Highlights
- •Three methods to autoregulation index (ARI) estimation from spontaneous variability were applied.
- •All methods for ARI estimation differentiated original and surrogate data.
- •Even when ARI estimates were correlated, a significant constant bias could be present.
- •Autonomic response to postural stressor was diverse in subjects with or without syncopal episodes.
- •ARI estimates were similar in subjects with or without syncopal episodes.
Abstract
Three approaches to the assessment of cerebrovascular autoregulation (CA) via the
computation of the autoregulation index (ARI) from spontaneous variability of mean
arterial pressure (MAP) and mean cerebral blood flow velocity (MCBFV) were applied:
1) a time domain method (TDM); 2) a nonparametric method (nonPM); 3) a parametric
method (PM). Performances were tested over matched and surrogate unmatched pairs.
Data were analyzed at supine resting (REST) and during the early phase of 60° head-up
tilt (TILT) in 13 subjects with previous history of postural syncope (SYNC, age: 28 ± 9 yrs.;
5 males) and 13 control individuals (noSYNC, age: 27 ± 8 yrs.; 5 males). Analysis
was completed by computing autonomic markers from heart period (HP) and systolic arterial
pressure (SAP) variability series via spectral approach. HP and SAP spectral indexes
suggested that noSYNC and SYNC groups exhibited different autonomic responses to TILT.
ARI analysis indicated that: i) all methods have a sufficient statistical power to
separate matched from unmatched pairs with the exception of nonPM applied to impulse
response; ii) ARI estimates derived from different methods might be uncorrelated and,
even when correlated, might exhibit a significant bias; iii) orthostatic stressor
did not induce any evident ARI change in either noSYNC or SYNC individuals; iv) this
conclusion held regardless of the method. Methods for the ARI estimation from spontaneous
variability provide different ARIs but none indicate that noSYNC and SYNC subjects
have different dynamic component of CA.
Keywords
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Article info
Publication history
Published online: November 18, 2021
Accepted:
November 15,
2021
Received in revised form:
October 20,
2021
Received:
April 1,
2021
Identification
Copyright
© 2021 Elsevier B.V. All rights reserved.
