VENTILATORY AND LACTATE THRESHOLD DETERMINATIONS IN HEALTHY NORMALS AND CARDIAC PATIENTS - METHODOLOGICAL PROBLEMS

In healthy normal individuals (n = 69), coronary patients with myocard ial 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 O-2 (EqO(2)), gas exchange ratio (R) and end-tidal partial pressure of oxygen. Lact ate threshold [LAT, log lactate vs log oxygen uptake (VO2)] was also d etermined. Analysis focused on rate of success of threshold determinat ion, comparability of threshold methods, reproducibility and interobse rver variability. Cycle ergometry protocols with ramp-like mode and gr aded steady-state mode used in exercise testing were considered separa tely. In healthy normal individuals and coronary patients with myocard ial 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. Co mpared to LAT, VO2 at VT was significantly higher using R and EqO(2) m ethods 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 < 0.005, respectively). No difference was observed betw een VO2 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 d etermination from duplicate determinations was between 3.9% and 6.2% c orresponding to a VO2 of 52.2 and 89.2 ml . min(-1)). Interobserver va riability was low (error between 0.3% and 5% corresponding to a VO2 of 9.8 and 68 ml . min(-1)). In CHF patients, interobserver variability was moderately greater (error between 4.6% and 8.2%, corresponding to a VO2 of 35.1 and 62.4 ml . min(-1)). To optimize threshold determinat ion, standardized procedures are suggested.