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 patients with primary pulmonary hypertension (PPH) and normal subjects was measured to determine the relationship between NO production and the diffusion capacity of the lung (KCO). Expired air was collected from eight patients with PPH and 20 healthy volunteers for analysis by a chemiluminescent analyser. Mean pulmonary artery pressure in the PPH patients was 59.5 +/- 6.45 mmHg and their mean cardiac output was 2.95 +/- 0.35 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 in 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 the KCO (r = 0.7; n = 30; p < 0.001). When corrected, KCO differences in exhaled 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 capillary volume in these patients rather than a decreased basal production of NO.