Chest wall and pulmonary contributions to the total respiratory airway and tissue mechanics in rats: effects of altered lung volume

Changes in lung mechanics are in the centre of interest in rat models of respiratory diseases; however, they are frequently inferred from total respiratory system indices that are biased by chest wall properties. Thus, we assessed the separate contribution of the lung and chest wall compartments to the total respiratory system mechanics in rats, and we also evaluated the influence of altered lung volume on these estimates. The forced oscillation technique was applied in anesthetized, mechanically ventilated rats (n=14) to obtain mechanical impedance of the total respiratory system (Zrs) at 0, 3 and 6 cmH2O positive end-expiratory pressure (PEEP) levels. Oesophageal pressure was measured by a self-made balloon to separate Zrs into pulmonary (ZL) and chest wall (Zw) components. A model containing a frequency-independent Newtonian resistance (R), inertance (I) and a constant-phase tissue damping (G) and elastance (H), was fitted to Zrs, ZL, and Zw spectra. The contribution of Zw to the total respiratory R and I was negligible (3.8±5.6[SD]% and 5.5±23%) at all PEEP levels. However, the participation of Zw in G and H was significant at PEEP0 (17±10% and 12±6%, p These findings demonstrate that airway parameters can be accurately assessed from respiratory system mechanical assessments. However, the contribution of the chest wall to the viscoelastic parameters of the total respiratory tissues should be taken into account when these indices are used to estimate lung parenchymal mechanics, particularly at high PEEP levels. Grant support: NKFIH K115253 and GINOP-2.3.2-15-2016-00006