INHALED NITRIC-OXIDE - EFFECTS ON HEMODYNAMICS, MYOCARDIAL-CONTRACTILITY, AND REGIONAL BLOOD-FLOW IN DOGS WITH MECHANICALLY INDUCED PULMONARY-ARTERY HYPERTENSION

Background: Pulmonary artery hypertension with right ventricular failu re is a frequent complication that occurs immediately after heart tran splantation in which the use of inhaled nitric oxide may be effective. Methods: The effects of pulmonary artery hypertension and nitric oxid e on myocardial function and on pulmonary and systemic hemodynamic par ameters were evaluated in eight anesthetized dogs. Pulmonary artery hy pertension was induced by successive microbead injections into the pul monary circulation. Results: Microbead injections resulted in overt pu lmonary artery hypertension (pulmonary artery pressure, + 190%; pulmon ary vascular resistance, + 389%; ratio of pulmonary vascular resistanc e to systemic vascular resistance, 0.41). Results: The end-diastolic l ength of the right ventricular outflow tract increased significantly a long with an increase in right ventricular contractility (peak first d erivative of left ventricular pressure as a function of time, + 100%; outflow tract systolic shortening, + 19%). Despite this compensatory m echanism, the increased pulmonary barrier resulted in a decrease in st roke volume (-31%). Systemic effects were observed, such as an increas e in heart rate that maintained the cardiac output despite a decrease in left ventricular end-diastolic length (end-diastolic length in regi on of left anterior descending artery, -9%). Right myocardial and sept al blood flows were also significantly increased. Conclusions: Nitric oxide administration restored the stroke volume with a decrease in pul monary artery hypertension and an improvement of the pulmonary vascula r resistance to systemic vascular resistance ratio. Systemic blood pre ssure and coronary perfusion remained unaffected. This selective effec t on the pulmonary circulation should be considered a major advantage of nitric oxide inhalation in the treatment of right ventricular dysfu nction in acute pulmonary hypertension.