Cardio-respiratory characterization of the autonomic balance

The autonomic balance is often measured using the low frequency (LF) and high frequency (HF) powers of the heart beat-to-beat intervals. However, these indices do not adequately integrate the influence of respiration and have been widely criticized. We studied the autonomic balance with measures from the heart beat-to-beat intervals taking into account the respiratory activity. Using cardiac and respiratory data acquired simultaneously from healthy volunteers in supine and orthostatic positions, we found that the investigated measures convey changes in the auto-nomic balance in a physiologically meaningful manner in contrast to the classic LF and HF indices.