Natália Maria Perseguini

Effect of age on complexity and causality of the cardiovascular control: comparison between model-based and model-free approaches.

The proposed approach evaluates complexity of the cardiovascular control and causality among cardiovascular regulatory mechanisms from spontaneous variability of heart period (HP), systolic arterial pressure (SAP) and respiration (RESP). It relies on construction of a multivariate embedding space, optimization of the embedding dimension and a procedure allowing the selection of the components most suitable to form the multivariate embedding space. Moreover, it allows the comparison between linear model-based (MB) and nonlinear model-free (MF) techniques and between MF approaches exploiting local predictability (LP) and conditional entropy (CE). The framework was applied to study age-related modifications of complexity and causality in healthy humans in supine resting (REST) and during standing (STAND). We found that: 1) MF approaches are more efficient than the MB method when nonlinear components are present, while the reverse situation holds in presence of high dimensional embedding spaces; 2) the CE method is the least powerful in detecting age-related trends; 3) the association of HP complexity on age suggests an impairment of cardiac regulation and response to STAND; 4) the relation of SAP complexity on age indicates a gradual increase of sympathetic activity and a reduced responsiveness of vasomotor control to STAND; 5) the association from SAP to HP on age during STAND reveals a progressive inefficiency of baroreflex; 6) the reduced connection from HP to SAP with age might be linked to the progressive exploitation of Frank-Starling mechanism at REST and to the progressive increase of peripheral resistances during STAND; 7) at REST the diminished association from RESP to HP with age suggests a vagal withdrawal and a gradual uncoupling between respiratory activity and heart; 8) the weakened connection from RESP to SAP with age might be related to the progressive increase of left ventricular thickness and vascular stiffness and to the gradual decrease of respiratory sinus arrhythmia.

Spectral and symbolic analysis of the effect of gender and postural change on cardiac autonomic modulation in healthy elderly subjects

The objective of this study was to use linear and non-linear methods to investigate cardiac autonomic modulation in healthy elderly men and women in response to a postural change from the supine to the standing position. Fourteen men (66.1 ± 3.5 years) and 10 women (65.3 ± 3.3 years) were evaluated. Beat-to-beat heart rate was recorded in the supine and standing positions. Heart rate variability was studied by spectral analysis, including both low (LFnu-cardiac sympathetic modulation (CSM) indicator) and high (HFnu-cardiac vagal modulation (CVM) indicator) frequencies in normalized units as well as the low frequency/high frequency (LF/HF) ratio. Symbolic analysis was performed using the following indexes: 0V% (CSM indicator), 1V% (CSM and CVM indicators), 2LV% (predominantly CVM indicator) and 2ULV% (CVM indicator). Shannon entropy was also calculated. Men presented higher LFnu and LF/HF ratio and lower HFnu and 1V% symbolic index (57.56, 4.14, 40.53, 45.96, respectively) than women (24.60, 0.45, 72.47, 52.69, respectively) in the supine position. Shannon entropy was higher among men (3.53) than among women (3.33) in the standing position, and also increased according to postural change in men (3.25; 3.53). During postural change, the LFnu (24.60; 49.85) and LF/HF ratio (0.45; 1.72) increased, with a concomitant decrease in HFnu (72.47; 47.56) and 2LV% (14.10; 6.95) in women. Women presented increased CSM in response to postural change and had higher CVM and lower CSM than men in the supine position. In conclusion, women in the age range studied presented a more appropriate response to a postural change than men, suggesting that cardiac autonomic modulation may be better preserved in women than in men.

Effect of the Postural Challenge on the Dependence of the Cardiovascular Control Complexity on Age

Short-term complexity of heart period (HP) and systolic arterial pressure (SAP) was computed to detect age and gender influences over cardiovascular control in resting supine condition (REST) and during standing (STAND). Healthy subjects (n = 110, men = 55) were equally divided into five groups (21–30; 31–40; 41–50; 51–60; and 61–70 years of age). HP and SAP series were recorded for 15 min at REST and during STAND. A normalized complexity index (NCI) based on conditional entropy was assessed. At REST we found that both NCIHP and NCISAP decreased with age in the overall population, but only women were responsible for this trend. During STAND we observed that both NCIHP and NCISAP were unrelated to age in the overall population, even when divided by gender. When the variation of NCI in response to STAND (ΔNCI = NCI at REST-NCI during STAND) was computed individually, we found that ΔNCIHP progressively decreased with age in the overall population, and women were again responsible for this trend. Conversely, ΔNCISAP was unrelated to age and gender. This study stresses that the complexity of cardiovascular control and its ability to respond to stressors are more importantly lost with age in women than in men.

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.

Circulatory and Ventilatory Power: Characterization in Patients with Coronary Artery Disease

Background Circulatory power (CP) and ventilatory power (VP) are indices that have been used for the clinical evaluation of patients with heart failure; however, no study has evaluated these indices in patients with coronary artery disease (CAD) without heart failure. Objective To characterize both indices in patients with CAD compared with healthy controls. Methods Eighty-seven men [CAD group = 42 subjects and healthy control group (CG) = 45 subjects] aged 40–65 years were included. Cardiopulmonary exercise testing was performed on a treadmill and the following parameters were measured: 1) peak oxygen consumption (VO2), 2) peak heart rate (HR), 3) peak blood pressure (BP), 4) peak rate-pressure product (peak systolic HR x peak BP), 5) peak oxygen pulse (peak VO2/peak HR), 6) oxygen uptake efficiency (OUES), 7) carbon dioxide production efficiency (minute ventilation/carbon dioxide production slope), 8) CP (peak VO2 x peak systolic BP) and 9) VP (peak systolic BP/carbon dioxide production efficiency). Results The CAD group had significantly lower values for peak VO2 (p < 0.001), peak HR (p < 0.001), peak systolic BP (p < 0.001), peak rate-pressure product (p < 0.001), peak oxygen pulse (p = 0.008), OUES (p < 0.001), CP (p < 0.001), and VP (p < 0.001) and significantly higher values for peak diastolic BP (p = 0.004) and carbon dioxide production efficiency (p < 0.001) compared with CG. Stepwise regression analysis showed that CP was influenced by group (R2 = 0.44, p < 0.001) and VP was influenced by both group and number of vessels with stenosis after treatment (interaction effects: R2 = 0.46, p < 0.001). Conclusion The indices CP and VP were lower in men with CAD than healthy controls.

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.

Maximal expiratory pressure and valsalva manoeuvre do not produce similar cardiovascular responses in healthy men

What is the central question of this study? This is the first study to evaluate and describe the cardiovascular responses during maximal expiratory pressure compared with the Valsalva manoeuvre, and whether those responses are similar. What is the main finding and its importance? This study showed that the duration of the manoeuvres appears to be responsible for the different physiological mechanisms involved in the cardiovascular responses to each manoeuvre and that the intensity of expiratory effort was related to the response in maximal expiratory pressure. These results are important to identify the risks to which subjects are exposed when performing these manoeuvres.

Short-term complexity of cardiovascular oscillations during orthostatic change in aging

Complexity of R-R intervals (RR) and systolic arterial pressure (SAP) variability were computed to detect the aging process influence over cardiovascular control in resting supine (REST) and standing position (STAND). One hundred healthy subjects were divided into five groups (n=20 for each), according to age: 21-30; 31-40; 41-50; 51-60; 61-70. The RR and SAP series were recorded for 15 minutes at REST and STAND. Short sequences of RR and SAP were analyzed by conditional entropy. At REST, RR complexity showed reduction with age in 61-70, and SAP complexity decreased, starting from 31-40. Changes in cardiovascular control complexity, induced by STAND, reveal the difficulty of elderly individuals in dealing with sympathetic stressors.

Baroreflex response to orthostatic challenge: Effect of aging

Aging causes changes in cardiovascular control. The aim of the study was to analyze the effects of age on baroreflex sensitivity of healthy individuals of different ages, through cross-spectral analysis. One hundred and ten individuals divided into 5 age groups were evaluated. Heart period (HP) and systolic blood pressure (SBP) were derived from ECG and blood pressure signals recorded simultaneously for 15 minutes in the supine and orthostatic position. The gain of the transfer function from SBP to HP was taken as an index of baroreflex sensitivity (BRSgain) and computed in low (LF) and high frequency (HF). In both positions and in both bands, BRSgain fell with age, thus suggesting a decrease magnitude of the HP response to SAP changes with age.