Nitric oxide production by the alveolar compartment of the lungs in cirrhotic patients

Abstract

In cirrhotic patients, alveolar nitric oxide (NO) concentration is increased. This may be secondary to increased output of NO produced by the alveoli (V'(A,NO)) and/or to decreased lung transfer factor of NO. In advanced liver cirrhosis, NO produced by the alveoli may play a role in abnormalities of pulmonary haemodynamics and gas exchanges. In cirrhotic patients, we aimed to measure V'(A,NO) and to compare V'(A,NO) with pulmonary haemodynamics and gas exchange parameters. Measurements were performed in 22 healthy controls and in 29 cirrhotic patients, of whom eight had hepatopulmonary syndrome. Exhaled NO concentrations were measured at multiple expiratory flow rates to derive alveolar NO concentration. V'(A,NO) was the product of alveolar NO concentration by single breath lung transfer factor for NO. V'(A,NO) was increased in patients (median (range) 260 (177-341) nL x min(-1)) compared with controls (79 (60-90), p<0.0001). Alveolar-arterial oxygen tension difference failed to correlate with V'(A,NO). However, cardiac index correlated positively and systemic vascular resistance correlated negatively with V'(A,NO) (r = 0.56, p = 0.001 and r = -0.52, p = 0.004, respectively). In cirrhotic patients, NO was produced in excess by the alveolar compartment of the lungs. Alveolar NO production was associated with hyperdynamic circulatory syndrome but not with arterial oxygenation impairment.