Geert Kleinnibbelink

Acute Cardiac Responses vs. Cardiac Remodelling 3 67 INTRODUCTION Exercise training results in remodelling of the heart, including chamber enlargement and hypertrophy. 1 Studies examining the impact of exercise training on cardiac remodelling have predominantly focused on left ventricular (LV) adaptation, with few studies revealing right ventricle (RV) changes to training. 2-4 To better understand the effects of exercise on RV and LV function, recent studies suggest a relative larger increase in wall stress for the RV versus LV during exercise. 5 These acute effects of exercise on cardiac function may be of importance. Indeed, cardiac remodelling seems mechanistically related to the repeated exposure to acute changes in wall stress. Therefore, in-exercise echocardiographic indices of cardiac function may (partly) relate to the presence of subsequent cardiac remodelling. However, no study directly examined this hypothesis in relation to exercise training and remodelling in humans. Recently, the strain-area/volume loop has been introduced to allow for the assessment of simultaneous structure and strain across the cardiac cycle providing mechanical insight into cardiac function. 6 We found that post-surgery changes in LV strain-volume loop characteristics relate to subsequent cardiac remodelling in patients with aortic stenosis. 7 Therefore, these changes may serve as a proxy of changes in wall stress. Furthermore, we observed different RV loop characteristics in the ‘four cornerstones’ of the Mitchell classification of sports potentially due to their difference in cardiac structure and function. 6 Possibly, these differences in strain-area/volume loops may relate to cardiac remodelling to exercise training. Therefore, the strain-area loop, in conjunction with other measures of cardiac function, may provide insight into cardiac adaptation to exercise training. The aim of this study was to relate pre-training changes in cardiac function during low-to- moderate-intensity exercise to subsequent adaptations to a 12-week hypoxic endurance exercise training program on cardiac structure, function and mechanics (i.e. longitudinal strain and strain-area/volume loops) in healthy individuals. We specifically choose hypoxic exercise since, due to a smaller reduction in pulmonary vascular resistance compared to normoxic exercise 8 , this type of exercise causes a higher RV afterload. 9-12 Indeed, we showed that 45 minutes high-intensity running exercise under hypoxia lowers pulmonary acceleration time, increases right atrial size and lowers the late diastolic uncoupling of