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.     

Blood pressure waveform analysis by means of wavelet transform

The assessment of cardiovascular function by means of arterial pulse wave analysis (PWA) is well established in clinical practice. PWA is applied to study risk stratification in hypertension, with emphasis on the measurement of the augmentation index as a measure of aortic pressure wave reflections. Despite the fact that the prognostic power of PWA, in its current form, still remains to be demonstrated in the general population, there is general agreement that analysis and interpretation of the waveform might provide a deeper insight in cardiovascular pathophysiology. We propose here the use of wavelet analysis (WA) as a tool to quantify arterial pressure waveform features, with a twofold aim. First, we discuss a specific use of wavelet transform in the study of pressure waveform morphology, and its potential role in ascertaining the dynamics of temporal properties of arterial pressure waveforms. Second, we apply WA to evaluate a database of carotid artery pressure waveforms of healthy middle-aged women and men. Wavelet analysis has the potential to extract specific features (wavelet details), related to wave reflection and aortic valve closure, from a measured waveform. Analysis showed that the fifth detail, one of the waveform features extracted applying the wavelet decomposition, appeared to be the most appropriate for the analysis of carotid artery pressure waveforms. What remains to be assessed is how the information embedded in this detail can be further processed and transformed into quantitative data, and how it can be rendered useful for automated waveform classification and arterial function parameters with potential clinical applications.     

Pulse pressure waveform estimation using distension profiling with contactless optical probe

The pulse pressure waveform has, for long, been known as a fundamental biomedical signal and its analysis is recognized as a non-invasive, simple, and resourceful technique for the assessment of arterial vessels condition observed in several diseases. In the current paper, waveforms from non-invasive optical probe that measures carotid artery distension profiles are compared with the waveforms of the pulse pressure acquired by intra-arterial catheter invasive measurement in the ascending aorta. Measurements were performed in a study population of 16 patients who had undergone cardiac catheterization. The hemodynamic parameters: area under the curve (AUC), the area during systole (AS) and the area during diastole (AD), their ratio (AD/AS) and the ejection time index (ETI), from invasive and non-invasive measurements were compared. The results show that the pressure waveforms obtained by the two methods are similar, with 13% of mean value of the root mean square error (RMSE). Moreover, the correlation coefficient demonstrates the strong correlation. The comparison between the AUCs allows the assessment of the differences between the phases of the cardiac cycle. In the systolic period the waveforms are almost equal, evidencing greatest clinical relevance during this period. Slight differences are found in diastole, probably due to the structural arterial differences. The optical probe has lower variability than the invasive system (13% vs 16%). This study validates the capability of acquiring the arterial pulse waveform with a non-invasive method, using a non-contact optical probe at the carotid site with residual differences from the aortic invasive measurements.     

动脉压力波形分析在麻醉诱导期的应用

为探索动脉波形分析方法的临床意义,使用波形分离法与储存压力波模型对采集到的25例进行全麻手术的高龄患者的动脉压力波形进行波形分析,在获得[Pf]、[Pb]以及[Pe]、[Pr]等波形形态参数后,将诱导前后的参数变化量与临床生命指标变化量进行相关性分析。在本文的研究群体中,波形分离法与储存压力波模型的参数均与诱导中的血压和心率变化量有相关性,其中△[Pe]与临床指标△PP相关系数最高（r=0.926）。从生理病理学的角度对波形参数的变化进行解读,旨在探索波形分析在诱导期对全麻患者麻醉水平的应用价值,可为动脉压力波形分析及其应用提供新的理论基础和技术方案。     

Estimation of arterial pulse wave velocities in the frequency domain: method and clinical considerations

Pulse wave patterns at a finger and a toe are obtained using photoplethysmography. The data recorded at two recording sites are transformed by digital filters into six waveforms and the transmission time of each wave is estimated by the crosscorrelation function. Relationships between the transmission times, age, and parameters obtained from several laboratory tests are examined using multiple regression analysis. The results may be summarised as follows: the power of photoplethysmograms of a finger and a toe is concentrated in the range below 6 or 8 Hz; age correlates highly with the transmission time of a pulse wave rather than with velocity; the multiple correlation coefficients between age and the transmission times is 0·853 in male and 0·866 in female; there are no differences of transmission time among disease types; the correlations between age and other parameters measured by laboratory tests, that is, total cholesterol, phospholipid, triglyceride, β-lipoprotein, are very small.     

Noninvasive measurement of arterial diameters in humans using ultrasound echoes with prefiltered waveforms

A system for the direct measurement of the inner diameters of selected human arteriesin situ has been developed. Ultrasound pulses are emitted perdendicular to the vessel axis, and reflected from the wall material interfaces. Improved depth resolution is achieved by using a high-frequency transducer, and by inverse filtering of the signal. This is performed by emitting a waveform calculated beforehand to give an optimum time resolution in the received echo. Echoes from both innerand outer surfaces of the vessel walls are discriminated, and the inter-echo time intervals can be measured with an accuracy of 33ns, corresponding to approximately 26μm. By repeating the measurements through the cardiac cycle, the diameter variations can be accurately described.     

Assessment of the agreement between photoplethysmographic and arterial waveform respiratory variation in patients undergoing spine surgery

Abstract

Respiratory variation in the arterial blood pressure and photoplethysmographic (PPG) waveforms have both been shown to predict the haemodynamic response to volume administration. Whether or not the two can be considered interchangeable is controversial. Twenty-three patients undergoing spine surgery received both a 20 gauge intra-arterial catheter and a Masimo adult adhesive SpHb sensor connected to a Radical-7 monitor. Pulse pressure variation (PPV) was calculated off-line at 1-min intervals. Pleth Variability Index (PVI) and Perfusion Index data were recorded. After exclusion of outliers, agreement between PPV and PVI was assessed using a repeated measures Bland-Altman approach. Concordance between changes in PPV and PVI was assessed using a four-quadrant plot with a 20% zone of exclusion. In total, 6549?min of data were collected. Repeated measures Bland-Altman analysis identified a bias of 2.2% and 95% confidence intervals of ±15.3% (limits of agreement ?13.1 and +17.6%). The concordance rate between changes in PPV and changes in PVI was 51%. The agreement between respiratory variation in the arterial blood pressure and PPG waveforms is poor and these two should not be considered interchangeable. Changes in PPV are unrelated to changes in PVI. The data, combined with recently published work from other authors, suggests that the low frequency oscillations in the PPG waveform are not related to the low frequency oscillation in the systemic arterial blood pressure tracing and may be related to changes in venous pressure, peripheral tone or other physiologic phenomena yet to be described.     

原发性高血压患者颈动脉斑块及动脉僵硬度与血清尿酸水平的关系*

 目的：研究原发性高血压（essential hypertension,EH）患者颈动脉斑块性质及动脉僵硬度与血清尿酸（uric acid,UA）水平的关系。方法：选择EH患者92例,健康对照组30例;对所有研究对象行相关血液生化检查,检测颈总动脉内中膜厚度（IMT）、颈动脉斑块和颈股动脉脉搏波传导速度（CFPWV）。结果：EH组的血清UA明显高于对照组［（361.51±83.81)μmol/L vs (317.03±62.22) μmol/L,P<0.05］;EH组IMT及异常检出率较对照组明显升高［(0.69±0.14) mm vs (0.60±0.12) mm,42.39% vs 10.00%,P<0.05］;45例EH患者检出颈动脉斑块,随着颈动脉斑块严重程度增高,血清UA水平依次增高［（285.25±78.41) μmol/L、(341.19±63.99) μmol/L和(401.33±88.49) μmol/L,P<0.05］;软斑块组（n=11）的血清UA水平较硬斑块组（n=34）显著增高［（389.00±69.45) μmol/L vs (323.03±72.71) μmol/L,P<0.05］。多元线性逐步回归分析显示CFPWV与年龄（r=0.414）、收缩压（r=0.224）、脉压（r=0.270）和血清UA（r=0.219）呈显著正相关（P<0.05）。结论：血清UA水平增高是EH发病的危险因素之一,血清UA水平可反映颈动脉斑块的严重程度及稳定性,EH患者随着血清UA水平增高大动脉弹性减退。     

Noninvasive investigation of blood pressure changes using the pulse wave transit time: a novel approach in the monitoring of hemodialysis patients

Severe blood pressure changes are well known in hemodialysis. Detection and prediction of these are important for the well-being of the patient and for optimizing treatment. New noninvasive methods for this purpose are required. The pulse wave transit time technique is an indirect estimation of blood pressure, and our intention is to investigate whether this technique is applicable for hemodialysis treatment. A measurement setup utilizing lower body negative pressure and isometric contraction was used to simulate dialysis-related blood pressure changes in normal test subjects. Systolic blood pressure levels were compared to different pulse wave transit times, including and excluding the cardiac preejection period. Based on the results of these investigations, a pulse wave transit time technique adapted for dialysis treatment was developed and tried out on patients. To determine systolic blood pressure in the normal group, the total pulse wave transit time was found most suitable (including the cardiac preejection period). Correlation coefficients were r = 0.80 ± 0.06 (mean ± SD) overall and r = 0.81 ± 0.16 and r = 0.09 ± 0.62 for the hypotension and hypertension phases, respectively. When applying the adapted technique in dialysis patients, large blood pressure variations could easily be detected when present. Pulse wave transit time is correlated to systolic blood pressure within the acceptable range for a trend-indicating system. The method's applicability for dialysis treatment requires further studies. The results indicate that large sudden pressure drops, like those seen in sudden hypovolemia, can be detected.     

Noninvasive automatic measurement of arterial elasticity in human fingers and rabbit forelegs using photoelectric plethysmography

A new instrument for the noninvasive measurement of arterial elastic properties such as ‘pressure-volume relationship’ and ‘volume elastic modulus’ in human fingers or in rabbit forelegs has been designed using a transmittance infra-red photoelectric plethysmography technique. The measurement and display of the results by this system is carried out automatically by use of a conventional personal computer. Using this instrument, the progressive and regressive changes in arterial elastic properties have been clearly demonstrated in the forelegs of hyperlipoedemic rabbits with experimental atherosclerosis. The effect of vasodilation by isosorbide dinitrate on the finger arteries of patients with congestive heart failure was also successfully studied. This instrument is capable of a rapid and reliable measurement of arterial elasticity and appears to be useful not only in basic cardiovascular research laboratories but also in clinics.     

脉搏波传导速度测量算法的研究及其进展

动脉弹性功能下降是心血管疾病的早期特征之一,而动脉脉搏波速度能够很好地反映动脉弹性,因此准确测量动脉脉搏波速度对预防和治疗心血管疾病有很大的帮助。测量脉搏波速度的方法主要有两种:基于容积脉搏波的检测方法和基于压力波的检测方法,其检测精度取决于波速参考点的提取。波速参考点的提取方法主要有切线法、最低点法、峰值法以及斜率最大值点法。本文分析了现有测量算法的优点和存在的不足之处,探讨了国内外的研究动向,提出测量算法的改进方案。     

Transphyseal reconstruction of the anterior cruciate ligament using hamstring autograft in skeletally immature adolescents

Eleven skeletally immature adolescents underwent anterior cruciate ligament reconstruction using a transphyseal tibial and femoral tunnel. An autologous quadrupled hamstring tendon was used in all cases and the average follow-up was 77.7 months. Clinical results were evaluated using Lysholm knee scores and a return to pre-injury sports activities. Radiological results were evaluated using side-to-side differences of instrumented laxities and growth disturbances compared with the uninjured side on final follow-up orthoroentgenograms. The mean Lysholm score was 97.8 (range 94-100) and mean side-to-side laxity difference was 2.4 mm (range 1-4). Ten of 11 patients returned to pre-injury sports activity. No patient had a leg length discrepancy of over 1 cm or a significant abnormal angular deformity of the knee joint. Therefore, anterior cruciate ligament reconstruction using the transphyseal tunnel and hamstring autograft in skeletally immature adolescents is believed to be a reliable treatment method, which is not associated with significant leg length discrepancy or abnormal angular deformity of the knee joint.     

Estimation of pulmonary arterial pressure by a neural network analysis using features based on time-frequency representations of the second heart sound

The objective of the study was to develop a non-invasive method for the estimation of pulmonary arterial pressure (PAP) using a neural network (NN) and features extracted from the second heart sound (S2). To obtain the information required to train and test the NN, an animal model of pulmonary hypertension (PHT) was developed, and nine pigs were investigated. During the experiments, the electrocardiogram, phonocardiogram and PAP were recorded. Subsequently, between 15 and 50 S2 heart sounds were isolated for each PAP stage and for each animal studied. A Coiflet wavelet decomposition and a pseudo smoothed Wigner-Ville distribution were used to extract features from the S2 sounds and train a one-hidden-layer NN using two-thirds of the data. The NN performance was tested on the remaining one-third of the data. NN estimates of the systolic and mean PAPs were obtained for each S2 and then ensemble averaged over the 15–50 S2 sounds selected for each PAP stage. The standard errors between the mean and systolic PAPs estimated by the NN and those measured with a catheter were 6.0 mmHg and 8.4 mmHg, respectively, and the correlation coefficients were 0.89 and 0.86, respectively. The classification accuracy, using 23 mmHg mean PAP and 30 mmHg systolic PAP thresholds between normal PAP and PHT, was 97% and 91% respectively.     

Electrical stimulation using sine waveform prevents unloading-induced muscle atrophy in the deep calf muscles of rat

The aim of this study was to compare the effects of electrical stimulation by using rectangular and sine waveforms in the prevention of deep muscle atrophy in rat calf muscles. Rats were randomly divided into the following groups: control, hindlimb unloading (HU), and HU plus electrical stimulation (ES). The animals in the ES group were electrically stimulated using rectangular waveform (RS) on the left calves and sine waveform (SS) on the right calves, twice a day, for 2 weeks during unloading. HU for 2 weeks resulted in a loss of the muscle mass, a decrease in the cross-sectional area of the muscle fibers, and overexpression of ubiquitinated proteins in the gastrocnemius and soleus muscles. In contrast, electrical stimulation with RS attenuated the HU-induced reduction in the cross-sectional area of muscle fibers and the increase of ubiquitinated proteins in the gastrocnemius muscle. However, electrical stimulation with RS failed to prevent muscle atrophy in the deep portion of the gastrocnemius and the soleus muscles. Nevertheless, electrical stimulation with SS attenuated the HU-induced muscle atrophy and the up-regulation of ubiquitinated proteins in both gastrocnemius and soleus muscles. This indicates that SS was more effective in the prevention of deep muscle atrophy than RS. Since the skin muscle layers act like the plates of a capacitor, separated by the subcutaneous adipose layer, the SS can pass through this capacitor more easily than the RS. Hence, SS can prevent the progressive loss of muscle fibers in the deep portion of the calf muscles.     

Automatic measure of the split in the second cardiac sound by using the wavelet transform technique

This paper is concerned with the identification and automatic measure of the split in the second heart sound (S2) of the phonocardiogram signal (PCGs) for normal or pathological case. The second heart sound S2 consists of two acoustic components A2 and P2, the former is due to the closure of the aortic valve and the latter is due to the closure of the pulmonary valve. The aortic valve usually closes before the pulmonary valve, introducing a time delay known as "split". A automatic technique based on the discrete wavelet transform (DWT) and the continuous wavelet transform (CWT) is developed in this paper to measure the split of the second cardiac sound (S2) for the normal and pathological cases of the PCG signals. To quantify the splitting, the two components in S2 (i.e. A2 and P2) are identified and, the delay between the two components can be estimated. It is shown that the wavelet transform can provide best information and features of the split of S2 and the major components (A2 and P2) and consequently aid in medical diagnosis.     

Masked repetition and translation priming in second language learners: A window on the time-course of form and meaning activation using ERPs

Event-related potentials (ERPs) and masked translation priming served to examine the time-course of form and meaning activation during word recognition in second language learners. Targets were repetitions of, translations of, or were unrelated to the immediately preceding prime. In Experiment 1 all targets were in the participants' L2. In Experiment 2 all targets were in the participants' L1. In Exp 1 both within-language repetition and L1-L2 translation priming produced effects on the N250 component and the N400 component. In Experiment 2 only within-language repetition produced N250 effects, while both types of priming produced N400 effects. These results suggest rapid involvement of semantic representations during on-going form-level processing of printed words, and an absence of facilitatory connections between the form representations of non-cognate translation equivalents in L2 learners. The implications for bilingual theories of word processing are discussed.