Resistance to respiratory airflow of the extrapulmonary airways

Resistances to respiratory airflow of nasal, pharyngeal, laryngeal, and tracheobronchial airway segments were determined by computer processing of digitized differential pressure and flow signals in four healthy, awake, male adults seated and breathing spontaneously at rest, exclusively through decongested noses. Resistances of the nasal and pharyngeal segments in Pa/cm3 per second averaged 0.139 (SD ± 0.044) and 0.081 (SD ± 0.051), respectively, with no resistive evidence of compliance with airflow pressures. The laryngeal segment exhibited the reciprocal of compliance, expiratory resistances exceeded those of inspiration, averaging 0.125 (SD ± 0.037) and 0.035 (SD ± 0.013), respectively (.005 < P < .01). Tracheobronchial resistances during spontaneous resting breathing were too small to record reliably at the calibration used, and values augmented by voluntary hyperventilation averaged only 0.012 (SD ± 0.004). Laryngeal expiratory resistance approximated one fifth of the sum total of respiratory airflow resistances (including the pulmonary airways) and the authors suggest that, in addition to contributing to expiratory airflow braking, partial laryngeal closure induces orifice flow. This nonlaminar flow regime promotes the mucosal contact and mixing that enables greater than 30% of heat and water to be recovered from expiratory air by the human pharynx and nose.