Assessment of the amplitude of oscillations associated with high-frequency components of physiological tremor: impact of loading and signal differentiation

The goal of this study was accurate quantification of the amplitude of high-frequency components of physiological tremor (PT) in units of displacement, velocity, and acceleration. In addition, changes of amplitude with finger loading were compared within specific frequency bands. Index finger tremor was measured for 20 healthy subjects using a high-resolution laser, simultaneously with an accelerometer, under two conditions, unloaded and loaded (70 g). By use of an accurate filtering technique, oscillations within six predetermined frequency bands were isolated. Results showed that overall mean tremor amplitude under the unloaded condition was 0.0973 mm in displacement units, 4.525 mm s⁻¹ in velocity units, and 301.526 mm s⁻² in acceleration units. Although the mean amplitude of oscillations located within the 16.5–30 Hz band was 0.009 mm and represented only 10% of total tremor amplitude, amplitude of acceleration within the 16.5–30 Hz band was 191 mm s⁻² and represented 60% of total acceleration amplitude. Mean amplitude increased significantly with loading (displacement, t=−2.67, P=0.015; velocity, t=−4.33, P=0.000; acceleration, t=−3.48, P=0.002) but the magnitude of that change was different in each frequency band and its relative importance depended on the level of signal differentiation. Velocity was the only measure that retained sensitivity to changes in amplitude with loading in the low and high-frequency components of PT. In conclusion, this study provides, for the first time, accurate quantification of the amplitude of oscillation of high-frequency components of PT. In addition, it provides clear evidence that the velocity of tremor oscillation is more suitable for detection of the impact of finger loading because it enables detection of amplitude changes in both the low and high-frequency components of PT.