FIG. 12:  In terms of mechanisms of disease relevant to both OSA and cardiovascular disease, the first we will discuss here is sympathetic nerve activity.  Sympathetic activity can be assessed by measuring plasma or urine catecholamines, but it can also be measured by using microneurography.  The Figure illustrates shows a microneurographic electrode compared with a 22-gauge needle (upper left).  To use this the physician finds a peripheral nerve in the leg or the arm to stimulate from an external source, and once the nerve is located, the electrode is inserted into the nerve itself, kind of like tapping into a phone line, and the Figure illustrates the recording electrode inserted into the peroneal nerve.  This records feedback from the vasoconstrictor signal going from the brain to the peripheral blood vessels; the nerve impulse is carried through the electrode to a preamplifier, rectified, and integrated – and we will see examples of these nerve recordings in the next few Figures. 

This is a powerful recording technique in sleep apnea because the changes in apnea are fairly rapid and dynamic, and plasma or urine measurements of catecholamines will not reflect what is happening to the sympathetic nervous system; however tapping into the nerve signal from the brain to the blood vessels gives a clearer moment-by-moment picture of how the sympathetic nervous system is responding to episodes of OSA.