In a pressure-controlled breath, how does the pressure waveform respond to changes in patient lung characteristics?

• A. Increases with decreased lung compliance
• B. Decreases with increased airway resistance
• C. The pressure waveform is unaffected by changes in patient lung characteristics
• D. Fluctuates with tidal volume

Answer: (C)

In a pressure-controlled breath, the ventilator sets and maintains a specific peak airway pressure. That target pressure drives the pressure waveform, so the waveform amplitude stays essentially the same regardless of changes in the patient’s lung mechanics. If lung compliance decreases or airway resistance increases, the same pressure will still be reached, but the delivered tidal volume and the flow required to get there will change—the volume may drop with stiffer lungs or alter with resistance—but the pressure-time curve itself remains governed by the preset pressure limit. This is why the pressure waveform is considered unaffected by changes in lung characteristics.