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 (\u394NCI = NCI at REST-NCI during STAND) was computed individually, we found that \u394NCIHP progressively decreased with age in the overall population, and women were again responsible for this trend. Conversely, \u394NCISAP 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

Short-term complexity indexes of heart period and systolic arterial pressure variabilities provide complementary information

It is unclear whether the complexity of the variability of the systolic arterial pressure (SAP) provides complementary information to that of the heart period (HP). The complexity of HP and SAP variabilities was assessed from short beat-to-beat recordings (i.e., 256 cardiac beats). The evaluation was made during a pharmacological protocol that induced vagal blockade with atropine or a sympathetic blockade (beta-Adrenergic blockade with propranolol or central sympathetic blockade with clonidine) alone or in combination, during a graded head-up tilt, and in patients with Parkinson's disease (PD) without orthostatic hypotension undergoing orthostatic challenge. Complexity was quantified according to the mean square prediction error (MSPE) derived from univariate autoregressive (AR) and multivariate AR (MAR) models. We found that: 1) MSPEMAR did not provide additional information to that of MSPE AR; 2) SAP variability was less complex than that of HP; 3) because HP complexity was reduced by either vagal blockade or vagal withdrawal induced by head-up tilt and was unaffected by beta-Adrenergic blockade, HP was under vagal control; 4) because SAP complexity was increased by central sympathetic blockade and was unmodified by either vagal blockade or vagal withdrawal induced by head-up tilt, SAP was under sympathetic control; 5) SAP complexity was increased in patients with PD; and 6) during orthostatic challenge, the complexity of both HP and SAP variabilities in patients with PD remained high, thus indicating both vagal and sympathetic impairments. Complexity indexes derived from short HP and SAP beat-to-beat series provide complementary information and are helpful in detecting early autonomic dysfunction in patients with PD well before circulatory symptoms become noticeable

Baroreflex sensitivity in frailty syndrome

Frailty is related to a decrease in the physiological reserves, which causes difficulties in maintaining homeostasis. An example of physiological mechanisms for cardiovascular homeostasis is the baroreflex. The aim of this study was to compare baroreflex among frail, prefrail, and nonfrail individuals, in supine and orthostatic positions. Community-dwelling older adults were evaluated and categorized into frail, prefrail, or nonfrail groups, according to frailty phenotype. The RR interval (RRi) and systolic blood pressure (SBP) series were recorded for 15 min in the supine and 15 min in the orthostatic positions. Mean and variance of RRi and SBP, and baroreflex evaluated by phase, gain (α), and coherence (K2) were determined. A two-way repeated measures ANOVA, with Tukey's post hoc, was applied for group, position, and their interaction effects. The significance level established was 5%. Prefrail and frail participants did not present a significant decrease in mean values of RRi after postural challenge (893.43 to 834.20 ms and 925.99 to 857.98 ms, respectively). Frail participants showed a reduction in RRi variance in supine to orthostatic (852.04 to 232.37 ms2). Prefrail and frail participants showed a decrease in K2 after postural change (0.69 to 0.52 and 0.54 to 0.34, respectively). Frail participants exhibited lower values of K2 (0.34) compared to nonfrail and prefrail participants (0.61 and 0.52, respectively). Baroreflex indicated the presence of decoupling between heart period and SBP in frail and prefrail. Thus, reduced K2 might be a marker of the frailty process

Information transfer through the spontaneous baroreflex in healthy humans

Objectives: This study assesses the information transfer through the spontaneous baroreflex (i.e. through the pathway linking systolic arterial pressure to heart period) during an experimental condition soliciting baroreflex (i.e. head-up tilt). Methods: The information transfer was calculated as the conditional entropy of heart period given systolic arterial pressure using a mutual neighbor approach and uniform quantization. The information transfer was monitored as a function of the forecasting time k. Results: We found that during head-up tilt the information transfer at k = 0 decreased but the rate of rise of information transfer as a function of k was faster. Conclusions: We suggest that the characterization of the information transfer from systolic arterial pressure to heart period might complement the traditional characterization of the spontaneous baroreflex based on transfer function analysis

Linear and nonlinear analysis of postural control in frailty syndrome

BACKGROUND: Adaptive postural control can be impaired in the presence of frailty syndrome, given that this condition causes homeostatic dysregulation in physiological systems. OBJECTIVES: To compare the center of pressure (CoP) displacements of non-frail, pre-frail, and frail elderly subjects in the standing position before and after postural transition of sitting and rising from a chair, using linear and nonlinear methods. METHODS: Forty-two elderly subjects were divided into 3 groups: non-frail (n=15), pre-frail (n=15), and frail (n=12). The CoP displacements in the anteroposterior (AP) and mediolateral (ML) direction in the orthostatic position, 30s before and after sitting down and rising from a chair, were evaluated by means of linear measurements (root mean square (RMS), amplitude, and total average speed) and nonlinear measurements (corrected approximate entropy - CApEn), sample entropy (SampEn), and complexity index (CI) and its normalized versions. RESULTS: After sitting and rising, there was an increase in RMS in the ML direction in all groups and in the AP direction in the non-frail and frail groups. The frail group showed no reduction in entropy values in either direction, and the pre-frail group showed no reduction in the ML direction. CONCLUSIONS: The results of this study indicate that, in the presence of frailty syndrome, the organization of CoP displacements does not show less regularity after sitting and rising from a chair, reflecting a possible impairment of the integration of the systems involved in postural control