Chest
Volume 113, Issue 3, March 1998, Pages 602-611
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Clinical Investigations: Exercise
Comparison of Pulmonary Gas Exchange Measurements Between Incremental and Constant Work Exercise Above the Anaerobic Threshold

https://doi.org/10.1378/chest.113.3.602Get rights and content

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 [V˙d/V˙t]) measured during incremental exercise test (IET) and constant work (CW) exercise at a matched oxygen uptake ( Vo˙2).

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 Vo˙2 in the following: PaO2 (79 vs 79 mm Hg); arterial oxygen saturation (SaO2) (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.

Section snippets

Materials and Methods

Sixteen patients (11 men and 5 women) and 9 normal men were studied in the human performance laboratory of the William Beaumont Army Medical Center at an altitude of 1,270 m (barometric pressure, 656 mm Hg). The ABG and pulmonary gas exchange data from the nine normal subjects were extracted from a previous study.20 The data of the 16 patients were obtained from clinical cardiopulmonary exercise tests performed in patients referred to our laboratory for evaluation of dyspnea on exertion and/or

Results

Pulmonary function test results and anthropometric characteristics are summarized in Table 1 for both study groups (mean±SEM, and percent predicted values). The normal group consisted of healthy young men, with normal spirometry, lung volumes, and diffusing capacity. In the patients, the resting pulmonary function test results varied from normal to severely abnormal. For the patient group, the range of percent predicted values is presented to emphasize the fact that patients with varying

Discussion

Automated systems that use breath-by-breath analysis have facilitated the measurement of cardiopulmonary and pulmonary gas exchange variables during incremental exercise.25 However, sufficient uncertainty persists regarding the assumptions involved in the application of the mass balance equation in each breath during IET to warrant clinical validation of pulmonary gas exchange measurements using breath-by-breath analysis. There is a well-established variability in gas exchange values measured

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      Corroboration of incremental results may be achieved with ABG measurement during a 6-minute constant work exercise test at 60% to 70% of the maximum work achieved (≃ 90% o2peak). Recently, validation of pulmonary gas exchange measurements during IET above the AT has been reported.133 Abnormal widening of P(A-a)o2 with exercise usually reflects ventilation-perfusion ratio (/) mismatching but also can be caused by diffusion abnormalities, anatomic shunt, or reduced oxygen saturation in mixed venous blood worsening the / mismatching (shunt effect).119

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    The opinions or assertions contained herein are the private view of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. The investigators have adhered to the policies for protection of human subjects as prescribed in 40 CFR 46.

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