Toward Ambulatory Baroreflex Sensitivity: Comparison Between Indices of Arterial Line and Photoplethysmography in Male Volunteers
Bibliographic record
Abstract
Background: Baroreflex sensitivity (BRS) is the body's ability to adjust heart rate (HR) to control blood pressure. Traditionally, BRS is quantified by measuring HR changes (obtained via an electrocardiogram [ECG]) following alterations in arterial pressure (conventionally measured through an arterial line). However, the invasiveness of arterial line necessitates alternatives, such as the volume clamp method and the less invasive pulse photoplethysmography (PPG). Notably, the PPG method is also suitable for continuous and free-living conditions. Objective: This study aims to compare PPG-based features for BRS determination based on the volume clamp method and gold standard arterial line. Data from a previous study was used where the primary analysis focused on evaluating the accuracy of PPG-derived HR variability, while this analysis quantifies BRS by measuring HR changes following alterations in arterial line pressure or less invasive alternatives. In addition, we investigate the feasibility of assessing BRS patterns over 24 hours using data from a single volunteer. Methods: A total of 28 male volunteers (age 52, SD 7 y; BMI 27, SD 4 kg/m2) equipped with four sensing modalities: (1) arterial line [ABP], (2) infrared PPG, (3) volume clamp finger pressure (VCP), and (4) ECG, performed a protocol of 3 repetitive sessions in supine position. For the extended feasibility of continuous BRS measurement, ECG and PPG data were acquired for 24 hours in free-living conditions from a normotensive male volunteer (33 y). BRS index was calculated within the low-frequency window (0.04-0.15 Hz) averaging over all trials for each intervention and participant. A transfer function was estimated with systolic blood pressure (SBP) or its surrogate as input and HR (from the ECG) as output. Results: PPG-based BRS features, specifically the rise-decay time ratio (RDRatio) and pulse arrival time (PAT), demonstrate intraparticipant precision of 44% and 23%, respectively, with interparticipant variation of 91% and 53%. The correlation of BRSPAT,PPG and BRSRDRatio,PPG with the gold standard BRSSBP,ABP (SBP) is 0.66 and 0.56, respectively. During intervention, the correlations remain high for BRSRDRatio,PPG (rest: 0.75, paced-breathing: 0.50, and handgrip: 0.46) and BRSPAT,PPG (rest: 0.69, paced-breathing: 0.52, and handgrip: 0.62). In the 24-hour data, the BRSPAT,PPG and BRSRDRatio,PPG exhibit changes during the day corresponding to the activity levels and SBP variations. Notably, during the night, a cyclic rhythm is observed for both BRSPAT,PPG and BRSRDRatio,PPG. Conclusions: This study demonstrates that in male volunteers, PPG-based PAT and RDRatio BRS serve as suitable surrogates for gold-standard BRS derived from arterial line, showing the highest correlation and comparable intraparticipant coefficient variation. Furthermore, they show expected changes during controlled activities and a 24-hour feasibility test in free-living conditions.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".