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. 2024 Jan 8:14:1294239.
doi: 10.3389/fphys.2023.1294239. eCollection 2023.

Noninvasive characterization of peripheral sympathetic activation across sensory stimuli using a peripheral arterial stiffness index

Ziqiang Xu  1 , Reiji Anai  1 , Harutoyo Hirano  2 , Zu Soh  1 , Toshio Tsuji  1
Affiliations

Noninvasive characterization of peripheral sympathetic activation across sensory stimuli using a peripheral arterial stiffness index

Ziqiang Xu et al. Front Physiol. .

Abstract

Introduction: The peripheral arterial stiffness index has been proposed and validated as a noninvasive measure quantifying stimulus intensity based on amplitude changes induced by sympathetic innervation of vascular tone. However, its temporal response characteristics remain unclear, thus hindering continuous and accurate monitoring of the dynamic process of sympathetic activation. This paper presents a study aimed at modeling the transient response of the index across sensory stimuli to characterize the corresponding peripheral sympathetic activation. Methods: The index was measured using a continuous arterial pressure monitor and a pulse oximeter during experiments with local pain and local cooling stimuli designed to elicit different patterns of sympathetic activation. The corresponding response of the index was modeled to clarify its transient response characteristics across stimuli. Results: The constructed transfer function accurately depicted the transient response of the index to local pain and local cooling stimuli (Fit percentage: 78.4% ± 11.00% and 79.92% ± 8.79%). Differences in dead time (1.17 ± 0.67 and 0.99 ± 0.56 s, p = 0.082), peak time (2.89 ± 0.81 and 2.64 ± 0.68 s, p = 0.006), and rise time (1.81 ± 0.50 and 1.65 ± 0.48 s, p = 0.020) revealed different response patterns of the index across stimuli. The index also accurately characterized similar vasomotor velocities at different normalized peak amplitudes (0.19 ± 0.16 and 0.16 ± 0.19 a.u., p = 0.007). Discussion: Our findings flesh out the characterization of peripheral arterial stiffness index responses to different sensory stimuli and demonstrate its validity in characterizing peripheral sympathetic activation. This study valorizes a noninvasive method to characterize peripheral sympathetic activation, with the potential to use this index to continuously and accurately track sympathetic activators.

Keywords: noninvasive characterization; peripheral arterial stiffness index; peripheral sympathetic activation; sensory stimuli; transient response analysis.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Overview of the method for analyzing the response characteristics of the peripheral arterial stiffness index to sensory stimuli. The method comprises three parts: Measurements and stimuli, biosignal processing, and transient analyses. I: stimulus current intensity; T: stimulus temperature; ABP: arterial blood pressure; S(s): the Laplace transform of stimulus intensity; H β (s) and H P (s): transfer functions of peripheral arterial stiffness index β and palm sweat rate P, respectively.
FIGURE 2
FIGURE 2
Experimental configurations. (A) Experimental protocol. (B) A questionnaire displayed on the screen facing the participant (Japanese text in the image: “Please evaluate the degree of pain during the previous stimulus.”).
FIGURE 3
FIGURE 3
An example of impulse response and its characteristics analyzed in this study. The baseline indicates a steady state, i.e., the rest state. y(t): Impulse response; t: Time; τ: Dead time; T p : Peak time; T r : Rise time; A p : Baseline-to-peak amplitude.
FIGURE 4
FIGURE 4
Stimulus intensities and resulting sensory changes for all participants. (A) Current intensity in the local pain stimulus experiment. I c : Current intensity. (B) The VAS ratings on pain, cold, unpleasantness, and arousal under local pain and local cooling stimuli. The black point range lines represent the mean and standard deviation. The statistical test results based on the effect size δ and the Brunner–Munzel test with Holm adjustment are also shown (significance level: 1%). VAS: Visual analog scale.
FIGURE 5
FIGURE 5
Examples of measured heart rate (HR), continuous arterial blood pressure (ABP), photoplethysmogram (PPG), peripheral arterial stiffness index β, and palm sweat rate P from Participant A during a single trial, respectively. (A) The local pain stimulus experiment. (B) The local cooling stimulus experiment. The colored areas indicate each 60-s stimulus period.
FIGURE 6
FIGURE 6
Normalized peripheral arterial stiffness β n and palm sweat rate P n for all participants in the two experiments. (A,B) Their mean values over different periods. The gray dashed lines represent their group-averaged changes. The black point-range lines represent the mean and standard deviation (S.D.). The statistical test results based on the effect size δ and the Brunner–Munzel test with Holm adjustment are also shown (significance level: 1%). (C,D) Group-averaged results of β n and P n.
FIGURE 7
FIGURE 7
Assessment of transient response analysis results in one trial of Participant (A). (A) Normalized β n in the local pain stimulus experiment. (B) Normalized P n in the local pain stimulus experiment. (C) Normalized β n in the local cooling stimulus experiment. τ: Dead time.
FIGURE 8
FIGURE 8
Measurement and estimation results of β n and P n for Participant A in one trial of the local pain and local cooling stimulus experiments, respectively.
FIGURE 9
FIGURE 9
Evaluation results of the transient response analysis results of normalized β n and P n for all participants. (A) F P. (B) MSE. The statistical test results based on the effect size δ and the Brunner–Munzel test with Holm adjustment are also shown (significance level: 1%).
FIGURE 10
FIGURE 10
Results of the transient response characteristics of normalized β n and P n to local pain and local cooling stimuli for all participants. (A–D) Dead time τ, peak time T p , rise time T r , and baseline-to-peak amplitude A pn. The black point range lines represent the mean and standard deviation. The statistical test results based on the effect size δ and the Brunner–Munzel test with Holm adjustment are also shown (significance level: 1%).
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Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by JSPS KAKENHI Grant Number JP19H04442.

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