Evaluation of skeletal muscle tremor due to bronchodilator agents

Two methods of measuring skeletal muscle tremor when evaluating this side-effect of treatment with bronchodilator agents are described. The first method, involving drawing a line between two sinus curves, is simple and requires no special equipment. Each time that the line crosses one of the sinus curves this is registered as an error. The large variation in results is a disadvantage but this drawing method can be used when more sophisticated devices are not available. Skeletal muscle tremor recorded with a Grass accelerometer gives accurate results provided the method is carefully standardized and the resting period adequate. The dose-response curves obtained during infusions of beta-adrenergic-stimulating drugs are linearly related to the dose given and are highly reproducible. The tremor ratio has the advantage over absolute values of smaller variations. The first of three 30-s periods registered gives the lowest tremor value and least variation, so this is the period used for analysis. Subjective experience of tremor is related to the Grass recording. In some cases, however, there is marked discrepancy between subjective and objective evaluation of tremor, which may be explained by the masking effect of concomitant heart stimulation. When tremor is related to heart rate in a single experiment a regression line is obtained. Another drug may give a different slope. The two slopes demonstrate the different selectivity of the drugs for the beta-receptors in the heart and skeletal muscle.