The control of luteal function during gestation in the guinea-pig

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Relationships between oxygen uptake kinetics and maximal oxygen uptake

[Extract] Oxygen uptake (VO₂) kinetics describe the characteristics of the rate of change of V0₂ in response to a change in work rate. Subjects attaining higher maximal oxygen uptake (V0₂max) have faster VO₂ kinetics (Eβfeld et al., 1987). The purpose of this study was to use the pseudo random binary sequence (PRBS) exercise test to examine the strength of the relationship between V0₂max and VO₂ kinetics in a homogenous group of young, healthy women

VO₂ kinetics expressed as MRT is correlated with VO₂max when measured using a PRBS protocol

[Extract] Oxygen uptake (VO₂) kinetics, measured using a pseudo-random binary sequence (PRBS) exercise test, has been proposed as a convenient low intensity method of determining cardiovascular fitness in sports people unwilling or unable to perform maximal exercise (Edwards et al., 1999). Although frequency domain analysis of PRBS exercise has shown that VO₂ kinetics are related to maximal oxygen uptake (VO₂max) (Eβfeld 1987), the application of the PRBS technique to assess cardiovascular (CV) fitness has been limited perhaps because of the difficulty of interpreting the frequency responses. Calculation of the mean response time (MRT) provides an alternative to frequency domain analysis (Hughson et al., 1991) and has the advantage of providing a single test measure of VO₂ kinetics, however this technique has not been widely used. The purpese of this study was to utilise MRT to examine the relationship between VO₂ kinetics and VO₂max

Gas exchange kinetics in elite runners

[Extract] Oxygen uptake (VO₂) kinetics, measured in the frequency domain, have been shown to be faster in elite endurance runners compared to elite sprinters (Edwards et al., 1999). Since carbon dioxide output (VCO₂) kinetics have been shown to be delayed following 6 months sprint and strength training in footballers (Fukuoka et al 1997) it might be expected that VCO₂ kinetics would also differentiate sprinters from endurance runners

Time domain analysis of oxygen uptake kinetics in elite runners by pseudo random binary sequence (PRBS) exercise

Oxygen uptake kinetics assessed in the frequency domain are known to be differentially faster in elite endurance runners than in elite sprinters. Breath-by-breath data from PRBS testing have routinely been analysed by application of Fourier methods, however, it is possible to analyse the data in the time domain in the form of a Total Lag Time (TLT). In this study, correlational techniques were applied to yield an output response to a work rate input. An autocorrelation function was performed on the input work rate (WR) and a cross correlation function was performed on input (WR) and output (vO₂). The cross correlation function was analysed by fitting a linear summation of the ramp form of a two-component exponential function to a triangular pulse. Twelve elite male sprinters and 12 elite male endurance runners completed 3 identical PRBS cycles of 300 s with 20 s work rate changes between 25 and 85 W on an electrically braked cycle ergometer at a pedal cadence of 1 Hz. Oxygen uptake was measured on a breath-by-breath basis using a respiratory mass spectrometer. Statistical analysis using the analysis of variance revealed significantly faster oxygen uptake kinetics (TLT) in the elite endurance runners compared with the elite sprinters (33.3 s 3.39SD and 39.91 s 7.14SD respectively) (p < 0.01). The results of this study show that time domain analysis represents a possible alternative to frequency analysis in the study of oxygen uptake kinetics described by PRBS exercise

The test-retest reliability of gas exchange kinetics in humans using a pseudo random binary sequence exercise test

The purpose of this study was to compare the test-retest reliability of oxygen uptake (VO2) kinetics with carbon dioxide output (VCO2) kinetics using a pseudo random binary sequence (PRBS) exercise test. A reliable test of gas exchange kinetics would have the potential of being applied as a sports fitness test. Ten healthy male subjects agreed to participate in the study and all subjects completed two identical PRBS exercise tests (test 1 and test 2), separated by a 30 min period of inactivity. Three consecutive 300 s PRBS cycles were completed in each test with 20 s exercise intensity changes between 25 and 85 W using an electrically braked cycle ergometer. Fourier analysis was computed for frequencies 3.3, 6.7 and 10 mHz. Statistical analysis by two-way ANOVA with repeated measures did not reveal significant differences between test 1 and test 2 for either VO2 kinetics or VCO2 kinetics. Static gain of VO2 for test 1 [9.11 (SD 0.59) ml.min-1.W-1] and test 2 [9.23 (SD 0.64) ml.min-1.W-1] did not differ significantly between tests. The 95% limits of agreement for VCO2 kinetics displayed increased variability in comparison to VO2 kinetics at each frequency of amplitude ratio and phase shift. Systematic bias ranged between 0% and 4%, except at frequency 10 mHz of VCO2 kinetics phase shift which showed a 10% bias for slower VO2 kinetics in test 2. It is possible that the increased variability of VCO2 kinetics compared to VO2 kinetics might be attributable to a lower signal to noise ratio in VCO2 kinetics, variations in ventilation or the storage mechanisms of CO2. The lower variability of VO2 kinetics compared with VCO2 kinetics suggests that the PRBS test of VO2 kinetics has the greater potential for further development as an indicator of aerobic fitness

Sport-specific fitness testing differentiates professional from amateur soccer players where VO2max and VO2 kinetics do not

AIM:\ud The purpose of this study was to identify if sport-specific and cardiopulmonary exercise testing differentiated professional from amateur soccer players.\ud \ud METHODS:\ud Thirty six men comprising 18 professional (mean±s: age 23.2±2.4 years) and 18 amateur (mean±SD: age 21.1±1.6 years) soccer players participated and performed four tests on separate occasions: 1) a graded exercise test to determine VO2max; 2) four exercise transients from walking to 80%Δ for the determination of VO2 kinetics; 3) the Yo-Yo Intermittent Recovery Test level 2 (Yo-Yo IR2) and 4) a repeated sprint test (RST).\ud \ud RESULTS:\ud The players did not differ in VO2max (professional 56.5±2.9 mL.kg-1.min-1; amateur 55.7±3.5 mL.kg-1.min-1: P=0.484) or VO2 kinetic fundamental measures (τ1 onset, professional 24.5±3.2 s; amateur 24.0±1.8 s: τ1 cessation, professional 28.7±2.8 s; amateur 29.3±3.5 s: P=0.923). However, the amateurs were outperformed in the Yo-Yo IR2 (Professional 966±153 m; Amateur 840±156 m) (P=0.034) and RST (best time, professional 6.46±0.27 s; amateur 6.84±0.24 s, P=0.012).\ud \ud CONCLUSION:\ud Performance indices derived from field-based sport-specific performance tests identified significant differences between professional and amateur players (P<0.05). However, neither tests of VO2 kinetics nor VO2max differentiated between groups, suggesting laboratory tests of cardiorespiratory parameters are probably less consequential to soccer than sport-specific field-based observations

Weaning from mechanical ventilation in intensive care units across 50 countries (WEAN SAFE): a multicentre, prospective, observational cohort study

International audienceBackground: Current management practices and outcomes in weaning from invasive mechanical ventilation are poorly understood. We aimed to describe the epidemiology, management, timings, risk for failure, and outcomes of weaning in patients requiring at least 2 days of invasive mechanical ventilation. Methods: WEAN SAFE was an international, multicentre, prospective, observational cohort study done in 481 intensive care units in 50 countries. Eligible participants were older than 16 years, admitted to a participating intensive care unit, and receiving mechanical ventilation for 2 calendar days or longer. We defined weaning initiation as the first attempt to separate a patient from the ventilator, successful weaning as no reintubation or death within 7 days of extubation, and weaning eligibility criteria based on positive end-expiratory pressure, fractional concentration of oxygen in inspired air, and vasopressors. The primary outcome was the proportion of patients successfully weaned at 90 days. Key secondary outcomes included weaning duration, timing of weaning events, factors associated with weaning delay and weaning failure, and hospital outcomes. This study is registered with ClinicalTrials.gov, NCT03255109. Findings: Between Oct 4, 2017, and June 25, 2018, 10 232 patients were screened for eligibility, of whom 5869 were enrolled. 4523 (77·1%) patients underwent at least one separation attempt and 3817 (65·0%) patients were successfully weaned from ventilation at day 90. 237 (4·0%) patients were transferred before any separation attempt, 153 (2·6%) were transferred after at least one separation attempt and not successfully weaned, and 1662 (28·3%) died while invasively ventilated. The median time from fulfilling weaning eligibility criteria to first separation attempt was 1 day (IQR 0–4), and 1013 (22·4%) patients had a delay in initiating first separation of 5 or more days. Of the 4523 (77·1%) patients with separation attempts, 2927 (64·7%) had a short wean (≤1 day), 457 (10·1%) had intermediate weaning (2–6 days), 433 (9·6%) required prolonged weaning (≥7 days), and 706 (15·6%) had weaning failure. Higher sedation scores were independently associated with delayed initiation of weaning. Delayed initiation of weaning and higher sedation scores were independently associated with weaning failure. 1742 (31·8%) of 5479 patients died in the intensive care unit and 2095 (38·3%) of 5465 patients died in hospital. Interpretation: In critically ill patients receiving at least 2 days of invasive mechanical ventilation, only 65% were weaned at 90 days. A better understanding of factors that delay the weaning process, such as delays in weaning initiation or excessive sedation levels, might improve weaning success rates. Funding: European Society of Intensive Care Medicine, European Respiratory Society