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

Abstract

BackgroundA 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.

Simultaneous Characterization of Sympathetic and Cardiac Arms of the Baroreflex through Sequence Techniques during Incremental Head-Up Tilt

“…Indeed, the gradual increase of SEQ% cBR with tilt table inclination is in agreement with the results reported in Bahjaoui-Bouhaddi et al ( 2000 ), Porta et al ( 2016 ) and with the rise of the strength of the HP-SAP association along the temporal direction from SAP to HP reported in Porta et al ( 2011 ). The progressive decrease of cBRS SEQ with tilt table angles is in agreement with results given in Cooke et al ( 1999 ), Bahjaoui-Bouhaddi et al ( 2000 ), O'Leary et al ( 2003 ), Porta et al ( 2016 ) indicating that the more and more increased involvement of the cBR in governing HP-SAP variability interactions with the magnitude of the postural challenge is accompanied by the progressive decline of the effectiveness of this reflex. The reduction of cBRS SEQ is likely to be related to the reduction of HP in presence of virtually unmodified SAP values and to the reduced HP variation resulting from the vagal withdrawal in presence of an increased SAP variability linked to the increased modulation of the sympathetic discharge.…”

“…Graded head-up tilt induces a gradual sympathetic activation and vagal withdrawal occurring in response to baroreflex unloading associated to central hypovolemia (Montano et al, 1994 ; Cooke et al, 1999 ; Furlan et al, 2000 ; O'Leary et al, 2003 ; Kamiya et al, 2005 ; Fu et al, 2006 ; Porta et al, 2007 ; Lambert et al, 2008 ; Baumert et al, 2011 ; El-Hamad et al, 2015 ; Marchi et al, 2016 ; Porta et al, 2016 ). The modification of the state of the autonomic nervous system in response to head-up tilt with inclination lower than or equal to than 60° produced a significant tachycardia with limited variations of AP (Bahjaoui-Bouhaddi et al, 2000 ; O'Leary et al, 2003 ; Fu et al, 2006 ; Porta et al, 2011 ).…”

“…The study exploits the recently defined calibrated MSNA variability (Marchi et al, 2016 ) in association with spontaneous DAP variations to compute sBRS, while cBRS is computed over spontaneous HP and SAP variability via the traditional cBR sequence method (Bertinieri et al, 1985 ). sBRS and cBRS are calculated during the baroreflex unloading induced by an incremental head-up tilt protocol in healthy volunteers (Lambert et al, 2008 ) imposing a sympathetic activation (Marchi et al, 2016 ) and a reduction of cBRS (Cooke et al, 1999 ; Porta et al, 2016 ) and sBRS (Ichinose et al, 2006 ; Barbic et al, 2015 ; Marchi et al, 2015 ) proportional to the magnitude of the challenge. This study hypothesizes that sBRS decreases in proportion to the central hypovolemia induced by incremental head-up tilt and tests a posteriori that the proposed sBR sequence method can monitor this decrease.…”

Association between autonomic control indexes and mortality in subjects admitted to intensive care unit

“…Indeed, during MHUT the HP-SAP coupling at slow time scales, as monitored via 0V-0V% HP-SAP , was significantly smaller in NonSURVs than in SURVs, while the opposite situation was observed at faster time scales as indicated by the trend of 2LV-2LV% HP-SAP . This finding once again emphasized the pathological response of NonSURVs to the orthostatic stimulus that usually leads in healthy population to an increase of 0V-0V% HP-SAP and a decrease of 2LV-2LV% HP-SAP as an indication of the activation of the cardiac baroreflex 52 .…”

Assessing the strength of cardiac and sympathetic baroreflex controls via transfer entropy during orthostatic challenge

“…Given that the dependency of the strength of the causal link from DAP to MSNA burst rate is expected as a sign of the greater solicitation of sBR with the stimulus, we suggest that, in this specific experimental protocol exploiting a stimulus of limited intensity, the relevance of the stressor is not sufficient to reveal the progression of the genuine information transfer from DAP to MSNA burst rate. We conjecture that, given the low intensity of the postural challenge, MSNA burst rate might be predominantly under central commands [41] operating independently of DAP levels and to a lesser extent reflexively regulated via sBR, thus masking the expected positive relation of the strength of the directed information flow with tilt table inclination. In addition, taking together the gradual increase of the strength of the causal relation from SAP to HP and the steady behaviour of that from DAP to MSNA burst rate, we conclude that cBR is more responsive in regulating AP following postural challenge than sBR.…”