inbreaths

An inbreath, also called an inhalation or inspiration, is the phase of respiration during which air is drawn into the lungs. It is followed by an exhalation, or expiration, when air leaves the lungs. In everyday language, "inbreath" is often used to contrast with "outbreath" or "exhalation."

Physiology and mechanism: Inhalation begins with the coordinated action of the diaphragm, which contracts and moves downward, and the external intercostal muscles, which raise the rib cage. This expansion of the thoracic cavity lowers intrapulmonary pressure below atmospheric pressure, allowing air to flow through the airways and fill the lungs until pressures equalize. Quiet breathing relies mainly on diaphragmatic and intercostal activity, while deeper or hurried breathing engages accessory muscles.

Volume and capacity: The amount of air inhaled with a normal breath is the tidal volume, typically around 400–600 mL in a healthy adult. Other relevant measures include inspiratory reserve volume (the additional air that can be inhaled after a normal breath) and inspiratory capacity, which, together with residual volume and functional residual capacity, reflect overall lung function. Lung volumes are commonly assessed with spirometry and related tests.

Clinical and practical contexts: Abnormal inbreaths can indicate respiratory distress, restrictive or obstructive lung disease, or compromised diaphragmatic function. Shallow, rapid inbreaths may be observed in anxiety, pain, or fatigue. In singing, speech, and athletic training, breath management emphasizes controlled inbreaths to maintain steady airflow and vocal or physical performance across activities.

Etymology and usage: The term "inbreath" is used interchangeably with inhalation or inspiration in many texts, though usage may vary by discipline. The concept is foundational to respiratory physiology, medicine, and exercise science.