Exhaling

Exhaling is the act of expelling air from the lungs, the second phase of ventilation, following inhalation. It helps replenish air in the alveoli and removes carbon dioxide produced by metabolism.

In quiet breathing, exhalation is mostly passive, driven by the elastic recoil of the lung tissue and chest wall. Muscles that had expanded the chest during inhalation relax, and air flows out along a pressure gradient until the intrapulmonary pressure equals atmospheric pressure.

In forced exhalation, the abdominal muscles contract to increase intra-abdominal pressure, helping push the diaphragm upward. The internal intercostal muscles may contract to depress the ribs, reducing thoracic volume more rapidly. Air is expelled more quickly, as seen in talking, singing, coughing, and vigorous exercise. Pursed-lip breathing can modulate expiratory flow and reduce the work of breathing in some situations.

Regulation of exhalation, like inhalation, is controlled by the respiratory center in the brainstem. Chemoreceptors monitor carbon dioxide and pH levels, adjusting the rate and depth of expiration to maintain blood gas balance. Exhaled air is typically humidified and warmed as it leaves the airways, and its composition reflects the body’s metabolic state.

Clinical and cultural aspects: Abnormal exhalation patterns can arise in respiratory diseases such as COPD and asthma, where expiration may be prolonged or laborious. Breathing techniques, including diaphragmatic breathing and pursed-lip breathing, are used therapeutically. Exhalation is essential in vocalization, wind instruments, and various breathing training practices in sport and mindfulness.