What is the intrapleural pressure at rest in a breathing cycle?

Intrapleural pressure at rest in a breathing cycle is indeed negative. This negative pressure is crucial for maintaining the lung's inflation and proper functioning of the respiratory system. The negative intrapleural pressure is created by the opposing forces of the lungs trying to collapse (due to their elastic properties) and the chest wall wanting to expand. This pressure helps keep the lungs inflated and is vital for the mechanics of breathing.

When the lungs expand during inhalation, the negative pressure in the pleural cavity becomes even more negative, further facilitating lung expansion. During exhalation, while the pressure does increase slightly, it still remains negative during normal resting conditions. This characteristic of intrapleural pressure is essential for ensuring that air is drawn into the lungs effectively and that the alveoli remain open, promoting efficient gas exchange.