Effects of normoxic versus hyperoxic hyperventilation followed by apnea on right ventricular strain in patients with multi-vessel coronary artery disease

Abstract

Introduction Hypocapnia and hyperoxia are coronary vasoconstrictors, whereas hypercapnia acts as a coronary vasodilator. Prior to anaesthetic induction, patients receive a FiO2 of 1.0 and are asked to take deep breaths. Resulting hyperoxic hypocapnia may be aggravated by excessive manual ventilation. Subsequent apnea during intubation increases paCO2. So far it remains unclear whether and how such rapid blood gas alterations impact right ventricular (RV) function, especially so in the presence of coronary artery disease (CAD). Cardiovascular magnetic resonance (CMR) imaging is useful to assess subtle changes of myocardial function and constitutes the gold standard for RV imaging. The objective of this CMR study is to compare RV function of healthy persons and patients with CAD during a typical hyperventilation-apnea maneuver. Methods Ten healthy participants and 25 patients with stable, well-defined multi-vessel CAD underwent a CMR study. After baseline imaging at room air, subjects hyperventilated for 60 seconds (HV) and then maintained apnea for 30s. Cine images of two ventricular short axis slices were acquired at baseline and from the end of HV throughout the breath-hold. After reequilibration, participants breathed oxygen (10L/min) for 5 minutes via a non-rebreathing mask and repeated the same respiratory maneuver under oxygen inhalation. CMR cine images were analyzed for RV global peak circumferential strain (RVGCS) for each group and condition. Results Healthy participants showed no significant RVGCS changes within or between normoxic or hyperoxic respiratory maneuvres, although HV enhanced strain numerically. CAD patients showed significant attenuation of RVGCS at the end of the hyperoxic HV-apnea sequence (baseline, -13.5±4.7 % vs. hyperoxic apnea, -11.8±4.9 %; p= 0.047), but not after the respective sequence at room air (-13.8±4.1%, p=0.611). In 20% of the CAD patients the hyperoxic HV-apnea sequence attenuated RVGCS by more than 5% from normoxic baseline. The figure shows RVGCS of both groups during the maneuver (more negative numbers representing better systolic contractile function, i.e., circumferential shortening). Discussion At the conclusion of an induced respiratory maneuver, which resembles a hyperoxic anaesthesia induction sequence, awake CAD patients exhibit significant attenuation of RV peak circumferential strain. This response could be haemodynamically relevant during anaesthesia induction in high-risk CAD patients and needs to be investigated further in a scenario of general anaesthesia.