Correlation analysis of arterial pressure waveform morphology similarity and relative pulse transit time using cardiovascular hardware simulator and hemodynamic model.

Hypertension is highly prevalent in the United States and worldwide. In the United States, 1 in 3 adults (≈73 million people) have hypertension. The financial and human costs of hypertension are substantial. The estimated costs attributable to hypertension in the United States alone in 2010 were $70 billion direct costs for medical treatments and $24 billion indirect costs because of lost productivity.1 Awareness and treatment of hypertension have improved considerably during the past several decades: >80% of all people with hypertension are aware of the condition and 75% are using antihypertensive medications.2,3 However, despite enormous effort and treatment-related expenditures, only 53% of those with documented hypertension have their blood pressure controlled.3 Older age (Figure 1), left ventricular hypertrophy, and obesity are important risk factors for uncontrolled or drug-resistant hypertension.4 Importantly, the foregoing are also risk factors for increased aortic stiffness.5 Figure 1. Hypertension prevalence and control rates as a function of age in the National Health and Nutrition Examination Survey 2003 to 2004. Data derived from Wong et al.44 During the past 2 decades, measures of aortic stiffness have emerged as important risk factors for progression of blood pressure and incident cardiovascular disease. Carotid femoral pulse wave velocity (CFPWV), a measure of aortic wall stiffness, increases markedly with age, particularly after midlife. For example, Framingham Heart Study investigators have shown that the prevalence of CFPWV ≥12 m/s increases from a few percentage before 50 years of age to ≥60% after 70 years of age (Figure 2A). Importantly, elevated CFPWV is associated with high risk for incident hypertension (Figure 2B) and cardiovascular disease (Figure 2C). Figure 2C should be interpreted within the context that a normal value (<95th percentile) for CFPWV in a healthy Framingham Heart Study reference sample <50 years of age was 8.1 …

Cardiovascular parameters are most often assessed at rest, and in many cases in the supine position. This generally facilitates measurement procedures and obviates the need to account for external and usually complex confounding factors, other than those related to the inherent physiology being investigated. Although the supine resting position may be relevant for some part of circadian living, a large part of human activity is characterized by locomotion and the upright posture. Physiological adaptations to locomotion are studied under controlled conditions and at varying degrees of exercise. However, although primary measures of basic physiological quantities (e.g. stroke volume) can be obtained with some level of confidence at rest in supine position, it becomes extremely difficult to measure them during exercise, and so they are generally derived from other measurable quantities, with the associated errors. Notwithstanding this, the large body of work done so far on the physiological response to exercise has been extremely beneficial in elucidating both underlying and adaptive mechanisms for the function of the circulatory system. On the other hand, assessment of the changes occurring in cardiovascular variables when shifting from supine to standing is the procedure most commonly adopted to explore the response of cardiovascular control mechanisms to gravitational challenges, both when investigating physiological adaptations to the upright posture in healthy individuals and when assessing alterations in cardiovascular regulation in patients with a variety of diseases.

Heritability of arterial stiffness and central blood pressure

Smart healthcare services are continuously is increasing due to rapid industrialization and increasing chronic diseases. Significant research has focused on monitoring the health of an individual health in real time and to prevent disease in advance. This paper implemented a wearable ECG and PPG measurement system to conveniently monitor personal health in daily life. The proposed system used pulse transit time, the time difference between ECG and PPG R-peak signals. To evaluate the proposed system performance, we compared it with an existing commercial system to observe blood pressure and pulse wave changes according to posture, and validated the effectiveness of the proposed system.

Increasing adiposity with a clinical endpoint of obesity is associated with a progressive increase in risk of cardiovascular diseases (CVD). However, we are only beginning to understand the physiological and pathophysiological mechanisms by which excessive body fat storage causes CVD. In this issue of Hypertension , the findings of Wildman et al1 extend and strengthen previous observations2–5 by showing that changes in arterial stiffness, as measured by aortic pulse-wave velocity (PWV), are related to changes in body weight over a 2-year follow-up period in healthy men and women aged 20 to 40 years. Weight gain was associated with an increase, whereas weight loss was associated with a decrease in aortic PWV, independent of changes in blood pressure. The greatest increases in aortic PWV were observed in those subjects who gained the most weight (≥4.5 kg). Importantly, the changes in aortic PWV were related to changes in body mass index (BMI), indicating that the associations with body weight were mediated by changes in adiposity (rather than fat-free mass). Changes in aortic PWV over time also were related to baseline body weight, BMI, and waist circumference (an indirect measure of abdominal adiposity), providing evidence that higher initial levels of total and abdominal body fatness are associated with greater future increases in arterial stiffness. The study included subjects with a broad range of BMI, suggesting that the findings are applicable to both nonobese and obese adults in the general population. An important finding was that black adults demonstrated greater increases in weight gain-adjusted and blood pressure-adjusted aortic PWV over time, suggesting that they undergo greater increases in arterial stiffness in response to the same age-associated weight gain compared with whites. These observations provide further support for the emerging concept that adiposity-driven weight gain during adulthood contributes significantly to the adverse changes …

Feasibility of waveform separation of central aortic pressure pulse based on lognormal flow wave approximation

Heart rate (HR) is a valuable and widespread measure for physical training programs, although its description of conditioning is limited to the cardiac response to exercise. More comprehensive measures of exercise adaptation include cardiac output (Q̇), stroke volume (SV) and oxygen uptake (V̇O2), but these physiological parameters can be measured only with cumbersome equipment installed in clinical settings. In this work, we explore the ability of pulse transit time (PTT) to represent a valuable pairing with HR for indirectly estimating Q̇, SV and V̇O2 non-invasively. PTT was measured as the time interval between the peak of the electrocardiographic (ECG) R-wave and the onset of the photoplethysmography (PPG) waveform at the periphery (i.e. fingertip) with a portable sensor. Fifteen healthy young subjects underwent a graded incremental cycling protocol after which HR and PTT were correlated with Q̇, SV and V̇O2 using linear mixed models. The addition of PTT significantly improved the modeling of Q̇, SV and V̇O2 at the individual level ( for SV, 0.548 for Q̇, and 0.771 for V̇O2) compared to predictive models based solely on HR ( for SV, 0.503 for Q̇, and 0.745 for V̇O2). While challenges in sensitivity and artifact rejection exist, combining PTT with HR holds potential for development of novel wearable sensors that provide exercise assessment largely superior to HR monitors.

In this research Seismocardiogram (SCG) signal was used for timing the proximal pulse while pulse-plethysmogram (PPG) was used for timing the dorsal pulse for computing pulse transit time (PTT). Lower body negative pressure (LBNP) was applied for gradually reducing the pulse pressure in 9 subjects. The correlation between the pulse pressure and PTT derived using SCG was studied. It was determined that a significant correlation existed between PTT and pulse pressure for 7 out of the 9 subjects studied with an average significant correlation of 0.88±0.05. The results from this research show a potential application for a system including SCG and PPG to be used in an estimation or trending of pulse pressure.

RésuméLa pression artérielle est la résultante d’une composante stable, la pression artérielle moyenne, et d’une composante pulsatile, la pression pulsée, cette derniÈre étant largement déterminée par la rigidité des gros troncs artériels. Les lésions des organes cibles demeurent un élément majeur de la prise en charge de l’hypertension artérielle. De récentes données montrent que la diminution de la pression artérielle systolique joue un rôle déterminant dans la protection des hypertendus vis-à-vis du risque d’événements cardiovasculaires, mais que cette diminution n’est pas le seul facteur en cause puisque des antihypertenseurs qui diminuent la pression artérielle dans des proportions équivalentes ne confÈrent pas tous le même degré de protection cardiovasculaire. Les différences existant entre ces médicaments pourraient être liées à des propriétés propres à chacun d’entre eux, tel par exemple l’effet exercé sur la pression pulsée centrale ou périphérique. La pression pulsée diffÈre significativement selon qu’elle est mesurée au niveau central ou périphérique, et c’est, bien sûr, à la pression pulsée centrale que le cœur est soumis. Il a été établi que la pression pulsée centrale constitue un facteur prédictif de mortalité de toutes causes au cours de l’insuffisance rénale terminale, ce qui n’est pas le cas de la pression pulsée périphérique. L’un des principaux facteurs qui déterminent la pression pulsée aortique est la rigidité des parois artérielles, car celle-ci conditionne la quantité d’énergie absorbée par les gros troncs artériels. Trois études épidémiologiques ont montré que la rigidité artérielle est elle-même un facteur prédictif indépendant du risque de décÈs de toutes causes, de mortalité cardiovasculaire, d’événement coronaire et d’accident vasculaire cérébral chez les patients hypertendus. La pression pulsée et la rigidité artérielle constituent donc deux cibles importantes des traitements antihypertenseurs, qui doivent se montrer efficaces non seulement sur l’élévation de la pression artérielle au niveau des artÈres humérales, mais aussi sur la rigidité des grosses artÈres, afin d’assurer une protection efficace des organes cibles.La première preuve de é des antihypertenseurs sur ces différentes composantes a été fournie par une étude ayant comparé la plurithérapie perindopril/indapamide à l“aténolol. Dans cette étude, seule la plurithérapie diminue significativement la pression pulsée centrale et la rigidité artérielle.

BackgroundVascular transit time (VTT) is the propagation time of a pulse wave through an artery; it is a measure for arterial stiffness. Because reliable non-invasive VTT measurements are difficult, as an alternative we measure pulse transit time (PTT). PTT is defined as the time between the R-wave on electrocardiogram and arrival of the resulting pulse wave in a distal location measured with photoplethysmography (PPG). The time between electrical activation of the ventricles and the resulting pulse wave after opening of the aortic valve is called the pre-ejection period (PEP), a component of PTT. The aim of this study was to estimate the variability of PEP at rest, to establish how accurate PTT is as approximation of VTT.MethodsPTT was measured and PEP was assessed with echocardiography (gold standard) in three groups of 20 volunteers: 1) a control group without cardiovascular disease aged <50 years and 2) aged >50 years, and 3) a group with cardiovascular risk factors, defined as arterial hypertension, dyslipidemia, kidney failure and diabetes mellitus.ResultsPer group, the mean PEP was: 1) 58.5 ± 13.0 ms, 2) 52.4 ± 11.9 ms, and 3) 57.6 ± 11.6 ms. However, per individual the standard deviation was much smaller, i.e. 1) 2.0–5.9 ms, 2) 2.8–5.1 ms, and 3) 1.6–12.0 ms, respectively. There was no significant difference in the mean PEP of the 3 groups (p = 0.236).ConclusionIn conclusion, the intra-individual variability of PEP is small. A change in PTT in a person at rest is most probably the result of a change in VTT rather than of PEP. Thus, PTT at rest is an easy, non-invasive and accurate approximation of VTT for monitoring arterial stiffness.

Studies have demonstrated that a notable increase in arterial stiffening can signify the presence of cardiovascular abnormalities, such as hypertension. Presently, the mercury sphygmomanometer continues to be the clinical gold standard to identify such abnormalities, but due to its measuring nature it cannot be used for continuous observation. Pulse transit time (PTT), which has an inverse relationship with blood pressure (BP), is proposed here as a simple and non-invasive technique to monitor hypertension in children. In order to minimize inter-subject PTT differences, all obtained PTT data were normalized to the study population. The results indicated that normalized mean PTT value is able to differentiate hypertensive from normal children in a significant (p < 0.01) manner in both upper and lower limbs. Preliminary findings herein suggest that PTT can be useful tool to monitor for hypertension in children especially during prolonged clinical observations.

Prophylactic treatment has been proved to reduce hypotension incidence after spinal anesthesia during cesarean labor. However, the use of pharmacological prophylaxis could carry out undesirable side-effects on mother and fetus. Thus, the prediction of hypotension becomes an important challenge. Hypotension events are hypothesized to be related to a malfunctioning of autonomic nervous system (ANS) regulation of blood pressure. In this work, ANS responses to positional changes of 51 pregnant women programmed for a cesarean labor were explored for hypotension prediction. Lateral and supine decubitus, and sitting position were considered while electrocardiographic and pulse photoplethysmographic signals were recorded. Features based on heart rate variability, pulse rate variability (PRV) and pulse transit time (PTT) analysis were used in a logistic regression classifier. The results showed that PRV irregularity changes, assessed by approximate entropy, from supine to lateral decubitus, and standard deviation of PTT in supine decubitus were found as the combination of features that achieved the best classification results sensitivity of 76%, specificity of 70% and accuracy of 72%, being normotensive the positive class. Peripheral regulation and blood pressure changes, measured by PRV and PTT analysis, could help to predict hypotension events reducing prophylactic side-effects in the low-risk population.

Pulse pressure assessment in the human fetal descending aorta

Pulse wave velocity (PWV) is defined as the speed of conduction of a pressure wave generated by cardiac systole through the arterial tree. It may be non-invasively estimated from the pulse transit time that is measured as the interval between the R wave on an electrocardiogram and first inflexion point of the paired plethysmographic wave recorded from a finger pulse oximeter [1]. Within a simple two-component Windkessel model of the arterial system, PWV is proportional to the square root of arterial elastance [2]. Elastance is defined as the ratio of pulse pressure (PP) to stroke volume (SV). PWV might therefore provide a non-invasive estimate of cardiac output.

Pulse contour analysis (PCA) provides detailed evaluations of the accelerative and decelerative phases of the arterial pulse waveform, potentially associated with large artery stiffness and vascular ageing. Previous studies have reported age-related associations (both structural and functional) with PCA markers and stiffness. However, changes in functional stiffness under a drug produced due to the interplay of blood pressure and heart rate were not explored. In this work, we investigate the variation of PCA markers derived from the second derivative of invasive pressure waveform recorded from the carotid artery of an anaesthetized porcine model under drug intervention. The variations in PCA markers are compared with the functional stiffness surrogates (pulse wave velocity (PWV) _ regional and local), which are clinically relevant markers that vary with blood pressure and heart rate. Local and regional PWV was measured from pulse transit time, obtained from the carotid artery for the former and carotid-femoral artery for the latter. Group average local and regional PWV varied at least by 83.26%, and group average PCA markers by 25.19% for a 57.75% change in pulse pressure. PCA markers: b/a and c/a had statistically significant highest correlation (r = 0.63, r = −0.93 respectively, p < 0.001) with local PWV and pulse pressure (r = 0.73, r = −0.97 respectively, p < 0.001), whereas c/a and d/a had statistically significant highest correlation (r = −0.96, r = −0.98 respectively, p < 0.001) with regional PWV. The study helps understand the selective associations of PCA markers (through multivariate regression analysis) on local, regional stiffness and pulse pressure. Such PCA markers potentially provide information useful for developing vascular index matrices.