Final answer:
In volume-controlled ventilation, both peak and plateau pressures rise together when lung compliance decreases or airway resistance increases, consistent with Boyle's Law.
Step-by-step explanation:
Regarding volume-controlled ventilation (VCV) and the difference in pressures that cannot be directly measured in pressure-controlled ventilation (PCV), the correct statement is 'Peak and plateau pressures rise together.' This happens because in VCV, the ventilator delivers a set volume to the patient, and peak pressure will vary based on the patient's lung compliance and airway resistance. When lung compliance decreases or airway resistance increases, both peak and plateau pressures will rise together since the volume is kept constant. It should be noted that Boyle's Law, which states that pressure and volume are inversely proportional when temperature and number of molecules are constant, is a fundamental concept in understanding these phenomena in respiratory mechanics.