Semi-quantitative tracking of intra-airway fluids by computed tomography.
BACKGROUND
Airway secretions are a source of complications for patients with acute and chronic lung diseases, yet lack of techniques to quantitatively track secretions hampers research into clinical measures to reduce their pathologic consequences.


METHODS
In a preserved swine lung model, we tracked a contrasted mucus simulant (CMS) using sequential computed tomography (CT). Known drivers of secretion movement - gravity and ventilation - were tested. Ten millilitres of CMS were unilaterally introduced (1 ml min(-1)) into the airways of 12 lung sets. After instillation, six lung sets were maintained prone and six were rotated 180 degrees . Subsequently, all were mechanically ventilated for 10 min. CTs were obtained before infusion, after infusion and after ventilation +/- rotation. For CT analysis, the lungs were partitioned into eight sub-cuboids using anatomic landmarks. The volumes of two CT number ranges representing CMS and poor aeration/collapse were computed in every sub-cuboid for each CT acquisition. Volume differences between study time points were used to quantify changes.


RESULTS
CMS and poor aeration/collapse volume change distributed gravitationally after infusion. After ventilation without rotation, the CMS and poor aeration/collapse volumes remained within the originally injected sub-cuboid, although the poor aeration/collapse volume expanded (27.3 +/- 6.1-->50.5 +/- 7.4 ml, P<0.05). After ventilation + rotation, there was a reduction in the CMS and poor/aeration collapse volumes in the originally injected sub-cuboid (14.4 +/- 1.7-->4.4 +/- 0.6 ml, P<0.05 and 18.3 +/- 3.8-->11.9 +/- 2.7 ml, P<0.05, respectively) accompanied by increases in the gravitationally opposite sub-cuboid (1.7 +/- 0.2-->11.1 +/- 1.1 ml, P<0.05 and 0.8 +/- 0.5-->40.6 +/- 3.5 ml, P<0.05, respectively).


CONCLUSIONS
Movement of fluids within the bronchial tree can be semi-quantitatively tracked with analysis of sequential CT acquisitions. In this isolated swine lung model, gravity had an important and brisk effect on movement of a viscous fluid, whereas ventilation tended to embed it peripherally.
Graf
Jerónimo
J
Pulmonary and Critical Care Research, Regions Hospital, St Paul, MN 55101, USA. jeronimograf@yahoo.com
Mentzelopoulos
Spyros D
SD
Adams
Alexander B
AB
Zhang
Jie
J
Tashjian
Joseph H
JH
Marini
John J
JJ
D000465:Algorithms; D000818:Animals; D003287:Contrast Media / Q000493:pharmacokinetics; D007472:Iohexol / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D008168:Lung / Q000000981:diagnostic imaging* / Q000378:metabolism*; D009093:Mucus / Q000000981:diagnostic imaging* / Q000378:metabolism*; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods*
D003287:Contrast Media; D007472:Iohexol; C038192:iopromide