MIXED EXPIRED NITRIC-OXIDE IN PRIMARY PULMONARY-HYPERTENSION IN RELATION TO LUNG DIFFUSION CAPACITY

The mixed expired nitric oxide (NO) production of the lungs of patient s with primary pulmonary hypertension (PPH) and normal subjects was me asured to determine the relationship between NO production and the dif fusion capacity of the lung (KCO). Expired air was collected from eigh t patients with PPH and 20 healthy volunteers for analysis by a chemlu minescent analyser. Mean pulmonary artery pressure in the PPH patients was 59.5 +/- 6.45 mmHg and their mean cardiac output was 2.95 +/- 0.3 5 l/min. All patients and subjects underwent measurements of FEV1, VC and KCO. The rate of production of NO in mixed exhaled air was lower i n the PPH group compared to the controls (2.85 +/- 0.7 vs. 4.69 +/- 0. 35 nM/min; p<0.05). There was a good correlation of expired NO with th e KCO (r=0.7; n=30; p<0.001). When corrected, KCO differences in exhal ed NO were not significant (p=0.09). We conclude that the low exhaled NO observed in PPH patients is a reflection of the reduced blood capil lary volume in these patients rather than a decreased basal production of NO.