Dysanaptic growth of conducting airways after pneumonectomy assessed by CT scan

In immature dogs after pneumonectomy (PNX), pulmonary viscous resistance is persistently elevated predominantly as a result of a high airway resistance (Raw). We examined the anatomical basis for this observation by using computerized tomography scans obtained from foxhounds 4-10 mo after right PNX. Airways of the left lower lobe were followed from generations z = 0 (trachea) to z = 12. By 4 mo post-PNX, airway length increased significantly relative to sham-operated dogs, but airway cross-sectional area (CSA) did not. By 10 mo post-PNX, average airway CSA was 24% above that in controls. Theoretically, the increased airway length and CSA should reduce lobar Raw by 50%. However, post-PNX airway dilatation did not normalize total CSA, and estimated resistance due to turbulence and convective acceleration increased threefold; i.e., the 50% reduction in lobar Raw would be offset by the loss of four of seven lobes. Thus the expected reduction in work of breathing in the whole animal is only similar to30%, consistent with previously measured work of breathing in pneumonectomized dogs. We conclude that airway structure adapts slowly and incompletely, resulting in limited functional compensation.