Joint Symbolic Analysis Research Articles

Assessing cardiorespiratory interactions via lagged joint symbolic dynamics during spontaneous and controlled breathing.

Introduction: Joint symbolic analysis (JSA) can be utilized to describe interactions between time series while accounting for time scales and nonlinear features. JSA is based on the computation of the rate of occurrence of joint patterns built after symbolization. Lagged JSA (LJSA) is obtained from the more classical JSA by introducing a delay/lead between patterns built over the two series and combined to form the joint scheme, thus monitoring coordinated patterns at different lags. Methods: In the present study, we applied LJSA for the assessment of cardiorespiratory coupling (CRC) from heart period (HP) variability and respiratory activity (R) in 19 healthy subjects (age: 27-35years; 8 males, 11 females) during spontaneous breathing (SB) and controlled breathing (CB). The R rate of CB was selected to be indistinguishable from that of SB, namely, 15 breaths·minute-1 (CB15), or slower than SB, namely, 10 breaths·minute-1 (CB10), but in both cases, very rapid interactions between heart rate and R were known to be present. The ability of the LJSA approach to follow variations of the coupling strength was tested over a unidirectionally or bidirectionally coupled stochastic process and using surrogate data to test the null hypothesis of uncoupling. Results: We found that: i) the analysis of surrogate data proved that HP and R were significantly coupled in any experimental condition, and coupling was not more likely to occur at a specific time lag; ii) CB10 reduced CRC strength at the fastest time scales while increasing that at intermediate time scales, thus leaving the overall CRC strength unvaried; iii) despite exhibiting similar R rates and respiratory sinus arrhythmia, SB and CB15 induced different cardiorespiratory interactions; iv) no dominant temporal scheme was observed with relevant contributions of HP patterns either leading or lagging R. Discussion: LJSA is a useful methodology to explore HP-R dynamic interactions while accounting for time shifts and scales.

Cardiorespiratory coupling strength in athletes and non-athletes

PurposeDespite the relevant presence of nonlinear components on heart period (HP) likely due to cardiorespiratory coupling (CRC), the HP is frequently analyzed in absence of concomitant recordings of respiratory movements (RESP). This study aims to assess the cardiovascular dynamics and CRC during postural challenge in athletes and non-athletes via joint symbolic analysis (JSA). MethodsA cross-sectional study was conducted in 50 men, aged between 20 and 40 yrs, divided into athletes (n = 25) and non-athletes (n = 25) groups. The electrocardiogram, blood pressure and RESP signals were recorded during 15 min in both supine position (REST) and after active postural maneuver (STAND). From the beat-to-beat series of HP, systolic arterial pressure (SAP) and RESP, we computed the time and frequency domain indexes and baroreflex sensitivity. The JSA was based on the definition of symbolic HP and RESP patterns and on the evaluation of the rate of their simultaneous occurrence in both HP and RESP series. ResultsThe JSA analysis was able to identify higher CRC strength at REST in athletes. Moreover, the response of CRC to STAND depended on the time scales of the analysis and was much more evident in athletes than in non-athletes, thus indicating a more reactive autonomic control in athletes. ConclusionAssessing CRC in athletes via JSA provides additional information compared to standard linear time and frequency domain tools likely due to the more relevant presence of nonlinearities in HP-RESP variability relationship.

Assessment of the Coupling Strength of Cardiovascular Control via Joint Symbolic Analysis during Postural Challenge in Recreational Athletes.

Short-term cardiovascular control, comprising cardiac baroreflex and mechanisms governing cardiac contractility and vascular properties, links heart period (HP) and systolic arterial pressure (SAP) fluctuations. It is activated during postural challenge and this activation is traditionally quantified via linear tools such as HP-SAP squared coherence function. In this study the ability of a nonlinear bivariate tool based on joint symbolic analysis (JSA) approach was tested against HP-SAP coherence function during orthostatic challenge in recreational athletes. We studied 9 men healthy cycling practitioners (age: 20-40 yrs) at rest in supine condition (REST) and during active standing (STAND). The JSA method is based on the definition of symbolic HP and SAP patterns and on the evaluation of the rate of their simultaneous occurrence in both HP and SAP series. HP-SAP squared coherence was computed in the low frequency band (LF, from 0.04 to 0.15 Hz). We found the expected response to the postural stimulus, namely the increase of sympathetic modulation and the contemporaneous vagal withdrawal. However, only JSA was able to detect the expected increase of association between HP and SAP variability series over slow time scales. This result suggests that recreational athletes have more relevant nonlinear interactions between HP and SAP that might be missed by traditional linear tools and might require nonlinear tools to be efficiently described.

Abstract MP081: Short-long-short Sequence of RR Intervals is Associated With Increased Risk of Sudden Cardiac Death: the Atherosclerosis Risk in Community Study

Introduction: A Short-long-short sequence of RR’ intervals frequently precedes ventricular tachyarrhythmia. However, an association of RR’ alternans with sudden cardiac death (SCD) in the general population has not been previously studied. Hypothesis: We hypothesized that RR’ alternans is associated with SCD. Methods: We analyzed baseline visit 10-second ECG in 14,250 participants of the Atherosclerosis Risk in Communities (ARIC) cohort (mean age 54.1±5.87y; 45% men; 74% white). Only normal sinus beats were included in the semi-automated analysis. Digital 12-lead ECG was transformed into orthogonal ECG, from which respiratory signal was derived. Joint symbolic analysis was used to assess increase or decrease in successive RR’ intervals and R-instant respiratory phases calculated using the Hilbert transform. Short-long-short or long-short-long RR’ sequence was defined as RR’ alternans. RR’ alternans occurring during respiratory phase transitions were not considered. SCD, non-SCD, and non-cardiac death served as competing outcomes. Three competing risks models were constructed. Model 1 was adjusted for age, sex, race, and study center. Model 2 was in addition adjusted for prevalent CVD. Model 3 was further adjusted for subclinical CVD, its risk factors, including traditional ECG predictors, and medications affecting SA or AV nodes. Results: Over median follow-up of 24.4 years, there were 497 SCDs (incidence 1.66 [95%CI 1.52-1.82], 742 non-sudden cardiac deaths (incidence 2.48 [95%CI 2.31-2.67], and 3,753 non-cardiac deaths (incidence 12.6 [95%CI 12.1-13.0]) per 1,000 person-years. RR alternans was present in 1,679(11.8%) participants. In competing risks analysis (Table) the presence of RR’ alternans, excluding those occurring due to respiratory phase changes, was independently associated with increased risk of SCD. Conclusion: In competing risks analysis the presence of RR’ alternans that are not due to respiratory phase transition is associated with SCD. Further study of RR’ alternans is warranted.

Nonlinear effects of respiration on the crosstalk between cardiovascular and cerebrovascular control systems.

Cardiovascular and cerebrovascular regulatory systems are vital control mechanisms responsible for guaranteeing homeostasis and are affected by respiration. This work proposes the investigation of cardiovascular and cerebrovascular control systems and the nonlinear influences of respiration on both regulations through joint symbolic analysis (JSA), conditioned or unconditioned on respiration. Interactions between cardiovascular and cerebrovascular regulatory systems were evaluated as well by performing correlation analysis between JSA indexes describing the two control systems. Heart period, systolic and mean arterial pressure, mean cerebral blood flow velocity and respiration were acquired on a beat-to-beat basis in 13 subjects experiencing recurrent syncope episodes (SYNC) and 13 healthy individuals (non-SYNC) in supine resting condition and during head-up tilt test at 60° (TILT). Results showed that JSA distinguished conditions and groups, whereas time domain parameters detected only the effect of TILT. Respiration affected cardiovascular and cerebrovascular regulatory systems in a nonlinear way and was able to modulate the interactions between the two control systems with different outcome in non-SYNC and SYNC groups, thus suggesting that the analysis of the impact of respiration on cardiovascular and cerebrovascular regulatory systems might improve our understanding of the mechanisms underpinning the development of postural-related syncope.

Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis.

ABSTRACTBackgroundA joint symbolic analysis (JSA) is applied to assess the strength of the cardiovascular coupling from spontaneous beat-to-beat variability of the heart period (HP) and the systolic arterial pressure (SAP) during an experimental protocol inducing a gradual baroreflex unloading evoked by postural change (i.e. graded head-up tilt).Method:The adopted JSA can quantify the degree of association between the HP and SAP variabilities as a function of the time scale of the HP and SAP patterns. Traditional linear tools assessing the HP-SAP coupling strength, such as squared correlation coefficient, squared coherence function, and percentage of baroreflex sequences, were computed as well for comparison.Results:We found that: i) JSA indicated that the strength of the cardiovascular coupling at slow temporal scales gradually increased with the magnitude of the orthostatic challenge, while that at fast temporal scales gradually decreased; ii) the squared correlation coefficient and percentage of baroreflex sequences did not detect this behavior; iii) even though squared coherence function could measure the magnitude of the HP-SAP coupling as a function of the time scale, it was less powerful than JSA owing to the larger dispersion of the frequency domain indexes.Conclusion:Due to its peculiar features and high statistical power, JSA deserves applications to pathological groups in which the link between HP and SAP variabilities is lost or decreased due to the overall depression or impairment of the cardiovascular control.

Joint symbolic dynamics for the assessment of cardiovascular and cardiorespiratory interactions

Beat-to-beat variations in heart period provide information on cardiovascular control and are closely linked to variations in arterial pressure and respiration. Joint symbolic analysis of heart period, systolic arterial pressure and respiration allows for a simple description of their shared short-term dynamics that are governed by cardiac baroreflex control and cardiorespiratory coupling. In this review, we discuss methodology and research applications. Studies suggest that analysis of joint symbolic dynamics provides a powerful tool for identifying physiological and pathophysiological changes in cardiovascular and cardiorespiratory control.

High-resolution joint symbolic analysis to enhance classification of the cardiorespiratory system in patients with schizophrenia and their relatives.

Schizophrenia as a mental illness is one of the most serious in the world. Patients with schizophrenia have an increased cardiac mortality rate, but the reasons for this remain unclear. In addition to other factors, the role of impaired autonomic regulation during acute psychosis has become more evident in different studies applying heart rate (HR) variability analyses. But, until now, respiration and cardiorespiratory regulation, which are important for homeostatic control, have not been considered. In this study, short-term cardiorespiratory couplings (CRCs) of 23 unmedicated patients with paranoid schizophrenia (SZO), 20 of their healthy first-degree relatives (REL) and 20 healthy subjects (CON) matched according to age and sex of SZO and REL were investigated by applying high-resolution joint symbolic dynamics (HRJSD) analysis. We found a significantly (p<0.0061) altered HR pattern, respiratory pattern and CRCs in SZO and only marginal alterations for the REL group in comparison with the CON group when we applied HRJSD. These results might be an indication of decreased vagal activity within the brainstem, an altered or suppressed interaction of the brainstem and higher regulatory centres, or panic- and anxiety-related changes in the brainstem associated with the acute psychosis of these patients.

Point:Counterpoint: Respiratory sinus arrhythmia is due to a central mechanism vs. respiratory sinus arrhythmia is due to the baroreflex mechanism

Blood pressure and heart periods fluctuate at respiratory frequencies in healthy humans. Some researchers ([8][1], [23][2]) explain this as a cause-and-effect relation: blood pressure changes trigger baroreflex-mediated R-R interval changes. Here I make the case that respiratory sinus arrhythmia is