A simple analytical model mimics complex physiological behavior

The authors have previously described the use of nonparametric transfer function analysis in combination with broadband respiration to compute the magnitude and phase relations between respiration, heart rate (HR), and arterial blood pressure (ABP). These experimental results have led to the formulation of a model of HR and ABP control which includes the mechanical feedforward from HR to ABP, the baroreflex feedback from ABP to HR, and respiration as a noise source which directly affects HR through central modulation of autonomic activity while affecting ABP through mechanical thoracic coupling. Despite the fact that causality was not built into the ABP-HR relation, analytic transfer functions from the model closely simulate many of the observed experimental phenomena. The findings suggest that the complex transfer relations observed with a relatively simple analysis of respiration, HR, and ABP can be understood in terms of a feedback loop between ABP and HR, with respiration as an external noise source.