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The Oxygen Uptake Plateau-A Critical Review of the Frequently Misunderstood Phenomenon.

ABSTRACT: A flattening of the oxygen uptake-work rate relationship at severe exercise indicates the achievement of maximum oxygen uptake [Formula: see text]. Unfortunately, a distinct plateau [Formula: see text] at [Formula: see text]is not found in all participants. The aim of this investigation was to critically review the influence of research methods and physiological factors on the [Formula: see text] incidence. It is shown that many studies used inappropriate definitions or methodical approaches to check for the occurrence of a [Formula: see text]. In contrast to the widespread assumptions it is unclear whether there is higher [Formula: see text] incidence in (uphill) running compared to cycling exercise or in discontinuous compared to continuous incremental exercise tests. Furthermore, most studies that evaluated the validity of supramaximal verification phases, reported verification bout durations, which are too short to ensure that [Formula: see text] have been achieved by all participants. As a result, there is little evidence for a higher [Formula: see text] incidence and a corresponding advantage for the diagnoses of [Formula: see text] when incremental tests are supplemented by supramaximal verification bouts. Preliminary evidence suggests that the occurrence of a [Formula: see text] in continuous incremental tests is determined by physiological factors like anaerobic capacity, [Formula: see text]-kinetics and accumulation of metabolites in the submaximal intensity domain. Subsequent studies should take more attention to the use of valid [Formula: see text] definitions, which require a cut-off at ~ 50% of the submaximal [Formula: see text] increase and rather large sampling intervals. Furthermore, if verification bouts are used to verify the achievement of [Formula: see text]/[Formula: see text], it should be ensured that they can be sustained for sufficient durations.

SUBMITTER: Niemeyer M

PROVIDER: S-EPMC8363556 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Leukocyte viability (determined by e.g. propidium iodide [PI] staining) is automatically measured by hematology analyzers to check for delayed bench time. Incidental findings in fresh blood samples revealed the existence of leukocytes with decreased viability in critically ill surgical patients. Not much is known about these cells and their functional and/or clinical implications. Therefore, we investigated the incidence of decreased leukocyte viability, the implications for leukocyte functioning and its relation with clinical outcomes. An automated alarm was set in a routine hematology analyzer (Cell-Dyn Sapphire) for the presence of non-viable leukocytes characterized by increased fluorescence in the PI-channel (FL3:630±30nm). Patients with non-viable leukocytes were prospectively included and blood samples were drawn to investigate leukocyte viability in detail and to investigate leukocyte functioning (phagocytosis and responsiveness to a bacterial stimulus). Then, a retrospective analysis was conducted to investigate the incidence of fragile neutrophils in the circulation and clinical outcomes of surgical patients with fragile neutrophils hospitalized between 2013-2017. A high FL3 signal was either caused by 1) neutrophil autofluorescence which was considered false positive, or by 2) actual non-viable PI-positive neutrophils in the blood sample. These two causes could be distinguished using automatically generated data from the hematology analyzer. The non-viable (PI-positive) neutrophils proved to be viable (PI-negative) in non-lysed blood samples, and were therefore referred to as 'fragile neutrophils'. Overall leukocyte functioning was not impaired in patients with fragile neutrophils. Of the 11 872 retrospectively included surgical patients, 75 (0.63%) were identified to have fragile neutrophils during hospitalization. Of all patients with fragile neutrophils, 75.7% developed an infection, 70.3% were admitted to the ICU and 31.3% died during hospitalization. In conclusion, fragile neutrophils occur in the circulation of critically ill surgical patients. These cells can be automatically detected during routine blood analyses and are an indicator of critical illness.

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The Oxygen Uptake Plateau-A Critical Review of the Frequently Misunderstood Phenomenon.

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