Dyspnea Post Pulmonary Embolism from VD/VT and Stroke Volume Defects During Exercise.

Many pulmonary embolism (PE) patients report dyspnea on exertion after long-term treatment. Increased physiological dead space proportion (V_D/V_T) and decreased cardiac stroke volume reserve may distinguish persistent effects of PE itself from symptoms reflecting comorbid conditions or deconditioning.

We retrospectively analyzed a consecutive series of incremental symptom-limited cardiopulmonary exercise tests that had been ordered to evaluate persistent dyspnea on exertion after long-term treatment for acute PE. Physiological V_D/V_T was determined at anaerobic threshold from exhaled CO₂ and transcutaneous pCO₂ (validated against p_aCO₂ measurements). Cardiac stroke volume reserve was estimated at rest and at anaerobic threshold by VO₂/pulse and previously validated estimates of C_a-vO₂.

Cardiopulmonary exercise tests were performed on 40 patients with post-PE dyspnea. In 65.0% (95% CI: 50.2%, 79.8%), V_D/V_T at anaerobic threshold was abnormally elevated, stroke volume reserve was decreased or both defects occurred. V_D/V_T at anaerobic threshold was abnormally elevated (≥ 0.27) in 35.0% (95% CI: 20.2%, 49.8%). V_D/V_T at anaerobic threshold significantly correlated with the extent of unmatched perfusion defects on subsequent VQ scans (p = 0.0085). In 55.0% (95% CI: 39.6%, 70.4%), stroke volume reserve at anaerobic threshold was abnormally decreased (≤ 128% of the resting value). Both defects were present in 25.0% (95% CI: 11.6%, 38.4%).

Increased V_D/V_T at anaerobic threshold and decreased stroke volume reserve during exercise are common among patients with dyspnea on exertion after long-term treatment of PE. The defects can be disclosed noninvasively by cardiopulmonary exercise testing.