Pilbeam's Mechanical Ventilation Practice Exam: Practice Test & Prep Guide

At the end of expiration, the intrapleural pressure (Ppl) is generally around -5 cm H2O. This negative pressure is crucial for maintaining lung inflation and preventing the lungs from collapsing.

During expiration, the diaphragm and intercostal muscles relax, allowing the thoracic cavity to decrease in volume. As the volume decreases, the pressure within the pleural space becomes more negative relative to atmospheric pressure, reaching approximately -5 cm H2O. This negative intrapleural pressure is essential, as it creates a pressure differential between the pleural space and the alveoli, helping to keep the lungs expanded against the chest wall.

Understanding this value is vital in mechanics of breathing, as it provides insight into how pressures work within the respiratory system and how they contribute to effective ventilation. The pressures at this phase are fundamental in distinguishing normal respiratory mechanics from pathological states, where altered intrapleural pressure can indicate various pulmonary conditions.