majority of the patients showed mismatching with the ventilator, although this effect was more pronounced in the groups with chronic obstructive pulmonary disease.
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Since the circulatory and pulmonary systems are both driven by pressure and share space in the thorax, it is inevitable that they interact. These mechanical interactions, whilst relatively few in number, are protean in their manifestations. The circulatory system of the critically ill is often particularly susceptible to interference from respiration. ⋯ This review will examine the basic physiological mechanisms through which the pulmonary and circulatory systems interact. These mechanisms will then be applied to a variety of weaning, positive end-expiratory pressure (PEEP), and cardiopulmonary resuscitation techniques. It is hoped that this will provide the tools to understand clinical observations which would otherwise appear inexplicable.
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Randomized Controlled Trial Clinical Trial
The effect of dipyridamole and theophylline on hypercapnic ventilatory responses: the role of adenosine.
The purine nucleoside, adenosine, has been implicated as a neuromodulator in central respiratory depression during prolonged exposure to hypoxia. It may also be a mediator of hypoxic hyperpnoea, acting on the carotid bodies. As there may be adenosine-sensitive mechanisms of hypoxic respiratory control, we sought to determine whether adenosine might be involved as a respiratory modulator in another central but non-oxygen-related control mechanism, the ventilatory response to hyperoxic hypercapnia. ⋯ However, neither the slope nor the PET, CO2 intercept of the relationship between ventilation or respiratory drive and PET, CO2 were altered by the study drugs under hyperoxic conditions. We conclude that endogenous adenosine-related mechanisms are unlikely to be involved in determining either the sensitivity or the threshold of the ventilatory response to carbon dioxide under hyperoxic conditions. However, in normoxia, a centrally-acting, tonic, adenosine-mediated, respiratory modulation is not ruled out.
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Comparative Study
Short-term variations in oscillatory and spirometric lung function indices among school children.
The aim of this study was to compare immediate, daily and weekly variation in respiratory resistance measured by means of the forced oscillation technique (Rrs,FOT) to spirometric indices in 7-12 year old children with chronic respiratory symptoms. The lung function measurements were performed in 19 children on 4 days, i.e. two consecutive days during two consecutive weeks. On each day, the measurements were carried out at the same time of day and always repeated three times. ⋯ When a reliability index was applied, the immediate variation in Rrs,FOT values was comparable to those of the airflow indices at specified lung volumes. Rrs,FOT was also the most sensitive index in the exercise challenge test, and therefore it seems to be suitable for detection of short-term functional changes in the respiratory system. However, the relatively low repeatability of Rrs,FOT over days and weeks may limit its applicability to longer-term follow-ups.