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

In this animal study we evaluated the dependence of the pulmonary diffusing capacity (DL) of nitric oxide (DL,NO) on ventilator-driven increases in alveolar volume. According to the common hypothesis as to whether DL,NO reflects the diffusive properties of the alveolar-capillary membrane, DL,NO should be improved by lung expansion. However, the influence of a simultaneous raise in intrapulmonary pressure is unknown. DL,NO was determined by applying the single-breath method to four anaesthetised paralysed rabbits (weight 3.2-3.5 kg) at various alveolar volumes (38-69 ml) and intrapulmonary pressures (0.15-12.5 mmHg). The animals were ventilated with room air, using a computerised ventilatory servo-system that was also employed to perform the single-breath manoeuvres. Inflation procedures were always started from residual volume (12-13.7 ml), using 0.05% NO in N2 as the indicator gas mixture. End-tidal PNO was determined by respiratory mass spectrometry. DL,NO increased simultaneously with lung expansion and with increasing intrapulmonary pressure (P<0.001). We conclude that the DL,NO provides a measure of the pulmonary diffusive properties that is not influenced by a pressure-induced impairment of pulmonary capillary blood flow.