Abstract
Since its introduction in the clinical practice, body plethysmography has assisted pneumologists in the diagnosis of respiratory diseases and patients’ follow-up, by providing easy assessment of absolute lung volumes and airway resistance. In the last decade, emerging evidence suggested that estimation of alveolar pressure by electronically-compensated plethysmographs may contain information concerning the mechanics of the respiratory system which goes beyond those provided by the simple value of airway resistance or conductance. Indeed, the systematic study of expiratory alveolar pressure-flow loops produced during spontaneous breathing at rest has shown that the marked expansion of expiratory loops in chronic obstructive pulmonary disease patients mainly reflects the presence of tidal expiratory flow-limitation. The presence of this phenomenon can be accurately predicted on the basis of loop-derived parameters. Finally, we present results suggesting that plethysmographic alveolar pressure may be used to estimate non-invasively intrinsic positive end-expiratory pressure (PEEPi) in spontaneously breathing patients, a task which previously could be only accomplished by introducing a balloon-tipped catheter in the esophagus.
Highlights
Since its introduction in the clinical practice, body plethysmography proved a valuable tool in the diagnosis of respiratory diseases, thanks to its ability to provide a non-invasive estimation of absolute lung volumes [1] and airway resistance (Raw ) [2,3,4]
Electronic compensation is potentially an attractive way to estimate Palv during spontaneous breathing at rest, and, recently, some efforts were undertaken to investigate whether plethysmographic Palv contains information that goes beyond the simple value of Raw or Raw -related parameters, such as specific resistance or conductance [19,20], that will not be discussed in the present essay
The effects of BD on Aexp were small (−17%) relative to those of the three patients who became nonflow-limited after BD (−61%). It appears that tidal expiratory flow limitation (tEFL) is responsible for a large part of Aexp in chronic obstructive pulmonary disease (COPD) patients breathing at rest, suggesting that loop-derived parameters can be used as predictors of the presence of tEFL
Summary
Since its introduction in the clinical practice, body plethysmography proved a valuable tool in the diagnosis of respiratory diseases, thanks to its ability to provide a non-invasive estimation of absolute lung volumes [1] and airway resistance (Raw ) [2,3,4]. The last strategy that allows to attenuate the thermal and metabolic artifacts is to subtract from ∆VS , electronically or digitally, a signal proportional to ∆Vth + ∆Vmet (electronic or digital compensation) This task is far from simple, as warming and humidification of air in the airways during inspiration, and cooling and loss of water vapor in the box during expiration are not instantaneous processes, nor have the same kinetics [13,14], as once believed [15,16]. The exact details of the algorithm used for the compensation, at least to our knowledge, are not always reported Despite these concerns, electronic compensation is potentially an attractive way to estimate Palv during spontaneous breathing at rest, and, recently, some efforts were undertaken to investigate whether plethysmographic Palv contains information that goes beyond the simple value of Raw or Raw -related parameters, such as specific resistance or conductance [19,20], that will not be discussed in the present essay.
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