Abstract 9577: Non-Invasive Estimation of Pulmonary Blood Flow Using Photoacoustic Spectroscopy in Patients with Congenital Heart Disease

Background: Measurements of pulmonary blood flow (PBF) using inert gas rebreathing technology have recently been enhanced by the introduction of photoacoustic spectroscopy (PAS). PAS is non-invasive, non-toxic, and can estimate PBF in <5 min. It has been employed successfully in adults with structurally normal hearts. Experience in patients with congenital heart disease (CHD) is, however, limited and its validity in patients with intracardiac shunts has not been evaluated. We compared estimates of PBF obtained with PAS technology to those obtained at cardiac catheterization. Methods: Fick-based estimates of PBF (using assumed oxygen consumption) were compared to PAS estimates in 50 CHD patients; 28 without intracardiac shunts, 10 with right to left (R-->L) shunts and 12 with left to right (L-->R) shunts. PAS estimates were acquired 1 day prior to catheterization while the patients were conscious, in a recumbent position. Fick-based estimates were acquired by individuals blinded to the PAS results. Results: Median age was 18.5 yrs (range 8-78). Among subjects without shunts or with R-->L shunts, Fick and PAS-based estimates of PBF correlated reasonably well (r=0.59 and 0.75, respectively; p<0.01 for both groups; r=0.72, p<0.0001 combined). Bland-Altman analysis revealed good agreement (mean bias 0.3±0.5 l/min/m 2 ; 95% limits of agreement -0.8 - +1.3 l/min/m 2 ), similar to historical comparisons of Fick and thermodilution techniques. In contrast, the correlation between PBF estimates among subjects with L-->R shunts was poor (r=0.24; p>0.05). Conclusion: PAS provides accurate, rapid estimates of PBF in children and adults with CHD who have no residual shunt, as well as those with R-->L shunts. Measurements in subjects with L-->R shunts are less reliable, likely due to early re-circulation. Algorithms that take this phenomenon into account may improve the reliability of PAS measurements in patients with L-->R shunts.