Oral airway flow dynamics in healthy humans

1. Oral airway resistance (R-O) is an important determinant of ore-nasal partitioning of airflow (e.g, during exercise and sleep); however, little is known of factors influencing its magnitude and measurement. 2. We developed a non-invasive standardized technique for measuring R-O (based on a modification of posterior rhinomanometry) and examined inspiratory R-O in 17 healthy male subjects (age, 38 +/- 2 years (mean +/- S.E.M.); height, 177 +/- 2 cm; weight, 83 +/- 3 kg). 3. Inspiratory R-O (at 0.41 s(-1)) was 0.86 +/- 0.23 cmH(2)O l(-1) s(-1) during resting mouthpiece breathing in the upright posture. R-O was unaffected by assumption of the supine posture, tended to decrease with head and neck extension and increased to 1.22 +/- 0.19 cmH(2)O l(-1) s(-1) (n = 10 subjects, P < 0.01) with 40-45 deg of head and neck flexion. When breathing via a mouth-mask R-O was 2.98 +/- 0.42 cmH(2)O l(-1) s(-1) (n = 7) and not significantly different from nasal airway resistance. 4. Thus, in awake healthy male subjects with constant jaw position, R-O is unaffected by body posture but increases with modest degrees of head and neck flexion. This influence on upper airway patency may be important when oral route breathing is associated with alterations in head and neck position, e.g. during sleep.