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

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