The Chest: Inhalation, Exhalation, and Respiratory Mechanics

The chest, or thoracic cavity, plays a central role in the respiratory process, which involves inhalation, exhalation, and the interaction of pressures. The diaphragm and other respiratory muscles contribute significantly to this process.

Inhalation

Inhalation, or inspiration, is the process of drawing air into the lungs. • Mechanics: • The diaphragm contracts and moves downward, increasing the vertical space in the thoracic cavity. • The external intercostal muscles lift the ribs outward and upward, expanding the chest in all directions. • Negative Pressure: • As the thoracic cavity expands, the pressure inside the lungs (intrapulmonary pressure) decreases below atmospheric pressure. • This negative pressure gradient pulls air into the lungs.

Exhalation

Exhalation, or expiration, is the process of expelling air from the lungs. • Mechanics: • At rest, exhalation is passive and occurs as the diaphragm and intercostal muscles relax. • The elastic recoil of the lungs and chest wall decreases thoracic cavity volume. • During forced exhalation, the internal intercostal and abdominal muscles contract to expel air more forcefully. • Positive Pressure: • As the chest cavity volume decreases, intrapulmonary pressure rises above atmospheric pressure, pushing air out of the lungs.

Role of the Diaphragm

The diaphragm is the primary muscle of respiration. • During inhalation, it contracts, flattens, and enlarges the thoracic cavity, creating negative pressure. • During exhalation, it relaxes and returns to its dome shape, reducing thoracic cavity volume and facilitating passive exhalation.

Positive and Negative Pressure in Breathing• Negative Pressure: • Occurs during inhalation when the chest expands, causing air to flow into the lungs. • Positive Pressure: • Occurs during exhalation when the chest cavity compresses, forcing air out.

This interplay of positive and negative pressures ensures efficient ventilation, oxygen delivery, and carbon dioxide removal.