Insight into oxygen deficit from phase relations between cardiopulmonary variables during intermittent exercise

Résumé fourni par la source

Background: At the start of exercise, individuals build up a certain level of O2 deficit, depending on their adaptation ability to the new physiological state. A greater O2 deficit represents slower V’O2 kinetics and is influenced by ventilation, diffusion, circulation and O­2-consumption by the muscles, but the interaction and to what extent each system contributes remains unclear. Aims and objectives: This study investigates the time-relations between periodic changes in cardiopulmonary variables during intermittent exercise, expressed by gain and phase. Methods: Ten healthy individuals performed four interval tests (6x1.5 minute of loaded or unloaded exercise). Measured were V’O2, V’CO2, tidal volume, breathing rate, heart rate and expiratory pressures. Tests were conducted in either supine or upright position and at moderate or high workload. The gain and phase relations between the measured parameters were calculated using MATLAB to assess their contribution to the O2 deficit. Results: Phase differences (φdiff) showed that mixed-expiratory PO2 responds earlier than V’O2 to the increased workrate (φdiff=17°, p<0.001), HR responds a bit earlier (φdiff=6°, p=0.09), and mixed-expiratory PCO2, V’CO2 and total ventilation respond later than V’O2 (φdiff=-16°, p=0.002, φdiff=-22°, p<0.001 and φdiff=-25°, p=0.002). The gain and phase between most cardiopulmonary parameters remained stable across the different positions and workloads. Conclusion: Mixed-expiratory PO2 precedes an increase in HR and VO2, which can be the trigger of the primary cardial and ventilatory responses, opposed to the often described PCO2. Cardiopulmonary kinetics seem stable across different workloads and positions.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.