USE OF AMPLITUDE-MODULATED BREATHING FOR ASSESSMENT OF CARDIORESPIRATORY FREQUENCY-RESPONSE WITHIN SUBRESPIRATORY FREQUENCIES

We present a neu technique which uses amplitude-modulated breathing pa tterns to obtain estimates of frequency response between respiration a nd heart rate within subrespiratory frequencies, Frequency response be tween respiration and heart rate has been previously estimated using b roadband respiration and metronomic breathing, However, the estimates obtained using these techniques show low coherence between respiration and heart rate within the subrespiratory frequencies (<0.12-0.15 Hz). The advantages of amplitude-modulated breathing are: enhancement in t he degree of perturbation within subrespiratory frequencies as indicat ed by relatively higher coherencies between respiration and heart rate (congruent to 0.7), and the subjects do not have to breathe at very l ow breathing frequencies or resort to breath holds, Use of a squared s ine wave carrier modulated by sinusoidal functions enabled us to obtai n energy distributions at subrespiratory frequencies without using dem odulation. Results obtained at eight subrespiratory frequencies from t en subjects show that the new technique is easy to implement and produ ces relatively higher coherence between respiration and heart rate, Th e advantage of the new technique in terms of enhancing the level of pe rturbations within subrespiratory frequencies is particularly importan t, because it is in this frequency range that the interpretation of va riability in heart rate in terms of autonomic origins is incompletely understood and is confounded by respiratory interactions.