Dilator naris muscle.

The human nose is an important organ of respiration which by virtue of its valvular influence becomes a significant effector of respiratory resistance over a wide range of ventilatory requirements. In man its effectiveness in this regard is related to its flow limiting segment (FLS) located at the limen nasi. Its passive valvular effect is additionally modified by active respiratory contractions of the dilator naris muscle (DNM) controlled through the VII cranial nerve by the brain stem respiratory center. Its behavior, quantitatively determined in human beings and experimental animals, is summarized. 1) In man, phasic DNM activity operates during eupneic nasal breathing and varies directly with ventilatory resistance. 2) The elimination of all measurable ventilatory resistance results in complete cessation of DNM activity. 3) Over time, reduced resistance produces difficulty in reestablishing dilator function once it is physiologically lost. 4) DNM respiratory activity is modified by pulmonary mechano- and pressure-receptors via afferent vagal pathways. The response of nasal dilators in valvular control, therefore, appears dependent on the physiologic integrity of the vagus nerves. It is our belief that nasal valvular control has not previously been appreciated in this context.