Development of causal interactions between systolic blood pressure and inter-beat intervals in humans between 11 and 23 years of age

Systolic blood pressure (SBP) changes control the cardiac inter-beat intervals (IBI) duration via baroreflex. Conversely, SBP is influenced by IBI via non-baroreflex mechanisms. Both causal pathways (feedback – baroreflex and feedforward – non-baroreflex) form a closed loop of the SBP – IBI interaction. The aim of this study was to assess the age-related changes in the IBI – SBP interaction. We have non-invasively recorded resting beat-to-beat SBP and IBI in 335 healthy subjects of different age, ranging from 11 to 23 years. Using a linear autoregressive bivariate model we obtained gain (Gain SBP,IBI , used traditionally as baroreflex sensitivity) and coherence (Coh SBP,IBI) of the SBP–IBI interaction and causal gain and coherence in baroreflex (Gain SBPIBI , Coh SBPIBI) and coherence in non-baroreflex (Coh IBISBP) directions separately. A non-linear approach was used for causal coupling indices evaluation (C SBPIBI , C IBISBP) quantifying the amount of information transferred between signals. We performed a correlation to age analysis of all measures. Coh IBISBP and C IBISBP were higher than Coh SBPIBI and C SBPIBI , respectively. Gain SBP,IBI increased and Coh SBPIBI decreased with age. The coupling indices did not correlate with age. We conclude that the feedforward influence dominated at rest. The increase of Gain SBP,IBI with age was not found in the closed loop model. A decrease of Coh SBPIBI could be related to a change in the cardiovascular control system complexity during maturation.