Periodic regression analysis for blood pressure and heart rate of patients on dialysis

For 48 hours, blood pressure (BP) and heart rate (HR) were measured using a portable automatic recorder at 30-minute intervals in patients undergoing hemodialysis (HD), or continuous ambulatory peritoneal dialysis (CAPD) and in healthy subjects. Time-series data obtained were analyzed by periodic regression using the fast fourier transform (FFT) for group comparative study. In healthy subjects and CAPD patients, both systolic and diastolic blood pressures (SBP & DBP) showed a regular pattern, decreasing during the night, and maintaining a 24-hour circadian rhythm, In HD patients, however, periodic regression curves for both SBP and DBP showed a characteristic pattern, in which no decreases occurred during the night on non-dialysis days. Rather, increases were seen from 11:00 pm to 6:00 am (midnight surge) despite decreases during the nights following dialysis days. The power density, which is a coefficient of determination for each periodic component calculated by FFT, suggests that the blood pressure of HD patients maintains a 48-hour rhythm rather than a 24-hour rhythm. Moreover, the power density of a 48-hour periodic component increased and the midnight surge was more clearly defined as daily urine output decreased and the body weight loss due to HD worsened. Thus, it is concluded that the 48-hour BP rhythm in HD patients is due to body fluid retention and short-term removal of fluid by HD. HR showed a regular 24-hour rhythm in HD patients as well as in the other groups, suggesting that HR may not be affected by the body fluid factor. Finally, data from HD patients with diabetes mellitus (DM) were analyzed. For SBP, DBP, and HR, only a 12-hour rhythm was detected, and neither a 24-hour nor 48-hour rhythm component was detected. This suggests that in HD patients with DM, the autonomic nervous factor is impaired along with the body fluid factor.