1. Heart rate variability can be used to evaluate autonomic balance, but it is unclear how inotropic therapy may affect the findings. The aim of the study was to assess whether heart rate variability can differentiate between sympathetic stimulation induced by inotrope infusion or by physical exercise.
2. Ten patients with chronic heart failure (64.3 ± 5.4 years of age) underwent four dobutamine infusions (8-min steps of 5 μg min−1 kg−1) and four supine bicycle exercise tests (5-min steps of 25 W). Plasma noradrenaline was evaluated, as well as the SD of R—R intervals, together with low-frequency (0.03–0.14 Hz) and high-frequency (0.15–0.4 Hz) components of heart rate variability using autoregressive spectral analysis.
3. Exercise and inotrope infusion produced similar changes in heart rate variability. An exercise load of 50 W and a dobutamine infusion of 15 μg min−1 kg−1 gave the following results respectively: heart rate, 120.3 ± 3.0 beats/min versus 110.2 ± 3.0 beats/min; SD, 16.0 ± 1.1 ms versus 16.3 ± 2.5 ms; low-frequency component, 4.3 ± 0.3 ln-ms2 versus 4.4 ± 0.3 ln-ms2 and high-frequency component, 2.6 ± 0.3 ln-ms2 versus 2.2 ± 0.3 ln-ms2. All comparisons were non-significant. The variables of heart rate variability showed high reproducibility in the same subject during different conditions. Noradrenaline was elevated by exercise from 326.0 ± 35.2 pg/ml to 860.1 ± 180.4 pg/ml (P < 0.05), but was unchanged by dobutamine infusion.
4. Heart rate variability changes cannot differentiate between dobutamine infusions and physical exercise, indicating that we should be cautious in evaluating patients undergoing inotropic therapy. The degree of receptor stimulations, rather than the level of sympathetic drive, would appear to determine the changes in heart rate variability.