BACKGROUND--Measurement of variables of metabolic gas exchange during exercise is widely used to assess the severity of heart failure. The variables derived however, are potentially dependent on motivation of the patient and duration of exercise. METHODS--The data from exercise tests in 23 patients with exertional breathlessness were analysed to derive the following three common indices of exercise tolerance: anaerobic threshold, extrapolated maximum oxygen consumption, and the ventilation to carbon dioxide production slope. The data were reanalysed with the data points from the first 90% of subsequent exercise, the first 75%, and finally the data up to the point where a respiratory gas exchange ratio of 1 was reached. RESULTS--The mean (SEM) anaerobic threshold was lower when computed from 90% of the data points than from 100% (13.2 (1.0) ml/kg/min v 12.5 (1.0), p < 0.001) and lower still from 75% (11.4 (0.7), p = 0.006 v 90%). Extrapolated maximum oxygen consumption was unchanged when computed from 90% of the data, but higher when computed from 75% (25.4 (2.1) ml/kg/min at 100% v 28.6 (2.1) at 75%, p < 0.001). The slope of the ventilation to carbon dioxide production ratio became progressively shallower measured from 90% and 75% of eventual exercise: 32.3 (1.5) from 100% v 30.0 (1.5) from 90%, p < 0.001; and 28.3 from 75%, p < 0.001 v 90%. At a respiratory gas exchange ratio of 1, extrapolated oxygen consumption was unchanged from the final calculation, anaerobic threshold was lower than at 100% of exercise (11.8 (0.9), p = 0.005) and the ventilation to carbon dioxide production slope was shallower (27.5 (1.4), p < 0.001). CONCLUSIONS--Anaerobic threshold tends to overestimate severity of exercise limitation and extrapolated maximum oxygen consumption and the ventilation to carbon dioxide production slope tend to underestimate severity. Extrapolated maximum oxygen consumption is the most reliable of the three measures, and is independent of effort provided that patients are encouraged to exercise to the point where the respiratory gas exchange ratio exceeds 1.
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机译：背景技术-运动中代谢气体交换变量的测量被广泛用于评估心力衰竭的严重程度。但是，导出的变量可能取决于患者的动机和运动时间。方法-对来自23名运动性呼吸困难患者的运动测试数据进行了分析，得出以下三个运动耐受性的常见指标：无氧阈值，推断的最大耗氧量和通气至二氧化碳的产生斜率。重新分析数据，包括随后进行的锻炼的前90％，最初的75％，最后是达到呼吸气体交换比1的数据。结果-从90％的数据点计算出的平均（SEM）无氧阈值比100％（13.2（1.0）ml / kg / min v 12.5（1.0），p <0.001）更低，而从75％更低％（11.4（0.7），p = 0.006 v 90％）。从90％的数据计算得出的推断最大耗氧量没有变化，但从75％的计算得出的值更高（100％时为25.4（2.1）ml / kg / min，75％时为28.6（2.1），p <0.001）。从最终运动的90％和75％测得，通气对二氧化碳产生率的斜率逐渐变浅：从100％的32.3（1.5）到90％的30.0（1.5），p <0.001；从75％降至28.3，p <0.001 v 90％。在呼吸气体交换比为1时，推断的氧气消耗量与最终计算结果相同，无氧阈值低于运动量的100％时的无氧阈值（11.8（0.9），p = 0.005），通向二氧化碳生成斜率的通风较浅（ 27.5（1.4），p <0.001）。结论-无氧阈值往往高估了运动受限的严重程度，并推断出最大的氧气消耗量，通向二氧化碳产生斜率的通气往往低估了严重程度。推断的最大耗氧量是这三项措施中最可靠的，并且与努力无关，只要鼓励患者进行锻炼，使呼吸气体交换率超过1。
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