Hypercapnia during maximal exercise in patients with chronic airflow obstruction.

The pattern of breathing during maximal oxygen uptake (Vo2max) was studied in 26 patients with chronic airflow obstruction (CAO), in whom the vital capacity (VC), forced expiratory volume in 1 s (FEV1) and residual volume (RV) were measured. The patients performed, on a cycle ergometer, in a sitting position, a submaximal (A) and a maximal (B) exercise in a single session during which three arterial blood samples (pH, PaCO2, PaO2, lactate) were taken: the first at rest, the second at the 10th min of steady-state 40 W exercise, and the third at maximal VO2. VE, VCO2, VO2, respiratory rate (RR) and VT were measured with an open circuit. Physiological dead space (VD) and alveolar to arterial O2 pressure differences (A-aPO2) were computed. According to the measured value of PaCO2 at maximal exercise, the patients were divided in non-hypercapnic (NH; PaCO2 less than 44 mmHg; n = 17) and hypercapnic (H; PaCO2 greater than 44 mmHg; n = 9) groups, and were compared with a group of normal subjects (N; n = 11). At rest, VC, FEV1, FEV1/VC ratio, TLC and PaO2 were more decreased in H than in NH patients. However, RV, VE, RR and VT did not differ between H and NH patients. PaCO2 at rest was comparable in N and H subjects but was significantly lower in NH patients. During B exercise, VE, VO2 and PaO2 were lower in H patients. With both A and B exercises, the H patients showed a lower VT and VT/VC ratio with a higher VD/VT ratio, while A-aPO2 were the same in NH and H patients.(ABSTRACT TRUNCATED AT 250 WORDS)