Changes in circadian rhythm in heart rate and parasympathetic nerve activity after an eastward transmeridian flight.

Distortions of the circadian rhythm structure of the heart rate and parasympathetic nerve activity after an eastward transmeridian flight were studied. We recorded the ambulatory electrocardiograms of 12 healthy young men for 11 days: 3 days in Tokyo before the flight and 8 days in San Francisco following it. Heart rate variability was determined by power spectrum analysis, and high frequency power (0.15-0.4 Hz) was used as the index of parasympathetic tone. The structural characteristics of the circadian rhythm were analyzed by dividing consecutive RR data into four parts: the preflight days, the second and third days, the fourth and fifth days (Days 5-6) and the sixth and seventh days. Eight of the 12 cases were analyzed completely. The circadian period of the heart rate decreased after the flight. The peak time of parasympathetic nerve activity shifted from the small hours to the daytime, the maximum shift being during days 5-6 after the flight. We concluded that a structural disturbance of the circadian rhythm of the heart rate and parasympathetic nerve activity were observed.