Daniel Roach1, Robert Sheldon2. 1. Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada. 2. Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada. Electronic address: sheldon@ucalgary.ca.
Abstract
PURPOSE: We hypothesized that heart period (HP) variability in the low frequency (LF) band is due to transient fluctuations of about 10 s in HP sequences, associated with fluctuations in blood pressure. METHODS: 10 healthy subjects, mean age 36 y, had HP and blood pressure acquired for 10 min each. Nonrandom HP fluctuations (ripples) lasting 6.7-20 s were detected using time-scrambled surrogate sequences as controls. RESULTS: Ripples were 99 ± 40 ms in amplitude, in concatenates 23.4 ± 7.4 s long. They co-occurred with similar blood pressure ripples with amplitudes 5 ± 5 mm Hg, correlating with them with r2 = 0.68 ± 0.10, slope 23.9 ± 10.8 ms/mm Hg, at an optimum lag of 2.16 ± 0.63 beats. A second HP structure consisting of transient tachycardias of 140 ± 53 ms lasting 15.1 ± 6.1 occurred singly. Together the two structures contributed 84% ± 8% of the total power in the LF band. CONCLUSION: The LF band is caused by two types of HP structures that occur at discrete times.
PURPOSE: We hypothesized that heart period (HP) variability in the low frequency (LF) band is due to transient fluctuations of about 10 s in HP sequences, associated with fluctuations in blood pressure. METHODS: 10 healthy subjects, mean age 36 y, had HP and blood pressure acquired for 10 min each. Nonrandom HP fluctuations (ripples) lasting 6.7-20 s were detected using time-scrambled surrogate sequences as controls. RESULTS: Ripples were 99 ± 40 ms in amplitude, in concatenates 23.4 ± 7.4 s long. They co-occurred with similar blood pressure ripples with amplitudes 5 ± 5 mm Hg, correlating with them with r2 = 0.68 ± 0.10, slope 23.9 ± 10.8 ms/mm Hg, at an optimum lag of 2.16 ± 0.63 beats. A second HP structure consisting of transient tachycardias of 140 ± 53 ms lasting 15.1 ± 6.1 occurred singly. Together the two structures contributed 84% ± 8% of the total power in the LF band. CONCLUSION: The LF band is caused by two types of HP structures that occur at discrete times.