title: Comparison of pulmonary gas exchange measurements between incremental and constant work exercise above the anaerobic threshold.
abstract: OBJECTIVE
  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).
  
  
  METHODS
  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.
  
  
  METHODS
  El Paso, Tex, located at an altitude of 1,270 m (barometric pressure, 656 mm Hg).
  
  
  METHODS
  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.
  
  
  METHODS
  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 (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.
authors.affiliation: Department of Clinical Investigation, William Beaumont Army Medical Center, El Paso 79920-5001, USA. zeballos@flash.net
authors.forename: R J
authors.initials: RJ
authors.lastname: Zeballos
authors.forename: I M
authors.initials: IM
authors.lastname: Weisman
authors.forename: S M
authors.initials: SM
authors.lastname: Connery
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold; D002245:Carbon Dioxide / Q000097:blood; D004417:Dyspnea / Q000503:physiopathology; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange; D012126:Respiratory Dead Space; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen