- Email: [email protected]
Measurement of the arterial pulse wave with biomagnetic technique
International Congress Series 1300 (2007) 472 – 475
www.ics-elsevier.com
Measurement of the arterial pulse wave with biomagnetic technique T. Cordova-Fraga a,⁎, C.I. Huerta b , M. Sosa a , R. Huerta c , M. Vargas a , E. Hernández a , J.J. Bernal a b
a Instituto de Física, Universidad de Guanajuato, Mexico Instituto de Investigaciones sobre el Trabajo, Universidad de Guanajuato, Mexico c Universidad Veracruzana, Mexico
Abstract. An alternative to assess arterial pulse wave (APW) is proposed. The blood pressure changes measurement at the jugular anatomical region, using a differential magnetic gradiometer was performed through sensing the slight mechanical pulsations of the skin without applied manual pressure. A well defined waveform, resembling general features of the electrocardiogram QRS complex, is obtained. The potential application of a non-expensive clinical monitoring of the APW measured at the jugular region and at other point of interest could be the precise pulse time differences to performed arterial pulse wave velocity (APWV) measurements. © 2007 Elsevier B.V. All rights reserved. Keywords: Pulswave; Biomagmetic; Magnetic marker
1. Introduction The APWV is considered the gold standard method of measuring arterial elasticity or stiffness. The assessment is performed through the inverse relation between the APWV and the square root of the vessel wall compliance. There are some standard methodologies to measure APWV like Doppler ultrasonography [1]. This technique performs flow pulse measurement as opposed to the pressure pulse of this work. Piezoelectric device techniques [2] perform transcutaneous monitoring ⁎ Corresponding author. Loma del Bosque 103, Lomas del campestre, 37170 León, Gto., Mexico. Tel.: +52 477 488 5100x8454; fax: +52 477 488 5100 8410. E-mail addresses: [email protected], [email protected] (T. Cordova-Fraga). 0531-5131/ © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2006.12.074
T. Cordova-Fraga et al. / International Congress Series 1300 (2007) 472–475
473
Fig 1. Schematic diagram of the experimental setup.
of the pressure pulse. Photoplethysmography [3] which is a non-invasive optical technique using skin backscattered optical signals that measures variations in skin blood volume and perfusion, taking into account components that are synchronous with respiratory and cardiac rhythms. The external methodologies still have some problems like the pressure applied in the case of the PPG method [4]. The wave velocity varies over the range from about 12 m/s to 15 m/s in stiff peripheral arteries, whereas in normal arteries it has a velocity in the range of 7 to 9 m/s and the deviation of the normal values is used to diagnose peripheral vascular disease [5] for risk stratification, monitoring disease progression and evaluating treatment. In this work a sensor composed by a magnetic first order gradiometer for monitoring the APW was implemented. The method is based on the measurements of the magnetic flux changes produced by the vibrations of a small magnet attached to the jugular anatomical region. 2. Materials and procedure The magnetometer device was assembled with two identical coils of n = 400 loops of magnet wire No. 38 and diameter 28 mm, they were arranged in a first order gradiometer with baseline 48 mm and linearity range from 22 to 50 ± 7 mm. A magnetic marker was held on skin, over the subject aorta artery in order to induce a magnetic field in the magnetometer by the mechanical movements. Subjects underwent a simultaneous measurement of the cardiac frequency, with the implemented biomagnetic modality and a clinical Baumanometer.
Fig 2. Comparison between an ECG obtained from the medical routine procedure and one from our proposal. a) Typical waveform from a common ECG. b) Wave pattern from a volunteer obtained with our sensor.
474
T. Cordova-Fraga et al. / International Congress Series 1300 (2007) 472–475
Fig 3. a) Typical filtered data of heart rate for one subject, obtained with our magnetic device. A passband filter from 10 to 110 cpm was used to filter the data. b) A basic Fourier transform of these data.
The magnetic data were recorded at a frequency of 300 Hz in a LabVIEW platform. In Fig. 1 a schematic diagram of the experimental setup is shown. Using this arrangement one measurement was performed on each subject during 3 min. 3. Analysis A comparison between an ECG obtained by the medical routine procedure and one with our device was made. The typical waveform from a common ECG record is presented in Fig. 2a. It has three main characteristics: the P waveform, the QRS waveform, and the T waveform; while in Fig. 2b it is shown a typical wave pattern associated to the arterial pulse wave of a healthy volunteer, as obtained with the sensor proposed in this paper. The general features of the ECG waveform is drawn by the magnetic device, that is three peaks sequenced, corresponding roughly to the P, QRS and T features of ECG waveform. The data was filtered to leave frequencies from 10 to 110 cpm. Basic Fourier transform was performed to confirm that most of the wave features have mainly the heart rate frequency and that other frequencies appear far away from this one, in order to assure negligible influence on the main oscillation or easy discrimination. 4. Results Fig. 3a shows a typical filtered data of a pulse wave for one subject, obtained with our magnetic device. A passband filter from 10 to 110 cpm was used to filter the data shown in Fig. 3a. A basic Fourier transform of these data is shown in Fig. 3b. This confirms that just the frequency of the respiration which is too low (around 18 cpm) and that for the heart rate are associated with the pulse measured (peak around 90 cpm). 5. Discussion This Biomagnetic probe seems to be adequate to perform routine clinical evaluations of the APW. The medical application of this assessments and the advantage of this methodology opposed to the current techniques, aside of the easiness and cheapness, is a matter of
T. Cordova-Fraga et al. / International Congress Series 1300 (2007) 472–475
475
further investigations. However, taking as a reference the jugular and performing the measurement at any other anatomical region or taking a normal ECG would be possible to assess the APWV by pulse time difference. It is evident that a strict validation of this technique in any application as APWV or other, must include formal interpretation in terms of the links among heart electrical activity, artery pressure changes, mechanical properties of skin and subcutaneous tissue and mechanical properties of the blood vessel walls (compliance, elasticity or stiffness). Acknowledgments This work was partially supported by CONACyT project No. 2003-CO2-44058. The authors also thank J. C. Martínez, H. Ayala and J. M. Noriega for their technical support. References [1] J.S. Wrigh, et al., Aortic compliance measured by non invasive Doppler ultrasound: description of a method and its reproducibility, Clin. Sci. (Colch) 78 (1990) 463–468. [2] J. McLaughlin, et al., Piezoelectric sensor determination of arterial pulse wave velocity, Physiol. Meas. 24 (3) (Aug 2003) 693–702. [3] Stavros Loukogeorgakis1, et al., Validation of a device to measure arterial pulse wave velocity by a photoplethysmographic method, Physiol. Meas. 23 (2002) 581–596. [4] X.F. Teng, Y.T. Zhang, The effect of applied sensor contact force on pulse transit time, Physiol. Meas. 27 (2006) 675–684. [5] T. Kanda, et al., Arterial pulse wave velocity and risk factors for peripheral vascular disease, Eur. J. Appl. Physiol. Occup. Physiol. 82 (1–2) (2000) 1–7.
www.ics-elsevier.com
Measurement of the arterial pulse wave with biomagnetic technique T. Cordova-Fraga a,⁎, C.I. Huerta b , M. Sosa a , R. Huerta c , M. Vargas a , E. Hernández a , J.J. Bernal a b
a Instituto de Física, Universidad de Guanajuato, Mexico Instituto de Investigaciones sobre el Trabajo, Universidad de Guanajuato, Mexico c Universidad Veracruzana, Mexico
Abstract. An alternative to assess arterial pulse wave (APW) is proposed. The blood pressure changes measurement at the jugular anatomical region, using a differential magnetic gradiometer was performed through sensing the slight mechanical pulsations of the skin without applied manual pressure. A well defined waveform, resembling general features of the electrocardiogram QRS complex, is obtained. The potential application of a non-expensive clinical monitoring of the APW measured at the jugular region and at other point of interest could be the precise pulse time differences to performed arterial pulse wave velocity (APWV) measurements. © 2007 Elsevier B.V. All rights reserved. Keywords: Pulswave; Biomagmetic; Magnetic marker
1. Introduction The APWV is considered the gold standard method of measuring arterial elasticity or stiffness. The assessment is performed through the inverse relation between the APWV and the square root of the vessel wall compliance. There are some standard methodologies to measure APWV like Doppler ultrasonography [1]. This technique performs flow pulse measurement as opposed to the pressure pulse of this work. Piezoelectric device techniques [2] perform transcutaneous monitoring ⁎ Corresponding author. Loma del Bosque 103, Lomas del campestre, 37170 León, Gto., Mexico. Tel.: +52 477 488 5100x8454; fax: +52 477 488 5100 8410. E-mail addresses: [email protected], [email protected] (T. Cordova-Fraga). 0531-5131/ © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2006.12.074
T. Cordova-Fraga et al. / International Congress Series 1300 (2007) 472–475
473
Fig 1. Schematic diagram of the experimental setup.
of the pressure pulse. Photoplethysmography [3] which is a non-invasive optical technique using skin backscattered optical signals that measures variations in skin blood volume and perfusion, taking into account components that are synchronous with respiratory and cardiac rhythms. The external methodologies still have some problems like the pressure applied in the case of the PPG method [4]. The wave velocity varies over the range from about 12 m/s to 15 m/s in stiff peripheral arteries, whereas in normal arteries it has a velocity in the range of 7 to 9 m/s and the deviation of the normal values is used to diagnose peripheral vascular disease [5] for risk stratification, monitoring disease progression and evaluating treatment. In this work a sensor composed by a magnetic first order gradiometer for monitoring the APW was implemented. The method is based on the measurements of the magnetic flux changes produced by the vibrations of a small magnet attached to the jugular anatomical region. 2. Materials and procedure The magnetometer device was assembled with two identical coils of n = 400 loops of magnet wire No. 38 and diameter 28 mm, they were arranged in a first order gradiometer with baseline 48 mm and linearity range from 22 to 50 ± 7 mm. A magnetic marker was held on skin, over the subject aorta artery in order to induce a magnetic field in the magnetometer by the mechanical movements. Subjects underwent a simultaneous measurement of the cardiac frequency, with the implemented biomagnetic modality and a clinical Baumanometer.
Fig 2. Comparison between an ECG obtained from the medical routine procedure and one from our proposal. a) Typical waveform from a common ECG. b) Wave pattern from a volunteer obtained with our sensor.
474
T. Cordova-Fraga et al. / International Congress Series 1300 (2007) 472–475
Fig 3. a) Typical filtered data of heart rate for one subject, obtained with our magnetic device. A passband filter from 10 to 110 cpm was used to filter the data. b) A basic Fourier transform of these data.
The magnetic data were recorded at a frequency of 300 Hz in a LabVIEW platform. In Fig. 1 a schematic diagram of the experimental setup is shown. Using this arrangement one measurement was performed on each subject during 3 min. 3. Analysis A comparison between an ECG obtained by the medical routine procedure and one with our device was made. The typical waveform from a common ECG record is presented in Fig. 2a. It has three main characteristics: the P waveform, the QRS waveform, and the T waveform; while in Fig. 2b it is shown a typical wave pattern associated to the arterial pulse wave of a healthy volunteer, as obtained with the sensor proposed in this paper. The general features of the ECG waveform is drawn by the magnetic device, that is three peaks sequenced, corresponding roughly to the P, QRS and T features of ECG waveform. The data was filtered to leave frequencies from 10 to 110 cpm. Basic Fourier transform was performed to confirm that most of the wave features have mainly the heart rate frequency and that other frequencies appear far away from this one, in order to assure negligible influence on the main oscillation or easy discrimination. 4. Results Fig. 3a shows a typical filtered data of a pulse wave for one subject, obtained with our magnetic device. A passband filter from 10 to 110 cpm was used to filter the data shown in Fig. 3a. A basic Fourier transform of these data is shown in Fig. 3b. This confirms that just the frequency of the respiration which is too low (around 18 cpm) and that for the heart rate are associated with the pulse measured (peak around 90 cpm). 5. Discussion This Biomagnetic probe seems to be adequate to perform routine clinical evaluations of the APW. The medical application of this assessments and the advantage of this methodology opposed to the current techniques, aside of the easiness and cheapness, is a matter of
T. Cordova-Fraga et al. / International Congress Series 1300 (2007) 472–475
475
further investigations. However, taking as a reference the jugular and performing the measurement at any other anatomical region or taking a normal ECG would be possible to assess the APWV by pulse time difference. It is evident that a strict validation of this technique in any application as APWV or other, must include formal interpretation in terms of the links among heart electrical activity, artery pressure changes, mechanical properties of skin and subcutaneous tissue and mechanical properties of the blood vessel walls (compliance, elasticity or stiffness). Acknowledgments This work was partially supported by CONACyT project No. 2003-CO2-44058. The authors also thank J. C. Martínez, H. Ayala and J. M. Noriega for their technical support. References [1] J.S. Wrigh, et al., Aortic compliance measured by non invasive Doppler ultrasound: description of a method and its reproducibility, Clin. Sci. (Colch) 78 (1990) 463–468. [2] J. McLaughlin, et al., Piezoelectric sensor determination of arterial pulse wave velocity, Physiol. Meas. 24 (3) (Aug 2003) 693–702. [3] Stavros Loukogeorgakis1, et al., Validation of a device to measure arterial pulse wave velocity by a photoplethysmographic method, Physiol. Meas. 23 (2002) 581–596. [4] X.F. Teng, Y.T. Zhang, The effect of applied sensor contact force on pulse transit time, Physiol. Meas. 27 (2006) 675–684. [5] T. Kanda, et al., Arterial pulse wave velocity and risk factors for peripheral vascular disease, Eur. J. Appl. Physiol. Occup. Physiol. 82 (1–2) (2000) 1–7.