Oral airway flow dynamics in healthy humans

1. Oral airway resistance (R-O) is an important determinant of ore-nasal pa rtitioning 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 (ba sed on a modification of posterior rhinomanometry) and examined inspiratory R-O in 17 healthy male subjects (age, 38 +/- 2 years (mean +/- S.E.M.); he ight, 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) du ring resting mouthpiece breathing in the upright posture. R-O was unaffecte d by assumption of the supine posture, tended to decrease with head and nec k extension and increased to 1.22 +/- 0.19 cmH(2)O l(-1) s(-1) (n = 10 subj ects, 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 sig nificantly 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 ne ck flexion. This influence on upper airway patency may be important when or al route breathing is associated with alterations in head and neck position , e.g. during sleep.