The Effects of Relative Exercise Intensity vs Individual Metabolism on LV Twist and Untwisting Rate

Abstract

Left ventricular twist and untwisting rate ('LV twist mechanics') are fundamental to cardiac function during exercise. However, studies have reported large inter‐individual variability in LV twist mechanics which complicates the interpretation of patient responses. To determine the source of variability in LV twist mechanics during exercise, this study aimed to examine whether LV twist mechanics respond more consistently to the same relative exercise intensity compared with exercise performed at individual anaerobic threshold (IAT). 16 healthy non‐endurance trained males (Age: 22±4 years, O2peak: 45.5±6.9 ml/min/kg, range of IAT: 32–69% of O2peak) were enrolled. Following assessment at rest, each volunteer performed short‐duration exercise at: i) the same relative exercise intensity, 40%peak, ii) at 2% above their IAT and iii) at 40%peak during hypoxia (FiO2=12%). No differences in LV volumes were observed during exercise conditions (p>0.05). However, LV twist mechanics responded more consistently during 40%peak compared with exercise at IAT (F‐ratio 2.080). When exercise at 40%peak was performed in hypoxia, LV twist mechanics increased (P<0.05) but the variability of responses remained similar to 40%peak in normoxia. Overall, LV twist mechanics were related to myocardial work. In conclusion, LV twist mechanics respond more consistently during exercise at the same relative intensity than IAT and diagnostic exercise tests in the clinical and research setting should be standardized accordingly. Importantly, the response during hypoxia suggests that the interpretation of LV twist mechanics must take into account the prevailing myocardial work, which may further improve the diagnostic accuracy.No external funding was required for this study.