Kristjan Pilt - Academia.edu (original) (raw)

Papers by Kristjan Pilt

2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2013

The study was carried out in order to analyse the changes in photoplethysmographic (PPG) signal w... more The study was carried out in order to analyse the changes in photoplethysmographic (PPG) signal waveform, which are caused by cold and warm stimulation. The study was carried out on 7 subjects. The right hand was immersed in cold and warm water up to the wrist during the experiment. The PPG signal was registered from right hand index finger. As a reference, the temperatures of index finger and pulse transit time (PTT) values were measured. A correlation of r = -0.70 was found between normalised slope of the PPG signal and the subject's age. The normalised slope increased noticeably due to the cold and decreased due to the warm water stimulation. It was opposite to the expected results with PTTs and the behaviour has to be investigated in future studies.

IFMBE Proceedings, 2013

ABSTRACT

2012 13th Biennial Baltic Electronics Conference, 2012

ABSTRACT Current work is a pilot study of long-term research of non-invasive pulse wave velocity ... more ABSTRACT Current work is a pilot study of long-term research of non-invasive pulse wave velocity (PWV) measurement method in peripheral arteries. The main objective of this study is to determine most appropriate algorithm for detection of pressure wave equiphase point and calculate accurate pulse transit time (PTT) between two pulse waves. To understand which algorithm gives the most accurate values, we decided to compare mathematical methods with manual method. The manual method was used as a reference. As a result, a linear relationship between the reference method and maximum point determination method of pressure wave second derivative was found, also between the reference method and the method using pressure wave adaptive level of 30% and 50%.

Physiological Measurement, 2014

The aim of this research was to assess the validity of the photoplethysmographic (PPG) waveform i... more The aim of this research was to assess the validity of the photoplethysmographic (PPG) waveform index PPGAI for the estimation of increased arterial stiffness. For this purpose, PPG signals were recorded from 24 healthy subjects and from 20 type II diabetes patients. The recorded PPG signals were processed with the analysis algorithm developed and the waveform index PPGAI similar to the augmentation index (AIx) was calculated. As a reference, the aortic AIx was assessed and normalized for a heart rate of 75 bpm (AIx@75) by a SphygmoCor device. A strong correlation (r = 0.85) between the PPGAI and the aortic AIx@75 and a positive correlation of both indices with age were found. Age corrections for the indices PPGAI and AIx@75 as regression models from the signals of healthy subjects were constructed. Both indices revealed a significant difference between the groups of diabetes patients and healthy controls. However, the PPGAI provided the best statistical discrimination for the group of subjects with increased arterial stiffness. The waveform index PPGAI based on the inexpensive PPG technology can be considered as a perspective measure of increased arterial stiffness estimation in clinical screenings.

IFMBE Proceedings, 2009

Pulse delay is measured between ECG signal R-peak and 50% of PPG signal rising front value. Regis... more Pulse delay is measured between ECG signal R-peak and 50% of PPG signal rising front value. Registered PPG signal can be with low noise-to-signal ratio. For better PPG rising front detection, the PPG signal is preprocessed with adaptive comb filter, which is using ECG signal as reference. Comb filter averages the signal over constant number of periods. Due to it, the computed result for pulse delay is averaged as well.

2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2009

AC component of photoplethysmography signal carries important information for diagnostics. Regist... more AC component of photoplethysmography signal carries important information for diagnostics. Registered signal may be affected by noises, which are sharing the same bandwidth. Adaptive comb filter is used for the AC component extraction. Due to filter averaging behavior it decreases the signal shape difference between consecutive beats. Comb filter needs to be adjusted for PPG signal. Comb filter new weight values are determined through numerical computation. Experiments with generated photoplethysmographic signals were carried out to compare adjusted and non-adjusted adaptive sum comb filter.

Estonian Journal of Engineering, 2010

Pulse transit time, which correlates with blood pressure, is measured between the electrocardiogr... more Pulse transit time, which correlates with blood pressure, is measured between the electrocardiogram R-wave peak and 50% raising front level of a photoplethysmographic (PPG) signal. Registered PPG signal bandwidth may be shared by noise and therefore the signal raising front is undetectable. Electrocardiogram reference adaptive sum comb filter was used to extract the harmonic components of the PPG signal and suppress the noises between them. Averaging effect of the filter on the PPG signal was studied and adjustments were made. The influence of the comb filtered PPG signal on the measurement of pulse transit time was analysed.

2010 Annual International Conference of the IEEE Engineering in Medicine and Biology, 2010

Current work is a part of long term research, which aim is to study the possibilities to diagnose... more Current work is a part of long term research, which aim is to study the possibilities to diagnose the atherosclerosis in early stadium by using pulse wave velocity and its waveform analysis. The mobile experimental measurement complex is built and technically tested for the long term study in hospital. Measurement complex consists of ten physiological signal recording channels and reference devices: Sphygmocor, Arteriograph, Finapres. The measurements with this complex are planned to carry out during six month on patients with different severity of coronary disease and diabetes.

IFMBE Proceedings, 2007

... US 2006/0264771 A1 2. BG Asmar, R. Asmar, RP Moore (2000) Device and met-hod for assessing ca... more ... US 2006/0264771 A1 2. BG Asmar, R. Asmar, RP Moore (2000) Device and met-hod for assessing cardiovascular function. ... Author: Kristjan Pilt Institute: Department of Biomedical Engineering Street: Ehitajate tee 5 City: Tallinn, 19086 Country: Estonia Email: kristjan.pilt@gmail ...

IFMBE Proceedings, 2008

ABSTRACT

2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2008

Measured PPG signals are often contaminated with different noises and artifacts. For clinical dia... more Measured PPG signals are often contaminated with different noises and artifacts. For clinical diagnostics, it is important to have accurate signals. Removing noises and motion artifacts from PPG signal has been actual also in previous studies. In this study, we are proposing new adaptive impulse correlated filter (AICF) improvement for plethysmographic signals. It uses ECG signal to create reference with unit impulses. All signals, which do not correlate with reference signal, will be filtered out. To show, how the filter acts with artifacts with low SNR, the experiment was conducted.

2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007

For applications where PPG signal AC component needs to be measured without disturbances in its s... more For applications where PPG signal AC component needs to be measured without disturbances in its shape and recorded digitally with high digitalization accuracy, the step-by-step DC component eliminator is developed. This paper describes step-by-step DC component eliminator, which is utilized with analogue comparator and operational amplifier. It allows to record PPG signal without disturbances in its shape in 24-hours PPG signal monitoring system. The experiments with PPG signal have been carried out.

Scandinavian Cardiovascular Journal, 2011

Objective. To assess the association between QT interval, QT dispersion and main cardiovascular r... more Objective. To assess the association between QT interval, QT dispersion and main cardiovascular risk factors in Tallinn women population aged 50 -69 years. Design. A random sample of Tallinn population, 302 women underwent 12-lead rest ECG, echocardiography and laboratory tests. Corrected QT interval and QT dispersion were calculated. Results . The signifi cant correlation coeffi cients for corrected QT interval and dispersion were observed with systolic, diastolic, pulse pressure, blood pressure value grade, heart rate, left ventricular mass index, and total cardiovascular risk grade. According to the data of multiple logistic regression, risk factors independently associated with prolonged QTc and QTD were arterial hypertension: OR 2.69, p Ͻ 0.001 and OR 3.29, p Ͻ 0.001, pulse pressure Ն 60 mm Hg: OR 2.62, p Ͻ 0.001 and OR 3.04, p Ͻ 0.001, age Ͼ 65 years: OR 2.44, p Ͻ 0.001 and OR 1.91, p Ͻ 0.01, family history of cardiovascular disease: OR 2.02, p Ͻ 0.01 and OR 2.48, p Ͻ 0.001, left ventricular hypertrophy: OR 2.78, p Ͻ 0.001 and OR 5.29, p Ͻ 0.001. Multivariable linear regression data showed an independent association between corrected QT interval, QT dispersion and systolic blood pressure: β ϭ 0.32, p Ͻ 0.001 and β ϭ 0.39, p ϭ 0.003, pulse pressure: β ϭ 0.21, p ϭ 0.004 and β ϭ 0.27, p Ͻ 0.001, blood pressure value grade: β ϭ 0.35, p Ͻ 0.001 (for QT dispersion only), heart rate: β ϭ 0.21, p Ͻ 0.001 and β ϭ −0.19, p ϭ 0.001, left ventricular mass index: β ϭ 0.23, p Ͻ 0.001 and β ϭ 0.27, p Ͻ 0.001. Conclusion . In Tallinn women population, electrocardiographic parameters refl ecting ventricular repolarization are associated with systolic blood pressure, pulse pressure, blood pressure value grade, heart rate and left ventricular hypertrophy. Scand Cardiovasc J Downloaded from informahealthcare.com by 89.235.243.253 on 10/12/12 For personal use only. Scand Cardiovasc J Downloaded from informahealthcare.com by 89.235.243.253 on 10/12/12

TheScientificWorldJournal, 2013

The ability to identify premature arterial stiffening is of considerable value in the prevention ... more The ability to identify premature arterial stiffening is of considerable value in the prevention of cardiovascular diseases. The "ageing index" (AGI), which is calculated from the second derivative photoplethysmographic (SDPPG) waveform, has been used as one method for arterial stiffness estimation and the evaluation of cardiovascular ageing. In this study, the new SDPPG analysis algorithm is proposed with optimal filtering and signal normalization in time. The filter parameters were optimized in order to achieve the minimal standard deviation of AGI, which gives more effective differentiation between the levels of arterial stiffness. As a result, the optimal low-pass filter edge frequency of 6 Hz and transitionband of 1 Hz were found, which facilitates AGI calculation with a standard deviation of 0.06. The study was carried out on 21 healthy subjects and 20 diabetes patients. The linear relationship (r = 0.91) between each subject's age and AGI was found, and a linear...

2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2013

The study was carried out in order to analyse the changes in photoplethysmographic (PPG) signal w... more The study was carried out in order to analyse the changes in photoplethysmographic (PPG) signal waveform, which are caused by cold and warm stimulation. The study was carried out on 7 subjects. The right hand was immersed in cold and warm water up to the wrist during the experiment. The PPG signal was registered from right hand index finger. As a reference, the temperatures of index finger and pulse transit time (PTT) values were measured. A correlation of r = -0.70 was found between normalised slope of the PPG signal and the subject's age. The normalised slope increased noticeably due to the cold and decreased due to the warm water stimulation. It was opposite to the expected results with PTTs and the behaviour has to be investigated in future studies.

IFMBE Proceedings, 2013

ABSTRACT

2012 13th Biennial Baltic Electronics Conference, 2012

ABSTRACT Current work is a pilot study of long-term research of non-invasive pulse wave velocity ... more ABSTRACT Current work is a pilot study of long-term research of non-invasive pulse wave velocity (PWV) measurement method in peripheral arteries. The main objective of this study is to determine most appropriate algorithm for detection of pressure wave equiphase point and calculate accurate pulse transit time (PTT) between two pulse waves. To understand which algorithm gives the most accurate values, we decided to compare mathematical methods with manual method. The manual method was used as a reference. As a result, a linear relationship between the reference method and maximum point determination method of pressure wave second derivative was found, also between the reference method and the method using pressure wave adaptive level of 30% and 50%.

Physiological Measurement, 2014

The aim of this research was to assess the validity of the photoplethysmographic (PPG) waveform i... more The aim of this research was to assess the validity of the photoplethysmographic (PPG) waveform index PPGAI for the estimation of increased arterial stiffness. For this purpose, PPG signals were recorded from 24 healthy subjects and from 20 type II diabetes patients. The recorded PPG signals were processed with the analysis algorithm developed and the waveform index PPGAI similar to the augmentation index (AIx) was calculated. As a reference, the aortic AIx was assessed and normalized for a heart rate of 75 bpm (AIx@75) by a SphygmoCor device. A strong correlation (r = 0.85) between the PPGAI and the aortic AIx@75 and a positive correlation of both indices with age were found. Age corrections for the indices PPGAI and AIx@75 as regression models from the signals of healthy subjects were constructed. Both indices revealed a significant difference between the groups of diabetes patients and healthy controls. However, the PPGAI provided the best statistical discrimination for the group of subjects with increased arterial stiffness. The waveform index PPGAI based on the inexpensive PPG technology can be considered as a perspective measure of increased arterial stiffness estimation in clinical screenings.

IFMBE Proceedings, 2009

Pulse delay is measured between ECG signal R-peak and 50% of PPG signal rising front value. Regis... more Pulse delay is measured between ECG signal R-peak and 50% of PPG signal rising front value. Registered PPG signal can be with low noise-to-signal ratio. For better PPG rising front detection, the PPG signal is preprocessed with adaptive comb filter, which is using ECG signal as reference. Comb filter averages the signal over constant number of periods. Due to it, the computed result for pulse delay is averaged as well.

2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2009

AC component of photoplethysmography signal carries important information for diagnostics. Regist... more AC component of photoplethysmography signal carries important information for diagnostics. Registered signal may be affected by noises, which are sharing the same bandwidth. Adaptive comb filter is used for the AC component extraction. Due to filter averaging behavior it decreases the signal shape difference between consecutive beats. Comb filter needs to be adjusted for PPG signal. Comb filter new weight values are determined through numerical computation. Experiments with generated photoplethysmographic signals were carried out to compare adjusted and non-adjusted adaptive sum comb filter.

Estonian Journal of Engineering, 2010

Pulse transit time, which correlates with blood pressure, is measured between the electrocardiogr... more Pulse transit time, which correlates with blood pressure, is measured between the electrocardiogram R-wave peak and 50% raising front level of a photoplethysmographic (PPG) signal. Registered PPG signal bandwidth may be shared by noise and therefore the signal raising front is undetectable. Electrocardiogram reference adaptive sum comb filter was used to extract the harmonic components of the PPG signal and suppress the noises between them. Averaging effect of the filter on the PPG signal was studied and adjustments were made. The influence of the comb filtered PPG signal on the measurement of pulse transit time was analysed.

2010 Annual International Conference of the IEEE Engineering in Medicine and Biology, 2010

Current work is a part of long term research, which aim is to study the possibilities to diagnose... more Current work is a part of long term research, which aim is to study the possibilities to diagnose the atherosclerosis in early stadium by using pulse wave velocity and its waveform analysis. The mobile experimental measurement complex is built and technically tested for the long term study in hospital. Measurement complex consists of ten physiological signal recording channels and reference devices: Sphygmocor, Arteriograph, Finapres. The measurements with this complex are planned to carry out during six month on patients with different severity of coronary disease and diabetes.

IFMBE Proceedings, 2007

... US 2006/0264771 A1 2. BG Asmar, R. Asmar, RP Moore (2000) Device and met-hod for assessing ca... more ... US 2006/0264771 A1 2. BG Asmar, R. Asmar, RP Moore (2000) Device and met-hod for assessing cardiovascular function. ... Author: Kristjan Pilt Institute: Department of Biomedical Engineering Street: Ehitajate tee 5 City: Tallinn, 19086 Country: Estonia Email: kristjan.pilt@gmail ...

IFMBE Proceedings, 2008

ABSTRACT

2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2008

Measured PPG signals are often contaminated with different noises and artifacts. For clinical dia... more Measured PPG signals are often contaminated with different noises and artifacts. For clinical diagnostics, it is important to have accurate signals. Removing noises and motion artifacts from PPG signal has been actual also in previous studies. In this study, we are proposing new adaptive impulse correlated filter (AICF) improvement for plethysmographic signals. It uses ECG signal to create reference with unit impulses. All signals, which do not correlate with reference signal, will be filtered out. To show, how the filter acts with artifacts with low SNR, the experiment was conducted.

2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007

For applications where PPG signal AC component needs to be measured without disturbances in its s... more For applications where PPG signal AC component needs to be measured without disturbances in its shape and recorded digitally with high digitalization accuracy, the step-by-step DC component eliminator is developed. This paper describes step-by-step DC component eliminator, which is utilized with analogue comparator and operational amplifier. It allows to record PPG signal without disturbances in its shape in 24-hours PPG signal monitoring system. The experiments with PPG signal have been carried out.

Scandinavian Cardiovascular Journal, 2011

Objective. To assess the association between QT interval, QT dispersion and main cardiovascular r... more Objective. To assess the association between QT interval, QT dispersion and main cardiovascular risk factors in Tallinn women population aged 50 -69 years. Design. A random sample of Tallinn population, 302 women underwent 12-lead rest ECG, echocardiography and laboratory tests. Corrected QT interval and QT dispersion were calculated. Results . The signifi cant correlation coeffi cients for corrected QT interval and dispersion were observed with systolic, diastolic, pulse pressure, blood pressure value grade, heart rate, left ventricular mass index, and total cardiovascular risk grade. According to the data of multiple logistic regression, risk factors independently associated with prolonged QTc and QTD were arterial hypertension: OR 2.69, p Ͻ 0.001 and OR 3.29, p Ͻ 0.001, pulse pressure Ն 60 mm Hg: OR 2.62, p Ͻ 0.001 and OR 3.04, p Ͻ 0.001, age Ͼ 65 years: OR 2.44, p Ͻ 0.001 and OR 1.91, p Ͻ 0.01, family history of cardiovascular disease: OR 2.02, p Ͻ 0.01 and OR 2.48, p Ͻ 0.001, left ventricular hypertrophy: OR 2.78, p Ͻ 0.001 and OR 5.29, p Ͻ 0.001. Multivariable linear regression data showed an independent association between corrected QT interval, QT dispersion and systolic blood pressure: β ϭ 0.32, p Ͻ 0.001 and β ϭ 0.39, p ϭ 0.003, pulse pressure: β ϭ 0.21, p ϭ 0.004 and β ϭ 0.27, p Ͻ 0.001, blood pressure value grade: β ϭ 0.35, p Ͻ 0.001 (for QT dispersion only), heart rate: β ϭ 0.21, p Ͻ 0.001 and β ϭ −0.19, p ϭ 0.001, left ventricular mass index: β ϭ 0.23, p Ͻ 0.001 and β ϭ 0.27, p Ͻ 0.001. Conclusion . In Tallinn women population, electrocardiographic parameters refl ecting ventricular repolarization are associated with systolic blood pressure, pulse pressure, blood pressure value grade, heart rate and left ventricular hypertrophy. Scand Cardiovasc J Downloaded from informahealthcare.com by 89.235.243.253 on 10/12/12 For personal use only. Scand Cardiovasc J Downloaded from informahealthcare.com by 89.235.243.253 on 10/12/12

TheScientificWorldJournal, 2013

The ability to identify premature arterial stiffening is of considerable value in the prevention ... more The ability to identify premature arterial stiffening is of considerable value in the prevention of cardiovascular diseases. The "ageing index" (AGI), which is calculated from the second derivative photoplethysmographic (SDPPG) waveform, has been used as one method for arterial stiffness estimation and the evaluation of cardiovascular ageing. In this study, the new SDPPG analysis algorithm is proposed with optimal filtering and signal normalization in time. The filter parameters were optimized in order to achieve the minimal standard deviation of AGI, which gives more effective differentiation between the levels of arterial stiffness. As a result, the optimal low-pass filter edge frequency of 6 Hz and transitionband of 1 Hz were found, which facilitates AGI calculation with a standard deviation of 0.06. The study was carried out on 21 healthy subjects and 20 diabetes patients. The linear relationship (r = 0.91) between each subject's age and AGI was found, and a linear...