LES EFFETS DE L'HYPOXIE CHEZ LE SUJET SAIN ET PATHOLOGIQUE

This thesis investigates the effects of hypoxia in both healthy and diseased areas. Using freediving as a base, hemodynamic adjustments triggered by voluntary breath-holding were studied in trained breath-hold divers (study 1) to be then compared with non-divers (study 2). Moreover, both hemodynamic and ventilatory responses to hypoxia were investigated in trained breath-hold divers (study 3). Plasma adenosine concentration was also measured to clarify pathophysiological mechanisms underlying transient loss of consciousness during breath-holding (study 4). Finally, the effects of intermittent hypoxia were investigated on cardiometabolic risk factors in overweight or obese adults (study 5). Overall, the results tend to show that hypoxia induce efficient cardio-ventilatory adjustments in trained breath-hold divers as well as beneficial metabolic adaptations in obese adults. Based upon piecewise regression analyses, the occurrence of a new physiological event during breath-holding has been demonstrated, i.e. the “oxygen-conserving breaking point”. This particular point and subsequent hemodynamic adjustments appears to increase the oxygen-conserving potential of the human diving reflex, therefore delaying hypoxia in oxygen-sensitive organs. Negative chronotropic properties of adenosine might however induce transient loss of consciousness during severe hypoxemia induced by prolonged breath-holding. These results, as well as the increased hypoxic ventilatory response in divers, suggest that breath-holding training might be an alternative strategy to induce altitude pre-acclimatization. Besides, moderate intermittent hypoxia might have beneficial outcomes on cardiometabolic risk factors, suggesting that this environment is the cause of, as well as a promising therapeutic approach in people suffering from metabolic disorders.Ce travail de thèse se propose d’étudier les effets de l’hypoxie dans un contexte sain et pathologique. En prenant tout d’abord comme support l’apnée, nous explorons les ajustements hémodynamiques déclenchés par un arrêt volontaire de la respiration chez des apnéistes (étude 1) pour ensuite les comparer chez des sujets non familiarisés à cette pratique sportive (étude 2). Les réponses hémodynamiques et ventilatoires à l’hypoxie ont ensuite été analysées afin de déterminer si la pratique de l’apnée influence les paramètres cardio-ventilatoires en altitude simulée (étude 3). L’adénosine a par ailleurs été dosée pour mieux comprendre les mécanismes physiopathologiques à l’origine de la syncope en apnée (étude 4). Enfin, les effets de l’hypoxie normobarique intermittente sont étudiés sur les principaux facteurs de risques cardio-métaboliques chez des personnes obèses ou en surpoids (étude 5). L’ensemble des résultats tend à montrer que l’hypoxie entraîne des modifications efficientes tant sur le plan cardio-ventilatoire chez les apnéistes que métabolique chez les personnes obèses. En s’appuyant sur la construction et la validation de modèles de régression, nous mettons en évidence l’existence d’un événement physiologique auparavant inconnu lors de l’apnée, i.e. le « point d’économie d’oxygène ». Mis en lumière dans plusieurs conditions expérimentales, celui-ci marque le point de départ d’une remarquable rupture des cinétiques hémodynamiques dont l’objectif premier est de renforcer l’économie d’oxygène, retardant in fine l’hypoxie tissulaire des organes nobles. Les propriétés chronotropes négatives de l’adénosine seraient néanmoins susceptibles de déclencher une syncope en fin d’apnée en cas d’hypoxémie extrême chez certains individus. Ces résultats ainsi que la hausse de la réponse ventilatoire à l’hypoxie des apnéistes, suggèrent que la pratique de l’apnée pourrait être une alternative de pré-acclimatation à l’altitude naturelle. Outre ces effets, une dose hypoxique « modérée » administrée de façon intermittente parviendrait également à réduire certains facteurs de risques cardio-métaboliques, faisant de cet environnement une cause, mais aussi une thérapeutique non médicamenteuse prometteuse pour la prise en charge de personnes souffrant de troubles métaboliques

Effect of Additional Respiratory Muscle Endurance Training in Young Well- Trained Swimmers

International audienceWhile some studies have demonstrated that respiratory muscle endurance training (RMET) improves performances during various exercise modalities, controversy continues about the transfer of RMET effects to swimming performance. The objective of this study was to analyze the added effects of respiratory muscle endurance training (RMET; normocapnic hyperpnea) on the respiratory muscle function and swimming performance of young well-trained swimmers. Two homogenous groups were recruited: ten swimmers performed RMET (RMET group) and ten swimmers performed no RMET (control group). During the 8-week RMET period, all swimmers followed the same training sessions 5-6 times/week. Respiratory muscle strength and endurance , performances on 50-and 200-m trials, effort perception , and dyspnea were assessed before and after the intervention program. The results showed that ventilatory function parameters , chest expansion, respiratory muscle strength and endurance, and performances were improved only in the RMET group. Moreover, perceived exertion and dyspnea were lower in the RMET group in both trials (i.e., 50-and 200-m). Consequently , the swim training associated with RMET was more effective than swim training alone in improving swimming performances. RMET can therefore be considered as a worthwhile ergogenic aid for young competitive swimmers

Modeling the diving bradycardia: Toward an “oxygen-conserving breaking point”?

International audienc

Intermittent normobaric hypoxia alters substrate partitioning and muscle oxygenation in obese individuals: implications for fat burning

International audienceThis single-blind, crossover study aimed to measure and evaluate the short-term metabolic responses to continuous and intermittent hypoxic patterns in individuals with obesity. Indirect calorimetry was used to quantify changes in resting metabolic rate (RMR), carbohydrate (CHO ox , %CHO) and fat oxidation (FAT ox , %FAT) in nine individuals with obesity pre- and post-: (i) breathing normoxic air [normoxic sham control (NS-control)]; (ii) breathing continuous hypoxia (CH); or (iii) breathing intermittent hypoxia (IH). A mean peripheral oxygen saturation (SpO 2 ) of 80-85% was achieved over a total of 45 minutes of hypoxia. Throughout each intervention pulmonary gas exchanges - oxygen consumption ( ), carbon dioxide production ( - and deoxyhaemoglobin concentration ( [HHb]) in the vastus lateralis were measured. Both RMR and CHO ox measured pre- and post-interventions were unchanged following each treatment: NS-control; CH; or IH (all p > 0.05). Conversely, a significant increase in FAT ox was evident between pre- and post-IH (+44%, p = 0.048). While the mean [HHb] values significantly increased during both IH and CH ( p<0.05), the greatest zenith of [HHb] was achieved in IH compared to CH ( p = 0.002). Furthermore, there was a positive correlation between ∆[HHb] and the shift in FAT ox measured pre- and post-intervention. It is suggested that during IH the increased bouts of muscle hypoxia, revealed by elevated ∆[HHb], coupled with cyclic periods of excess post-hypoxia oxygen consumption (EPHOC, inherent to the intermittent pattern) played a significant role in driving the increase in FAT ox post-IH

Intermittent hypoxia revisited: a promising non-pharmaceutical strategy to reduce cardio-metabolic risk factors?

International audienc

Possible causes of narcosis-like symptoms in freedivers.

During deep-sea freediving, many freedivers describe symptoms fairly similar to what has been related to inert gas narcosis in scuba divers. This manuscript aims to present the potential mechanisms underlying these symptoms. First, known mechanisms of narcosis are summarized while scuba diving. Then, potential underlying mechanisms involving the toxicity of gases (nitrogen, carbon dioxide and oxygen) are presented in freedivers. As the symptoms are felt during ascent, nitrogen is likely not the only gas involved. Since freedivers are frequently exposed to hypercapnic hypoxia toward the end of the dive, it is proposed that carbon dioxide and oxygen gases both play a major role. Finally, a new "hemodynamic hypothesis" based on the diving reflex is proposed in freedivers. The underlying mechanisms are undoubtedly multifactorial and therefore require further research and a new descriptive name. We propose a new term for these types of symptoms: freediving transient cognitive impairment.info:eu-repo/semantics/publishe

Hemodynamic adjustments during breath-holding in trained divers

International audienc

Cardio-ventilatory responses to poikilocapnic hypoxia and hypercapnia in trained breath-hold divers

International audienc

Do elite breath-hold divers suffer from mild short-term memory impairments?

International audienc

Effect of additional respiratory muscle endurance training in young well-trained swimmers.

International audienceWhile some studies have demonstrated that respiratory muscle endurance training (RMET) improves performances during various exercise modalities, controversy continues about the transfer of RMET effects to swimming performance. The objective of this study was to analyze the added effects of respiratory muscle endurance training (RMET; normocapnic hyperpnea) on the respiratory muscle function and swimming performance of young well-trained swimmers. Two homogenous groups were recruited: ten swimmers performed RMET (RMET group) and ten swimmers performed no RMET (control group). During the 8-week RMET period, all swimmers followed the same training sessions 5-6 times/week. Respiratory muscle strength and endurance, performances on 50- and 200-m trials, effort perception, and dyspnea were assessed before and after the intervention program. The results showed that ventilatory function parameters, chest expansion, respiratory muscle strength and endurance, and performances were improved only in the RMET group. Moreover, perceived exertion and dyspnea were lower in the RMET group in both trials (i.e., 50- and 200-m). Consequently, the swim training associated with RMET was more effective than swim training alone in improving swimming performances. RMET can therefore be considered as a worthwhile ergogenic aid for young competitive swimmers. Key PointsRespiratory muscle endurance training improves the performance.Respiratory muscle endurance training improves the ventilatory function parameters, chest expansion, respiratory muscle strength and endurance.Respiratory muscle endurance training decreases the perceived exertion and dyspnea.Respiratory muscle endurance training can be considered as a worthwhile ergogenic aid for young competitive swimmers