subglotal

Subglottal refers to the region of the airway located below the glottis—the opening between the vocal folds inside the larynx. The subglottal system comprises the subglottal space, including the trachea and lungs, and is the source of the driving air pressure for phonation. The term contrasts with supraglottal (above the glottis), which includes the pharynx and oral cavity.

Physiology: During phonation, the lungs generate air pressure (subglottal pressure). The vocal folds partially close and tremble under this pressure, converting aerodynamic energy into sound. Subglottal pressure acts as the driving force for vocal fold vibration; higher pressure generally increases loudness and can influence pitch depending on vocal fold tension. The glottal opening and rate of closure determine the resulting acoustic signal, which then resonates in the supraglottal vocal tract.

Measurement and variation: Subglottal pressure is commonly measured in centimeters of water (cm H2O) using specialized equipment. Normal conversational speech typically requires modest subglottal pressures, with higher values used for shouting or singing. Subglottal pressure interacts with laryngeal adjustments, including vocal fold tension and closed quotient, to shape voice quality.

Clinical and linguistic relevance: Subglottal pressure is a key parameter in voice science, voice therapy, and singing pedagogy. Abnormalities in the subglottal system, such as impaired lung function or laryngeal pathology, can affect phonation. In linguistics, subglottal conditions influence voice onset time and vowel quality through their impact on the source signal.