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

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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 ( T LNOSS) or the single breath method ( T LNOSB), making the hypothesis that NO transfer is only limited by the membrane. Alterations in T LNOSS 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. T LNOSB at rest and maximal oxygen consumption ( V ˙ O 2 max ) were also measured in 18 other subjects. At rest T LNOSS with method 2 was 192% of the value given by method 1. T LNOSS with method 1 increased by 50% with 80% MAP as it did not change with method 2. Method 2 seemed inaccurate. T LNOSB at rest, which is closely related to Dm, was correlated to age and V ˙ O 2 max , T LNO SB = 182 − 1.2 age + 24.3 V ˙ O 2 max ( l min − 1 ) ( p < 0.01, r 2 = 0.72). The T LNOSS and T LNOSB 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 T LNOSS 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.