Oral airway flow dynamics in healthy humans

Abstract

1. Oral airway resistance (RO) is an important determinant of oro-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 RO (based on a modification of posterior rhinomanometry) and examined inspiratory RO in 17 healthy male subjects (age, 36 +/- 2 years (mean +/- s.e.m.); height, 177 +/- 2 cm; weight, 83 +/- 3 kg). 3. Inspiratory RO (at 0.4 l s-1) was 0.86 +/- 0.23 cmH2O l-1 s-1 during resting mouthpiece breathing in the upright posture. RO was unaffected by assumption of the supine posture, tended to decrease with head and neck extension and increased to 1.22 +/- 0.19 cmH2O 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 RO was 2.98 +/- 0.42 cmH2O 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, RO 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.

Figure 1. Measurement of oral resistance

Schematic diagram of the experimental set-up for measuring oral resistance. A pneumotachograph was used to measure oral airflow (V). Pressures were measured at the mouthpiece (P_mouth) and in the nasal mask (P_{oropharyngeal}). Since the nasal mask was occluded, mask pressure corresponded to pressure in the oropharyngeal airway.

Figure 2. Transoral pressure-flow curves

Representative example of power functions P = a V ^b fitted to the inspiratory transoral pressure-flow data from one subject in the neutral control position (A) and at 45 deg flexion (B) and 45 deg extension (C). Note that the flexion curve (B) is steeper than both A and C as reflected by the larger a constant of the power function. Transoral pressures (horizontal dashed lines) were calculated at an oral flow of 0.4 l s⁻¹ (vertical dotted line) from each fitted power function and used to compute oral resistance values.

Figure 3. Effect of head and neck posture on oral airway resistance

Inspiratory oral airway resistance values (at 0.4 l s⁻¹) for different head and neck positions in ten normal subjects. In A the different symbols represent individual subjects, while B shows group mean values. Bars represent +1 s.e.m.*P < 0.005 compared with control. †P < 0.005 compared with 40-45 deg flexion.