Author(s): DIEDERICH-AMAND, M., TORDEUR, C., RABINEAU, J., AMIN, H., BALALI, P., ABDESSATER, E., VAN DE BORNE, P., FAORO, V., Institution: ULB, Country: BELGIUM, Abstract-ID: 2241

INTRODUCTION:
Intermittent hypoxia training is increasingly used by athletes or in clinical settings to reproduce altitude-like stimuli and enhance endurance performance. Despite its growing application, the acute cardiovascular adjustments to graded normobaric hypoxia remain insufficiently characterized, particularly at the level of cardiac mechanical function. Wearable technologies represent an emerging tool in athletic performance evaluation, enabling non-invasive, field-deployable monitoring of beat-to-beat cardiac dynamics. Kinocardiography (KCG), integrating seismocardiography (SCG) and ballistocardiography (BCG), allows such assessment. SCG captures thoracic micro-accelerations generated by myocardial contraction and valvular events, reflecting systolic and diastolic mechanical activity, whereas BCG quantifies whole-body recoil induced by pulsatile blood ejection into the great vessels, providing an index of central aortic flow dynamics. The present study aimed to characterize cardiovascular mechanical responses to acute graded normobaric hypoxia (FiO₂ 0.16 and 0.13
METHODS:
Sixteen healthy adults (8W/8M) completed five randomized 20-min exposures: normoxia, poikilocapnic and isocapnic hypoxia at fraction of inspired O2 (FiO₂ ) of 0.16 and 0.13. Beat-to-beat blood pressure (BP), stroke volume (SV), cardiac output (CO), total peripheral resistance (TPR), and baroreflex sensitivity (BRS) were obtained from Finapres. SCG and BCG were recorded with sternal and lumbar sensors respectively to calculate systolic kinetic energy (iKQT) over the QT interval.
RESULTS:
Oxygen pulsed pressure SpO₂ declined with hypoxia severity (94% at 0.16; 89% at 0.13) and CO rose proportionally (p < 0.001) exclusively via heart rate (HR), whereas SV. While diastolic BP and TPR remained stable. BRS decreased (p = 0.022); with a modest systolic rise (+6 mmHg).SCG iKQT rose at 0.13 vs normoxia (p = 0.001) and vs 0.16 (p = 0.007); BCG increased (p = 0.013). Mixed models showed SCG and BCG were inversely associated to SpO₂ (β =–0.012, p=0.003;, β = –0.096, p=0.025), while BCG was correlated with SV (β =1.611, p=0.031). Isocapnia further increased SCG and BCG at FiO2=0.13 (p≈0.01), indicating that hypocapnia attenuates but does not abolish cardiac mechanical stress.
CONCLUSION:
Normobaric hypoxia induces graded cardio-vascular adjustments characterized by preserved SV, tachycardia-mediated CO elevation, slight SBP elevation and reduced BRS. Kinocardiography demonstrates sensitivity to hypoxia-induced mechanical stress and discriminates responses under distinct CO₂ conditions, capturing augmented kinetic energy when isocapnia prevents hypocapnic attenuation. These findings position KCG as a promising wearable tool to quantify hypoxia-related hemodynamic load in athletes; however, its responsiveness and physiological relevance after exercise remain to be established.