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Ventilation-perfusion relationships following experimental pulmonary contusion

¹U.S. Army Institute of Surgical Research, Fort Sam Houston, Texas; ²Department of Surgery, Blanchfield Army Community Hospital, Fort Campbell, Kentucky; ³Southwest Foundation for Biomedical Research, San Antonio, Texas; ⁴Department of Surgery, William Beaumont Army Medical Center, El Paso, Texas

Submitted 18 March 2006 ; accepted in final form 7 June 2007

Ventilation-perfusion changes after right-sided pulmonary contusion (PC) in swine were investigated by means of the multiple inert gas elimination technique (MIGET). Anesthetized swine (injury, n = 8; control, n = 6) sustained a right-chest PC by a captive-bolt apparatus. This was followed by a 12-ml/kg hemorrhage, resuscitation, and reinfusion of shed blood. MIGET and thoracic computed tomography (CT) were performed before and 6 h after injury. Three-dimensional CT scan reconstruction enabled determination of the combined fractional volume of poorly aerated and non-aerated lung tissue (VOL), and the mean gray-scale density (MGSD). Six hours after PC in injured animals, Pa_O2 decreased from 234.9 ± 5.1 to 113.9 ± 13.0 mmHg. Shunt (Q_S) increased (2.7 ± 0.4 to 12.3 ± 2.2%) at the expense of blood flow to normal ventilation/perfusion compartments (97.1 ± 0.4 to 87.4 ± 2.2%). Dead space ventilation (V_D/V_T) increased (58.7 ± 1.7% to 67.2 ± 1.2%). MGSD increased (–696.7 ± 6.1 to –565.0 ± 24.3 Hounsfield units), as did VOL (4.3 ± 0.5 to 33.5 ± 3.2%). Multivariate linear regression of MGSD, VOL, V_D/V_T, and Q_S vs. Pa_O2 retained VOL and Q_S (r² = .835) as independent covariates of Pa_O2. An increase in Q_S characterizes lung failure 6 h after pulmonary contusion; Q_S and VOL correlate independently with Pa_O2.

ventilation-perfusion mismatch; shunt; multiple inert gas elimination technique; computed tomography