[The advantageous effects of a prolonged intravenous load with a nitroglycerin solution on the lesser circulation in...

To evaluate the sequence of hemodynamic changes and the potential loss of efficacy of i.v. 24-hour nitroglycerin (NTG) infusion at constant rate we studied 15 NYHA III Class patients. NTG infusion, titrated to reduce pulmonary artery wedge pressure (PWP) less than 15 mm Hg, was continued for 24 hours at mean rate of 144 +/- 16 (50-250) micrograms/min. Hemodynamic data were monitored every 3 hours. Acute changes were pronounced and significant in mean pulmonary artery pressure (mPAP), peak V-wave of indirect left atrial pressure, right atrial pressure (RAP), mean blood pressure (mBP), and heart rate (HR). Significant attenuation of these effects was registered by the 9th hour. RAP rose already by the 6th hour. From the 9th to the 24th hour PWP, mPAP, peak V-wave remained significantly decreased, but not mBP and RAP. HR rose during hours 9-12 in comparison to hours 0-3 and to the 21st hour. The data show rapid development of tolerance of systemic (but not pulmonary) vascular beds to NTG.