James H. Silver
Measurement of nitric oxide (NO) or a suitable index marker such as nitrite could potentially be used in the diagnosis of various vascular diseases. Among its many functions, nitric oxide plays important roles in ischemia/reperfusion injury. Nitrite has recently been found to generate nitric oxide under conditions of ischemia or hypoxia. Research into the biology of the nitrite anion may impact a wide range of vascular diseases, such as stroke, acute myocardial infarction, cardiac arrest, sepsis, or other diseases. As nitrite begins to be evaluated for its therapeutic impact on these diseases in clinical trials, it may be important to obtain frequent or continuous measurements of NO or nitrite levels in real time in order to optimize such therapies. In addition, if nitrite therapy becomes successful in these trials, it may become necessary to provide clinicians with tools to monitor the effect of such therapy in real time. This review summarizes currently available methods for measuring nitric oxide and nitrite, along with the advantages and disadvantages of each, including a novel method for real-time, continuous measurement of plasma nitrite from blood. The specificity of such measurements can be optimized by evaluating the concentration, kinetics, and location of the signal, which will allow physicians to perform differential diagnoses. Finally, several examples of vascular diseases in which nitric oxide plays a significant role, and in which monitoring NO or an index marker in real time could potentially provide clinically important information, are discussed.