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

This 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 (CHOox, %CHO), and fat oxidation (FATox, %FAT) in nine individuals with obesity pre and post: 1) breathing normoxic air [normoxic sham control (NS-control)], 2) breathing continuous hypoxia (CH), or 3) breathing intermittent hypoxia (IH). A mean peripheral oxygen saturation ([Formula: see text]) of 80-85% was achieved over a total of 45 min of hypoxia. Throughout each intervention, pulmonary gas exchanges, oxygen consumption (V̇o2) carbon dioxide production (V̇co2), and deoxyhemoglobin concentration (Δ[HHb]) in the vastus lateralis were measured. Both RMR and CHOox measured pre- and postinterventions were unchanged following each treatment: NS-control, CH, or IH (all P > 0.05). Conversely, a significant increase in FATox was evident between pre- and post-IH (+44%, P = 0.048). Although the mean Δ[HHb] values significantly increased during both IH and CH (P < 0.05), the greatest zenith of Δ[HHb] was achieved in IH compared with CH (P = 0.002). Furthermore, there was a positive correlation between Δ[HHb] and the shift in FATox measured pre- and postintervention. It is suggested that during IH, the increased bouts of muscle hypoxia, revealed by elevated Δ[HHb], coupled with cyclic periods of excess posthypoxia oxygen consumption (EPHOC, inherent to the intermittent pattern) played a significant role in driving the increase in FATox post-IH.

Shadow electrochemiluminescence imaging of giant liposomes opening at polarized electrodes.

In this work, the release of giant liposome (∼100 µm in diameter) content was imaged by shadow electrochemiluminescence (ECL) microscopy. Giant unilamellar liposomes were pre-loaded with a sucrose solution and allowed to sediment at an ITO electrode surface immersed in a solution containing a luminophore ([Ru(bpy)3]2+) and a sacrificial co-reactant (tri-n-propylamine). Upon polarization, the electrode exhibited illumination over its entire surface thanks to the oxidation of ECL reagents. However, as soon as liposomes reached the electrode surface, dark spots appeared and then spread over time on the surface. This observation reflected a blockage of the electrode surface at the contact point between the liposome and the electrode surface, followed by the dilution of ECL reagents after the rupture of the liposome membrane and release of its internal ECL-inactive solution. Interestingly, ECL reappeared in areas where it initially faded, indicating back-diffusion of ECL reagents towards the previously diluted area and thus confirming liposome permeabilization. The whole process was analyzed qualitatively and quantitatively within the defined region of interest. Two mass transport regimes were identified: a gravity-driven spreading process when the liposome releases its content leading to ECL vanishing and a diffusive regime when ECL recovers. The reported shadow ECL microscopy should find promising applications for the imaging of transient events such as molecular species released by artificial or biological vesicles.

Electrochemiluminescent imaging of a NADH-based enzymatic reaction confined within giant liposomes.

Herein, transient releases either from NADH-loaded liposomes or enzymatic reactions confined in giant liposomes were imaged by electrochemiluminescence (ECL). NADH was first encapsulated with the [Ru(bpy)3]2+ luminophore inside giant liposomes (around 100 µm in diameter) made of DOPC/DOPG phospholipids (i.e., 1,2-dioleolyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycerol-3-phospho-(1'-rac-glycerol) sodium salt) on their inner- and outer-leaflet, respectively. Then, membrane permeabilization triggered upon contact between the liposome and a polarized ITO electrode surface and ECL was locally generated. Combination of amperometry, photoluminescence, and ECL provided a comprehensive monitoring of a single liposome opening and content release. In a second part, the work is focused on the ECL characterization of NADH produced by glucose dehydrogenase (GDH)-catalyzed oxidation of glucose in the confined environment delimited by the liposome membrane. This was achieved by encapsulating both the ECL and catalytic reagents (i.e., the GDH, glucose, NAD+, and [Ru(bpy)3]2+) in the liposome. In accordance with the results obtained, NADH can be used as a biologically compatible ECL co-reactant to image membrane permeabilization events of giant liposomes. Under these conditions, the ECL signal duration was rather long (around 10 s). Since many enzymatic reactions involve the NADH/NAD+ redox couple, this work opens up interesting prospects for the characterization of enzymatic reactions taking place notably in artificial cells and in confined environments.

Hot water immersion: Maintaining core body temperature above 38.5°C mitigates muscle fatigue.

PURPOSE: Hot water immersion (HWI) has gained popularity to promote muscle recovery, despite limited data on the optimal heat dose. The purpose of this study was to compare the responses of two exogenous heat strains on core body temperature, hemodynamic adjustments, and key functional markers of muscle recovery following exercise-induced muscle damage (EIMD). METHODS: Twenty-eight physically active males completed an individually tailored EIMD protocol immediately followed by one of the following recovery interventions: HWI (40°C, HWI40 ), HWI (41°C, HWI41 ) or warm water immersion (36°C, CON36 ). Gastrointestinal temperature (Tgi ), hemodynamic adjustments (cardiac output [CO], mean arterial pressure [MAP], and systemic vascular resistance [SVR]), pre-frontal cortex deoxyhemoglobin (HHb), ECG-derived respiratory frequency, and subjective perceptual measures were tracked throughout immersion. In addition, functional markers of muscle fatigue (maximal concentric peak torque [Tpeak ]) and muscle damage (late-phase rate of force development [RFD100-200 ]) were measured prior to EIMD (pre-), 24 h (post-24 h), and 48 h (post-48 h) post-EIMD. RESULTS: By the end of immersion, HWI41 led to significantly higher Tgi values than HWI40 (38.8 ± 0.1 vs. 38.0°C ± 0.6°C, p < 0.001). While MAP was well maintained throughout immersion, only HWI41 led to increased (HHb) (+4.2 ± 1.47 µM; p = 0.005) and respiratory frequency (+4.0 ± 1.21 breath.min-1 ; p = 0.032). Only HWI41 mitigated the decline in RFD100-200 at post-24 h (-7.1 ± 31.8%; p = 0.63) and Tpeak at post-48 h (-3.1 ± 4.3%, p = 1). CONCLUSION: In physically active males, maintaining a core body temperature of ~25 min within the range of 38.5°C-39°C has been found to be effective in improving muscle recovery, while minimizing the risk of excessive physiological heat strain.

Monitoring the Breath-Hold Training Load during an Ecological Session: A Pilot Study.

This study aimed to create a training load index to measure physiological stress during breath-hold (BH) training and examine its relationship with memory performance. Eighteen well-trained BH divers (Age: 35.8±6.6 years, BH training practice: 5.3±4.5 years) participated in this study. During a standard 1.5-hour BH training in the pool, perceived exertion, heart rate, distance, and duration were measured. The training load index was modelled on the basis of a TRIMP (TRaining IMPulse) with four different equations and was used to measure the stress induced by this BH training. A reference value, based on the ratio between the average heart rate during all BHs and the lowest heart rate during BH training, was used for comparing training load index. Memory assessment was conducted both before and after this training. Of the four equations proposed, equation no. 4, named aTRIMP for "apnoea," showed the strongest correlation with our reference value (r=0.652, p<0.01). No difference was found between any of the memory tests before and after the BH training. The aTRIMP was a new representative index for monitoring habitual training of well-trained BH divers. Furthermore, this training had no negative impact on memory performance.

Risk profiles of elite breath-hold divers.

This study aimed to determine a typical profile of elite breath-hold divers (BHDs), in relation to loss of consciousness (LOC) and episodic memory. Forty-four BHDs were evaluated during a world championship with anthropometric and physiological measurements, psychosociological factors and memory assessment. Seventy-five percent of the BHDs had at least one LOC with the predominance being men (p < 0.05). Thirty six percent of BHDs presented a low-risk profile and 64% a high-risk profile with no particular psychological pattern. Stepwise multiple linear regression showed that body fat, years of BH practice, age and forced vital capacity explained a significant amount of the variance of LOC for all BHDs (F(4,39) = 16.03, p < 0.001, R2 = 0.622, R2Adjusted = 0.583). No correlation was found between resting physiological parameters and their training or depth performances. In conclusion, anthropometric data, pulmonary factors and breath-holding experience were predictive of LOC in elite BHDs, with men taking more risks. BHDs episodic memory was not impaired.

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.

Dynamic Electrochemiluminescence Imaging of Single Giant Liposome Opening at Polarized Electrodes.

In this work, the characterization of release events from liposomes has been addressed quantitatively by an electrochemiluminescence (ECL) imaging strategy. First, ECL reagents ([Ru(bpy)3]2+ and tripropylamine) were encapsulated in sealed giant asymmetrical liposomes (100 µm in diameter) made of DOPG/DOPC phospholipids. After sedimentation on an indium tin oxide electrode material, the opening of liposomes was triggered by polarization of the surface. Under these conditions, amperometry, epifluorescence imaging, and ECL imaging were combined and synchronized to monitor and image the rupture of giant liposomes during the release and subsequent ECL emission of their redox content. Amperometry allowed the quantification of the content released from single liposomes. The location and status of liposomes (closed or opened) were assessed by epifluorescence imaging. ECL provided the image of the efflux of matter after liposome opening. This original ECL imaging approach favorably compares with strictly photoluminescent or electrochemical techniques and appears to be adapted for the investigation of membrane rupture/permeation events.

Electrochemical Fluorescence Switch of Organic Fluorescent or Fluorogenic Molecules.

This short review is aimed at emphasizing the most prominent recent works devoted to the fluorescence modulation of organic fluorescent or fluorogenic molecules by electrochemistry. This still expanding research field not only addresses the smart uses of known molecules or the design of new ones, but also investigates the development of instrumentation providing time- and space-resolved information at the molecular level. Important considerations including fluorescent/fluorogenic probes, reversible/irreversible fluorescence switch, direct/indirect fluorescence modulation, or environment properties are especially scrutinized in recent works dealing with bioanalysis perspectives.

Simulations of amperometric monitoring of exocytosis: moderate pH variations within the cell-electrode cleft with the buffer diffusion.

Amperometry with ultramicroelectrodes is nowadays a routine technique to investigate neurotransmitter secretion by vesicular exocytosis at the single-cell level. This electroanalytical tool allows one to understand many aspects of the vesicular release in terms of mechanisms. However, the electrochemical detection relies on the oxidation of released neurotransmitters that produce 2H+ and thus the possible acidification of the cell-electrode cleft. In a previous work, we considered a model involving the H+ diffusion or/and its reaction with buffer species. In this article, we report a more general model which takes into account the ability of buffer species to move and to be regenerated within the cell-electrode cleft. As a consequence, the pH within the cleft is still equal to its physiological value regardless of the electrochemical detection of the vesicular release for usual exocytotic cell frequencies. This confirms that amperometry at the single-cell level is a very robust technique for investigating vesicular exocytosis.

Exercise with End-expiratory Breath Holding Induces Large Increase in Stroke Volume.

Eight well-trained male cyclists participated in two testing sessions each including two sets of 10 cycle exercise bouts at 150% of maximal aerobic power. In the first session, subjects performed the exercise bouts with end-expiratory breath holding (EEBH) of maximal duration. Each exercise bout started at the onset of EEBH and ended at its release (mean duration: 9.6±0.9 s; range: 8.6-11.1 s). At the second testing session, subjects performed the exercise bouts (same duration as in the first session) with normal breathing. Heart rate, left ventricular stroke volume (LVSV), and cardiac output were continuously measured through bio-impedancemetry. Data were analysed for the 4 s preceding and following the end of each exercise bout. LVSV (peak values: 163±33 vs. 124±17 mL, p<0.01) was higher and heart rate lower both in the end phase and in the early recovery of the exercise bouts with EEBH as compared with exercise with normal breathing. Cardiac output was generally not different between exercise conditions. This study showed that performing maximal EEBH during high-intensity exercise led to a large increase in LVSV. This phenomenon is likely explained by greater left ventricular filling as a result of an augmented filling time and decreased right ventricular volume at peak EEBH.

Mediator-Microorganism Interaction in Microbial Solar Cell: a Fluo-Electrochemical Insight.

Microbial solar cells that mainly rely on the use of photosynthesic organisms are a promising alternative to photovoltaics for solar electricity production. In that way, we propose a new approach involving electrochemistry and fluorescence techniques. The coupled setup Electro-Pulse-Amplitude-Modulation ("e-PAM") enables the simultaneous recording of the produced photocurrent and fluorescence signals from the photosynthetic chain. This methodology was validated with a suspension of green alga Chlamydomonas reinhardtii in interaction with an exogenous redox mediator (2,6-dichlorobenzoquinone; DCBQ). The balance between photosynthetic chain events (PSII photochemical yield, quenching) and the extracted electricity can be monitored overtime. More particularly, the nonphotochemical quenching induced by DCBQ mirrors the photocurrent. This setup thus helps to distinguish the electron harvesting from some side effects due to quinones in real time. It therefore paves the way for future analyses devoted to the choice of the experimental conditions (redox mediator, photosynthetic organisms, and so on) to find the best electron extraction.

Effects of Breath-Hold Deep Diving on the Pulmonary System.

This short review focuses on pulmonary injury in breath-hold (BH) divers. When practicing their extreme leisure sport, they are exposed to increased pressure on pulmonary gas volumes, hypoxia, and increased partial gas pressures. Increasing ambient pressures do present a serious problem to BH deep divers, because the semi-rigid thorax prevents the deformation required by the Boyle-Mariotte law. As a result, a negative-pressure barotrauma (lung squeeze) with acute hemoptysis is not uncommon. Respiratory maneuvers such as glossopharyngeal insufflation (GI) and glossopharyngeal exsufflation (GE) are practiced to prevent lung squeeze and to permit equalizing the paranasal sinuses and the middle ear. GI not only impairs venous return, thereby provoking hypotension and even fainting, but also produces intrathoracic pressures likely to induce pulmonary barotrauma that is speculated to induce long-term injury. GE, in turn, further increases the already negative intrapulmonary pressure, thereby favoring alveolar collapse (atelectasis). Finally, hypoxia seemingly not only induces brain injury but initiates the opening of intrapulmonary shunts. These pathways are large enough to permit transpulmonary passage of venous N2 bubbles, making stroke-like phenomena in deep BH divers possible.

Downstream Simultaneous Electrochemical Detection of Primary Reactive Oxygen and Nitrogen Species Released by Cell Populations in an Integrated Microfluidic Device.

An innovative microfluidic platform was designed to monitor electrochemically four primary reactive oxygen (ROS) and reactive nitrogen species (RNS) released by aerobic cells. Taking advantage of the space confinement and electrode performances under flow conditions, only a few experiments were sufficient to directly provide significant statistical data relative to the average behavior of cells during oxidative-stress bursts. The microfluidic platform comprised an upstream microchamber for cell culture and four parallel microchannels located downstream for separately detecting H2O2, ONOO-, NO·, and NO2-. Amperometric measurements were performed at highly sensitive Pt-black electrodes implemented in the microchannels. RAW 264.7 macrophage secretions triggered by a calcium ionophore were used as a way to assess the performance, sensitivity, and specificity of the integrated microfluidic device. In comparison with some previous evaluations achieved from single-cell measurements, reproducible and relevant determinations validated the proof of concept of this microfluidic platform for analyzing statistically significant oxidative-stress responses of various cell types.

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

PURPOSE: The study aims to investigate the effects of moderate intermittent hypoxia (IH) on key cardio-metabolic risk factors in overweight and obese subjects. METHODS: Six subjects were exposed to 10 sessions of moderate IH over 2 weeks (based on [Formula: see text]; ~70 min per session). Measures were made of blood glucose (GLU) and lactate (La-); high (HDLc) and low-density lipoproteins (LDLc); triglycerides (TRG), systolic (SBP), and diastolic blood pressure (DBP); and cardiac autonomic indices [root mean square of successive R-R interval differences (RMSSD) and short-term fractal scaling exponent (DFAα1)]. RESULTS: GLU decreased and La- increased following a single IH session (6.21 ± 1.62 vs. 5.32 ± 1.03 mmol L-1; p < 0.05; 1.14 ± 0.21 vs. 1.47 ± 0.22 mmol L-1), but no sustained change after 10 sessions of IH occurred (p > 0.05). Conversely, LDLc (3.00 ± 0.68 vs. 2.51 ± 0.60 mmol L-1; p < 0.05), LDLc/HDLc ratio (2.52 ± 0.66 vs. 2.26 ± 0.70 mmol L-1; p < 0.05), and SBP (118.6 ± 13.3 vs. 109.6 ± 11.3 mmHg; p < 0.05) were all significantly decreased after 10 sessions. CONCLUSION: A short course of recurrent IH appears to be a safe and effective non-pharmacological method of reducing key cardiovascular risk factors associated with metabolic disorders.

Electrocatalytic Mechanism Involving Michaelis-Menten Kinetics at the Preparative Scale: Theory and Applicability to Photocurrents from a Photosynthetic Algae Suspension With Quinones.

In the past years, many strategies have been implemented to benefit from oxygenic photosynthesis to harvest photosynthetic electrons and produce a significant photocurrent. Therefore, electrochemical tools were considered and have globally relied on the electron transfer(s) between the photosynthetic chain and a collecting electrode. In this context, we recently reported the implementation of an electrochemical set-up at the preparative scale to produce photocurrents from a Chlamydomonas reinhardtii algae suspension with an appropriate mediator (2,6-DCBQ) and a carbon gauze as the working electrode. In the present work, we wish to describe a mathematical modeling of the recorded photocurrents to better understand the effects of the experimental conditions on the photosynthetic extraction of electrons. In that way, we established a general model of an electrocatalytic mechanism at the preparative scale (that is, assuming a homogenous bulk solution at any time and a constant diffusion layer, both assumptions being valid under forced convection) in which the chemical step involves a Michaelis-Menten-like behaviour. Dependences of transient and steady-state corresponding currents were analysed as a function of different parameters by means of zone diagrams. This model was tested to our experimental data related to photosynthesis. The corresponding results suggest that competitive pathways beyond photosynthetic harvesting alone should be taken into account.

The oxygen-conserving potential of the diving response: A kinetic-based analysis.

We investigated the oxygen-conserving potential of the human diving response by comparing trained breath-hold divers (BHDs) to non-divers (NDs) during simulated dynamic breath-holding (BH). Changes in haemodynamics [heart rate (HR), stroke volume (SV), cardiac output (CO)] and peripheral muscle oxygenation [oxyhaemoglobin ([HbO2]), deoxyhaemoglobin ([HHb]), total haemoglobin ([tHb]), tissue saturation index (TSI)] and peripheral oxygen saturation (SpO2) were continuously recorded during simulated dynamic BH. BHDs showed a breaking point in HR kinetics at mid-BH immediately preceding a more pronounced drop in HR (-0.86 bpm.%-1) while HR kinetics in NDs steadily decreased throughout BH (-0.47 bpm.%-1). By contrast, SV remained unchanged during BH in both groups (all P > 0.05). Near-infrared spectroscopy (NIRS) results (mean ± SD) expressed as percentage changes from the initial values showed a lower [HHb] increase for BHDs than for NDs at the cessation of BH (+24.0 ± 10.1 vs. +39.2 ± 9.6%, respectively; P < 0.05). As a result, BHDs showed a [tHb] drop that NDs did not at the end of BH (-7.3 ± 3.2 vs. -3.0 ± 4.7%, respectively; P < 0.05). The most striking finding of the present study was that BHDs presented an increase in oxygen-conserving efficiency due to substantial shifts in both cardiac and peripheral haemodynamics during simulated BH. In addition, the kinetic-based approach we used provides further credence to the concept of an "oxygen-conserving breaking point" in the human diving response.

A Dual Functional Electroactive and Fluorescent Probe for Coupled Measurements of Vesicular Exocytosis with High Spatial and Temporal Resolution.

In this work, Fluorescent False Neurotransmitter 102 (FFN102), a synthesized analogue of biogenic neurotransmitters, was demonstrated to show both pH-dependent fluorescence and electroactivity. To study secretory behaviors at the single-vesicle level, FFN102 was employed as a new fluorescent/electroactive dual probe in a coupled technique (amperometry and total internal reflection fluorescence microscopy (TIRFM)). We used N13 cells, a stable clone of BON cells, to specifically accumulate FFN102 into their secretory vesicles, and then optical and electrochemical measurements of vesicular exocytosis were experimentally achieved by using indium tin oxide (ITO) transparent electrodes. Upon stimulation, FFN102 started to diffuse out from the acidic intravesicular microenvironment to the neutral extracellular space, leading to fluorescent emissions and to the electrochemical oxidation signals that were simultaneously collected from the ITO electrode surface. The correlation of fluorescence and amperometric signals resulting from the FFN102 probe allows real-time monitoring of single exocytotic events with both high spatial and temporal resolution. This work opens new possibilities in the investigation of exocytotic mechanisms.

Vesicular exocytosis and microdevices - microelectrode arrays.

Among all the analytical techniques capable of monitoring exocytosis in real time at the single cell level, electrochemistry (particularly amperometry at a constant potential) using ultramicroelectrodes has been demonstrated to be an important and convenient tool for more than two decades. Indeed, because the electrochemical sensor is located in the close vicinity of the emitting cell ("artificial synapse" configuration), much data can be gathered from the whole cell activity (secretion frequency) to the individual vesicular release (duration, fluxes or amount of molecules released) with an excellent sensitivity. However, such a single cell analysis and its intrinsic benefits are at the expense of the spatial resolution and/or the number of experiments. The quite recent development of microdevices/microsystems (and mainly the microelectrode arrays (MEAs)) offers in some way a complementary approach either by combining spectroscopy-microscopy or by implementing a multianalysis. Such developments are described and discussed in the present review over the 2005-2014 period.

Ischaemia-modified albumin during experimental apnoea.

Ischaemia-modified albumin (IMA) is a marker of the release of reactive oxygen species (ROS) during hypoxaemia. In elite divers, breath-hold induces ROS production. Our aim was to evaluate the kinetics of IMA serum levels during apnea. Twenty breath-hold divers were instructed to perform a submaximal static breath-hold. Twenty non-diver subjects served as controls. Blood samples were collected at rest, every minute, at the end of breath-hold, and 10 min after recovery. The IMA level increased after 1 min of breath-hold (p < 0.003) and remained high until recovery. Divers were separated into 2 groups: subjects who held their breath for less than 4 min (G-4) and those who held it for more than 4 min (G+4). After 3 min of apnoea, the increase of IMA was higher in the G-4 group than in the G+4 group (p < 0.008). However, at the end of apnoea, the IMA level did not differ between groups. If IMA level was globally correlated with the apnoea duration, it is interesting to note that the higher IMA level was not found in the best divers. Similarly, if arterial blood oxygen saturation (SpO2) was globally inversely correlated with apnoea duration, the lowest SpO2 at the end of breath-hold was not found in the divers that performed the best apnoea. We concluded that these divers save their oxygen. The IMA level provides a useful measure of resistance to hypoxaemia.