Changes in heart rate variability before and after surgery in patients with pheochromocytoma.

We assessed ambulatory blood pressure and heart rate variability in two female patients with pheochromocytoma. The ambulatory blood pressure and ECG R-R intervals were measured during a 24-h period with a portable recorder before and 3 weeks after surgery. A power-spectral analysis of R-R intervals was performed to obtain the low-frequency (LF) and high-frequency (HF) components. The percentage of differences between adjacent normal R-R intervals >50 ms (pNN50) was also calculated. In both patients, the plasma epinephrine and norepinephrine levels decreased markedly after surgery. The 24-h blood pressures also decreased after surgery. In both patients, the 24-h average LF component, HF component, and pNN50 decreased after surgery, while the 24-h average LF/HF ratio increased after surgery. These results suggest that high circulating catecholamines inhibit central sympathetic neural outflow and augment parasympathetic nerve activity in patients with pheochromocytoma.