Serial distribution of airway geometry from acoustic impedance data.

Cross-sectional areas of airways vary with distance from the airway opening to alveoli. Existing techniques for estimating the serial distribution of airway cross section are invasive or depend on interpretations of indirect measurements. A rapid, noninvasive technique based on acoustic impedance data for estimating airway cross section as a function of distance has been described. Cross-sectional areas returned by this technique from measurements in a positive cast of human central airways out to subsegmental bronchi corresponded closely with areas determined from direct measurements. In vagotomized dogs, measurements indicate that vagal stimulation results in reduction of airway cross section at all distances, whereas histamine aerosol caused bronchoconstriction only at larger distances (i.e., peripheral airways). Vagotomy in the dog results in an apparent dilation in most airways to areas twice those in the control state. This increase in airway cross section is larger than has been reported previously. Measurements in humans indicate an apparent overestimation in tracheal cross-sectional areas. These findings might be caused by overestimations in area due to airway wall compliance in the intact human and in the dog without vagal tone. This technique may still be capable of providing useful information about the serial distribution of airway properties.