Metaboreflex response to isometric handgrip exercise in people with Parkinson disease

Abstract

The metaboreflex is a peripheral feedback mechanism involved in the neural regulation of cardiovascular response to exercise. In young, healthy adults, this reflex responds to the accumulation of exercise- induced metabolites in active skeletal muscle, stimulating an increase in sympathetic nerve activity. This results in vasoconstriction and a significant rise in blood pressure, assisting in the maintenance of adequate muscle perfusion during physical activity (Smith, Mitchell, & Garry, 2005). The purpose of this study was to evaluate metaboreflex response to isometric handgrip exercise in participants with idiopathic Parkinson Disease (N=IO) and in an age-matched control group limited (N=3) due to difficulties with recruitment. Metaboreflex response was evaluated using a standard protocol; heart rate and blood pressure were evaluated during (a) rest, (b) isometric handgrip at 40% of maximal voluntary contraction force, (c) post- exercise circulatory occlusion, and (d) recovery. These measurements were repeated following participation in an eight- week community exercise programme to determine the impact of initiation of regular physical activity on metaboreflex response in people with Parkinson Disease (PD). Consistent with previous studies, participants with PD demonstrated a significant elevation in heart rate in response to isometric handgrip exercise (p< 0.001). Heart rate returned to baseline values upon cessation of exercise. There was no observable blood pressure response to isometric handgrip or post- exercise circulatory occlusion in either the PD or age- matched control groups suggesting a diminished metaboreflex response in both. The diminished metaboreflex response seen in both the PD and control groups suggests impairment in peripheral response to exercise. As participants in both groups were significantly older than in previously reported literature (greater than 70 years o f age compared to 55 - 66 years o f age), this has important implications for future research and the monitoring of response to physical activity in older adults and people with PD, as altered responsiveness o f this system may negatively impact upon fatigue and exercise tolerance in both populations.