Andris Grabovskis

Photoplethysmography Analysis of Artery Properties in Patients with Cardiovascular Diseases

In this study arterial parameters of healthy subjects were compared to those of patients with cardiovascular diseases. The photoplethysmography (PPG) measurements of blood volume pulsations have been performed. Using a novel algorithm for analysis of simultaneously measured ear and finger PPG signals, arterial parameters were evaluated in representative groups of healthy subjects and patients with cardiovascular diseases. Digital volume pulse (DVP), pulse cycle duration (T), augmentation index (AIx), reflection index (RI) and transit time of reflected wave (RTT) were evaluated in every heartbeat cycle. Correlations between the AIx and RI, T and RTT, AIx and standard deviation of AIx, RTT and standard deviation of RTT showed differences between the healthy subjects and patients.

Effect of probe contact pressure on the photoplethysmographic assessment of conduit artery stiffness

Abstract. Currently, photoplethysmography (PPG) is a frequently studied optical blood pulsation detection technique among biophotonic and biomedical researchers due to the fact that it shows high potential for estimating the arterial stiffness (AS). The extraction of diagnostically useful information requires standardized measurement procedure with good repeatability. However, the effects of a crucially important factor—the optimal contact pressure (CP) of the probe—are often ignored. Also, CP values are not reported to evaluate those effects. It is hypothesized that AS estimated from PPG pulse wave 2nd derivative parameter b/a is strongly inconsistent when recorded at nonoptimal probe CP. Our pilot study confirmed this during in vivo PPG recordings from conduit artery sites on five healthy subjects at variable probe CP (0 to 15 kPa) by using 880 nm reflectance type sensor, force transducer, and PPG alternating current (AC) signal pulse area derived optimal CP criterion. The b/a values, calculated from PPG with variable CP, showed variation >300  percent. In contrast, at the optimal CP, the b/a showed high repeatability (coefficient of variability <5  percent). The effect has been explained with exponential pulse pressure-volume relationship model which indicates the optimal CP range.

The analysis of blood flow changes under local anesthetic input using non-contact technique

In this work photoplethysmography imaging (PPGI) technique was used to obtain blood flow changes in human skin under regional anesthesia (RA). PPGI was evaluated from video taken by video camera for 26 patients 2 minutes before and immediately after RA, using custom developed software. Results showed that blood flow obtained by PPGI increases immediately after RA effect and the amplitude of PPGI showed correlation with temperature changes in human skin (r=0.8±0.14, p<0.0001). We found that PPGI technique can be usable for non-contact monitoring of quality of RA.

Usability of photoplethysmography method in estimation of conduit artery stiffness

Three channel photoplethysmography (PPG) signal waveform studies of leg conduit arteries during a provocative occlusion test were performed. PPG waveform second derivative amplitude ratio and arterial pulse wave velocity values showed significant correlations with ultrasound (US) reference method of local and regional arterial stiffness (AS), showing the ability to use PPG for AS change quantitative assessment.

Photoplethysmography system for blood pulsation detection in unloaded artery conditions

Photoplethysmography (PPG) is an optical method of blood pulsation recording and has been extensively studied for decades. Recently PPG is widely used in the medical equipment for patient monitoring and in laboratories for research and physiological studies. In spite of the technological progress in the field of medical equipment, there are no generally accepted standards for clinical PPG measurements up to date. One of the most important factors affecting PPG waveform is the contact pressure between tissue and PPG probe. The aim of the current study was to develop and evaluate a system for software-assisted PPG signal acquisition from the unloaded artery. Novel PPG waveform derived Optimal Pressure Parameter (OPP) has been proposed as the reliable indicator of unloaded artery condition. We affirm that PPG measurements provided in balanced transmural arterial pressure conditions might serve as a reference for the unification of contact manner optical plethysmography methods. It is a step forward towards the standardization of the PPG methodology, and showed that the maximal value of the OPP, obtained in the particular experimental trial, indicates the optimal PPG probe contact pressure at that moment. Our developed system has been validated in the experimental series and showed the possibility of determining the correct PPG contact pressure value with high repeatability. It is concluded that this system can provide the necessary feedback to perform reliable PPG signal acquisition from the unloaded conduit artery.

Multi-spectral photoplethysmography biosensor

A photoplethysmography (PPG) signal can provide very useful information about a subjects hemodynamic status in a hospital or home environment. A newly developed portable multi-spectral photoplethysmography device has been used for studies of 11 healthy subjects. The developed optical fiber biosensor comprises one multi-wavelength laser diode (405nm, 660nm and 780nm) and a single photodiode with multi-channel signal output processing and built in Li-ion accumulator; special software was created for visualization and measuring of the MS-PPG signals. ARM7TDMI-S LPC2148, NXP (founded by Philips) 32 bit processor with clock frequency of 60 MHz performs measurement and analysis of the signal.

Reliability of Hemodynamic Parameters Measured by a Novel Photoplethysmography Device

Three channel photoplethysmography (PPG) signal pulse wave studies of the leg’s conduit arteries during rest conditions were performed. The obtained data of each channel showed similar values, proving arterial PPG as a reliable and repeatable method to assess arterial waveform parameters. A validation experiment was carried out by acquiring signals from three identical IR PPG sensors, which were placed on different sites over the leg’s conduit arteries during rest conditions. Coefficients of variation (CV) were calculated at a 95% confidence interval by comparing results of each subject during multiple attempts. This data processing leads us to certain criteria of improvements in our methodology. Results show that the arterial PPG technique can give trusted and accurate information about the changes in hemodynamics, and therefore, makes it promising for early diagnostics of vascular disease.

A photoplethysmography device for multipurpose blood circulatory system assessment

A novel method for photoplethysmography (PPG) signal detection has been proposed and implemented in a three channel prototype device. The current design is simple, low cost and does not require sophisticated analogue circuits. The prototype was evaluated by physiological measurements and recorded PPG signals from conduit arteries of human subject.

Snapshot hyperspectral system for noninvasive skin blood oxygen saturation monitoring

The present study introduces recently developed compact hyperspectral snapshot system (device and software) for skin oxygen saturation monitoring. This prototype device involves compact snapshot hyperspectral camera, multi-wavelength illuminator, optical filter and crossed polarizers. The device was validated using reference color samples and and in-vivo during finger arterial occlusion tests. The prototype system demonstrated good performance of skin hyperspectral measurements in spectral range of 500-630nm. The results confirmed reliability of developed system for in-vivo assessment of skin blood oxygen saturation.

Hyperspectral evaluation of skin blood oxygen saturation at baseline and during arterial occlusion

Skin capillary blood oxygen saturation is a clinically important diagnostic parameter, which provides valuable information for timely treatment of pathological conditions e.g. sepsis, hypoxemia or decompression illness. Hyperspectral imaging is non-invasive optical techniques with high clinical potential, however its use for skin blood oxygen saturation detection is still challenging, therefore in the present study, a method for in-vivo manipulation of skin oxygen saturation was developed, and reliability of the method evaluated by means of hyperspectral imaging in detection of oxygen saturation. In order to produce alterations of skin capillary blood parameters and oxygen saturation, the proximal phalanx of the right middle finger was occluded with a pneumatic cuff for 25 minutes. During the last minute of occlusion, the hyperspectral cubes (HIS) of both occluded and intact finger were captured, and capillary blood sample was collected for analysis with portable whole blood analyzer (REF). The group mean values for SaO2 in intact finger skin was HIS: 89.46%±8.79% versus REF: 95.13±1.46 % and in occluded finger HSI: 25.85% ±14.00%, versus REF: 22.73±9.09 % displaying a small difference between two independent techniques, which indicate the reliability of finger occlusion model.