Determination of regional pulmonary blood flow with systemically injected nonentrapped microspheres

Abstract

Radioactive microspheres (MS) injected into the systemic circulation shunt to the venous side of the circulation and are trapped in the lung vasculature. We hypothesized that regional pulmonary perfusion could be determined by using systemically injected shunted MS. In seven anesthetized mechanically ventilated foxhounds, regional pulmonary perfusion was measured at baseline and during experimental acute respiratory distress syndrome with MS injected into both the right and left atrium (protocol 1). Methodological error of the MS technique was assessed by simultaneous injection of two different batches of MS into the right atrium (protocol 2). Measurement of perfusion during baseline and during experimental acute respiratory distress syndrome with shunted MS had a mean bias of 0.8 and 5.6% and mean precision of 19.2 and 34.7% (r = 0.94 and r = 0.95), respectively, compared with data from nonshunted MS. Simultaneous perfusion measurements displayed bias of -2.7 and 6% and precision of 8.2 and 5.3% (r = 0.98 and r = 0.99), respectively. Systemic shunt should be high for this method to prevent bronchial circulation from imposing significant error. We conclude that systemically injected MS can be used for simultaneous measurement of regional systemic and regional pulmonary perfusion, provided that MS that shunted in the first pass are measured in lung tissue.