Chronotropic Incompetence During Exercise Testing in Obese Adolescents

In adolescents with obesity cardiopulmonary exercise testing (CPET) has become an important clinical examination providing valuable information with regard to the integrative exercise responses, including the pulmonary, cardiovascular and muscular systems.

During CPET, mechanical constraints in ventilation, an elevated risk for hypoxia and chronotropic incompetence (CI) (defined as the inability of the heart to increase its rate with increased activity), or compromised cardiac function (e.g. lowered heart rate (HR) recovery, chronotropic index and stroke volume) are often observed in obese adults. Moreover, several studies regarding exercise capacity and cardiopulmonary responses to maximal endurance exercise testing have been performed in obese adolescents. Despite these previous investigations in obese adolescents it remains controversial whether cardiopulmonary disturbances can be observed consistently during CPET. However, a number of studies have reported a suboptimal response to exercise, in particular a reduced peak heart rate (HRpeak) and peak cycling power output (Wpeak). Adult obesity modifies cardiac behavior, including resting HR and CI, which has a marked effect on exercise capacity. Therefore, chronotropic variables are the most important factors that affect exercise performance. It has been shown that both peak and resting HR account for over forty percent of variability of exercise capacity. Interestingly, resting HR and HR response to exercise, including a blunted HR increase, low chronotropic index and HR recovery, are important predictors of all-cause mortality and cardiovascular death, at least in adults. These changes in HR during and recovery from CPET are mediated by the balance between sympathetic and vagal activity of the autonomic nervous system. Adverse cardiovascular outcomes associated with the metabolic syndrome may be mediated by autonomic dysfunction, whereby obesity is characterized by sympathetic predominance and a decrease in vagal activity in the basal state, where reduced sympathetic responsiveness has been observed during exercise. Therefore, these multiple exercise risk markers could provide valuable clinical information regarding cardiometabolic health. Nonetheless HR behavior during CPET has not been described in obese adolescents. The goal of this study is to examine the HR behavior of obese adolescents during CPET to clarify whether this population suffer from CI.