Sources of error in partial rebreathing pulmonary blood flow measurements in lungs with emphysema and pulmonary embolism

Studies of the accuracy of partial rebreathing measurements of pulmonary blood flow (PBF) in patients with abnormal lungs have not fully explained the sources of error. We used computer models of emphysema and pulmonary embolism incorporating both ventilation-perfusion ( V˙/ Q˙) and ventilation-volume ( V˙/V) heterogeneity to investigate systematic errors in partial rebreathing PBF measurements. We studied (i) errors produced under usual conditions, (ii) effects of recirculation, (iii) effects of alveolar–proximal airway and alveolar-capillary Pco2 and V˙CO2 differences, (iv) effects of alveolar V˙/ Q˙ inhomogeneity and (v) effects of rebreathing time. In the pulmonary embolism model the systematic error is only acceptable (