Abstract 13761: Operating Test Characteristics of Respiratory Exchange Ratio as a Noninvasive Measure of Anaerobic Threshold
Introduction: Defining anaerobic threshold is an important clinical variable in cardiopulmonary exercise (CPX) stress testing as it qualifies exercise effort and plays a major role in determining the cause of exercise limitation. The optimal cutoff point for using respiratory exchange ratio (RER) as an alternative to invasively obtained anaerobic threshold (iAT) is unknown.
Hypothesis: We assessed the hypothesis that the optimal cutoff point for RER can be defined.
Methods: We subjected 50 consecutive patients referred for CPX to effort-limited submaximal stress test. Oxygen consumption and carbon dioxide production data were obtained by the Ultima CPX™ metabolic stress testing system (MGC Diagnostics Corp., St. Paul, MN). Invasive lactate and pH measurements at rest and peak levels of exercise were obtained through brachial arterial line using the ABL800 FLEX analyzer (Radiometer Medical, Brønshøj, Denmark). The iAT was defined as a decrease in pH by >0.04 or an increase in lactate by >7 mmol/L between measurements at peak and rest.
Results: Both sensitivity (Sn) and negative predictive value (NPV) rose when the cutoff point of RER was decreased from 1.15 to 1.10 or 1.05, with Sn reaching 91% at cutoff of 1.05 (Table 1). Specificity (Sp) dropped from 72% at 1.15 to 67% at 1.10 and 50% at 1.05, with little effect on positive predictive value (PPV). Overall, a cutoff point of RER >1.10 provides the highest accuracy (80%) and the best compromise between Sn (88%) and Sp (67%). ROC curve revealed RER >1.10 to be the optimal cutoff point. Kappa statistic between RER and iAT revealed moderate agreement for the cutoff points of 1.05 (0.43; p=0.0012) and 1.10 (0.55; p<0.0001) and fair agreement for the cutoff point of 1.15 (0.38; p=0.0053).
Conclusions: This is the first study in clinical patients to determine optimal RER value for ascertaining iAT. RER of 1.10 appears to produce the best compromise between Sn and Sp as well as PPV and NPV in achieving anaerobic threshold noninvasively.
- © 2013 by American Heart Association, Inc.