A 50-year-old client is prescribed to take nitrate each day for his condition. As a competent nurse, you know the result of nitrate administration is:
A. Decreased myocardial oxygen demand.
B. Increased myocardial oxygen demand.
C. Increased left ventricular end-diastolic volume.
D. Increased atrial pressure.
Correct Answer: A. Decreased myocardial oxygen demand
Nitrate administration will result in reduced preload and a decrease in myocardial oxygen demand and left ventricular end-diastolic volume. Nitrates exert their pharmacological effect by being activated by mitochondrial or cytosolic aldehyde dehydrogenase (ALDH2) into nitric oxide (NO), an endothelium-derived relaxing factor (EDRF). NO is generally produced by the endothelium to dilate the blood vessels; however, endothelial dysfunction in diseases such as atherosclerosis can deplete NO levels.
Option B: The venodilation increases the venous capacitance and lowers the preload; this subsequently lowers the left ventricular end-diastolic pressure, resulting in a reduction in myocardium workload, which decreases the oxygen demand of the heart.
Option C: The decreased intracellular calcium levels subsequently inhibit myosin light chain kinase, and the unphosphorylated myosin light chain causes myosin head to detach from actin, resulting in smooth muscle relaxation.
Option D: Nitrates exert their effects by dilating venous vessels, coronary arteries, and small arterioles; its maximal vasodilation is in the venous vessels. At higher doses, nitrates can also exert significant coronary artery dilation, allowing blood flow to ischemic areas during coronary artery occlusion and vasospastic angina.