Kalju Meigas

Self-mixing in a diode laser as a method for cardiovascular diagnostics

Our aim is the development of a simple optical method for pulse wave profile, pulse wave delay time, and blood flow measurement. The method is based on recording the Doppler frequency shift related to a moving target--blood vessel walls or small particles. The Doppler signal is detected using the self-mixing that occurs in the diode laser cavity when radiation scatters back from the moving target into the laser and interferes with the field inside. Two different ways can be simultaneously used for the self-mixing signal extraction: a photodiode accommodated in the rear facet of the diode laser package and a resistor from the laser pump current. An experimental device with a pigtail laser diode is developed that is able to detect the pulsation of major arteries with potentially useful information, including the pulse wave profile and the pulse wave delay time. The pulse wave delay time in different regions of the human body is measured relative to the electrocardiogram (ECG) signal. Also the flow velocity of a liquid suspension containing particles the size of erythrocytes (equivalent to blood flow) is measured. Registered signals are stored after digitalization and preprocessed using LabView for a Windows environment. The described device has the application of the self-mixing method and highlights significant advantages of simplicity, compactness, and robustness as well as the self-aligning and self-detecting abilities of such method, compared with the use of conventional interferometric method.

Continuous blood pressure monitoring using pulse wave delay

Proposed paper is a part of a research to develop a convenient method for continuous monitoring of blood pressure by non-invasive and non-oscillometric way. The method is based on a presumption that there is a singular relationship between the velocity of pulse wave and blood pressure for a person. The detection of the velocity of pulse wave is based on the registration of the mechanical movements of blood vessels walls and computing the time delay in different regions of the human body using an ECG as a reference signal. Additional information about the blood pressure evaluation is gotten from the photoplethysmographic (PPG) channel. Used optical method, which is able to detect pulsation profiles of the blood vessels, is based on the self-mixing that occurs in the diode laser cavity when the radiation, scattered back by the skin into the laser, interferes with the field inside it and causes the changes of the laser pump current. National Instruments software LabView for Windows is used for output signal digitalization and processing purposes.

New Photoplethysmographic Signal Analysis Algorithm for Arterial Stiffness Estimation

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 subjects age and AGI was found, and a linear model with regression line was constructed. For diabetes patients, the mean AGI value difference from the proposed model y AGI was found to be 0.359. The difference was found between healthy and diabetes patients groups with significance level of P < 0.0005.

Pulse Wave Velocity in Continuous Blood Pressure Measurements

This paper is a part of research which is focused on the development of the convenient device for continuous non-invasive monitoring of arterial blood pressure by noninvasive and non-oscillometric way. Potentially useful parameter for continuous monitoring of blood pressure could be the pulse wave velocity between different regions of human body. It has been demonstrated that systolic blood pressure estimation from this parameter is possible with acceptable accuracy by personal calibration of the method for particular patient. However, most of previous studies are focused on utilizing such measurement on patients in critical conditions; the data of experiments with healthy subjects are quite limited. The blood pressure estimation method is based on a presumption that there is a singular relationship between the pulse wave velocity in arterial system and blood pressure. The measurement of pulse wave velocity involves the registration of two time markers, one of which is based on ECG R peak detection and another on the detection of pulse wave in peripheral arteries. As a result of current study it is shown that with the correct personal calibration it is possible to estimate beat-to-beat systolic arterial blood pressure with comparable accuracy to conventional noninvasive methods.

Assessment of Pulse Wave Velocity and Augmentation Index in different arteries in patients with severe coronary heart disease

The aim of this study was to assess pulse wave velocity (PWV) and augmentation index in different arteries in patients with severe coronary heart disease (CHD). Signal measurements were obtained from 28 subjects. Severe coronary heart disease was confirmed by coronary angiography. Aortic PWV and augmentation Index were measured using the TENSIOMed Arteriograph. Four other pulse wave velocities (upper limb PWVx, upper limb PWV2, upper limb PWV3 and lower limb PWV) were obtained using PowerLab 4/20T device. It was found that aortic PWV was significantly increased in the CHD group compared with that in the control group (P<0.01). Augmentation index was significantly increased in the CHD group compared with the control group (P<0.01). This study shows the strong association of aortic stiffness and atherosclerosis. Pulse wave analysis can provide inexpensive and noninvasive means for studying changes in the elastic properties of the vascular system with the coronary heart disease.

An experimental measurement complex for probable estimation of arterial stiffness

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.

Simple coherence method for blood flow detection

The blood flow velocity registration method using an optical coherent photo detection in a diode laser is presented. The dependence of signal on distance and non-conventional self- mixing interferences has bene discussed. Also, an experimental device with pigtail laser diode is developed. This device is able to measure blood flow velocity or velocity of liquid suspension containing particles with size of erythrocytes. During experiments the liquid suspension containing polymer micro spheres with spheres diameter 7.0 microns and density 1.05 g/cc was used instead of real blood. The basis of the registration is the self-mixing that occurs in diode laser cavity when the radiation scattered back by the particles into the laser interferes with the field inside it and causes a changes of a laser pump current. National Instruments software LabView for Windows is used for output signal digitalization and pre-processing purposes. There is good correlation between calculated and measured with proposed device values of different velocities. Described device as application of self-mixing method highlighted the significant advantages of simplicity, compactness, and robustness as well as the self-aligning and self-detecting abilities of such methods when compared with the use of conventional interferometric methods.

Coherent photodetection for pulse profile registration

The arterial pulse profile registration method using an optical coherent photodetection in a diode laser is presented. An experimental device with pigtail laser diode has been developed. This device is able to detect pulsation profiles of major arteries with potentially useful information including pulse wave velocity and profile of pulse pressure. The basis of the registration is the self- mixing that occurs in the diode laser cavity when the radiation, scattered back by the skin into the laser, interferes with the field inside it and causes the changes of the laser pump current. These changes are being registered in two different ways simultaneously; with using a photodiode accommodated in the rear facet of the diode laser package and with a help of small resistance resistor from the chain of laser pump current. The delay of pulse wave in different regions of human body is measured relatively to ECG signal. Registered signals are sorted after digitalization and pre-processed using LabView for Windows environment.

Echocardiographic assessment of the different left ventricular geometric patterns in middle‐aged men and women in Tallinn

The aim of this study was to determine the association of left ventricular (LV) geometry with sex, age, arterial hypertension and obesity in Tallinn. In a framework of a population study for cardiovascular risk factors, echocardiography was carried out in 325 men and 398 women (69.3% of all 1043 participants aged 35–59) in 1999–2001. Left ventricular hypertrophy was defined if left ventricular mass (LVM), LVM/height and LVM/body surface area were 294 g, 163 g/m and 150 g/m 2 in men, and 198 g, 121 g/m and 120 g/m 2 in women, respectively. LV geometry was analysed according to four types generally recognized (with regard to relative wall thickness >0.45). The prevalence of concentric hypertrophy was similar in men and women: 7.7% and 9.1%. The prevalence of eccentric hypertrophy was significantly higher in women than in men (33.3% vs 4.9%). Concentric remodelling was also found in women more often than in men (9.5 vs 5.5%; p < 0.05). Regardless of sex and age, concentric hypertrophy was never found in participants with blood pressure <140/90. In hypertensives, there was a tendency for age‐related increase of concentric hypertrophy prevalence: the latter was higher in women than in men: 39.1% vs 25.5%; p < 0.05. In examinees with BMI <30, this type of LV geometry was seldom found: in 3.1% of men and 5.0% of women; p < 0.05. In obese persons, it increased with age, reaching 26.5% in men and 21.2% in women (p < 0.05). The prevalence of eccentric hypertrophy in men increased with age, and with hypertension and obesity. The prevalence of concentric remodelling in men was not related to BMI; it was significantly more often found in older age groups and in hypertensives. In women, the prevalence of eccentric hypertrophy and concentric remodelling was not related to age, hypertension or obesity.

Second derivative analysis of forehead photoplethysmographic signal in healthy volunteers and diabetes patients

The second derivative analysis has been used to characterize the changes in forehead photoplethysmographic (PPG) signal, which are caused by the stiffness of blood vessels. Before the distinctive wave amplitudes were measured the forehead PPG signals from healthy volunteers and diabetes patients were filtered, two times differentiated, normalized in length, and averaged. The correlation relationships between normalized amplitudes and age were found. The values of normalized amplitudes b/a and d/a were found to be influenced by the stiffness of the blood vessels.