Fig. 5. (A, B ) Intraesophageal pressure (Pes) waveform error as a function of reducing Pes waveform energies after low-pass filtering before (A ) and after (B ) acute lung injury. Waveform error (%) is the maximum value for the end-inspiratory onset to end-expiratory onset amplitude error after low-pass filtering at chosen cut-off frequencies defined from reducing waveform energy contents (reducing % areas under the curve). ALI = acute lung injury; max Hz = highest Pes waveform frequency (largest waveform EI–EE bandwidth) found at maximum waveform errors of 5% or more or 3% or more; PesB, PesA = mean intraesophageal pressure waveforms at baseline (top ) and in ALI (bottom ), at physiologic (Pa^CO2of 30–40 mmHg) or artificially elevated airway pressures.