Approach to the estimation of alveolar pressure from noninvasive measurement of upper airway resistance.

An alternative to whole body plethysmography is proposed for estimating upper airway resistance. The feasibility study indicates that the method should be suitable for diagnostic and clinical purposes, following a proper survey and the testing of its reproducibility. 11 subjects are asked to breath normally through 12 small resistances while flow and pressure are monitored at the mouth. Chest movements are recorded by sampling a chest cross-section, and relative variations of the cross-section are compared to the expired and inspired volumes. No viscoelastic effects are significantly documented so that in a first approximation a model consisting only of resistors is applied to the airways. In each subject the patterns of the flow and mouth-pressure are heuristically estimated as a polynomial function of the added resistance. From the fit of the resistor model, the internal resistance of the airways is estimated as that value able to link the flow-resistance function to the pressure-resistance function, according to the classic Kirchhoff laws. We obtain resistances of (mean resistance +/- SD) 2.9 +/- 1.1, range 1.1 to 5.2, hPasdm-3 during expiration and 2.5 +/- 0.8, range 1.3 to 3.7, hPasdm-3 during inspiration.