Nasal and oral airway pressure-flow relationships.

We examined the inspiratory and expiratory pressure-flow relationships of both the oral and nasal airways before and after exercise in normal upright subjects. With the use of a partitioned facemask, nasal resistance was measured using posterior rhinomanometry, and oral resistance was measured by recording transoral pressure during oral breathing. Both the nasal and oral pressure-flow relationships for inspiration and expiration were curvilinear and were well described by a power function of the form delta P = aVb (where P is pressure, V is flow, a and b are constants) (r2 = 0.96 +/- 0.01). The exponent b describes the curvilinearity of the pressure-flow curve and can be used to infer the flow regimen. At rest, the inspiratory nasal and oral curves suggested a similar degree of turbulence (b = 1.77 +/- 0.06 and 1.83 +/- 0.04, respectively). However, inspiratory flow regimens were inferred to be more turbulent than those during expiration both before and after exercise. After exercise, decreases in inspiratory nasal resistance at low flows were associated with a change in flow regimen from fully turbulent to orifice flow over the entire flow range. Thus the application of a power function to nasal and oral pressure-flow data permits representation of the whole relationship and allows insight into the nature of the flow regimens.