Oxygen Transport in Normobaric versus Hypobaric Hypoxia

BACKGROUND: Various physiological changes occur in the human body when ascending to altitude. Exposure to hypoxia increases heart rate and decreases arterial oxygen saturation (SaO2), with both changes being expedited during exercise. Incremental exercise in ambient conditions decreases muscle oxygenation, specifically with increasing intensity. Previous research has examined heart rate and SaO2 in response to normobaric versus hypobaric hypoxia. However, there is lack of research examining muscle oxygenation in response to these conditions. Therefore, additional research investigating acute responses to normobaric and hypobaric hypoxia during exercise is warranted. PURPOSE: To examine acute responses in arterial and muscle tissue oxygenation during incremental exercise in normobaric versus hypobaric hypoxia. METHODS: Eight recreationally active males and females between the ages of 19 and 45 will be recruited. Subjects will complete an incremental cycle test to volitional fatigue in three conditions in a randomized counter balanced order, normobaric normoxia (20.9% O2, 760 mmHg), normobaric hypoxia (14.3% O2, 760 mmHg) and hypobaric hypoxia (20.9% O2, 530mmHg). Two of the three trials will be conducted in an environmental chamber (Darwin, St. Louis, MO) to simulate normobaric normoxia at 350 m and normobaric hypoxia at 3094 m. The third trial will be conducted in Leadville, Colorado at 3094 m. Rating of perceived exertion, heart rate, blood oxygenation, respiration rate, muscle tissue oxygenation and whole body gases will be analyzed during the trials

Effect of inlet conditions on taylor bubble length in microchannels

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.The effect of inlet conditions on the frequency and size of the bubbles that form during gas-liquid Taylor flow in microchannels is investigated in this paper. Three different inlet configurations, T-, Y- and Mjunction as well as three test channels with hydraulic diameters 0.345mm, 0.577mm and 0.816mm were used. The test fluids were nitrogen and water or octane, that have different surface tension. It was found that bubble length increased with increasing gas flowrate, gas inlet size and liquid surface tension and decreasing liquid flowrate. From the different inlet configurations, the M-junction resulted in the largest bubbles and the Y-junction in the smallest ones particularly at low liquid flowrates. The experimental bubble sizes were tested against a number of literature correlations but the agreement was not very good. Two new correlations were developed for the T- and the Y-junctions to calculate the unit cell (one bubble and one slug) frequency from which the bubble length can be found. Bubble lengths predicted from these correlations were in good agreement with experimental ones obtained from video recordings

Simplified mechanistic model for the separation of dispersed oil-water horizontal pipe flows

A mechanistic model that predicts the separation of oil-water dispersed horizontal pipe flows was investigated. Different droplet diameter averages were implemented in the model and the accuracy of the resulting predictions was assessed by comparing each case against experimental data. The experimental data used was obtained in a pilot scale two-phase flow facility using tap water and oil (828 kg m-3, 5.5 mPa s) as test fluids. The results show that the separation length is highly sensitive to the drop diameter, but further investigation is required to determine which drop diameter average produces more accurate predictions of the flow profile

On path-complete Lyapunov functions: geometry and comparison

We study optimization-based criteria for the stability of switching systems, known as Path-Complete Lyapunov Functions, and ask the question “can we decide algorithmically when a criterion is less conservative than another'”. Our contribution is twofold. First, we show that a Path-Complete Lyapunov Function, which is a multiple Lyapunov function by nature, can always be expressed as a common Lyapunov function taking the form of a combination of minima and maxima of the elementary functions that compose it. Geometrically, our results provide for each Path-Complete criterion an implied invariant set. Second, we provide a linear programming criterion allowing to compare the conservativeness of two arbitrary given Path-Complete Lyapunov functions

Low temperature steam reforming of methane : A combined isotopic and microkinetic study

The authors would like to acknowledge Professors Joris W. Thybaut and Guy B. Marin, Laboratory for Chemical Technology of Ghent University, for providing the Micro-Kinetic Engine (MKE) code based on which the model presented in the current work has been developed.Peer reviewedPostprin

Higher Muscle Tissue Oxygenation When Exposed to Hypobaric Hypoxia Than Normobaric Hypoxia

There has been recent debate on the potential difference in physiological response between exposure to simulated altitude (normobaric hypoxia) and terrestrial altitude (hypobaric hypoxia). Purpose: To determine the difference in the physiological response to normobaric and hypobaric hypoxia during exercise. Methods: Eight recreationally active subjects (27 ± 5 y old, 73.1 ± 7.4 kg body weight, 170.6 ± 6.7 cm height, and 19.3 ± 9.2 % body fat) completed incremental cycling exercise to volitional fatigue in three separate environments: normobaric normoxia (NN; 350 m), normobaric hypoxia (NH; simulated 3094 m), and hypobaric hypoxia (HH; 3094 m). Heart rate, blood oxygen saturation, and muscle tissue oxygenation were measured at rest and continuously throughout the exercise trials. Results: Blood oxygen saturation (SpO2) was ~10% higher in NN compared to the two hypoxic conditions (p \u3c 0.001) at rest and all exercise stages, with no difference between NH and HH (p \u3e 0.05). Heart rate was higher at rest in HH (98 ± 13 bpm) compared to NN (83 ± 15 bpm, p = 0.011) and NH (84 ± 14 bpm, p = 0.001) which persisted until 165 watts at which point no difference was observed (p \u3e 0.05). Muscle tissue oxygenation was 17% higher in HH compared to NN and 19% higher than NH throughout exposure (p \u3c 0.05). Conclusion: This data indicates that the hypoxic stress resulting from normobaric and hypobaric hypoxia are not the sameand that hypobaric hypoxia may not result in hypoxia at the level of the tissue

Expression of a catalytically inactive mutant form of glutathione peroxidase 4 (Gpx4) confers a dominant-negative effect in male fertility.

The selenoenzyme Gpx4 is essential for early embryogenesis and cell viability for its unique function to prevent phospholipid oxidation. Recently, the cytosolic form of Gpx4 was identified as an upstream regulator of a novel form of non-apoptotic cell death, called ferroptosis, whereas the mitochondrial isoform of Gpx4 (mGpx4) was previously shown to be crucial for male fertility. Here, we generated and analyzed mice with targeted mutation of the active site selenocysteine (Sec) of Gpx4 (Gpx4_U46S). Mice homozygous for Gpx4_U46S died at the same embryonic stage (E7.5) as Gpx4-/- embryos as expected. Surprisingly, male mice heterozygous for Gpx4_U46S presented subfertility. Subfertility was manifested in a reduced number of litters from heterozygous breedings and an impairment of spermatozoa to fertilize oocytes in vitro. Morphologically, sperm isolated from heterozygous Gpx4_U46S mice revealed many structural abnormalities particularly in the spermatozoan midpiece due to improper oxidation and polymerization of sperm capsular proteins and malformation of the mitochondrial capsule surrounding and stabilizing sperm mitochondria. These findings are reminiscent of sperm isolated from selenium-deprived rodents or from mice specifically lacking mGpx4. Due to a strongly facilitated incorporation of Ser in the polypeptide chain as compared to Sec at the UGA codon, expression of the catalytically inactive Gpx4_U46S was found to be strongly increased. Since the stability of the mitochondrial capsule of mature spermatozoa depends on the moonlighting function of Gpx4 both as an enzyme oxidizing capsular protein thiols and being a structural protein, tightly controlled expression of functional Gpx4 emerges being key for full male fertility

GEOMATIC TECHNIQUES FOR THE OPTIMIZATION OF SKI RESOURCES

Climate change is already affecting the entire world, with extreme weather conditions such as drought, heat waves, heavy rain, floods and landslides becoming more frequent, including Europe. In according to Paris agreement and relative European announcement of Carbon neutrality (by 2050), the saving of water and energy supplies is a fundamental aspect in the management of resources in production, sports, hospitality facilities and so on. Some methodologies for the optimization of the consumption of natural resources are required. This article describes an activity aimed at measuring, monitoring and analysing the thickness of the snowpack on the ski slopes during the winter season to permit a sustainable approach of snowmaking in alpine ski areas . The authors propose a methodology based on the integration of multitemporal surface (ground/snow) survey by Autonomous Aerial Vehicle (AAV) and low cost GNSS receivers mounted on snow groomers for a RTK (Real Time Kinematic) solution. To obtain a complete snow surface digital models with poor detailed images on ski slopes, some pre-processing techniques have been analysed to locally improve contrast and details with a local high pass filtering. The methodology has been employed in two study areas (Limone Piemonte, Prato Nevoso) located in the province of Cuneo, in the southern alpine area of Piedmont