Effects of nitroglycerin on blood viscosity and hemodynamics

The purpose of this study was to determine the effects of nitroglycerin on blood and plasma viscosity, Forty-nine healthy subjects participated in the study: 35 subjects (18 women and 17 men; mean age 39.8 +/- 5.8 years) received nitroglycerin, and 14 subjects (6 women and 8 men; mean age, 35.0 +/- 3.8 years) received placebo. Treatment included a 50-mg nitroglycerin patch that was applied for 4 hours and that released 20 to 25 mu g/cm(2) per hour, Before and during drug treatment, blood samples were collected and a capillary tube viscometer was used to measure viscosity. After nitroglycerin application, blood viscosity was significantly lower than baseline throughout the study, with a maximum decrease (10.93%) seen at 120 minutes (P < 0.001). Although the plasma viscosity was lower than baseline values during the study, the maximum significant decrease (4.8%) was seen at 45 minutes (P < 0.05). Decreases in plasma and blood viscosity were significant compared with placebo. According to Poiseuille's hydrodynamics equation, a 10.93% decrease in viscosity causes a 12.39% increase in blood flow rate. If the body keeps blood dow rate and vessel radius constant, a 10.93% decrease in viscosity can lead to a 10.93% decrease in blood pressure. These results showed that a significant decrease in blood viscosity, an increase in blood flow rate, and a decrease in ischemia and circulatory load in the form of decreased blood pressure can be achieved with nitroglycerin administration. One of the antianginal mechanisms of nitroglycerin may be an increase in blood flow rate by means of its viscosity-decreasing effect, The effect of the viscosity-decreasing drugs on ischemia should be investigated clinically.