The effects of regional pulmonary blood flow on protein flux measurements with PET

We used PET to evaluate whether changes in regional pulmonary blood flow (PBF) or plasma volume (PV) affect calculations of the pulmonary transcapillary escape rate (PTCER) for ⁶⁸Ga-labeled transferrin. We reduced PBF in five dogs by inflating a right atrial balloon. Regional PBF decreased 25% to 174 ± 40 ml/min/100 ml lung without a change in PV or PTCER. In eight other dogs, we decreased PBF and PV via controlled arterial hemorrhage. PBF decreased 45% to 110 ± 33 ml/min/100 ml lung and PV decreased 22% without a change in PTCER. We also used a series of computer simulations to evaluate the effect of even greater reductions in regional PBF on PTCER calculations. These simulations showed, in support of the experimental data, that if PBF was >40 ml/min/100 ml lung, PTCER could be accurately measured. However, below this level, PV was increasingly underestimated and PTCER overestimated. The results indicate the sensitivity of the PTCER calculation to errors in the PV measurement, especially in regions of markedly reduced regional PBF.