1,721,005 research outputs found
The decrease of maximal oxygen consumption in hypoxia : a mirror image of the oxygen equilibrium curve.
No full textEffects of prolonged bed rest on cardiovascular oxygen transport during submaximal exercise in humans
No full texthe hypothesis was tested that prolonged bed rest impairs O2 transport during exercise, which implies a lowering of cardiac output Qc and O2 delivery (QaO2). The following parameters were determined in five males at rest and at the steady-state of the 100-W exercise before (B) and after (A) 42-day bed rest with head-down tilt at -6 degrees: O2 consumption (VO2), by a standard open-circuit method; Qc, by the pressure pulse contour method, heart rate (fc), stroke volume (Qh), arterial O2 saturation, blood haemoglobin concentration ([Hb]), arterial O2 concentration (CaO2), and QaO2. The VO2 was the same in A and in B, as was the resting fc. The fc at 100 W was higher in A than in B (+17.5%). The Qh was markedly reduced (-27.7% and -22.2% at rest and 100 W, respectively). The Qc was lower in A than in B [-27.6% and -7.8% (NS) at rest and 100 W, respectively]. The CaO2 was lower in A than in B because of the reduction in [Hb]. Thus also QaO2 was lower in A than in B (-32.0% and -11.9% at rest and at 100 W, respectively). The present results would suggest a down-regulation of the O2 transport system after bed rest
Effects of step duration in incremental ramp protocols on peak power and maximal oxygen consumption
No full textA new interpolation-free procedure for breath-by-breath analysis of V’O2 in exercise transients
No full textIntroduction. Interpolation methods circumvent poor time resolution of breath-by-breath oxygen uptake (VO2) kinetics at exercise onset. We report an interpolation-free approach to the improvement of poor time resolution in the analysis of VO2 kinetics.
Methods. Noiseless and noisy (10% Gaussian noise) synthetic data were generated by Monte Carlo method from pre-selected parameters (Exact Parameters). Each data set comprised 10 O2-on transitions with noisy breath distribution within a physiological range. Transitions were superposed (no interpolation, None), then analysed by bi-exponential model. Fitted model parameters were compared with those from interpolation methods (average transition after Linear or Step 1-sec interpolations), applied on the same data. Experimental data during cycling were also analysed. The 95% confidence interval around a line of parameters’ equality was computed to analyse agreement between exact parameters and corresponding parameters of fitted functions.
Results. The line of parameters’ equality stayed within confidence intervals for noiseless synthetic parameters with None, unlike Step and Linear, indicating that None reproduced Exact Parameters. Noise addition reduced differences among pre-treatment procedures. Experimental data provided lower phase I time constants with None than with Step.
Conclusion. In conclusion, None revealed better precision and accuracy than Step and Linear, especially when phenomena characterized by time constants of less than 30 sec are to be analysed. Therefore, we endorse the utilization of None to improve the quality of breath-by-breath VO2 data during exercise transients, especially when a double exponential model is applied and phase I is accounted for
CARDIOVASCULAR ADJUSTMENTS TO AND FROM PROLONGED DRY AND IMMERSED APNOEA IN RESTING BREATH-HOLD DIVERS
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