Comparison between probabilistic and Wiener-Granger causality in assessing modifications of the cardiac baroreflex control with age.

BACKGROUND: Probabilistic causality (PC) is a framework for checking that the occurrence of a cause raises the probability of the effect by comparing the probability of the effect conditioned and unconditioned to the cause. Even though it is less frequently utilized with respect to the more traditional model-based Wiener-Granger causality (WGC) that is based on the predictability improvement of an effect resulting from the inclusion of the presumed cause in the multivariate linear regression model, PC has the advantage of being model-free. OBJECTIVE: The aim of the study is to apply the PC framework to assess the evolution of cardiac baroreflex control with age from spontaneous fluctuations of heart period (HP) and systolic arterial pressure (SAP) and to compare it to the more common WGC approach. APPROACH: We studied 100 healthy humans (54 males, age: 21-70 years, 20 subjects for each 10 years bin). HP and SAP were extracted on a beat-to-beat basis from 5 min recordings of electrocardiogram and plethysmographic arterial pressure at rest in supine position (REST) and during active standing (STAND) under spontaneous breathing. The WGC ratio (WGCR) was computed as the log ratio of the prediction error variance of the autoregressive model on HP to that on HP with exogenous SAP. The PC ratio (PCR) was computed as the probability of observing an HP ramp given an associated parallel SAP variation divided by the probability of observing an HP ramp. MAIN RESULTS: The WGCR and PCR suggested the gradual impairment of cardiac baroreflex with age, especially during STAND. Moreover, they were significantly associated both at REST and during STAND but the degree of the PCR-WGCR association was weak. SIGNIFICANCE: PC can be effectively exploited to assess modification of the cardiovascular control during senescence even though a limited agreement was observed with WGC.

Influence of age and gender on the phase and strength of the relation between heart period and systolic blood pressure spontaneous fluctuations.

Aging affects baroreflex regulation. The effect of senescence on baroreflex control was assessed from spontaneous fluctuations of heart period (HP) and systolic arterial pressure (SAP) through the HP-SAP gain, while the HP-SAP phase and strength are usually disregarded. This study checks whether the HP-SAP phase and strength, as estimated, respectively, via the phase of the HP-SAP cross spectrum (PhHP-SAP) and squared coherence function (K2HP-SAP), vary with age in healthy individuals and trends are gender-dependent. We evaluated 110 healthy volunteers (55 males) divided into five age subgroups (21-30, 31-40, 41-50, 51-60, and 61-70 yr). Each subgroup was formed by 22 subjects (11 males). HP series was extracted from electrocardiogram and SAP from finger arterial pressure at supine resting (REST) and during active standing (STAND). PhHP-SAP and K2HP-SAP functions were sampled in low-frequency (LF, from 0.04 to 0.15 Hz) and in high-frequency (HF, above 0.15 Hz) bands. Both at REST and during STAND PhHP-SAP(LF) showed a negative correlation with age regardless of gender even though values were more negative in women. This trend was shown to be compatible with a progressive increase of the baroreflex latency with age. At REST K2HP-SAP(LF) decreased with age regardless of gender, but during STAND the high values of K2HP-SAP(LF) were more preserved in men than women. At REST and during STAND the association of PhHP-SAP(HF) and K2HP-SAP(HF) with age was absent. The findings points to a greater instability of baroreflex control with age that seems to affect to a greater extent women than men. NEW & NOTEWORTHY Aging increases cardiac baroreflex latency and decreases the degree of cardiac baroreflex involvement in regulating cardiovascular variables. These trends are gender independent but lead to longer delays and asmaller degree of cardiac baroreflex involvement in women than in men, especially during active standing, with important implications on the tolerance to an orthostatic stressor.

Assessing the evolution of redundancy/synergy of spontaneous variability regulation with age.

OBJECTIVE: We exploited a model-based Wiener-Granger causality method in the information domain for the evaluation of the transfer entropy (TE) and interaction TE (ITE), the latter taken as a measure of the net balance between redundancy and synergy, to describe the interactions between the spontaneous variability of heart period (HP) and systolic arterial pressure (SAP) and the effect of respiration (R) on both variables. APPROACH: Cardiac control was typified via the genuine TE from SAP to HP, that from R to HP, and the ITE from SAP and R to HP, while vascular control was characterized via the genuine TE from HP to SAP, that from R to SAP, and the ITE from HP and R to SAP. The approach was applied to study age-related modifications of cardiac and vascular controls in a cohort of 100 healthy humans (age from 21 to 70 years, 54 males) recorded at supine rest (REST) and during active standing (STAND). A surrogate approach was exploited to test the significance of the computed quantities. MAIN RESULTS: Trends of the genuine information transfer with age, already present in literature, were here confirmed. We originally found that: (i) at REST redundancy was predominant over synergy in both vascular and cardiac controls; (ii) the predominance of redundancy of the cardiac control was not affected by postural challenge, while STAND reduced redundancy of vascular control; (iii) the net redundancy of the cardiac control at REST gradually decreased with age, while that of vascular control remained stable; (iv) during STAND net redundancy of both cardiac and vascular controls was stable with age. SIGNIFICANCE: The study confirms the relevance of computing genuine information transfer in cardiovascular control analysis and stresses the importance of evaluating the ITE to quantify the degree of redundancy of physiological mechanisms operating to maintain cardiovascular homeostasis.