Experimental pendulum air in the flail chest

Abstract

Conditions for occurrence of pendulum airflow under spontaneous ventilation were studied in adult dogs with flail chest experimentally constructed by removing three ribs and the chest wall. Pendulum air flow was recorded pneumotachometrically from outside the body by intubation to the bronchi. Despite objections to the occurrence of pendulum air by many investigators, we found that pendulum airflow occurs under various conditions. The main factors facilitating the occurrence included 1) Significant differences in airway pressure and ventilatory volume between the lungs on the injured and the opposite side. 2) A high frequency of respiration. 3) Increased resistance in the upper airway. The pendulum airflow occurred not only at the area of tracheal bifurcation but also in the peripheral bronchial airway in the ipsi-lateral thorax of the flail chest. However, pendulum airflow was observed only transiently coinciding with the time of change from one phase of respiration to the other, and volume of pendulum airflow was considered to be so minimal that it had no significant deleterious influence on the alveolar ventilation. In cases of marked dysfunction of the chest wall or with increasing upper airway resistance, pendulum airflow may disturb alveolar ventilation to a considerable extent.

Pendelluft in the bronchial tree

“…Clinically, pendelluft can be observed during mechanical ventilation of patients with unilateral chest or lung injury, where the two lungs can sometimes be seen inflating and deflating out of phase with each other (6,16). More subtle pendelluft is sometimes observed as a gradual drop in pressure during an end-inspiratory pause, which may be caused by airflow between the different regions of the lungs.…”

Pendelluft is not the major contributor to respiratory insufficiency in dogs with flail chest: a mathematical analysis

“…However, our simulation with a two order of magnitude range of EFc should cover the nonlinear effect, suggesting that the phase difference between the sides may remain small even with a nonlinear Evc. The mediastinal septum separating the lungs is not rigid, therefore, ventilation of each lung is, to some extent, dependent on the other lung due to the pleural pressure gradient [3,12]. However, the mediastinum may function mainly as an elastic element so that it would not create appreciable further phase difference between the ventilation of the lungs.…”

“…ZRS measured in our frequency range reflects the mechanical properties of both airways and the respiratory tissue (lung parenchyma and chest wall). RRs at low frequencies, largely the frequency-dependent segment, reflects mainly the tissue resistive property, which is represented by the parameter B, while the frequency-independent asymptotic segment at high frequencies indicates airway resistance which is expressed by RAW [3,4]. XRS is characterized by respiratory tissue mechanical constituents, i.e., its resistive (B) and elastic (A) properties.…”

“…The model employed consisted of a single conduit connected in series with an alveolar region surrounded by viscoelastic respiratory tissue, which is formulated as, ZRS(C0) = RAW + Brc/4.6co + ir --i(A + 0.25B + Blogo~)/co where RAW and IAw denote airway resistance and inertance, and A and B respiratory tissue elastance and resistance, respectively. 9 The model is widely accepted to characterize the respiratory mechanics in normal conditions [3,4], though it does not consider uneven ventilation. We used this model since the flail chest was thought not to produce appreciable ventilation nonhomogeneity, as discussed in the Results and Discussion.…”

“…It has long been said that flail chest produces respiratory insufficiency expressed by the term "pendelluft", i.e., to-and-fro air flow between the lungs of the intact and flail chest sides during spontaneous breathing [1]. However, conflicting results have been reported where pendelluft does not necessarily play a major role in respiratory failure [2,3]. Therefore, we desired to explain the differences among those studies by introducing mathematical models into respi-ratory mechanics in an experimentally produced flail chest.…”