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

High arterial CO2 pressure (PaCO2) measured in athletes during exercise suggests inadequate hyperventilation. End-tidal CO2 pressure (P ET CO2) is used to estimate PaCO2 However, PETCO2 also depends on exercise intensity (CO2 production, V̇CO2) and ventilation efficiency (being PETCO2 function of respiratory rate). We evaluated PETCO2 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 PETCO2 at respiratory compensation (RC): Group 1 (PETCO2 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 (V̇) was similar, but in Group 3, a greater tidal volume (Vt) and lower respiratory rate (RR) were observed. Peak exercise workload and V̇O2 were lowest in Group 1 and similar between Group 2 and 3. Group 3 subjects also showed high peak V̇CO2 suggesting a greater glycolytic metabolism. In conclusion, a high PETCO2 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.