Lung, chest wall, and total respiratory system resistances and elastances in the normal range of breathing.

We measured total respiratory system and lung and chest wall resistances (Rrs, Rl, and Rcw) and elastances (Ers, El, and Ecw) in awake, relaxed human subjects during sinusoidal volume forcing at the mouth from 0.2 to 0.6 Hz with tidal volumes (VT) of 6 to 18% VC at constant mean airway pressure. In addition, we repeated measurements with the lowest VT at a lower airway pressure and therefore at a lower mean lung volume (Vl). Rrs and Rcw decreased with increasing respiratory frequency (f) and VT, but Rl was independent of f and VT. All resistances were higher at the lower Vl. Ers and Ecw increased with increasing f and decreased with increasing VT. El increased slightly with increasing f but was not affected by VT. All elastances tended to increase at the lower Vl. We conclude that in the normal range of breathing amplitude and frequency, (1) lung properties are nearly constant if mean lung volume does not change, and (2) f and VT dependencies of total respiratory system properties are caused by the chest wall.