Tohoku J. Exp. Med., 2004, 203 (1)

Beat-to-Beat Evaluation of Systolic Time Intervals during Bicycle Exercise Using Impedance Cardiography

TAKASHI ONO, MIHARU MIYAMURA, YOSHIFUMI YASUDA,¹ TOMONORI ITO,¹ TOSHIKAZU SAITO,² TOSHIMICHI ISHIGURO,² MAKOTO YOSHIZAWA³ and TOMOYUKI YAMBE⁴

Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya 464-8601, ¹Health Science Center, Toyohashi University of Technology, Toyohashi, 441-8580, ²Chunichi-denshi Co. Ltd., Nagoya 458-8525, ³Information Synergy Center, and ⁴Institute of Development, Aging and Cancer, Tohoku University, Sendai 980-8575

In order to elucidate the beat-to-beat changes of the systolic time intervals (STI) during exercise, we proposed new techniques relating to an adaptive filter and detection algorithms for B- and X-points in the impedance cardiograph (ICG). Six male subjects underwent a ramp bicycle exercise up to maximum intensity during which an ECG, ICG and phonocardiogram (PCG) were continuously measured. Following the application of an adaptive filter, the scaled Fourier linear combiner (SFLC), to the first derivative (dZ/dt) of the base impedance (ΔZ) and PCG waveforms, the B- and X-points were automatically determined. For the B-point detection we used three criteria: the zero-crossing point (B_zero), the 15% response point (B_15%) of the negative peak of the dZ/dt (dZ/dt_min) and a new algorithm (B_new). The X-point was separately determined by using the ICG and PCG waveforms. It was found that the shape of the dZ/dt waveform directly affected the determination of the B- and X-points. The B-points determined using B_zero and B_15% criteria were sometimes unstable caused by the location of a notch preceding the dZ/dt_min compared to the B_new. The time difference between the X-points measured by the ICG and PCG was mostly within ± 20 milliseconds but statistically significant. Although a wide variation was seen in R-R intervals, the STI were more stable. The relationships between HR and STI from rest to maximal exercise showed a gentle curvilinear relationship. It is suggested that the STI can be obtained precisely on a beat-to-beat basis by using the adaptive filter and detection algorithms for the inflection points of the ICG even during maximum exercise.

keywords —— left ventricular ejection time; pre-ejection period; total systolic interval; impedance cardiography; ramp exercise

© 2004 Tohoku University Medical Press

===============================

Address for reprints: Yoshifumi Yasuda, Health Science Center, Toyohashi University of Technology, 1-1 Hibarigaoka, Tenpaku, Toyohashi 441-8580, Japan.

e-mail: yasuda@hse.tut.ac.jp