Frequency dependence of ventilation distribution in normal and obstructed lungs

Abstract

Differences in regional pulmonary time constant may cause ventilation distribution to vary with breathing frequency and frequency-dependent changes in regional ventilation per unit volume might be expected. The regional distribution of inhaled 133Xe was measured at 10 and 60 breaths/min in normal subjects and in patients with a clinical diagnosis of chronic bronchitis or asthma. Breathing frequency had no significant effect on ventilation distribution in normals but in patients with chronic bronchitis, ventilation decreased in the lower lung regions at 60 breaths/min compared with 10 breaths/min. In 6 asthmatic patients, the lung regions demonstrating the greatest frequency-dependent reductions in ventilation, which were assumed to have the greatest time constants, also showed decreased ventilation-perfusion ratios (.ovrhdot.V/.ovrhdot.Q) measured by standard 133Xe techniques. Bronchodilator increased ventilation more than perfusion in these regions and .ovrhdot.V/.ovrhdot.Q ratio increased toward the normal range. Measurement of the frequency dependence of regional ventilation apparently provides information about the relative distribution of airway obstruction, and airway function in the most obstructed lung regions in asthmatics is improved following bronchodilator therapy.