Correlation between inflection of heart rate/work performance curve and myocardial function in exhausting cycle ergometer exercise

Summary The heart rate/work performance (f_c/W) curve is usually S-shaped but a flattening at the top is not always seen. By means of radionuclide ventricular scintigraphy, the left ventricular ejection fraction (LVEF) of 15 sports students was investigated. The behaviour of the f_c/W curve during cycle ergometry with increasing exercise intensities was examined. During exercise, the LVEF showed a distinct initial increase reaching roughly constant values at stress levels below-maximum, and sometimes even falling again. The inflections of the f_c/W curve and left ventricular ejection fraction/performance curve (LVEFPC) were calculated from a second degree polynomial fit. From this function, the slopes of the tangents at the points of aerobic threshold and maximum performance were calculated together with the differences of the angles as a measure of the f_c/W curve and LVEFPC inflections. It follows that the f_c/W curve inflection became less pronounced or was even absent altogether when the decrease in LVEF towards the end of the ergometer exercise became more distinct. A significant negative correlation was found between the existence and extent of the f_c/W curve inflection and the stress-dependent myocardial function, expressed as the inflection of the LVEFPC (P<0.01, r=0.673). Thus, it would seem that the absence of a f_c/W curve inflection was related to a diminished stress-dependent myocardial function.