A. Stankus - Klaipeda University, Mechatronics Science Institute

1. Comparison of point-to-point and multipoint human artery pulse wave transit time measurement algorithms A. Stankus - Klaipeda University, Mechatronics Science Institute Ž. Lukošius - Klaipeda University, Department of Informatics Engineering D. Aponkus - Klaipeda University, Department of Informatics Engineering V. Stankus - Kaunas University of Technology, Department of Physics M. Kurmis - VU Institute of Mathematics and Informatics, Software engineering department A. Andziulis - Klaipeda University, Department of Informatics Engineering U. Locans - Ventspils University College ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

2. PWV (PTT) can be estimated in several ways: • Between the peak of ECG R-wave and the peak of the pulse wave, • Between two points in different pulse waves, • Multipoint. • So far, there is no well-established methodology, which could provide high accuracy and convenience. ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

3. Problems in PTT/PWV estimation • Selection of the physical origin of the signal recording, • filters, • diversity of the selected PTT identification points, • physiological errors (isovolumetric ventricular contraction time), • inaccurate distance measurement in ‘‘foot-to-foot’’or “point-to-point” time calculation methods. ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

4. The aim of investigation • to compare the accuracy of the point-to-point PTT measurement methods with the accuracy of multi-point measurement methods. ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

5. Methods • The research was carried out with: • 18 healthypeople, • age from 18 to 25 years old. • Each test lasted 3-4 minutes. • ECG and two-channel electroplethysmograph were used to record pulse waves. ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

6. Methods • Signals were discretised by: • 16-bit analog to digital converter • 1 kHz sampling rate, • 450 samples set. • R-wave of the ECG was used as synchronization trigger ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

7. Placement of the electrodes ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

8. Triggered ECG signal, knee and ankle pulse waves ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

9. Point-to-point time measurement ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

10. Cross-correlation function between the second order derivatives of two waves (multipoint) ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

11. Statistical analysis of investigated indicators ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

12. Results (1) • Using point to point measurements: • the greatest values of PTT were found to be when estimated between the peaks of the second order derivatives, • the lowest – when the beginning of the pulse wave was estimated using regressive method. • difference – about 6 ms. ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

13. Results (2) • Using the multipoint method: • maximum time period was found when calculation of the phase latency was done between the derivatives of the pulse waves, • an exceptionally short time was observed when the phase latency was calculated using the cross-correlation function between the first order derivatives of the waves, • the difference – about 10 ms. ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

14. PWV statistical indicators and the differences between them expressed by the Student (N=18) ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania

15. Conclusions • Comparative analysis showed that using the different algorithms for the pulse wave analysis the results can differ significantly. • Only stability of incoming parameters in dynamics enables selection of several algorithms. • The most stable measurements were obtained using the time calculation algorithms between the peaks of the first and second order derivatives of the waves. • Multipoint (cross-correlation and cross-spectral) analytical methods showed that accurate results can be obtained from the second order derivatives of the pulse wave. ELECTRONICS‘ 2012 18-20 June, Palanga, Lithuania