Imaging study reveals new ways to widen blood vessels

Pharmacological stress agents given to patients during a cardiac stress test can cause severe side effects, but a new study using PET/MR imaging has revealed that using arterial carbon dioxide (PaCO2) can safely and efficiently widen blood vessels.

The study, published in The Journal of Nuclear Medicine, could make it safer for patients to receive stress tests that assess heart function.

"We have overcome these technical difficulties by incorporating new technology that can accurately, precisely and rapidly control arterial blood gas levels, and we have quantified the myocardial blood flow (MBF) response with 13N-ammonia PET, the gold standard approach for measuring MBF, in a clinically relevant animal model," said Rohan Dharmakumar, PhD, of the Cedars-Sinai Medical Center and University of California in Los Angeles, in a statement. "We report for the first time that a physiologically tolerable increase in PaCO2 (approximately 25 mmHg) amplifies MBF more than two-fold, a key feature of clinically meaningful coronary vasodilators used for cardiac stress testing."

The study was completed on three groups of dogs, ones without coronary stenosis, those with non-flow limiting stenosis and those with pre-administered caffeine. Results showed that for all groups PaCO2 was just as effective at inducing MBF as the standard dose of adenosine and performs better than adenosine in animals who were previously given caffeine.

"This key finding opens the door to a completely new protocol for cardiac stress testing—one that has the potential to benefit numerous patients who are contraindicated for commonly used pharmacological stress agents,” Dharmakumar said. "Since hypercapnia is safe and effective when its magnitude is tightly controlled, it could also empower repeat stress testing in target populations with heart disease—overcoming a limitation of current stress tests that rely on injectable pharmacological agents."