Non-invasive assessment of pulmonary microcirculation at rest and exercise in patients with previous pulmonary thromboembolism

Abstract

There is renewed interest in non-invasive tests to assess residual lung microcirculatory abnormalities after pulmonary thromboembolism. Lung transfer capacity for carbon monoxide (DLCO) is weighted towards CO uptake by blood microcirculation whereas DL for nitric oxide (NO) is weighted towards the transport of NO through the alveolar-capillary membrane. We therefore hypothesized that, compared to controls, dyspneic patients with previous large or massive pulmonary thromboembolism would present with larger decrements in DLCO than DLNO and lower pulmonary blood flow (PBF) by inert gas rebreathing. Fourteen patients (10 females) with previous imaging-proved pulmonary embolism and 10 healthy controls (9 females) performed at rest and 25W measurements of DLNO and DLCO (HypAir, Medisoft™) and PBF by nitrous oxide uptake (Innocor, Innovision™). At rest, DLNO (93±24 vs 118±25% pred) and DLCO (93±24 vs 118±25% pred) were significantly lower in patients than controls (p 0.05). Albeit not significantly, PBF tended to be lower in patients than controls at similar rates of O2 uptake (3.9±1.2 L/min vs. 4.3±1.2 L/min vs). Our results do not support the use of DLNO/DLCO ratio or inert gas rebreathing to assess microcirculatory abnormalities in patients with previous pulmonary embolism. The role of these tests in patients with chronic thromboembolic pulmonary hypertension, however, remains open to investigation.