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Excerpt
SUBJECTS:The previously described arteriovenous carboxyhemoglobin (COHb) difference may be caused either by carbon monoxide (CO) production in the lung and/or the left heart (1), because the CO producing enzyme heme oxygenase (HO) is found in both organs. Additionally HO-1 is induced in the ischemic heart (2). Thus we tested the hypothesis that the COHb gradient is due to cardiac CO production in normal, postischemic and, infarcted heart. INTERVENTIONS:With approval of the Government Animal Research Committee, the experiments were carried out in 12 conscious, adult dogs, chronically instrumented with a pulmonary artery (PA), left atrium (LA) and aorta catheter (either sex, weight 22-35 kg). Pulsed doppler blood flow velocity probes (20 MHz) were fitted around the left anterior descending coronary artery (LAD). To measure the regional myocardial wall thickening fraction, 10 MHz pulsed Doppler crystals were sutured to the myocardium in the LAD perfused myocardium. The myocardial blood flow was measured using colored microspheres. 6 dogs received 10 min of LAD ischemia to induce myocardial stunning, the other 6 dogs a complete LAD occlusion. Experiments were only conducted after the animals had recovered completely from the instrumentation. 3 days simultaneously blood gas samples in the pulmonary artery, the left atrium and in the aorta were withdrawn every 3 hours and analyzed by a blood gas analyzer/oximeter (ABL 620; Radiometer AB, Copenhagen, Denmark). Data Analyzes: repeated-measures two-way of variance followed by Bonferroni-corrected Student's t-test whenever appropriate (p < 0.05 = significant). Shown as mean and ± standard error of the mean. MAIN RESULTS:At all time points, there was a significant difference between the COHb concentrations in the PA and the LA (0.5 ± 0.1) and no difference in COHb levels between the LA and the aorta in non-, postischemic and infarcted heart (Other blood gas parameters were normal) CONCLUSION:The PA to aortic COHb gradient is of pulmonary origin in chronically instrumented dogs.
