Attenuation of Coronary Blood Flow Response by Hyperoxia

Abstract

BACKGROUND: Assessing the coronary response to vasoactive stimuli is common in clinical cardiac exams; a short breathhold may be used to induce an increase in coronary blood flow. Arterial blood gases have a known profound effect on coronary flow. While hypercapnia increases myocardial blood flow, hypocapnia decreases it. There is little data about the effects of hyperoxia. The assessment of hyperoxic conditions is in particular importance to cardiac patients because of the common use of supplemental oxygen in clinical situations. This study investigates the impact of a vasodilating breathhold stimulus at different baseline blood oxygen and carbon dioxide levels. METHODS: In 16 swine, blood flow in the LAD was measured with a perivascular probe. In 10 of these animals an acute stenosis of the left anterior descending artery (LAD) was induced using a hydraulic occluder. Arterial blood gas levels were targeted to reach nine levels (O2/ CO2): combinations of paO2 of 70, 100 or >300mmHg and a paCO2 of 30, 40 or 50 mmHg. Ventilator breathholds were induced at each baseline ranging from 3-25s in duration and flow was expressed as a percent-change (D-%) over the breath-hold stimulus. This blood flow response was compared between the groups accounting for the breathhold duration and baseline gas levels and displayed in a heatmap. For the figure, data points were grouped into 5s blocks, and blocks without at least three data points are shown as beige. RESULTS: Ten animals with a significant LAD stenosis (FFR¼ 0.63AE0.02) underwent 432 breath-holds, while the six control animals had 279 breath-holds. For both groups, flow increased with breath-holds from all hypoxic and normoxic baselines (red), whereas only minimal responses to the breathholds were observed during hyperoxia. Accounting for breathhold duration, the response from the breath-hold was significantly stronger for the healthy than the stenotic animals at both hypoxia and normoxia, but this was not observed with