NO diffusing capacity of rabbit lungs increases with ventilator-driven lung expansion

Pulmonary NO and C18O2 uptake during pressure-induced lung expansion in rabbits

In artificially ventilated animals we investigated the dependence of the pulmonary diffusing capacities of nitric oxide (NO) and doubly 18O-labeled carbon dioxide (DLNO, DLC18O2) on lung expansion with respect to ventilator-driven increases in intrapulmonary pressure. For this purpose we applied computerized single-breath experiments to 11 anesthetized paralyzed rabbits (weight 2.8-3.8 kg) at various alveolar volumes (45-72 ml) by studying the almost entire inspiratory limb of the respective pressure/volume curves (intrapulmonary pressure: 6-27 cmH2O). The animals were ventilated with room air, employing a computerized ventilatory servo-system that we designed to maintain mechanical ventilation and to execute the particular lung function tests automatically. Each single-breath maneuver was started from residual volume (13.5+/-2 ml, mean+/-SD) by inflating the rabbit lungs with 35-55 ml indicator gas mixture containing 0.05% NO in N2 or 0.9% C18O2 in N2. Alveolar partial pressures of NO and C18O2 were measured by respiratory mass spectrometry. Values of DLNO and DLC18O2 ranged between 1.55 and 2.49 ml/(mmHg min) and 11.7 and 16.6 ml/(mmHg min), respectively. Linear regression analyses yielded a significant increase in DLNO with simultaneous increase in alveolar volume (P<0.005) and intrapulmonary pressure (P<0.023) whereas DLC18O2 was not improved. Our results suggest that the ventilator-driven lung expansion impaired the C18O2 blood uptake conductance, finally compensating for the beneficial effect of the increase in alveolar volume on DLC18O2 values.

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 (T(LNO)SS) or the single breath method (T(LNO)SB), making the hypothesis that NO transfer is only limited by the membrane. Alterations in T(LNO)SS 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(LNO)SB at rest and maximal oxygen consumption (V(.-)O(2)max) were also measured in 18 other subjects. At rest T(LNO)SS with method 2 was 192% of the value given by method 1. T(LNO)SS with method 1 increased by 50% with 80% MAP as it did not change with method 2. Method 2 seemed inaccurate. T(LNO)SB 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(LNO)SS and T(LNO)SB 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(LNO)SS 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.