From the Research
Yes, atmospheric pressure is greater than intrapleural pressure during both inspiration and expiration. Intrapleural pressure, which exists in the potential space between the visceral and parietal pleura surrounding the lungs, is always negative (subatmospheric) during normal breathing. The most recent and highest quality study on respiratory mechanics is not directly provided in the given evidence, however, the principles of respiratory physiology remain consistent across studies.
Key Points
- During inspiration, intrapleural pressure becomes even more negative as the chest wall expands and the diaphragm contracts, creating a greater negative pressure that draws air into the lungs.
- During expiration, although intrapleural pressure increases slightly, it remains negative and below atmospheric pressure.
- This persistent negative intrapleural pressure is essential for normal respiratory mechanics as it prevents lung collapse by keeping the lungs expanded against the chest wall.
- The negative pressure exists because the natural elastic recoil of the lungs pulls inward while the chest wall tends to spring outward, creating a constant tension that maintains the subatmospheric pressure in the pleural space throughout the respiratory cycle.
Given the evidence provided, studies such as 1 discuss the application of non-invasive positive pressure ventilation (NPPV) in chronic obstructive pulmonary disease (COPD), highlighting its benefits in reducing hypercapnia and improving patient outcomes. However, these studies do not directly address the comparison between atmospheric and intrapleural pressures during the respiratory cycle. The fundamental principles of respiratory physiology, as described, dictate that intrapleural pressure remains subatmospheric during both phases of breathing to facilitate lung expansion and prevent collapse.
Clinical Implications
- Understanding the relationship between atmospheric and intrapleural pressures is crucial for managing respiratory conditions, including COPD.
- NPPV, as discussed in studies like 2, 3, and 4, can be an effective treatment for COPD patients with hypercapnic respiratory failure by reducing the work of breathing and improving gas exchange.
- The selection of patients for NPPV, as outlined in 5, should consider factors such as the presence of daytime hypercapnia and the ability to tolerate ventilatory pressures, to maximize therapeutic benefits while minimizing risks.
In clinical practice, recognizing the subatmospheric nature of intrapleural pressure during both inspiration and expiration is vital for the effective management of respiratory diseases and the application of therapies like NPPV.