Measurements of regional ventilation pulmonary gas volume: theory and error analysis with special reference to positron emission tomography.

Abstract

The adaptation to PET of the steady-state technique for the measurement of alveolar ventilation, based on the short-lived radionuclide 19Ne (T1/2 = 17.4 sec), allows the steady-state lung model to be analyzed in a quantitative way under well-defined geometrical conditions. The regional gas volume is essential to this analysis, and regional measurements of the pulmonary gas volume based on transmission tomography are presented and validated in this paper. The accuracy of the steady-state method rests largely with the validity of the lung model applied to describe the transport of tracer in the lung. This study considers tracer transport and mixing within individual lung regions. Blood flow and the alveolar-to-capillary exchange of gases do not significantly affect the values obtained, not even in regions with highly abnormal ventilation/perfusion ratios. A nonuniform intra-regional gas flow distribution results in an underestimation of the regional ventilation, determined by the dispersion of the ventilatory turnover rates of alveolar gas within the region. In the normal lung this underestimation is negligible. In disease, a mixing within the resolution volume of units that are almost non-ventilated and units that perform normally may result in an underestimation of alveolar ventilation by up to 60%.