Would obstruction be expected on a pulmonary function test (PFT) after a left pneumonectomy?

Pulmonary Function Test Findings After Left Pneumonectomy

After a left pneumonectomy, a restrictive pattern rather than obstruction would typically be expected on pulmonary function testing (PFT). This is primarily due to the significant reduction in lung volume following removal of the entire left lung.

Expected PFT Changes Following Left Pneumonectomy

Volume Changes

• Significant reduction in Total Lung Capacity (TLC)
• Reduced Vital Capacity (VC)
• Reduced Forced Vital Capacity (FVC)
• Reduced FEV1 (Forced Expiratory Volume in 1 second) in absolute terms

Pattern of Impairment

• Normal or increased FEV1/VC ratio (typically >85-90%) 1
• Convex flow-volume curve pattern
• Preserved airflow rates relative to lung volumes

Physiological Explanation

After pneumonectomy, the primary physiological change is a substantial reduction in lung volume rather than airway narrowing. According to the European Respiratory Society guidelines, a restrictive ventilatory defect is characterized by:

1. Reduction in TLC below the 5th percentile of predicted value
2. Normal FEV1/VC ratio 1

The BTS guidelines for patient selection for lung cancer surgery explain that pneumonectomy patients typically lose approximately 35% of their preoperative FEV1 1, but this represents a volume loss rather than airflow obstruction.

Clinical Implications

Research shows that pneumonectomy patients experience:

• 35% reduction in preoperative FEV1
• 23% reduction in exercise capacity at 6 months post-surgery 2

This disproportionate loss of pulmonary function relative to exercise capacity is important to note, as PFT values alone may exaggerate the functional impairment experienced by patients.

Assessment of Postoperative Function

When evaluating patients for pneumonectomy, physicians should calculate the estimated postoperative FEV1 using:

Estimated postoperative FEV1 = preoperative FEV1 × (1 - fraction of total perfusion in resected lung)

This calculation helps predict the expected restrictive pattern 1.

Common Pitfalls in Interpretation

1. Mistaking reduced FEV1 alone for obstruction without considering the FEV1/VC ratio
2. Failing to recognize that pneumonectomy creates a restrictive, not obstructive, pattern
3. Overestimating functional impairment based solely on PFT values without considering actual exercise capacity

In summary, a left pneumonectomy results in a restrictive ventilatory pattern on PFTs characterized by reduced lung volumes with preserved or increased FEV1/VC ratio, not an obstructive pattern.