THE HEMODYNAMIC-EFFECTS OF HYPOXEMIA IN ANESTHETIZED PIGS - A COMPARISON BETWEEN RIGHT HEART CATHETER AND ECHOCARDIOGRAPHY

During hypoxemia, hypoxic pulmonary vasoconstriction and tachycardia a re often observed in association with increases in pulmonary artery pr essure and cardiac output. Nevertheless, the hemodynamic consequences of hypoxemia have never been evaluated by echocardiography and simulta neously compared with invasive hemodynamic variables. Fourteen open-ch est, anesthetized piglets (weight 29-36 kg) were submitted to progress ive hypoxemia and reoxygenation. Usual invasive hemodynamic variables were obtained from peripheral and central heart catheters. Direct epic ardial echocardiography was used to measure right and left ventricular areas on a short-axis view at mid-papillary level. The mean pulmonary artery pressure (MPAP) increased with pulmonary vascular resistance i n a dose-related manner as the fraction of inspired oxygen (FIo(2)) de clined FIom 0.5 to 0.12. The MPAP correlated with right ventricular en d-diastolic area (RVEDA) only at FIo(2) 0.08. There was a 49% reductio n in left ventricular end systolic wall stress (LVESWS) between FIO2 0 .5 and 0.08. Left ventricular ejection fraction area (LVEFA) increased by 33% above baseline and correlated with the decrease in LVESWS. No correlation was observed between left ventricular end-diastolic area a nd pulmonary artery occlusion pressure or left atrial pressure and bet ween cardiac output and LVEFA. Systemic vascular resistance underestim ates the magnitude of changes in LVESWS but overestimates the afterloa d compared with LVESWS. This study demonstrates that, for the lowest F Io(2) (0.08), changes in MPAP correlated with changes in RVEDA but not in pulmonary vascular resistance. Moreover, LVESWS decreases signific antly in a dose-related manner under progressive hypoxemia and normali zes immediately after reoxygenation. This study also shows that, under hypoxemic conditions, echocardiography enhances understanding of hemo dynamic changes compared with right heart catheterization alone. Impli cations: Acute hypoxemia in pigs is responsible for pulmonary vasocons triction-induced pulmonary hypertension (which is restricted by the ri ght ventricular failure), as well as a Pao(2)-dependent decrease in le ft ventricular afterload. These changes are better displayed by echoca rdiography than by right heart catheter.