Chapter 37 Assessment of cardiovascular autonomic function

Publisher Summary The evaluation of cardiovascular autonomic function is the cornerstone of the clinical assessment of autonomic function. As the anatomic location of the cardiovascular autonomic nervous system renders it inaccessible to direct physiological testing, a group of tests that assess autonomic function and dysfunction has been developed to circumvent this problem by measuring end-organ responses to various physiological and pharmacological perturbations. These tests include heart-rate variability with deep respiration, heart-rate response to a Valsalva maneuver, and heart-rate response to postural change. Laboratory or bedside tests of heart-rate variability with deep breathing are usually performed in the supine position where vagal tone is greatest. The test is performed typically over six respiratory cycles, although some have advocated ten cycles, the mean of the five largest responses from eight respiratory cycles, or three cycles. The Valsalva maneuver provides a potential measure of sympathetic, vagal, and baroreceptor function. The maneuver is typically performed by blowing through a mouthpiece connected to a mercury manometer for 15 or 20 s.