Independent determinants of second derivative of the finger photoplethysmogram among various cardiovascular risk factors in middle-aged men

Black Soybean Seed Coat Extract Improves Endothelial Function and Upregulates Oxidative Stress Marker Expression in Healthy Volunteers by Stimulating Nitric Oxide Production in Endothelial Cells

Black soybean seed coat extract (BE) contains multiple bioactive polyphenols, including flavan-3-ols and anthocyanins. BE improves endothelial function; however, it is unclear whether BE protects endothelial cells from senescence. In this study, we examined the effects of BE on endothelial cell senescence and vascular function in healthy individuals. High concentrations of glucose were used to induce senescence in bovine aortic endothelial cells incubated with BE. Senescence, vascular function, and oxidative stress markers were measured. Incubation with BE remarkably inhibited senescence-associated β-galactosidase and lactate dehydrogenase activities and dose dependently reduced intracellular reactive oxygen species levels in bovine aortic endothelial cells. BE treatment increased the levels of endothelial nitric oxide synthase (eNOS) mRNA and endothelial nitric oxide (NO) metabolites and increased the mRNA expression of klotho, a gene associated with an antiaging phenotype. To examine the effects of BE in humans, we conducted a clinical study using the second derivative of the fingertip photoplethysmogram to investigate vascular function and aging in 24 healthy volunteers. The participants consumed BE supplements (100 mg/day) or a placebo for 2 weeks. When compared with the placebo group, the BE group showed considerably improved vascular function, NO metabolite levels, and oxidative stress. These results suggest that BE supplementation improves endothelial function, possibly through antioxidant activity and NO production, and may consequently reduce the cardiovascular risk associated with aging. BE supplementation may be an effective and safe approach to reduce the risk of atherosclerosis and cardiovascular disease; however, additional studies investigating chronic vascular inflammation are needed.

Feasibility of home-based tracking of insulin resistance from vascular stiffness estimated from the photoplethysmographic finger pulse waveform

In this study, we explored the utility of post-prandial vascular stiffness as a surrogate measure for the estimation of insulin resistance (IR), which is a pre-diabetic condition. A cohort of 51 healthy young adults of varying Body mass index values (BMI) were studied by fasting plasma values of insulin and glucose; fasting and post-meal finger photoplethysmography (PPG), and electrocardiogram (ECG). Insulin resistance was estimated by Homeostatic model assessment-Insulin resistance 2 (HOMA-IR2) using fasting plasma insulin and glucose. Vascular stiffness was estimated by reciprocal of pulse arrival time (rPAT) from ECG and finger PPG at five time points from fasting to 2-hours post oral glucose ingestion. We examined if insulin resistance is correlated with meal induced vascular stiffness changes supporting the feasibility of using finger PPG for the estimation of insulin resistance. HOMA-IR2 was found to be positively correlated with early rise (0- to 30- minutes post meal) and delayed fall (30- to 120-minutes) of rPAT. Correlation persisted even after the effect of BMI has been partialled out in sub-group analysis. We conclude that finger PPG based pulse waveform and single lead ECG has the potential to be used as a non-invasive method for the assessment of insulin resistance. As both signals viz., ECG and PPG can be easily acquired using wearable and other low-cost sensing systems, the present study can serve as a pointer for the development of accessible methods of monitoring and longitudinal tracking of insulin resistance in health and pathophysiological states.

Diagnostic Features and Potential Applications of PPG Signal in Healthcare: A Systematic Review

Recent research indicates that Photoplethysmography (PPG) signals carry more information than oxygen saturation level (SpO2) and can be utilized for affordable, fast, and noninvasive healthcare applications. All these encourage the researchers to estimate its feasibility as an alternative to many expansive, time-wasting, and invasive methods. This systematic review discusses the current literature on diagnostic features of PPG signal and their applications that might present a potential venue to be adapted into many health and fitness aspects of human life. The research methodology is based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines 2020. To this aim, papers from 1981 to date are reviewed and categorized in terms of the healthcare application domain. Along with consolidated research areas, recent topics that are growing in popularity are also discovered. We also highlight the potential impact of using PPG signals on an individual’s quality of life and public health. The state-of-the-art studies suggest that in the years to come PPG wearables will become pervasive in many fields of medical practices, and the main domains include cardiology, respiratory, neurology, and fitness. Main operation challenges, including performance and robustness obstacles, are identified.

Assessing hemodynamics from the photoplethysmogram to gain insights into vascular age: A review from VascAgeNet

The photoplethysmogram (PPG) signal is widely measured by clinical and consumer devices, and it is emerging as a potential tool for assessing vascular age. The shape and timing of the PPG pulse wave are both influenced by normal vascular aging, changes in arterial stiffness and blood pressure, and atherosclerosis. This review summarizes research into assessing vascular age from the PPG. Three categories of approaches are described: 1) those which use a single PPG signal (based on pulse wave analysis), 2) those which use multiple PPG signals (such as pulse transit time measurement), and 3) those which use PPG and other signals (such as pulse arrival time measurement). Evidence is then presented on the performance, repeatability and reproducibility, and clinical utility of PPG-derived parameters of vascular age. Finally, the review outlines key directions for future research to realize the full potential of photoplethysmography for assessing vascular age.

Photoplethysmographic Prediction of the Ankle-Brachial Pressure Index through a Machine Learning Approach

Cardiovascular disease is a leading cause of death. Several markers have been proposed to predict cardiovascular morbidity. The ankle-brachial index (ABI) marker is defined as the ratio between the ankle and the arm systolic blood pressures, and it is generally assessed through sphygmomanometers. An alternative tool for cardiovascular status assessment is Photoplethysmography (PPG). PPG is a non-invasive optical technique that measures volumetric blood changes induced by pulse pressure propagation within arteries. However, PPG does not provide absolute pressure estimation, making assessment of cardiovascular status less direct. The capability of a multivariate data-driven approach to predict ABI from peculiar PPG features was investigated here. ABI was measured using a commercial instrument (Enverdis Vascular Explorer, VE-ABI), and it was then used for a General Linear Model estimation of ABI from multi-site PPG in a supervised learning framework (PPG-ABI). A Receiver Operating Characteristic (ROC) analysis allowed to investigate the capability of PPG-ABI to discriminate cardiovascular impairment as defined by VE-ABI. Findings suggested that ABI can be estimated form PPG (r = 0.79) and can identify pathological cardiovascular status (AUC = 0.85). The advantages of PPG are simplicity, speed and operator-independency, allowing extensive screening of cardiovascular status and associated cardiovascular risks.

Evaluation of Cardiorespiratory Function During Cardiopulmonary Exercise Testing in Untreated Hypertensive and Healthy Subjects

Objective: This study aimed to compare differences in cardiorespiratory function between untreated hypertensive subjects (UHS) and healthy subjects (HS) during cardiopulmonary exercise testing (CPET). Additionally, it also aimed to explore the potential mechanisms of different exercise responses in cardiorespiratory function before, during and after CPET. Methods: Thirty subjects (15 UHS and 15 HS) were enrolled. Photoplethysmography (PPG), respiratory signal, and ECG were simultaneously collected while subjects were performing CPET. Fiducial points (a, b, c, d, e) were extracted from the second derivative of the PPG (SDPPG), and the ratios b/a, c/a, d/a, e/a, and (b-c-d-e)/a (named Aging Index, AGI) were calculated as markers of systolic and diastolic function. Additionally, respiratory rate was calculated and analyzed. Results:Before CPET, there were no significant differences in b/a, d/a, and AGI between two groups. However, after CPET, b/a (-0.9 ± 0.19 vs. -1.06 ± 0.19, p-value = 0.03) and AGI (-0.49 ± 0.75 vs. -1.15 ± 0.59, p-value = 0.011) of the UHS group were significantly higher than those of the HS. The d/a (-0.32 ± 0.24 vs. -0.14 ± 0.17, p-value = 0.024), and c/a (-0.33 ± 0.26 vs. -0.07 ± 0.19, p-value = 0.004) were significantly lower in UHS than those in HS. In contrast, before CPET, e/a (0.22 ± 0.11 vs. 0.32 ± 0.09, p-value = 0.007) in UHS was significantly lower than that in HS, while after CPET there was no significant difference between the two groups in this variable. In addition, during CPET, AGI (p-value = 0.003), and respiratory rate (p-value = 0.000) in UHS were significantly higher in comparison with before CPET. Conclusions: Different exercise responses showed the differences of cardiorespiratory function between UHS and HS. These differences not only can highlight the CV risk of UHS, but also can predict the appearance of arterial stiffness in UHS. Additionally, during CPET, significant differences in AGI, autonomic nervous function and respiratory activity assessed by respiratory rate were found between the two groups in comparison with before CPET.

An adaptive delineator for photoplethysmography waveforms

Photoplethysmography (PPG) waveforms are rich in cardiovascular information, and hence, their analysis is significant in the diagnosis and prevention of cardiovascular diseases (CVDs). The second derivative of photoplethysmography (SDPPG) analysis for the accurate detection of significant points in characterising the PPG waveform is challenging. In this paper, a SDPPG analysis algorithm is proposed based on a resampling technique which normalises the signal and ensures the presence of all significant points of interest in all its recurrences. The proposed delineator detects a, b and e waves in SDPPG, which are based on the combined analysis of PPG waveforms and their second derivatives, characterising them beat-by-beat by electrocardiogram (ECG) signals. Experiments have been conducted on 46 PPG signal records, each of 10-s duration with low and varying amplitudes, and regular and irregular heart rhythms for healthy adults, as well as unhealthy and aged patients obtained from the large-scale openly available database PhysioNet. Based on the experiments conducted, it is found that the proposed algorithm performs better than existing methods in terms of sensitivity and positive predictivity with a highest sensitivity of 99.84% with respect to a (onset) and b waves, 99.67% for e waves (dicrotic notch), and 100% of positive predictivity for a and b waves and 99.82% in case of e waves.

Second derivative of the finger photoplethysmogram and cardiovascular mortality in middle-aged and elderly Japanese women

The second derivative of the digital photoplethysmogram (SDPTG) is an indicator of arterial stiffness. The ratio of the height of the d wave to the a wave of the SDPTG (d/a) is associated with functional peripheral vascular tension and represents aortic-blood pressure (BP) augmented by reflection waves from the periphery. This longitudinal study aimed to investigate the relationship between SDPTG and cardiovascular mortality in middle-aged and elderly Japanese women. From 1998 to 2008, we recruited 4373 women (50-79 years old at baseline) who underwent medical check-ups and SDPTG measurement. The SDPTG index (d/a) was calculated from the wave component height, and was divided into quartiles (Q) according to the d/a value. The median follow-up period was 9.0 years. The d/a value was negatively associated with age and BP, and positively associated with heart rate and body height. Using the Cox proportional hazards model, the hazard ratios for cardiovascular mortality for Q2, Q3 and Q4 were significantly higher than that of Q1. In multivariate analysis, the hazard ratio was 2.30 for Q3 (95% confidence interval (CI): 1.06-4.99, P<0.05) and 2.60 for Q4 (95% CI: 1.21-5.60, P<0.05), after adjustment for age, height, body mass index, BP levels, heart rate and other atherosclerosis-related factors. The hazard ratios of cardiovascular mortality for Q3 and Q4 were significantly higher compared with the reference (Q1). Thus, the SDPTG d/a is an independent predictor of cardiovascular mortality in middle-aged and elderly Japanese women.

Usefulness of the second derivative of the finger photoplethysmogram for assessment of end-organ damage: the J-SHIPP study

Early detection of pathological changes in the vasculature is required to identify individuals at risk of cardiovascular diseases. Noninvasive measurement of the second derivative of photoplethysmogram (SDPTG) might aid in evaluating vascular aging. Here we clarified the diagnostic significance of four SDPTG indices for end-organ damage. A total of 1613 community residents (65±10 years) were enrolled. Changes in blood flow volume at the forefinger were measured by photoplethysmography. SDPTG was computationally calculated from the plethysmogram, and the height of five peaks (a-e) on the SDPTG was measured. Carotid intima-media thickness (IMT), brachial-to-ankle pulse wave velocity (baPWV) and silent cerebral lesions were used as indices of end-organ damage. Multivariate analysis identified age, sex, systolic blood pressure and heart rate as strong determinants for the evaluated SDPTG indices, namely b/a, d/a and aging index ([b-d-c-e]/a). In addition, poor glycemic control and carotid IMT were also weakly associated with the SDPTG indices. Compared with other established risk factors, however, the association between the SDPTG indices and carotid IMT was weak or insignificant (b/a: β=0.069, P=0.002; d/a: β=-0.009, P=0.669; and aging index: β=0.047, P=0.037). Further, no significant association was noted between the SDPTG indices and silent lacunar infarction (b/a: P=0.111; d/a: P=0.263; and aging index: P=0.167) and periventricular hyperintensity (b/a: P=0.587; d/a: P=0.254; and aging index: P=0.429). Although the SDPTG indices evaluated here might represent structural and functional changes in arteries, they exhibited limited diagnostic significance for pathophysiological changes in large arteries, as well as small vessel diseases of the brain.

Computerized assessment of communication for cognitive stimulation for people with cognitive decline using spectral-distortion measures and phylogenetic inference

Therapeutic communication and interpersonal relationships in care homes can help people to improve their mental wellbeing. Assessment of the efficacy of these dynamic and complex processes are necessary for psychosocial planning and management. This paper presents a pilot application of photoplethysmography in synchronized physiological measurements of communications between the care-giver and people with dementia. Signal-based evaluations of the therapy can be carried out using the measures of spectral distortion and the inference of phylogenetic trees. The proposed computational models can be of assistance and cost-effectiveness in caring for and monitoring people with cognitive decline.

Associations between the autonomic nervous system and the second derivative of the finger photoplethysmogram indices

AIM

The indices of the second derivative of the finger photoplethysmogram(SDPTG) denote stiffness of large arteries, peripheral vascular resistance and vascular aging. However, the association between the autonomic nervous activity and the SDPTG indices has not yet been elucidated.

METHODS

The SDPTG and heart rate variability(HRV) were consecutively measured in the sitting position on the day before surgery in 168 patients 18-89 years of age. The relationships between the SDPTG indices(b/a, c/a, d/a and e/a) and HRV indices(power spectral analysis and time domain analysis parameters) were analyzed. The relationships between c/a and atherosclerosis-based conditions and risk factors for atherosclerosis were also evaluated.

RESULTS

The SDPTG index b/a was negatively associated and the d/a index was positively associated with the low-frequency(LF)(R=-0.44 and 0.42, respectively) and high-frequency(HF) components(R=-0.31 and 0.35, respectively). The SDPTG index c/a was also positively associated with the LF(R=0.40) and HF(R=0.44) components. A multivariate regression analysis showed that the LF, HF and heart rate were independent determinants of the c/a. Furthermore, the c/a values were significantly lower in the patients with hypertension, diabetes mellitus and hyperlipidemia than in those without these diseases, and a reduced c/a was significantly associated with increased serum triglyceride and total cholesterol concentrations.

CONCLUSIONS

These findings suggest that a decrease in c/a is associated with a reduced baroreflex response of the peripheral vasomotor activity and a decreased cardiac parasympathetic activity. Furthermore, a decrease in c/a was found to be associated with atherosclerosis-based conditions, such as hypertension, diabetes mellitus and hyperlipidemia.

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 subject's 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.

Factor structure of indices of the second derivative of the finger photoplethysmogram with metabolic components and other cardiovascular risk indicators

BACKGROUND

The second derivative of the finger photoplethysmogram (SDPTG) is an indicator of arterial stiffness. The present study was conducted to clarify the factor structure of indices of the SDPTG in combination with components of the metabolic syndrome (MetS), to elucidate the significance of the SDPTG among various cardiovascular risk factors.

METHODS

The SDPTG was determined in the second forefinger of the left hand in 1,055 male workers (mean age, 44.2±6.4 years). Among 4 waves of SDPTG components, the ratios of the height of the "a" wave to that of the "b" and "d" waves were expressed as b/a and d/a, and used as SDPTG indices for the analysis.

RESULTS

Principal axis factoring analysis was conducted using age, SDPTG indices, components of MetS, and the serum levels of C-reactive protein (CRP) and uric acid. Three factors were extracted, and the SDPTG indices were categorized in combination with age as the third factor. Metabolic components and the SDPTG indices were independently categorized. These three factors explained 44.4% of the total variation. Multiple logistic regression analysis revealed age, d/a, serum uric acid, serum CRP, and regular exercise as independent determinants of the risk of MetS. The odds ratios (95% confidence intervals) were 1.08 (1.04 to 1.11), 0.10 (0.01 to 0.73), 1.24 (1.06 to 1.44), 3.59 (2.37 to 5.42), and 0.48 (0.28 to 0.82), respectively.

CONCLUSION

The SDPTG indices were categorized in combination with age, and they differed in characteristics from components of MetS or inflammatory markers. In addition, this cross-sectional study also revealed decrease of the d/a as a risk factor for the development of MetS.

Effects of safflower seed extract on arterial stiffness

Safflower seed extract (SSE) contains characteristic polyphenols and serotonin derivatives (N-( p-coumaroyl) serotonin and N-feruloylserotonin), which are reported to inhibit oxidation of low-density lipoprotein (LDL), formation of atherosclerotic plaques, and improve arterial stiffness as assessed by pulse wave analysis in animal models. The effects of long-term supplementation with SSE on arterial stiffness in human subjects were evaluated. This doubleblind, placebo-controlled study was conducted in 77 males (35–65 years) and 15 postmenopausal females (55–65 years) with high-normal blood pressure or mild hypertension who were not undergoing treatment. Subjects received SSE (70 mg/day as serotonin derivatives) or placebo for 12 weeks, and pulse wave measurements, ie, second derivative of photoplethysmogram (SDPTG), augmentation index, and brachial-ankle pulse wave velocity (baPWV) were conducted at baseline, and at weeks 4, 8, and 12. Vascular age estimated by SDPTG aging index improved in the SSE-supplemented group when compared with the placebo group at four (P = 0.0368) and 12 weeks (P = 0.0927). The trend of augmentation index reduction (P = 0.072 versus baseline) was observed in the SSE-supplemented group, but reduction of baPWV by SSE supplementation was not observed. The SSE-supplemented group also showed a trend towards a lower malondialdehyde-modified-LDL autoantibody titer at 12 weeks from baseline. These results suggest long-term ingestion of SSE in humans could help to improve arterial stiffness.