Ashutosh et al 1report that inhaled nitric oxide (iNO) lowers pulmonary vascular resistance (PVR) in stable patients with chronic obstructive pulmonary disease (COPD) receiving long term oxygen therapy (24 hours' treatment, randomised, double blind, crossover study). Oxygen was delivered via face mask at a rate of 2 l/min into which NO was diluted down from 200 ppm (cylinder) to achieve a final concentration of 25 ppm inspired. The authors conclude that vasodilation and relaxation of the pulmonary arterial bed is responsible for the fall in PVR.

Pulmonary arterial pressures were measured by cardiac catheterisation. Expired air was collected for five minutes and carbon dioxide output (V˙co ₂) and deadspace/tidal volume ratio (Vd/Vt) were measured. Cardiac output (CO) was determined by the Fick equation using V˙co ₂ and calculations of arterial and mixed venous carbon dioxide contents from directly measured mixed venous and arterial oxygen and carbon dioxide (Po …