Pulmonary Function Test Changes Two Weeks After Acute Pulmonary Embolism
At two weeks post-PE, pulmonary function tests typically show a reduced diffusing capacity for carbon monoxide (DLCO), often to below 75% of predicted, while spirometry values (FEV1, FVC) and alveolar volume (VA) may be reduced but are highly variable and non-specific.
Primary PFT Abnormality: Reduced DLCO
- DLCO is significantly reduced in all patients with acute PE and serves as the most consistent and clinically useful PFT abnormality 1
- The reduction in DLCO to below 75% of predicted normal was found in all cases with abnormal lung scans and provides a useful screening test for PE 1
- A normal DLCO effectively excludes the diagnosis of PE, making it a valuable negative predictor 1
- The DLCO reduction persists despite anticoagulation therapy and tends to remain subnormal for extended periods (up to 3 years in some studies), even after lung scans normalize 1
Mechanism of DLCO Reduction
The reduction in DLCO is primarily explained by two components:
- Reduction in membrane diffusing capacity (DM) is the predominant mechanism, particularly correlating with central mass of embolism (r = -0.312; P = 0.047) 2
- DM remains significantly lower than healthy controls even at 7-month follow-up (P = 0.001), explaining the sustained decrease in DLCO despite modern PE treatment 2
- Loss of alveolar volume (VA) also contributes significantly to the DLCO reduction, particularly in submassive emboli 3
- Pulmonary capillary blood volume (Vc) shows less consistent correlation with PE extent compared to DM 2
Other PFT Abnormalities at Two Weeks
Alveolar Volume (VA):
- VA is significantly lower in acute PE patients compared to healthy controls (P < 0.001) 2
- VA improves significantly within 7 months but may not fully normalize 2
Spirometry (FEV1, FVC):
- Changes in FEV1 and FVC are too variable to be diagnostically helpful 1
- Vital capacity (VC) is significantly lower in acute PE but improves over time 2
- These measurements lack the consistency needed for reliable PE assessment 1
DLCO/VA Ratio (KCO):
- DLCO/VA is significantly lower in patients with acute PE than in healthy controls (P < 0.001) 2
- The DM/Vc relationship is significantly lower in patients with right ventricular dysfunction compared to healthy controls (P = 0.004) 2
Clinical Context and Follow-Up Considerations
Important Caveats:
- At 3-6 months post-PE, the ESC guidelines note that pulmonary function tests are largely within normal limits in most patients, even those with reduced maximal aerobic capacity on cardiopulmonary exercise testing 4
- This creates a clinical paradox: many patients report persistent dyspnea and functional limitation despite normalized PFTs 4
- The lack of association between PFT abnormalities and exercise impairment suggests that muscle deconditioning, rather than persistent pulmonary dysfunction, drives long-term symptoms in most cases 4
At Two Weeks Specifically:
- PFT abnormalities are most pronounced in the acute and early subacute phases (first 2-8 weeks) 2, 1
- DLCO reduction correlates with the extent of PE, particularly central embolic burden 2
- Patients with right ventricular dysfunction show more pronounced alterations in the DM/Vc relationship 2
Practical Algorithm for PFT Interpretation at Two Weeks Post-PE
Measure DLCO as the primary test: Expect reduction to <75% predicted in virtually all cases with confirmed PE 1
Assess DLCO components if available: Look for reduced DM (more specific for PE extent) and reduced VA 2, 3
Do not rely on spirometry alone: FEV1 and FVC changes are too inconsistent for diagnostic or prognostic value 1
Correlate with imaging and clinical status: DLCO abnormalities may persist long after lung scans normalize, suggesting ongoing physiological defects despite radiographic resolution 1
Plan follow-up at 3-6 months: Per ESC guidelines, routine clinical evaluation is recommended at this timeframe to assess for persistent symptoms, though PFTs may normalize even in symptomatic patients 4