The aim of this study was to assess the usefulness of
nitric oxide (NO) output measurement at multiple expiratory flow rates during diseases characterized by increased exhaled NO (FE(NO)) that could come from alveolar (
liver cirrhosis) or
bronchial (asthma) sources. It has been proposed that NO output measurements expressed as a function of expiratory flow allow alveolar NO concentration (FA(NO)) and maximal bronchial NO output (
Qbr,max (NO)) to be computed. In 36 healthy nonsmoking subjects, we found that maximal bronchial NO output (37 +/- 3 nl/min) was correlated with the height of the subjects (p = 0.02). Alveolar NO concentration was 5.1 +/- 0.3 (SEM) ppb, which represented 31 +/- 2% and 61 +/- 3% of FE(NO) at 50 and 200 ml/s expiratory flow rate, respectively. Nonsmoking subjects with
asthma (n = 28) were characterized by an increase in
Qbr,max (NO) (133 +/- 14 nl/min) as compared with healthy nonsmoking subjects (p < 0.0001). FE(NO)50, FE(NO)200, and
Qbr,max (NO) were equally efficient in differentiating subjects with
asthma from healthy subjects. Patients with
liver cirrhosis (n = 26, 14 smokers and 12 nonsmokers) had an increased FA(NO) compared with healthy subjects (
cirrhosis: 8.3 +/- 0.9 ppb, healthy nonsmokers [n = 36] and smokers [n = 20], n = 56: 4.7 +/- 0.3 ppb, p < 0.05), which was correlated with the alveolar-arterial
oxygen difference (p = 0.007). FA(NO) and FE(NO)200, but not FE(NO)50 values, allowed patients with
liver cirrhosis to be differentiated from healthy subjects. These results suggest that a two-compartment model for NO output allows the increase in FE(NO) from alveolar sources to be differentiated from the increase from bronchial sources.