RELATIONSHIP BETWEEN HEART-RATE THRESHOLD, LACTATE TURN POINT AND MYOCARDIAL-FUNCTION

We examined the relationship between heart rate threshold (HRT), lacta te turn point (LTP) and myocardial function expressed as left ventricu lar ejection fraction (LVEF) determined by radionuclide ventriculograp hy. Two groups of subjects (G I: N = 8; G LI: N = 7) with and without a deflection of heart rate performance curve (HRPC) underwent sitting cycle ergometry. HRT (G I), aerobic threshold (AeT; G I, G II), and LT P (G I, G II) were determined by means of linear regression break poin t analysis. Also, a break point in LVEF performance curve (LVEFBP) was obtained. Power output at HRT and at LTP was not significantly differ ent between G I and G II (272.5+/-38.7 W; 294.3+/-20.6 W). Power outpu t at LVEFBP (G I: 182.6+/-31.7 W; G II: 211.8+/-21.5 W) was not signif icantly different to power output at LTP (G I: 194.2+/-32.7 W; G II: 2 15.2+/-24.4 W) and HRT (G I: 193.0+/-38.2 W). Significant differences (p<0.05) could only be found between G I and G II for heart rate (HR) at LTP (G I: 163.5+/-5.8 b.min(-1); G II: 154.4+/-6.7 b.min(-1)) and L VEF at the end of the load (LVEFend) (G I: 77.9+/-2.9 %; G II: 71.3+/- 7.0 %). The drop of LVEF at LVEFBP was significantly related to LTP in all cases. The present data suggest that the noninvasive determinatio n of anaerobic threshold by means of heart rate curve analysis is not always possible due to different response of myocardial function and h eart rate to graded cycle ergometer exercise. The cause for the differ ing behaviour of HR and LVEF requires further investigation.