Figure 1. Typical power spectral changes of heart rate variability in patients undergoing esophagectomy (51 yr, male), right pulmonary resection (57 yr, male), and left pulmonary resection (57 yr, male). In each panel, power spectrum of heart rate variability (10 sup -4 *symbol* Hz sup -1) plotted up to the frequency of 0.5 Hz. Note the power spectral peak in the low range below 0.2 Hz (low frequency) and the respiratory peak located at the frequency of breathing (high frequency) in the upper left panel. Both esophagectomy and right pulmonary resection diminished heart rate variability. In contrast, left pulmonary resection did not alter heart rate variability.