Jakovljevic Djordje G, Nunan David, Donovan Gay, Hodges Lynette D, Sandercock Gavin R H, Brodie David A
Research Centre for Society and Health, Buckinghamshire Chilterns University College, Chalfont Campus, Gorelands Lane, Chalfont St Giles, Buckinghamshire HP8 4AD, UK.
Eur J Appl Physiol. 2008 Mar;102(5):593-9. doi: 10.1007/s00421-007-0631-4. Epub 2007 Dec 11.
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.
有几种重复呼吸法可用于心输出量（Q(T)）测量。本研究的目的有三个：第一，比较平衡-CO₂、指数-CO₂和惰性气体-N₂O重复呼吸法所测得的静息Q(T)值；第二，评估这三种方法在静息状态下的可重复性。第三个目的是评估指数重复呼吸法和惰性气体重复呼吸法所得的运动峰值Q(T)估计值之间的一致性。共有18名健康受试者在不同日期到访运动实验室。以坐姿测量的Q(T)重复测量值之间间隔5分钟休息时间。12名参与者进行递增运动试验以确定峰值耗氧量。另外进行两次运动试验，使用指数重复呼吸法和惰性气体重复呼吸法测量运动峰值时的Q(T)。与平衡法（平均6.6 l min⁻¹）和惰性气体重复呼吸法（平均5.1 l min⁻¹；P < 0.01）相比，指数法在静息时得出的估计值显著更高（平均10.9 l min⁻¹）。所有方法的可重复性都很高，指数法的变异系数最大（5.3%）。在运动峰值时，指数重复呼吸法和惰性气体重复呼吸法之间无显著差异（P = 0.14）。一致性界限为-0.49至0.79 l min⁻¹。由于能够评估气体混合程度并估计肺内分流，我们认为惰性气体重复呼吸法有可能比本研究中使用的任何一种CO₂重复呼吸法更精确地测量Q(T)。在运动峰值时，指数重复呼吸法和惰性气体重复呼吸法的一致性界限均显示可接受。
