Comparison of Pulmonary Gas Exchange Measurements Between Incremental and Constant Work Exercise Above the Anaerobic Threshold

¹ From the Human Performance Laboratory, Department of Clinical Investigation, William Beaumont Army Medical Center, and Department of Anesthesiology and Internal Medicine, Texas Tech University Health Sciences Center, El Paso, Texas

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.

Key Words: alveolar-arterial oxygen pressure difference • arterial blood gases • cardiopulmonary exercise test • physiologic dead space to tidal volume ratio • steady-state exercise

Submitted on March 3, 1997
Accepted on August 19, 1997

This article has been cited by other articles:

				ATS/ACCP Statement on Cardiopulmonary Exercise Testing Am. J. Respir. Crit. Care Med., January 15, 2003; 167(2): 211 - 277. [Full Text] [PDF]