title: Corrected end-tidal P(CO(2)) accurately estimates Pa(CO(2)) at rest and during exercise in morbidly obese adults.
abstract: BACKGROUND
  Obesity affects lung function and gas exchange and imposes mechanical ventilatory limitations during exercise that could disrupt the predictability of Pa(CO(2)) from end-tidal P(CO(2)) (P(ETCO(2))), an important clinical tool for assessing gas exchange efficiency during exercise testing. Pa(CO(2)) has been estimated during exercise with good accuracy in normal-weight individuals by using a correction equation developed by Jones and colleagues (P(JCO(2)) = 5.5 + 0.9 x P(ETCO(2)) – 2.1 x tidal volume). The purpose of this project was to determine the accuracy of Pa(CO(2)) estimations from P(ETCO(2)) and P(JCO(2)) values at rest and at submaximal and peak exercise in morbidly obese adults.
  
  
  METHODS
  Pa(CO(2)) and P(ETCO(2)) values from 37 obese adults (22 women, 15 men; age, 39 ± 9 y; BMI, 49 ± 7; [mean ± SD]) were evaluated. Subjects underwent ramped cardiopulmonary exercise testing to volitional exhaustion. P(ETCO(2)) was determined from expired gases simultaneously with temperature-corrected arterial blood gases (radial arterial catheter) at rest, every minute during exercise, and at peak exercise. Data were analyzed using paired t tests.
  
  
  RESULTS
  P(ETCO(2)) was not significantly different from Pa(CO(2)) at rest (P(ETCO(2)) = 37 ± 3 mm Hg vs Pa(CO(2)) = 38 ± 3 mm Hg, P = .14). However, during exercise, P(ETCO(2)) was significantly higher than Pa(CO(2)) (submaximal: 42 ± 4 vs 40 ± 3, P < .001; peak: 40 ± 4 vs 37 ± 4, P < .001, respectively). Jones’ equation successfully corrected P(ETCO(2)), such that P(JCO(2)) was not significantly different from Pa(CO(2)) (submax: P(JCO(2)) = 40 ± 3, P = .650; peak: 37 ± 4, P = .065).
  
  
  CONCLUSIONS
  P(JCO(2)) provides a better estimate of Pa(CO(2)) than P(ETCO(2)) during submaximal exercise and at peak exercise, whereas at rest both yield reasonable estimates in morbidly obese individuals. Clinicians and physiologists can obtain accurate estimations of Pa(CO(2)) in morbidly obese individuals by using P(JCO(2)).
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX.
authors.forename: Vipa
authors.initials: V
authors.lastname: Bernhardt
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX.
authors.forename: Santiago
authors.initials: S
authors.lastname: Lorenzo
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX. Electronic address: TonyBabb@TexasHealth.org.
authors.forename: Tony G
authors.initials: TG
authors.lastname: Babb
authors.affiliation: McGill University Health Centre, Montreal, QC, Canada.
authors.forename: Gerald S
authors.initials: GS
authors.lastname: Zavorsky
mesh_terms: D000328:Adult; D015992:Body Mass Index; D002245:Carbon Dioxide / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D016014:Linear Models; D008168:Lung / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009767:Obesity, Morbid / Q000378:metabolism / Q000503:physiopathology*; D010100:Oxygen / Q000378:metabolism*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012146:Rest / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen