Haemodynamic effects of nitroglycerin in comparison with preload and sodium nitroprusside on patients after coronary...

To differentiate between the haemodynamic effects of intravenous nitroglycerin (NTG) and preload, left ventricular function curves were constructed for 10 patients with and without a steady NTG-infusion at left ventricular filling pressure (LVFP) levels of between 9 and 17 mmHg eight hours after coronary bypass grafting. The haemodynamic effects of NTG were compared with those caused by sodium nitroprusside (NP) at identical filling pressures. Although NTG as such decreased cardiac index (CI) (p less than 0.05), when systemic vasodilation was induced, CI was 18% greater with than without NTG at constant filling pressures (p less than 0.02). At identical LVFP, mean arterial pressure remained unchanged by NTG, whereas systemic vascular resistance was reduced by 16%. NTG augmented the left ventricular stroke work index (LVSWI) only in patients whose initial LVSWI was below 30 gm-m/m2 (a 20% increase, p less than 0.05). Although NTG relaxes the capacitance vessels more than the resistance vessels, its haemodynamic effects are far superior to the changes that can be induced by preload alteration alone. NTG enhances myocardial performance, especially if LVFP is kept balanced with the reduction of afterload. The increase in left ventricular pumping performance produced by NTG was 45% of the increase produced by NP at identical filling pressures. The results, however, indicate that NTG may affect the myocardial oxygen supply/demand ratio more favourably than NP.