Multivariate autoregressive spectral analysis: heart rate baroreflex and respiratory influence under administration of atropine and propranolol

In this study the authors introduce a trivariate autoregressive (AR) algorithm based on a model that takes into account, at the same time, all the possible interactions among heart rate (HR), arterial blood pressure (ABP), and instantaneous lung volume (ILV). Signals were acquired in 14 subjects during a tilting protocol with a random interval breathing technique and administration of atropine and propranolol. A bivariate AR algorithm was used to identify the typical HR and ABP spectral parameters of LF and HF power, and the LF/HF ratio. The cross-parameters obtained by the bivariate technique were then compared with results obtained using the trivariate model. As expected, differences were found in the comparison of the gain values. However, gain parameters were found to be good markers of autonomic activity in both techniques.