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• Postural hand tremor was quantitatively investigated on both sides in 21 patients suffering from unilateral reflex sympathetic dystrophy of the upper extremity. On the affected side, enhanced tremor amplitude, with a mean tremor frequency of 7.2 Hz, was found in 57% of the patients. The appearance of tremor did not correlate to the occurrence of a single clinical symptom of reflex sympathetic dystrophy. On loading with increasing weight, the frequency of this pathological tremor shifted toward lower values, as it is found in physiological tremor. However, the peak frequencies of the electromyogram remained more or less stable. On recovery from this condition, the reflex sympathetic dystrophy tremor disappeared. Acute sympatholytic intervention could normalize reflex sympathetic dystrophy tremor. This would suggest that the sympathetic supply of the affected extremity contributes to the tremor in reflex sympathetic dystrophy. In conclusion, it is suggested that reflex sympathetic dystrophy should be included among the causes of tremor. According to our findings, tremor in reflex sympathetic dystrophy should be regarded as an enhanced physiological tremor.

• Index finger tremor accompanying voluntary movement was studied in 19 agematched control subjects and in 19 grain industry employees chronically exposed to carbon disulfide-based fumigants. Visual judgments of tremor amplitude made by neurologists during clinical examinations equaled the sensitivity of computerized tremor amplitude measurements. Tremor frequency variations detectable only with computerized measurement were present in grain workers with and without increased tremor amplitudes. Frequency differences discriminated between normal subjects and 74% of the grain workers. The distribution of tremor frequency power in the grain workers was often sequestered at 5 to 7 Hz, reminiscent of tremor in idiopathic Parkinson's disease. These findings suggest that the measurement of subtle tremor frequency changes may provide an early indication of chronic carbon disulfide poisoning.

• 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.