Browsing by Subject "deoxygenation"

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  • Jilbert, Tom; Gustafsson, Bo G.; Veldhuijzen, Simon; Reed, Daniel C.; Helmond, Niels A. G. M.; Hermans, Martijn; Slomp, Caroline P. (2021)
    Hypoxia has occurred intermittently in the Baltic Sea since the establishment of brackish-water conditions at similar to 8,000 years B.P., principally as recurrent hypoxic events during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA). Sedimentary phosphorus release has been implicated as a key driver of these events, but previous paleoenvironmental reconstructions have lacked the sampling resolution to investigate feedbacks in past iron-phosphorus cycling on short timescales. Here we employ Laser Ablation (LA)-ICP-MS scanning of sediment cores to generate ultra-high resolution geochemical records of past hypoxic events. We show that in-phase multidecadal oscillations in hypoxia intensity and iron-phosphorus cycling occurred throughout these events. Using a box model, we demonstrate that such oscillations were likely driven by instabilities in the dynamics of iron-phosphorus cycling under preindustrial phosphorus loads, and modulated by external climate forcing. Oscillatory behavior could complicate the recovery from hypoxia during future trajectories of external loading reductions.
  • Rissanen, Antti-Pekka; Tikkanen, Heikki Olavi; Koponen, Anne S.; Aho, Jyrki M.; Peltonen, Juha E. (2018)
    Adaptations to long-term exercise training in type 1 diabetes are sparsely studied. We examined the effects of a 1-year individualized training intervention on cardiorespiratory fitness, exercise-induced active muscle deoxygenation, and glycemic control in adults with and without type 1 diabetes. Eight men with type 1 diabetes (T1D) and 8 healthy men (CON) matched for age, anthropometry, and peak pulmonary O-2 uptake, completed a 1-year individualized training intervention in an unsupervised real-world setting. Before and after the intervention, the subjects performed a maximal incremental cycling test, during which alveolar gas exchange (volume turbine and mass spectrometry) and relative concentration changes in active leg muscle deoxygenated (Delta[HHb]) and total (Delta[tHb]) hemoglobin (near-infrared spectroscopy) were monitored. Peak O-2 pulse, reflecting peak stroke volume, was calculated (peak pulmonary O-2 uptake/peak heart rate). Glycemic control (glycosylated hemoglobin A(1c) (HbA(1c))) was evaluated. Both T1D and CON averagely performed 1 resistance-training and 3-4 endurance-training sessions per week (similar to 1 h/session at similar to moderate intensity). Training increased peak pulmonary O-2 uptake in T1D (p = 0.004) and CON (p = 0.045) (group x time p = 0.677). Peak O-2 pulse also rose in T1D (p = 0.032) and CON (p = 0.018) (group x time p = 0.880). Training increased leg Delta[HHb] at peak exercise in CON (p = 0.039) but not in T1D (group x time p = 0.052), while no changes in leg Delta[tHb] at any work rate were observed in either group (p > 0.05). HbA(1c) retained unchanged in T1D (from 58 +/- 10 to 59 +/- 11 mmol/mol, p = 0.609). In conclusion, 1-year adherence to exercise training enhanced cardiorespiratory fitness similarly in T1D and CON but had no effect on active muscle deoxygenation or glycemic control in T1D.