Cardiac Ischemia Model for +G_z Using Miniature Swine and Baboons

Burns JW, Kruyer WB, Celio PV, Deering J, Loecker TH, Richardson LA, Fanton JW, Davis H, Dick EJ Jr. Cardiac ischemia model for +G_z using miniature swine and baboons. Aviat Space Environ Med 2008; 79:374–83. Background: Military aircrew with minimal coronary artery disease (MCAD) may be restricted from flying high-performance aircraft due to possible ischemia during high +G_z. An animal model is presented to provide ischemia data for a more informed decision. Methods: There were 18 swine that were placed on a high cholesterol/high fat diet for up to 57 wk. Five control swine were maintained on a standard swine diet. Also, nine male baboons had a constrictor placed around the left anterior descending coronary artery. Two baboons were sham-operated controls. The unanesthetized swine and baboons were infused with Tc-99m at the end of +G_z exposure and scanned for myocardial perfusion. Results: Five swine died unexpectedly before +G_z exposure with moderate-to-severe CAD. Dysrhythmias during +G_z were seen equally in both the control and experimental swine and in the baboons before and after stenosis, with or without propranolol. During +G_z, ECG ST-T wave changes suggesting ischemia were observed in the cholesterol swine but not the control swine, and in the baboons before and after stenosis, with or without propranolol. There was a positive relationship between a normal/abnormal ECG and a normal/abnormal myocardial perfusion scan in the swine and a weak relationship in the baboon before stenosis, but somewhat better after stenosis. Coronary histopathology showed normal vessels from the control swine and stenoses ranging from 0–95% from the cholesterol swine. Baboon stenosis averaged 37.6 ± 15.0%. Conclusions: In the swine and the baboon extended high levels of +G_z were associated with evidence of myocardial ischemia.