During an ANS evaluation, the CAN assessment comprises of the heart rate variability analysis and the cardiac autonomic reflexes tests or Ewing Tests. These test the function of the sympathetic and parasympathetic systems to identify cardiac autonomic neuropathy. There are a series of tests including the Valsalva ratio, deep breathing test, a change in posture and the difference in systolic pressure from sitting to standing position.
Heart rate variability is a variation in time interval between heartbeats. It is measured by the variation in the beat-to-beat intervals. The Autonomic nervous system plays a central role in heart rate variability. Depressed or reduced heart rate variability primarily means a lower ability of the ANS regulatory function to keep homeostasis, cope with internal and external stressors and resist disease and/or recover in proper time
The Valsalva maneuver involves holding the breath, bearing down and then blowing into a manometer without releasing air from the nose or mouth. Its purpose is to evaluate the parasympathetic system heart rate response and sympathetic system blood pressure response.
The deep breathing test involves deep breathing for a total of 60 seconds; five second intervals of inspiration and expiration. Its purpose is to evaluate the parasympathetic system heart rate response.
The postural change test involves a change in posture from lying down or sitting to standing. The purpose of the test is to evaluate the sympathetic system blood pressure response to standing and the parasympathetic evaluation of heart rate response.
The RR intervals and blood pressure analysis combine to give a diagnosis of cardiac autonomic neuropathy using a scoring system. Heart rate variability analysis at rest includes self-body regulation assessment related to the level of fitness in early stages of cardiac autonomic neuropathy. Cardiac autonomic reflex tests include heart rate variability and blood pressure analysis during Valsalva maneuver deep breathing and change of posture.