Ventilatory and lactate threshold determinations in healthy normals and cardiac patients: methodological problems

In healthy normal individuals (n = 69), coronary patients with myocardial ischaemia (n = 27) and patients with chronic heart failure (CHF, n = 33), four widely applied methods to determine ventilatory threshold (VT) were analysed: V-slope, ventilatory equivalent for O₂ (EqO₂), gas exchange ratio (R) and end-tidal partial pressure of oxygen. Lactate threshold [LAT, log lactate vs log oxygen uptake (\(\dot V{\text{O}}_2 \))] was also determined. Analysis focused on rate of success of threshold determination, comparability of threshold methods, reproducibility and interobserver variability. Cycle ergometry protocols with ramp-like mode and graded steady-state mode used in exercise testing were considered separately. In healthy normal individuals and coronary patients with myocardial ischaemia, at least three VT could be determined during ramp-like mode and two VT during graded steady-state mode, 82% of the time. For CHF patients, the rate of successful determination of VT was lower. Compared to LAT, \(\dot V{\text{O}}_2 \) at VT was significantly higher using R and EqO₂ methods of VT determination in healthy normal subjects (P < 0.01), and significantly higher when using all four methods in coronary patients (P < 0.01 or P < 0.05, respectively). No difference was observed between \(\dot V{\text{O}}_2 \) at VT and LAT in CHF patients. In healthy normal individuals, day-to-day reproducibility of VT and LAT was high (error of a single determination from duplicate determinations was between 3.9% and 6.2% corresponding to a \(\dot V{\text{O}}_2 \) of 52.2 and 89.2 ml·min ⁻¹). Interobserver variability was low (error between 0.3% and 5% corresponding to a \(\dot V{\text{O}}_2 \) of 9.8 and 68 ml·min⁻). In CHF patients, interobserver variability was moderately greater (error between 4.6% and 8.2%, corresponding to a \(\dot V{\text{O}}_2 \) of 35.1 and 62.4 ml·min⁻¹). To optimize threshold determination, standardized procedures are suggested.