Study objectives: To compare arterial blood gas (ABG) and pulmonary gas exchange variables (alveolar-arterial oxygen pressure difference [P(A-a)O2] and physiologic dead space to tidal volume ratio [VD/VT]) measured during incremental exercise test (IET) and constant work (CW) exercise at a matched oxygen uptake (Vo2).
Design: A comparison of IET and CW variables was accomplished using patient data from clinical referrals for cardiopulmonary exercise testing and control data not reported from a previous study.
Settings: El Paso, Tex, located at an altitude of 1,270 m (barometric pressure, 656 mm Hg).
Participants: Sixteen patients with dyspnea on exertion/exercise intolerance and nine normal subjects were evaluated above the anaerobic threshold (AT); seven patients were also studied below the AT.
Interventions: Participants had a maximal IET followed in 1 h by a 5-min CW test. Arterial blood samples were obtained from a radial catheter every other minute during IET and during minute 5 of CW. Cardiopulmonary measurements were obtained using an automated system in a breath-by-breath fashion (60-s averaging).
Results: Above the AT, no differences were observed in normal subjects between IET and CW at a matched Vo2 in the following: PaO2 (79 vs 79 mm Hg); arterial oxygen saturation (Sa02) (94% vs 94%); P(A-a)O2 (16 vs 16 mm Hg); and VD/VT (0.09 vs 0.09) (mean values). Similarly, no differences were observed in patients above the AT in PaO2 (69 vs 68), SaO2 (90 vs 90), and VD/VT (0.24 vs 0.23). PaCO2 was 2 mm Hg higher (36 vs 34) in normal subjects and in patients (34 vs 32) during IET. A significant (p<0.05), albeit clinically unimportant, difference was also observed in P(A-a)O2 (28 vs 29) in patients. No statistically significant differences were observed below the AT between IET and CW for any of the variables measured.
Conclusions: These data demonstrate the reliability of ABG and pulmonary gas exchange variables measured during 1-min IET for clinical use in patients and normal subjects. However, PaCO2 tends to be slightly higher during IET vs CW.