1511 - Acute Modulation of Heart Rate Fragmentation: Evaluating the Stress Response and Resonance Frequency Breathing

Evaluated whether (1) short bursts of physical (handgrip) and cognitive (2-Back test) stressors change Heart Rate Fragmentation (HRF) and (2) whether slow, paced resonance frequency breathing (RFB) influences HRF. Spearman correlations among HRF measures identified variables with independent properties for future clinical research.


Design:

Within-subject repeated measures across six conditions—baseline, acute stress, recovery, RFB, repeated stress, and final recovery— conducted in clinical exam suites. Thirty-one healthy medical students, faculty, and staff participated. Physical stress was induced via a hand-held dynamometer and cognitive load via the 2-Back memory task; slow breathing was guided with the HeartMath™ Inner Balance sensor and mobile app. HRF outcome variables: percentage of inflection points (PIP), inverse average length of acceleration/deceleration segments (IALS), percentage of short segments (PSS), percentage of alternating segments (PAS), and symbolic “word” patterns describing heart rate direction changes. Mean HRF values were compared to baseline using Shapiro-Wilk and Friedman tests.


Results:

During the 2-minute stress periods, HRF measures were largely unchanged. During RFB, symbolic and non-symbolic HRF values were reduced relative to baseline (all except W₂^S and W₁^H, p< 0.05). The percentage of symbolic HRF words with only hard inflections fell from 55% to 34%, while words with only soft inflections rose from 21% to 27%. Complex three‑inflection HRF words during RFB dropped from 21% to 5%, and HRF words without any inflections more than tripled (8% to 32%) relative to baseline. PIP, IALS, PSS, and W₀ were highly correlated (all r >0.7). PAS and W₃^Hwere strongly correlated (all r >0.7).


Conclusions:

HRF measures remained unchanged in response to acute stress but showed significantly less fragmentation during RFB. These observations suggest that the clinical benefits of RFB may be derived from reductions in HRF. Further investigation of HRF and RFB is needed to evaluate this relationship in disease pathology and identify potential clinical applications.