Membrane conductance in trained and untrained subjects using either steady state or single breath measurements of NO transfer

The aim of this work was to define the relationship between membrane conductance for NO (Dm) and physical activity by using either the steady state NO transfer (TLNOSS) or the single breath method (TLNOSB), making the hypothesis that NO transfer is only limited by the membrane. Alterations in TLNOSS with lung volume during tidal ventilation were measured in six subjects at rest and during steady exercise at 30, 60, and 80% of maximal aerobic power (MAP). A fast responding chemoluminescent NO analyser was used. Two calculation methods were used by sampling NO: (1) at mid-tidal volume, (2) in the middle of the alveolar plateau. TLNOSB at rest and maximal oxygen consumption (V˙O2max) were also measured in 18 other subjects. At rest TLNOSS with method 2 was 192% of the value given by method 1. TLNOSS with method 1 increased by 50% with 80% MAP as it did not change with method 2. Method 2 seemed inaccurate. TLNOSB at rest, which is closely related to Dm, was correlated to age and V˙O2max, TLNOSB=182−1.2age+24.3V˙O2max(lmin−1) (p < 0.01, r2 = 0.72). The TLNOSS and TLNOSB versus lung volume relationships suggest an influence of the breathing pattern on Dm. Dm can be estimated either by these two NO transfer methods, however the use of the TLNOSS method is highly sensitive to the alveolar sampling level. Dm increase during exercise is a function of MAP. Dm at rest decreases with age as it increases with MAP.