Chronotropic Incompetence During Exercise Testing as a Marker of Autonomic Dysfunction in Individuals with Early Parkinson's Disease

Background: An attenuated heart rate response to exercise, termed chronotropic incompetence, has been reported in Parkinson's disease (PD). Chronotropic incompetence may be a marker of autonomic dysfunction and a cause of exercise intolerance in early stages of PD. Objective: To investigate the relationship between chronotropic incompetence, orthostatic blood pressure change (supine standing), and exercise performance (maximal oxygen consumption, VO2peak) in individuals with early PD within 5 years of diagnosis not on dopaminergic medications. Methods: We performed secondary analyses of heart rate and blood pressure data from the Study in Parkinson's Disease of Exercise (SPARX). Results: 128 individuals were enrolled into SPARX (63.7 +/- 9.3 years; 57.0% male, 0.4 years since diagnosis [median]). 103 individuals were not taking chronotropic medications, of which 90 had a normal maximal heart rate response to exercise testing (155.3 +/- 14.0 bpm; PDnon-chrono) and 13 showed evidence of chronotropic incompetence (121.3 +/- 11.3 bpm; PDchrono, p < 0.05). PDchrono had decreased VO2peak compared to PDnon-chrono (19.7 +/- 4.5 mL/kg/min and 24.3 +/- 5.8 mL/kg/min, respectively, p = 0.027). There was a positive correlation between peak heart rate during exercise and the change in systolic blood pressure from supine to standing (r = 0.365, p < 0.001).