End-tidal pressure of CO₂ and exercise performance in healthy subjects

Abstract

High arterial CO₂ pressure (P _aCO₂) measured in athletes during exercise suggests inadequate hyperventilation. End-tidal CO₂ pressure (P _ETCO₂) is used to estimate P _aCO_2. However, P _ETCO₂ also depends on exercise intensity (CO₂ production, $\dot V{\text{CO}}_2$) and ventilation efficiency (being P _ETCO₂ function of respiratory rate). We evaluated P _ETCO₂ as a marker, which combines efficiency of ventilation and performance. A total of 45 well-trained volunteers underwent cardiopulmonary tests and were grouped according to P _ETCO₂ at respiratory compensation (RC): Group 1 (P _ETCO₂ 35.1–41.5 mmHg), Group 2 (41.6–45.7) and Group 3 (45.8–62.6). At anaerobic threshold, RC and peak exercise, ventilation ($\dot V{\text{E}}$) was similar, but in Group 3, a greater tidal volume (Vt) and lower respiratory rate (RR) were observed. Peak exercise workload and $\dot V{\text{O}}_2$ were lowest in Group 1 and similar between Group 2 and 3. Group 3 subjects also showed high peak $\dot V{\text{CO}}_2$ suggesting a greater glycolytic metabolism. In conclusion, a high P _ETCO₂ during exercise is useful in identifying a specific respiratory pattern characterized by high tidal volume and low respiratory rate. This respiratory pattern may belong to subjects with potential high performance.