ECSS Paris 2023: CP-PN09
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.
Read CV Martin Diederich-AmandECSS Paris 2023: CP-PN09
INTRODUCTION: In order to achieve the beneficial effects associated with the use of low external load blood flow restriction (BFR) training, it is recommended to apply a tourniquet cuff pressure of 40-80% of the individual arterial occlusion pressure (AOP). The AOP refers to the lowest pressure which is necessary to fully block arterial blood flow and can be affected by several factors (e.g., body position, limb circumference, systolic blood pressure). Generally, the AOP is determined in both limbs individually when performing bilateral BFR exercises, such as cycling, walking, or squats. However, since the tourniquet cuffs on both limbs are inflated simultaneously during bilateral BFR exercises, it is presently unknown whether the respective AOP must also be measured during bilateral tourniquet cuff inflation. To address this issue, the present investigation aimed to compare the AOP during unilateral versus bilateral tourniquet cuff inflation in the lower extremities. METHODS: Twenty-five young, healthy participants (8 females, 17 males, age: 24 ± 4 yrs, height: 176.0 ± 9.1 cm, weight: 73.4 ± 10.7 kg, body mass index: 23.6 ± 2.3 kg/m2) underwent one laboratory visit during which their individual AOP was determined using a standardized cuff inflation protocol and identified at the posterior tibial artery via Doppler ultrasound. In a randomized cross-over design, the AOP measurements were performed in supine, seated, and standing position starting with either unilateral or bilateral cuff inflation with a rest period of 5 min between assessments to restore homeostasis after change of body position. At the end of each AOP determination, blood pressure and heart rate were recorded. A 2 × 3 repeated measures analysis of variance was conducted for AOP, blood pressure, and heart rate. Mean differences (MD) and 95% confidence intervals (95%CI) were reported, with a significance level set at p < 0.05. Effect size Cohen’s d (d) was calculated and interpreted as trivial (d < 0.2), small (0.2 ≤ d < 0.5), medium (0.5 ≤ d < 0.8), and large (d ≥ 0.8). RESULTS: Across body positions, the AOP was higher during bilateral compared to unilateral tourniquet cuff inflation (MD = 3.2 mmHg [95%CI: 1.0, 5.4], p = 0.006, d = 0.12). In addition, AOP and heart rate increased as body position changed from supine to seated to standing position (p < 0.001, d = 0.76–1.94) while no differences were found for systolic blood pressure (p ≥ 0.373). CONCLUSION: Although statistically significant, the effect size for the difference between AOP during unilateral and bilateral tourniquet cuff inflation was only trivial. Thus, it does not appear necessary to determine AOP during bilateral tourniquet cuff inflation when performing bilateral BFR exercises. However, these results solely apply to young, healthy individuals and need to be verified for different inflation protocols, devices (i.e., manual versus automatic AOP determination), and populations (e.g., older adults, patients).
Read CV Robert BielitzkiECSS Paris 2023: CP-PN09
INTRODUCTION: Flow-mediated dilation (FMD) and NIRS-derived oxygen saturation (StO2) reperfusion slope are widely interpreted as markers of conduit artery endothelial function and vascular responsiveness at the macro- and microvascular levels, respectively. Integration of both techniques is useful to improve the detection of vascular adaptations to exercise training, especially when considering the potential influence of the exercise intensity domain. Thus, this study aimed to explore whether changes in FMD and NIRS-Reperfusion slope hemodynamic vascular adaptations occurred in response to intensity domain-specific endurance training. METHODS: 39 healthy, sedentary adults (17 females) were randomly assigned to three age-, sex-, and V̇O2max-matched groups. Groups were assigned to continuous cycling training groups in the moderate (MOD) and heavy (HVY) intensity domains 3 times per week for 10 weeks, or to a no-exercise control group (CTRL). Aerobic fitness (V̇O2max) was assessed during a ramp-incremental test to volitional exhaustion. %FMD, and StO2 reperfusion slope were measured during a vascular occlusion test investigating the brachial artery and the flexor-digitorum muscle, respectively. All measures were performed before (pre) and after 10 weeks of training (post). RESULTS: CTRL showed no significant differences between pre and post for V̇O2max (38.5 ± 7.3 vs 36.7 ± 8.7 mL·kg-1·min-1; p = 0.15), %FMD (8.42 ± 3.07 vs 7.89 ± 4.44 %), and StO2 reperfusion slope (0.90 ± 0.38 vs 0.88 ± 0.40 StO2⋅s-1) (p > 0.05 for all variables). MOD and HVY groups showed similar increases in V̇O2max (mL·kg-1·min-1, MOD, pre = 33.5 ± 5.0 vs post = 36.5 ± 6.8; HVY, pre = 30.3 ± 7.6 vs post = 34.8 ± 7.9), %FMD (%, MOD, pre= 6.28 ± 2.10 vs post = 8.27 ± 3.23; HVY, pre = 5.73 ± 1.94 vs post= 7.32 ± 4.33), and StO2 reperfusion slope (StO2⋅s-1, MOD, pre = 0.96 ± 0.48 vs post = 1.23 ± 0.50; HVY, pre = 0.78 ± 0.34 vs post = 1.14 ± 0.40) (p < 0.05 for all variables) with no difference between groups and no interaction groups x time (p > 0.05 for all variables). Whereas at post, StO2 reperfusion slope showed a moderate correlation with V̇O2max (r = 0.66, p < 0.05), %FMD did not (r = 0.09, p = 0.19). CONCLUSION: Both %FMD, a marker of conduit artery endothelial function, and StO2 reperfusion slope, a marker of microvascular responsiveness, detected vascular adaptations following 10 weeks of endurance training, regardless of the training intensity domain. However, only the StO2 reperfusion slope showed a significant correlation with V̇O2max after training. These findings reinforce the importance of evaluating changes in vascular function through combined assessments of micro- and macrovascular responses to better characterize vascular adaptations associated with improvements in cardiorespiratory fitness in healthy individuals.
Read CV Massimo TesoECSS Paris 2023: CP-PN09