Continuous quantification of respiratory and baroreflex control of heart rate: use of time-variant bivariate spectral analysis

The mutual interactions between respiration, heart rate (HR) and arterial blood pressure (ABP) can be described by parametric bivariate models. Application of these methods allows the opportunity to investigate short and long term events of pathophysiological interest occurring in the cardiovascular system. In this study, to improve the identification of respiratory control of HR (respiratory sinus arrythmia, RSA), and ABP control of HR (baroreflex), the frequency content of respiration and ABP were broadened. A bivariate autoregressive (AR) time-variant model was used to identify the typical HR and ABP spectral parameters of LF and HF power, and the LF/HF ratio. In addition, cross-parameters such as coherent power, LF and HF gain for ABP-HR, and RSA gain were computed. Similar results were obtained using a “batch” algorithm, but the time-variant technique was able to provide nearly continuous parameters, allowing for a real-time continuous monitoring of circulatory control