Importance of Tachogram Length and Period of Recording during Noninvasive Investigation of the Autonomic Nervous System

Methods: To test the influence of the length of the recording time, HRV indicator values calculated from 180, 300, 420, and 600 seconds recording periods (supine and standing) were compared. Also individual 3- minute periods (0-180 seconds, 180-360 seconds, 360-540 seconds) from 10-minute (supine and standing) tachograms were compared. Results: In the supine position, vagal-efferent HRV indicators were not influenced by tachogram length varying between 3 and 10 minutes (P > 0.05). Supine HRV indicator values representing combined sympathetic and parasympathetic influences were tachogram length-dependent (P < 0.05). During orthostatic stress all HRV indicators were tachogram length-dependent (P < 0.05). Upon standing up marked vagal withdrawal and sympathetic activation occurred. Vagal withdrawal tapered off during the 3-6-minute period after rising while indicators representing combined vagal and sympathetic activation were totally reversed. Conclusions: During application of orthostatic stress the exact starting point of recording, as well as the length of recording, is critical due to the activation and normalization of homeostatic mechanisms. Starting the tachogram recording too late will miss out on part of the initial response to change in body position. Longer recording times will give a combination of values recorded during the stress response and values obtained after stabilization in the standing position. Ann Noninvasive Electrocardiol 2011;16(2):131-139.