Parkinson's disease (PD) is characterized by movement impairments. Rigidity (stiffness) is one of PD's cardinal symptoms, which is defined as (1) increased resistance (hypertonia), and (2) constant resistance (uniformity) to an externally imposed movement about a joint persisting through its range of motion. Despite the breadth of studies of rigidity, our understanding of its physiological and biomechanical characters remains limited. There is no known mechanism available to account for the uniformity and the biomechanical properties of rigidity in terms of muscle reflex responses. The objective of the proposed study is to examine the mechanisms of parkinsonian rigidity by analyzing physiological and biomechanical information obtained in patients with rigidity. To accomplish this goal, we will pursue the following specific aims:
Aim 1 is to characterize the constant resistance of rigidity during imposed wrist flexion and extension movements by quantifying measured torque of the wrist joint.
Aim 2 is to assess the relative contribution of reflex responses in wrist flexor and extensor muscles to the overall torque resistance of rigidity.
Aim 3 is to examine the changes in torque resistance and muscle reflex responses associated with rigidity reduction induced by dopaminergic medication. Patients with PD and healthy subjects will participate in the proposed study. The wrist joint torque and electromyographic (EMG) activities of the wrist muscles will be measured during the imposed flexion and extension movements about the wrist. The movements at selected speeds and ranges will be generated by a computer-controlled servomotor. PD subjects will be tested during a temporary removal of medication (Off) and with medication (On). Torque and EMG signals will be quantified for characterization and evaluation of rigidity. A biomechanical model will be applied to assess the contribution of the flexor and extensor muscles to the uniform nature of rigidity. The intent of the study is to increase our understanding of the mechanisms of rigidity and to develop appropriate tools for quantification of this poorly understood symptom. The results may be useful for assessing outcomes in clinical trials and for evaluating the efficacy of therapeutic interventions.
Parkinson's disease (PD) significantly impairs patients'quality of life, which currently affects at least 1.5 million Americans and an additional 75,000 new cases each year. As the elderly population of the society grows, the incidence and prevalence of PD will continue to grow. The proposed study is of significant relevance to the public health and to the mission of the NIH.
