Low-density gas mixtures, such as
heliox, were shown to reduce the work of breathing and facilitate the distribution of inspired gas. Since supplemental ventilatory and
oxygen requirements may lead to
pulmonary inflammation and structural alterations, we hypothesized that by reducing these requirements,
heliox breathing may attenuate the acute inflammatory and structural changes associated with
acute lung injury. Spontaneously breathing neonatal pigs were anesthetized, instrumented, supported with
continuous positive airway pressure (CPAP), injured with
oleic acid, and randomized to
nitrox (n = 6) or
heliox (n = 5).F(I)O(2) was titrated for pulse oximetry (SpO(2)) 95 +/- 2% for 4 hr. Gas exchange and pulmonary mechanics were measured. Lungs were analyzed for
myeloperoxidase (MPO),
interleukin-8 (IL-8), and histomorphometery. Relationships between physiologic indices and cumulative lung structure and inflammatory indices were evaluated. With
heliox, compliance was significantly greater, while tidal volume, frequency, minute ventilation, F(I)O(2), arterial
carbon dioxide tension (PaCO(2)), MPO, and
IL-8 were significantly lower compared to
nitrox. The expansion index and number of exchange units were significantly greater with
heliox, while the exchange unit area (EUA) was smaller. MPO was significantly and positively correlated with F(I)O(2) (r = 0.76) and EUA (r = 0.63), and negatively correlated with number of open exchange units/field (r = -0.73). Compared to breathing
nitrox, these data indicate that
heliox improved the distribution of inspired gas, thereby recruiting more gas exchange units, improving gas exchange efficiency, reducing ventilatory and
oxygen requirements, and attenuating
lung inflammation. These data suggest that
heliox breathing may have the combined therapeutic benefits of attenuating
lung inflammation by reducing mechanical and oxidative stress in the clinical management of
acute lung injury.