FIGURE 6.

Global and regional MBF response to hypercapnia and adenosine after caffeine administration. (A) Representative short- and long-axis PET images acquired during peak myocardial uptake of ¹³N-ammonia under hypercapnia of PaCO₂ ∼60 mm Hg (CO₂), standard adenosine dose (Adenosine) and at baseline conditions with PaCO₂ ∼35 mm Hg (Rest) after caffeine administration. These visual results show that increase in myocardial uptake of radiotracer relative to rest to occur only under hypercapnia, but not under adenosine. For the case in A, rest and stress MBF (under hypercapnia and adenosine) and corresponding MPR are shown as polar maps in B. (C) MBF at rest before (Caff(−)) and after (Caff(+)) caffeine administration. HLA = horizontal long axis; VLA = vertical long axis.