Effets de l'entraînement et de l'hypoxie sur le contrôle neurovégétatif de la fonction cardiovasculaire évalué par la variabilité de la fréquence cardiaque

[Résumé en français] L'hypoxie aiguë et l'entraînement en endurance ont des effets opposés sur le système neurovégétatif et la fonction cardiovasculaire. Le modèle " living high-training low " (LHTL) pourrait limiter ces adaptations liées à l'entraînement en endurance seul. Un stage LHTL (16 h/j, 2500-3000m, 13 jours) limite la baisse de la fréquence cardiaque (FC) et de la modulation sympathique sur le cœur liée à l'entraînement alors que les résistances vasculaires et la pression artérielle sont augmentées (Etude 1). Ces adaptations semblent principalement dues à l'exposition à l'hypoxie (Etude 2). Des effets rémanents de l'hypoxie ont pu se prolonger jusqu'au début de la séance d'entraînement suivante et s'additionner avec la réponse à l'exercice. Il est peu probable que les effets de l'entraînement aérobie du stage LHTL se soient additionnés avec la réponse à l'hypoxie (Etude 3). L'analyse de la variabilité de la FC semble bien adaptée à l'évaluation du contrôle neurovégétatif lors d'études de terrain.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

A combined DFMA and TRIZ approach to the design of satellite antennas

Nowadays, companies' competrtrve advantage is directly connected with their capacity to develop cost-effective products with high quality and short time to market. Furthermore, in the market of electronic products, competitors are forced to pursue a systematic, market-oriented policy of innovation. The objective of this paper is to investigate the combined application of DFMA with the Theory of Inventive Problem Solving (TRIZ) in the synthesis of new design concepts. To this aim, in research collaboration between Tele System Electronic and the University of Padova, DFMA and TRIZ have been applied to the design of a new satellite antenna

Numerical modeling of bra wear during running

International audienceNumerical modelling of bras and their influence on breasts during sport could be a valuable tool for bra designers as it could avoid the development of prototypes and help improving the performances of bras. Such a model requires a model for the breasts and for the bra. Models of breasts are available in the literature but they are based on MRI data that are expensive and heavy to segment and mesh. One of the main issues to develop a breast numerical model is to define a reference state for the breast without gravity, to avoid errors in the evaluation of stresses during sport. Rajagopal et al. used water to cancel the effect of gravity on a part of the breast and define the reference state; this idea is followed in the present work. The present work is focused on modelling female breasts, simulating brawear and investigating the influence of the bra on stresses and strains in the breast. A particular objective of this work is to provide a model that can run fast enough on a regular computer, so that it is convenient to use for industrial and commercial purposes

Numerical simulation of breast deformation under static conditions

International audienc

Autonomic control of the cardiovascular system during acclimatization to high altitude : effects of sildenafil

Both acute hypoxia and sildenafil may influence autonomic control through transient cardiovascular effects. In a double-blind study, we investigated whether sildenalfil (Sil) could interfere with cardiovascular effects of hypoxia. Twelve healthy men [placebo (Pla) n = 6; Sil, n = 6] were exposed to an altitude of 4,350 m during 6 days. Treatment was continuously administered from 6 to 8 h after arrival at altitude (3 X 40 mg/day). The autonomic control on the heart was assessed by heart rate variability (HRV) during sleep at sea level (SL) and between day 1-2 and day 5-6 in hypoxia. Arterial pressure (AP) and total peripheral resistances (TPR) were obtained during daytime. There was no statistical difference between groups in HRV, AP, and TPR throughout the study. Hypoxia induced a decrease in R-R interval and an increase in AP in both groups. Low frequency-to-high frequency ratio increased at day 1-2 (Pla, P = 0.04; Sil, P = 0.02) and day 5-6 (Pla and Sil, P = 0.04) vs. SL, whereas normalized high-frequency power decreased only in Pla (P = 0.04, day 1-2 vs. SL). Normalized low-frequency power increased at high altitude (Pla and Sil, P = 0.04, day 5-6 vs. SL). TPR decreased at day 2 in Pla (P = 0.02) and tended to normalize at day 6 (P = 0.07, day 6 vs. day 2). Acute hypoxia induced a decrease in parasympathetic and increase in sympathetic tone, which tended to be reversed with acclimatization. Sil had no deleterious effects on the cardiovascular response to high-altitude exposure and its control by the autonomic nervous system

Interchangeability between heart rate and photoplethysmography variabilities during sympathetic stimulations

Photoplethysmography variability (PPGV) is currently considered to be a good surrogate to heart rate variability (HRV) measurements using the time between two pulse waves instead of RR intervals. Nevertheless, the interchangeability between HRV and PPGV has never been evaluated in situations with severe alterations in the autonomic nervous system (ANS). We aimed to identify the conditions for a correct utilization of PPGV in evaluating the consequences of sympathetic stimulations. Nine subjects performed three tests: active orthostatic test, slow walk and moderate and exhaustive cycling exercises in the supine position. Pulse waves at the fingertip and RR intervals were recorded at the same time. We used correlations and the Bland and Altman method to compare and evaluate interchangeability between several HRV indices. Bland and Altman analysis highlighted small discrepancies between PPGV and HRV for all HRV indices in the supine position and for [Formula: see text], [Formula: see text], LF(peak) and RMSSD in the upright position. During the slow walk, it was impossible to detect properly PPG peaks. We observed large differences between the two methods during the cycling exercise. In conclusion, PPGV can be used instead of HRV without reserve in the supine position but only for some HRV indices in the upright position and not during slow walk and cycling exercise

Autonomic adaptations in Andean trained participants to a 4220-m altitude marathon

Purpose: Both training and chronic hypoxia act on the autonomic nervous system. Because trained Andean high-altitude natives could perform a high-altitude marathon (4220 m above sea level) in 02:27:23 h, we hypothesized that living in chronic hypoxia does not limit the training-induced benefits on the autonomic modulation of the heart. Methods: Trained (N = 13) and sedentary (N = 11) Andean high-altitude natives performed an active orthostatic test. Eight of the trained subjects repeated the test 6-8 and 20-24 h after the end of a high-altitude marathon. Resting heart rate (HR) and the autonomic modulation of the heart were assessed by time domain and spectral analysis of HR variability (HRV): sympathetic (RR low frequency (LF)) and parasympathetic (RR high frequency (HF)) modulations, and sympathovagal balance (RR-LF:HF ratio). Results: Trained subjects exhibited a higher total power of HRV and a lower resting HR (+30%, P < 0.005) than sedentary subjects secondary to a higher and dominant parasympathetic modulation on sympathetic activity (RR-HF, RR-LF:HF ratio). At 6-8 h after the marathon, total power of HRV decreased (-69%), whereas resting HR increased from basal level (+22%), mainly because of a rise in sympathetic modulation (RR-LF, RR-LF:HF ratio). From 8 to 24 h of recovery, sympathetic modulation fell (RR-LF, RR-LF:HF ratio) and all HRV parameters were restored. Responses to the active standing position did not change between each recording session. Conclusion: Living in chronic hypoxia does not limit the training-induced benefits on the autonomic control of the cardiovascular system in Andean high-altitude ratives. The sympathetic predominance on the heart observed 6-8 h after the high-altitude marathon disappeared after 1 d of recovery. Therefore, living at high altitude does not impair the autonomic response to training