Orthostatic tremor during modification of standing

Area of Science:

• Neurology
• Human Physiology
• Biomedical Engineering

Background:

• Primary orthostatic tremor (OT) is a neurological condition characterized by involuntary muscle oscillations exclusively during upright stance.
• The precise mechanisms underlying OT generation remain incompletely understood, particularly the influence of afferent sensory feedback and postural control.
• Investigating how modifications to the standing condition affect OT can provide insights into its pathophysiology.

Purpose of the Study:

• To investigate the influence of altered standing conditions on the characteristics of primary orthostatic tremor.
• To differentiate the roles of afferent input, muscle forcing, and postural set in the generation of orthostatic tremor.

Main Methods:

• Surface electromyography (EMG) was recorded from tibialis anterior and gastrocnemius muscles in seven patients with primary OT.
• Two maneuvers were employed: 'relief' (lifting by a crane) and 'tilting' (using a tilting table to transition from standing to lying).
• Tremor frequency, intensity, coherence, and phase shifts between muscles were analyzed under different conditions.

Main Results:

• The 'relief' maneuver, which altered afferent input and muscle forcing but not postural set, did not significantly influence OT.
• The 'tilting' maneuver, which modified all three factors (afferent input, muscle forcing, and postural set), significantly altered tremor intensity and phase shifts.
• Tremor frequency and coherence remained unaffected by the tilting maneuver.

Conclusions:

• The findings suggest that postural set plays a crucial role in the generation of primary orthostatic tremor.
• Afferent input and muscle forcing appear to have a less significant role compared to postural set in modulating OT.
• Modifying the standing condition through tilting provides valuable data for understanding OT pathophysiology.