title: Comparison of cardiac output determined by different rebreathing methods at rest and at peak exercise.
abstract: Several rebreathing methods are available for cardiac output (Q (T)) measurement. The aims of this study were threefold: first, to compare values for resting Q (T) produced by the equilibrium-CO(2), exponential-CO(2) and inert gas-N(2)O rebreathing methods and, second, to evaluate the reproducibility of these three methods at rest. The third aim was to assess the agreement between estimates of peak exercise Q (T) derived from the exponential and inert gas rebreathing methods. A total of 18 healthy subjects visited the exercise laboratory on different days. Repeated measures of Q (T), measured in a seated position, were separated by a 5 min rest period. Twelve participants performed an incremental exercise test to determine peak oxygen consumption. Two more exercise tests were used to measure Q (T) at peak exercise using the exponential and inert gas rebreathing methods. The exponential method produced significantly higher estimates at rest (averaging 10.9 l min(-1)) compared with the equilibrium method (averaging 6.6 l min(-1)) and the inert gas rebreathing method (averaging 5.1 l min(-1); P < 0.01). All methods were highly reproducible with the exponential method having the largest coefficient of variation (5.3%). At peak exercise, there were non-significant differences between the exponential and inert gas rebreathing methods (P = 0.14). The limits of agreement were -0.49 to 0.79 l min(-1). Due to the ability to evaluate the degree of gas mixing and to estimate intra-pulmonary shunt, we believe that the inert gas rebreathing method has the potential to measure Q (T) more precisely than either of the CO(2) rebreathing methods used in this study. At peak exercise, the exponential and inert gas rebreathing methods both showed acceptable limits of agreement.
authors: Research Centre for Society and Health, Buckinghamshire Chilterns University College, Chalfont Campus, Gorelands Lane, Chalfont St Giles, Buckinghamshire HP8 4AD, UK. djordje.jakovljevic@bcuc.ac.uk
authors: Djordje G
authors: DG
authors: Jakovljevic
authors: David
authors: D
authors: Nunan
authors: Gay
authors: G
authors: Donovan
authors: Lynette D
authors: LD
authors: Hodges
authors: Gavin R H
authors: GR
authors: Sandercock
authors: David A
authors: DA
authors: Brodie
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D002245:Carbon Dioxide; D002302:Cardiac Output / Q000502:physiology*; D003627:Data Interpretation, Statistical; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D005741:Noble Gases; D010101:Oxygen Consumption / Q000502:physiology; D015203:Reproducibility of Results; D015656:Respiratory Mechanics / Q000502:physiology*
chemical_list: D005741:Noble Gases; D002245:Carbon Dioxide