A normative study of postural tremor of the hand.

In a normative study of amplitude, frequency, and variability of postural tremor of the hand in 97 normal subjects, 15 to 80 years old, tremor was transduced using accelerometers and characterized by power spectral analysis. Tremor amplitude ranged from a 0.0015- to 0.035-g peak at the dominant frequency. The modal tremor amplitude was 0.01-g peak, and the threshold for "visible tremor" was 0.007-g peak. The modal tremor frequency was constant at about 7 Hz in those subjects up to 70 years old and thereafter decreased to about 6 Hz. The mean range of variability of the dominant frequency was 2.5 Hz. The tremor pattern, characterized by the shape of spectra, varied greatly from a single finely tuned peak to multiple broad peaks. More than two thirds of normal subjects showed complex spectral patterns with more than one peak of significance. Passive resonance of the hand tissues was an important factor in determining dominant tremor frequencies in most subjects. Many subjects showed a strong, albeit variable , cardioballistic component. The results provide baseline data for studies of the effects of drugs on tremor, particularly in cases of "essential" tremor, and provide warnings that such studies require objective recording methods for adequate evaluation and need recourse to measurement of several factors of the tremor to elucidate the component of tremor affected by a drug. A scaling of tremor can be used in terms of reference to the strength of gravitational acceleration (1.0 g), which provides simple numerical relationships.