title: Use of acetylene breathing to determine cardiac output in young and older adults.
abstract: OBJECTIVE
  The aims of this investigation were: 1). to establish the day-to-day reproducibility of open-circuit acetylene breathing for measuring exercise cardiac output (Q(c)) in young and older adults; and 2). to compare estimates of Q(c) from open-circuit acetylene breathing with estimates of Q(c) from previously established closed-circuit acetylene rebreathing.
  
  
  METHODS
  Twenty men (10 young: 28 +/- 1 yr; 10 older: 61 +/- 1 yr (mean +/- SE)) performed cycle ergometry exercise on 3 separate days. Q(c) was estimated using open-circuit acetylene breathing on 2 d, and closed-circuit acetylene rebreathing on 1 d.
  
  
  RESULTS
  Open-circuit acetylene breathing was highly reproducible (young: standard error of measurement (SEM) = 1.52 L.min (-1) limits of agreement (LOA) = 0.2 +/- 4.2 L.min (-1), coefficient of variation 6% < CV < 8%, day 2 = (0.9 x day 1) + 2.4, r = 0.90, P< 0.001, r (2)= 0.82; older: SEM = 0.94 L.min (-1), LOA = 0.1 +/- 2.8 L.min (-1), 4% < CV < 10%, day 2 = (1.0 x day 1) + 0, r = 0.91, < 0.001, r(2) = 0.82). Estimates of Q(c) from open-circuit acetylene breathing demonstrated good agreement with closed-circuit acetylene rebreathing (young: SEM = 1.52 L.min (-1), LOA = 0.9 +/- 4.4 L.min (-1), 5% < CV < 10%, open-circuit = (1.0 x closed-circuit) + 1.5, r = 0.89, < 0.001, r (2) = 0.79; older: SEM = 1.13 L.min (-1), LOA = 0.1 +/- 3.2 L.min (-1), 5% < CV < 9%, open-circuit = (0.9 x closed-circuit) + 1.6, r = 0.88, < 0.001, r(2) = 0.78).
  
  
  CONCLUSIONS
  These results demonstrate that open-circuit acetylene breathing provides reproducible measurements of Q(c) during exercise that demonstrate good agreement with values obtained from the acetylene rebreathing procedure in young and older healthy men.
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Colorado at Boulder, Boulder, CO 80309-0354, USA. Christopher.Bell@Colorado.edu
authors.forename: Christopher
authors.initials: C
authors.lastname: Bell
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Monahan
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Donato
authors.forename: Brian E
authors.initials: BE
authors.lastname: Hunt
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Seals
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Beck
mesh_terms: D000114:Acetylene / Q000493:pharmacokinetics*; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D015203:Reproducibility of Results
chemical_list: D000114:Acetylene