Uldis Rubins

Finger and ear photoplethysmogram waveform analysis by fitting with Gaussians

Analysis of the contour of the blood volume pulse (VP) has become important because it contains much information about cardiovascular activity. Traditionally, pulse contour analysis requires first or higher derivatives to be calculated. This paper describes a novel algorithm for analysing simultaneously measured ear and finger photoplethysmography (PPG) signals. The algorithm separates the systolic wave and the diastolic wave of the VP and fits each of them with the sum of two Gaussian functions. The VP was obtained from PPG signals taken from 40 healthy subjects at each heartbeat cycle. From the evaluated VP, time values of the direct wave and three reflected waves were calculated, as well as the augmentation index (AI) and the reflection index (RI). The evaluated parameters were compared with those that were obtained by the derivative method, and it was demonstrated that the new method can be used to analyze VP waveforms.

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.

Real-Time Photoplethysmography Imaging System

Real-time non-contact photoplethysmography imaging (PPGI) system for high-resolution blood perfusion mapping in human skin has been proposed. The PPGI system comprises of LED lamp, webcam and computer with video processing software. The purpose of this study is to evaluate the reliability of the PPGI system when measuring blood perfusion. The validation study of PPGI and laser-Doppler perfusion imager (LDPI) was performed during local warming of palm skin. Results showed that the amplitude of PPGI increases immediately after warming and well correlated with the mean LDPI amplitude (R=0.92+-0.03, p<0.0001). We found that PPGI technique has good potential for non-contact monitoring of blood perfusion changes.

Multi-spectral skin imaging by a consumer photo-camera

The possibilities to perform multi-band spectral imaging by means of a consumer color camera without external filters have been studied. Images at up to 6 spectral bands may be extracted from a single color image after appropriate signal processing. The proposed technique was tested in pilot measurements of in-vivo skin hemoglobin maps and laser-excited autofluorescence images.

Monitoring of blood pulsation using non-contact technique

Time resolved detection and analysis of the skin back-scattered optical signals (reflection photople- thysmography or contact PPG) provide rich information on skin blood volume pulsations and can serve for car- diovascular assessment. The widely used contact PPG technique has many limitations, like high sensitivity to sensor movement etc. The newly developed non-contact PPG technique has been developed in this work. Poten- tial of the new technique for express-assessment of hu- man cardio-vascular condition has been demonstrated.

Imaging photoplethysmography for clinical assessment of cutaneous microcirculation at two different depths.

Abstract. The feasibility of bispectral imaging photoplethysmography (iPPG) system for clinical assessment of cutaneous microcirculation at two different depths is proposed. The iPPG system has been developed and evaluated for in vivo conditions during various tests: (1) topical application of vasodilatory liniment on the skin, (2) skin local heating, (3) arterial occlusion, and (4) regional anesthesia. The device has been validated by the measurements of a laser Doppler imager (LDI) as a reference. The hardware comprises four bispectral light sources (530 and 810 nm) for uniform illumination of skin, video camera, and the control unit for triggering of the system. The PPG signals were calculated and the changes of perfusion index (PI) were obtained during the tests. The results showed convincing correlations for PI obtained by iPPG530  nm and LDI at (1) topical liniment (r=0.98) and (2) heating (r=0.98) tests. The topical liniment and local heating tests revealed good selectivity of the system for superficial microcirculation monitoring. It is confirmed that the iPPG system could be used for assessment of cutaneous perfusion at two different depths, morphologically and functionally different vascular networks, and thus utilized in clinics as a cost-effective alternative to the LDI.

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.

RGB imaging system for mapping and monitoring of hemoglobin distribution in skin

A prototype R-G-B imaging system for mapping of skin hemoglobin distribution has been designed and tested. Device basically consists of a commercial RGB sensor (CMOS, max. frame rate 87 fps for VGA resolution), RGB LED ringlight illuminator and orthogonally orientated polarizers for reducing specular reflectance. The system was examined for monitoring of hemoglobin concentration changes during specific provocations - arterial/venous occlusions and heat test. Hemoglobin distribution maps of several skin malformations were obtained, as well.

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.

Micro-circulation of skin blood: optical monitoring by advanced photoplethysmography techniques

Blood micro-circulation in upper skin layers has been studied experimentally in real time by advanced two-channel photoplethysmography (PPG) techniques. The blood volume changes caused by micro-vessel expansion and dilution during the cardiac cycles have been detected by infrared optical contact sensors. A newly developed portable monitoring device comprising a lap-top computer was used for accumulation and processing of the bio-signals. Shapes of the PPG signals detected at different sites of the body were compared with these obtained by computer modeling.