The 24-h heart rate variability (HRV), as a means of assessing the modulation of the autonomic nervous function, was examined. The study was performed in asthmatic patients who used no drugs or received fenoterol four times daily, and in control subjects. HRV was assessed by calculation of indices based on statistical operations and power spectrum analysis of R-R intervals from continuous 5 min electrocardiograms. Fifteen patients receiving fenoterol were tested in the morning and in the afternoon before and after inhalation. The electrocardiograms of the remaining 16 asthmatic subjects and 10 controls were recorded 10 times during a 24-h span. The asthmatics not receiving the drug had an increased parasympathetic drive during the 24-h recording, especially at night, as compared to control groups, whereas asthmatic patients receiving fenoterol showed an increased adrenergic drive.
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