Estimating Arterial PCO2 from Flow-Weighted and Time-Average Alveolar PCO2 During Exercise

Effect of exercise intensity on the changes in alveolar slopes of carbon dioxide and oxygen expiratory profiles in humans

“…At rest and during exercise, the FO 2 and FCO 2 during the alveolar phase (phase III) of the respiratory cycle normally do not attain a real plateau but show an increase throughout this phase ( Fig. 1) (DeVries et al 1982;Cochrane et al 1982;Allen et al 1984;Whipp et al 1988). The details of these changes can now be assessed as more rapid and accurate breath-by-breath measurements of alveolar gas content are feasible.…”

“…The change in alveolar FCO 2 and FO 2 was determined by setting a cursor at the beginning of the alveolar phase of the respiration and again at its end 1979; Caruthers et al 1995;St.Croix et al 1995), the P A CO 2 is subject to intra-breath-variations due to continuing gas exchange during the breath even in thè`i deal'' lung (DuBois et al 1952;Hill et al 1973;Allen et al 1984;Grùnlund et al 1987;Whipp et al 1988). However, during exercise the P ET CO 2 can exceed the arterial PCO 2 or mean P A CO 2 by 6 mmHg or more (Whipp et al 1988). Therefore, it has been proposed that a mean P A CO 2 could be determined from the reconstructed intra-breath time-pro®le of changes in PCO 2 (DuBois et al 1952;Cochrane et al 1982;Whipp et al 1988;Robbins et al 1990).…”

“…However, during exercise the P ET CO 2 can exceed the arterial PCO 2 or mean P A CO 2 by 6 mmHg or more (Whipp et al 1988). Therefore, it has been proposed that a mean P A CO 2 could be determined from the reconstructed intra-breath time-pro®le of changes in PCO 2 (DuBois et al 1952;Cochrane et al 1982;Whipp et al 1988;Robbins et al 1990).…”

“…The anatomical or series dead space of the lung (Fowler 1948) 4. The mean P A CO 2 either for itself or its relationship to arterial PCO 2 (DuBois et al 1952;Cumming et al 1985;Whipp et al 1988;Robbins et al 1990). …”

Is breath-hold time an objective index of exertional dyspnoea in humans?

“…It is widely recognised that end-tidal gas tensions will be markedly dierent from the corresponding arterial values during exercise (e.g. Jones et al 1979;Whipp et al 1990). As a result of a breath-hold, however, these dierences are likely to be markedly reduced, if not abolished, on the ®rst (and rapid) postbreath-hold exhalation.…”