512 research outputs found
Closing volume : a reappraisal (1967–2007)
No full textMeasurement of closing volume (CV) allows detection of presence or absence of tidal airway closure, i.e. cyclic opening and closure of peripheral airways with concurrent (1) inhomogeneity of distribution of ventilation and impaired gas exchange; and (2) risk of peripheral airway injury. Tidal airway closure, which can occur when the CV exceeds the end-expiratory lung volume (EELV), is commonly observed in diseases characterised by increased CV (e.g. chronic obstructive pulmonary disease, asthma) and/or decreased EELV (e.g. obesity, chronic heart failure). Risk of tidal airway closure is enhanced by ageing. In patients with tidal airway closure (CV > EELV) there is not only impairment of pulmonary gas exchange, but also peripheral airway disease due to injury of the peripheral airways. In view of this, the causes and consequences of tidal airway closure are reviewed, and further studies are suggested. In addition, assessment of the “open volume”, as opposed to the “closing volume”, is proposed because it is easier to perform and it requires less equipment
Recumbent deoxygenation in mild/moderate liver cirrhosis: the “Clinodeoxia”. The ortho-clino paradigm
No full textBACKGROUND:
While the effects of postural change on arterial oxygenation have been well documented in normal subjects, and attributed to the relationship of closing volume (CV) to the tidal volume, in liver cirrhosis such postural changes have been evaluated mainly in a rare, peculiar clinical end-stage condition which is characterized by increased dyspnea shifting from supine to upright position ("platypnea"). The latter is associated with worsening of PaO2 ("orthodeoxia"). We evaluated the effects of postural changes on arterial oxygenation in patients affected by mild/moderate liver cirrhosis.
METHODS:
We performed pulmonary function tests and arterial blood gas evaluation in sitting and supine positions in 22 patients with mild/moderate liver cirrhosis, biopsy-proved, and 22 matched non-smokers control subjects.
RESULTS:
Recumbency elicited a decrease of PaO2 (Δ(sup-sit)PaO2) in 19 out of 22 controls and in all but one cirrhotics. The magnitude of this postural change was significantly (p = 0.04) greater in cirrhotics (9.6 ± 5.3%) compared to controls (6.7 ± 3.7%). In the subset of cirrhotics younger than 60 yrs and with PaO2 greater than 80 mmHg in sitting position, the Δ(sup-sit)PaO2 in recumbency further increased to 12 ± 5.8%, significantly (p = 0.014) greater than in same subgroup of controls (7.1 ± 3.8%).
CONCLUSIONS:
In mild/moderate liver cirrhosis the postural variations in PaO2 follow the normal trends, but are of greater magnitude probably as a consequence of hypoventilated units of lung for postural and disease-linked tidal airway closure, resulting in more pronounced recumbent hypoxemia ("clinodeoxia")
Regional Distribution of Gas in the Lung
No full textIn 1966, a paper entitled "Regional distribution of gas in the lung" was published in the Journal of Applied Physiology and became one of the 100 most-cited papers of clinical research from 1961 to 1978. The senior author provides the background and state-of-the art at the time of its publication, and reviews the main findings of the paper and subsequent developments
Respiratory energetics during exercise at high altitude
No full text The purpose of this study was to assess the effect of high altitude (HA) on work of breathing and external work capacity. On the basis of simultaneous records of esophageal pressure and lung volume, the mechanical power of breathing (W˙rs) was measured in four normal subjects during exercise at sea level (SL) and after a 1-mo sojourn at 5,050 m. Maximal exercise ventilation (V˙e max) and maximal W˙rs were higher at HA than at SL (mean 185 vs. 101 l/min and 129 vs. 40 cal/min, respectively), whereas maximal O2 uptake averaged 2.07 and 3.03 l/min, respectively. In three subjects, the relationship ofW˙rs to minute ventilation (V˙e) was the same at SL and HA, whereas, in one individual, W˙rs for any givenV˙e was consistently lower at HA. Assuming a mechanical efficiency (E) of 5%, the O2 cost of breathing at HA and SL should amount to 26 and 5.5% of maximal O2 uptake, whereas for E of 20% the corresponding values were 6.5 and 1.4%, respectively. Thus, at HA, W˙rs may substantially limit external work unless E is high. Although at SLV˙e max did not exceed the critical V˙e, at which any increase inV˙e is not useful in terms of body energetics even for E of 5%, at HAV˙e maxexceeded critical V˙e even for E of 20%. </jats:p
Effects of mechanical ventilation at low lung volume on respiratory mechanics and nitric oxide exhalation in normal rabbits
No full textLung mechanics, exhaled NO (NOe), and TNF-(alpha) in serum and bronchoalveolar lavage fluid were assessed in eight closed and eight open chest, normal anesthetized rabbits undergoing prolonged (3-4 h) mechanical ventilation (MV) at low volume with physiological tidal volumes (10 ml/kg). Relative to initial MV on positive end-expiratory pressure (PEEP), MV at low volume increased lung quasi-static elastance (+267 and +281%), airway (+471 and +382%) and viscolelastic resistance (+480 and +294%), and decreased NOe (-42 and -25%) in closed and open chest rabbits, respectively. After restoration of PEEP, viscoelastic resistance returned to control, whereas airway resistance remained elevated (+120 and +31%) and NOe low (-25 and -20%) in both groups of rabbits. Elastance remained elevated (+23%) only in closed-chest animals, being associated with interstitial pulmonary edema, as reflected by increased lung wet-to-dry weight ratio with normal albumin concentration in bronchoalveolar lavage fluid. In contrast, in 16 additional closed- and open-chest rabbits, there were no changes of lung mechanics or NOe after prolonged MV on PEEP only. At the end of prolonged MV, TNF-(alpha) was practically undetectable in serum, whereas its concentration in bronchoalveolar lavage fluid was low and similar in animals subjected or not subjected to ventilation at low volume (62 vs. 43 pg/ml). These results indicate that mechanical injury of peripheral airways due to their cyclic opening and closing during ventilation at low volume results in changes in lung mechanics and reduction in NOe and that these alterations are not mediated by a proinflammatory process, since this is expressed by TNF-(alpha) levels
Output of the Respiratory Centres
No full textNote:The control of breathing in animals is usually thought to depend on a "respiratory centre" in the central nervous system whichresponds to stimuli by changing its "output", or neural drive to respiratory muscles. A simple mechanical device for measuring themagnitude of this output is proposed. It consists of occluding the breathing passage at the beginning of inspiration and measuring thestatic pressure generated by the inspiratory effort. The technique is shown to be feasible in conscious men rebreathing carbon dioxide.Some of the necessary assumptions for the validity of the method are tested in anesthetized men. The measurement is used to study theadaptation of breathing in conscious men who change posture from sitting to supine, and assumptions about the relation between occlusion pressure and action of individual respiratory muscles are examined. The interpretation and limitations of the method are discussed.D'habitude on pense qu'il existe chez le système nerveux central des centres respiratoires qui répondent aux stimuli en changeant leur activité. Ici on propose une nouvelle méthode pour mesurer l'état d'activation des centres respiratoires qui est de boucher la voie aérienne au début de l'inspiration et d'enregistrer la pression négative produite par l'effort des muscles inspiratoires. Cette technique est praticable et peut être appliquée aux hommes éveilles, rein spirants du CO2 Des suppositions nécessaires avant que la méthode ne soit valide sont vérifiées chez l'homme anesthésie. Avec cette technique l'adaptation du système respiratoire est étudiée aux changements de position d'assise en celle de couchée. La relation entre la pression et l'action des muscles respiratoires individuelles est considérée. L'interprétation de la méthode est discutée, ainsi que ses limitations
El diccionari de l'Institut d'Estudis Valencians de 1937
No full textIn this article Casanova uses various archives –in particular that of Emili Beüt i Belenguer– to reconstruct the process of elaborating the general dictionary of Valencian. This dictionary was written during the Spanish civil war through the IEV, an organization in which Salvador played a decisive role. The author presents several dictionary entries and compares them with others from Pompeu Fabra's DGLC, and with other works
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