Cardiac Vagal Reactivation during Muscle Metaboreflex Activation Following Handgrip Exercise in Patients with Parkinson's Disease

Abstract

Parkinson's disease (PD) is a common neurodegenerative disorder classically characterized by symptoms of motor impairment, but also presenting with important non-motor impairments. There is evidence for the reduced activity of both the parasympathetic and sympathetic limbs of the autonomic nervous system at rest in PD. However, it is currently unclear if inappropriate autonomic adjustments are manifested during exercise in PD, including rapid parasympathetic adjustments that occur following cessation of exercise and at the onset of isolated post-exercise ischemia (PEI; muscle metaboreflex activation). Herein, we tested the hypothesis that, compared to older and young men, patients with PD present a lower heart rate (HR) recovery at the cessation of isometric handgrip exercise (i.e., onset of PEI) due to an attenuated cardiac vagal reactivation. Eleven patients with PD (66 ± 2 yr; Hoehn and Yahr score: 2 ± 1 a.u.; time since diagnosis: 7 ± 1 yr; means ± SD), 9 age-matched controls (66 ± 3 yr) and 10 young subjects (21 ± 1 yr) were recruited. Subjects performed 90-s of isometric handgrip exercise at 40% of maximal voluntary contraction followed by 3-min of PEI. Beat-to-beat HR (electrocardiography) was continuously measured during the experiment. HR recovery data were calculated as the absolute difference between HR at the end of the isometric exercise and HR at the end of the first 30-s of PEI. HR was significantly increased from rest during exercise in all groups, and increases were higher in young subjects compared to patients with PD and age-matched controls (Δ11 ± 5 vs. Δ10 ± 7 vs. Δ30 ± 15 beats.min−1; P < 0.001; for patients with PD, age-matched controls and young subjects, respectively). Following the cessation of exercise, the HR recovery was significantly lower in both patients with PD and age-matched controls compared to young subjects (Δ-10 ± 5 vs. Δ-14 ± 6 vs. Δ-26 ± 8 beats.min−1 at 30s; P < 0.001; for patients with PD, age-matched controls and young subjects, respectively). In summary, patients with PD and age-matched controls present blunted parasympathetic reactivation, as indicated by the lower HR recovery after exercise. However, contrary to our hypothesis, patients with PD do not have attenuated HR recovery at the cessation of isometric handgrip exercise and onset of PEI compared to age-matched controls, suggesting that parasympathetic reactivation was not further affected by the presence of PD.