What is the next step in managing a patient with a total lung capacity (TLC) of 123% and diffusing capacity of the lungs for carbon monoxide (DLCO) of 118%, who reports occasional shortness of breath (SOB) on exertion, and has not been seen since a previous date?

Management of Patient with Supranormal PFTs and Exertional Dyspnea

This patient requires cardiopulmonary exercise testing (CPET) as the next diagnostic step to identify the cause of exertional dyspnea when resting pulmonary function tests are normal or supranormal. 1, 2

Why Resting PFTs Are Insufficient

• A TLC of 123% and DLCO of 118% are both above normal limits, effectively ruling out restrictive lung disease, obstructive lung disease, and resting pulmonary vascular disease 1, 3
• Normal or supranormal DLCO (>80% predicted) argues strongly against interstitial lung disease, emphysema, and resting pulmonary arterial hypertension 1, 3
• Exertional dyspnea with normal resting PFTs occurs in multiple conditions that can only be identified during exercise, including heart failure with preserved ejection fraction (HFpEF), exercise-induced pulmonary hypertension, deconditioning, exercise-induced bronchoconstriction, and early pulmonary vascular disease 2, 1

Recommended Diagnostic Algorithm

Step 1: Obtain BNP or NT-proBNP

• BNP/NT-proBNP is the single most important initial test when cardiac and pulmonary workup is unrevealing 2
• BNP <100 pg/mL has 96-99% sensitivity for ruling out heart failure 2
• If BNP ≥100 pg/mL, proceed immediately to echocardiography to assess for HFpEF, diastolic dysfunction, valvular disease, or pulmonary hypertension 2

Step 2: Echocardiography (if BNP elevated)

• Evaluate left ventricular ejection fraction, diastolic parameters (E/A ratio, E/e' ratio), valve function, and right ventricular systolic pressure 2
• A negative cardiac stress test does not exclude HFpEF, which is particularly common in middle-aged women and presents with normal systolic function but diastolic dysfunction 2

Step 3: Cardiopulmonary Exercise Testing (if BNP normal)

• CPET is essential to distinguish between cardiac limitation, pulmonary gas exchange abnormalities, deconditioning, and exercise-induced bronchoconstriction when resting tests are normal 1, 2
• CPET will identify:
  • Reduced peak VO2 with low anaerobic threshold suggesting cardiac limitation or deconditioning 1
  • Elevated VE/VCO2 slope (>34) with increased dead space ventilation (VD/VT) indicating pulmonary vascular disease 1
  • Exercise-induced arterial desaturation suggesting pulmonary gas exchange abnormalities 1
  • Ventilatory limitation with reduced breathing reserve (<15% MVV) indicating respiratory mechanical limitation 1

Key Patterns to Identify on CPET

Exercise-Induced Pulmonary Hypertension

• VE/VCO2 slope >34, increased VD/VT, widened PA-aO2, and reduced peak O2 pulse with normal breathing reserve are 88% specific for pulmonary vascular resistance >120 dynes·sec·cm⁻⁵ 1
• This pattern occurs even when resting DLCO is normal in early pulmonary vascular disease 1, 4

Heart Failure with Preserved Ejection Fraction

• Reduced peak VO2, low anaerobic threshold, reduced O2 pulse, and oscillatory ventilation pattern 1
• Normal breathing reserve with premature exercise termination due to dyspnea 1

Deconditioning

• Reduced peak VO2 with normal O2 pulse slope, normal VE/VCO2, normal gas exchange, and early anaerobic threshold 1, 2
• Deconditioning is a common cause of exertional dyspnea in patients with normal resting cardiac and pulmonary function 2

Exercise-Induced Bronchoconstriction

• May not be detected on resting pulmonary function tests and requires exercise challenge or bronchoprovocation testing 2
• Look for fall in FEV1 >10% post-exercise 2

Critical Pitfalls to Avoid

• Do not assume normal resting PFTs exclude significant cardiopulmonary disease—many conditions only manifest during exercise 2, 1
• Do not rely solely on cardiac stress testing to exclude cardiac causes—stress tests primarily rule out obstructive coronary disease but miss HFpEF, valvular disease, and pulmonary hypertension 2
• Do not delay evaluation of unexplained dyspnea—it is associated with increased all-cause mortality and may represent early manifestations of serious disease 2

Additional Considerations

• If CPET suggests pulmonary vascular disease, consider CT pulmonary angiography and ventilation/perfusion scanning to evaluate for chronic thromboembolic disease 1
• If CPET suggests cardiac limitation, refer to cardiology for consideration of invasive hemodynamic assessment or advanced imaging 2
• Evaluate for anemia, thyroid dysfunction, or metabolic acidosis if not already completed 2