Mechanism of gravity-dependent atelectasis. Analysis by nonradioactive xenon-enhanced dynamic computed tomography.
OBJECTIVE
The physiologic mechanism of gravity-dependent atelectasis (GDA), a common finding identified during anesthesia, is not well understood. The purpose of this study was to determine whether an inherent reduction in alveolar volume or a reduction in alveolar ventilation is the more important causative factor for the development of GDA in an experimental animal model.


METHODS
After uniform reduction of lung volume in ten rabbits by artificially induced pneumoperitoneum, dynamic inhalation computed tomography (CT) was performed using 50% nonradioactive xenon in oxygen. Time-CT attenuation value curves were fitted to an exponential function, CT value = a - b x e(-kt), and K value, which is proportional to the alveolar ventilation/alveolar volume ratio, was calculated by regression analysis.


RESULTS
Gravity-dependent atelectasis occurred only in 5 of 10 rabbits. In this group, K values in the dorsal regions increased before the appearance of GDA. No significant change in K values in the ventral regions was observed.


CONCLUSIONS
One mechanism of GDA may be a preferential reduction in alveolar volume without small airway collapse rather than alveolar volume loss secondary to decreased ventilation.
Tomiyama
N
N
Department of Radiology, Osaka University Medical School, Japan.
Takeuchi
N
N
Imanaka
H
H
Matsuura
N
N
Morimoto
S
S
Ikezoe
J
J
Johkoh
T
T
Arisawa
J
J
Kozuka
T
T
D000818:Animals; D006112:Gravitation; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D011817:Rabbits; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014978:Xenon
D014978:Xenon