In recent years, great emphasis has been placed on the role of arterial stiffness in the development of cardiovascular diseases. Indeed, the assessment of arterial stiffness is increasingly used in the clinical assessment of patients. Although several papers have previously addressed the methodological issues concerning the various indices of arterial stiffness currently available, and their clinical applications, clinicians and researchers still report difficulties in selecting the most appropriate methodology for their specific use. This paper summarizes the proceedings of several meetings of the European Network for Non-invasive Investigation of Large Arteries and is aimed at providing an updated and practical overview of the most relevant methodological aspects and clinical applications in this area.

Expert consensus document on arterial stiffness: methodological issues and clinical applications

Expert consensus document on arterial stiffness : methodological issues and clinical applications. Commentary

Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. It is often used non-invasively to make measurements at the skin surface. The PPG waveform comprises a pulsatile ('AC') physiological waveform attributed to cardiac synchronous changes in the blood volume with each heart beat, and is superimposed on a slowly varying ('DC') baseline with various lower frequency components attributed to respiration, sympathetic nervous system activity and thermoregulation. Although the origins of the components of the PPG signal are not fully understood, it is generally accepted that they can provide valuable information about the cardiovascular system. There has been a resurgence of interest in the technique in recent years, driven by the demand for low cost, simple and portable technology for the primary care and community based clinical settings, the wide availability of low cost and small semiconductor components, and the advancement of computer-based pulse wave analysis techniques. The PPG technology has been used in a wide range of commercially available medical devices for measuring oxygen saturation, blood pressure and cardiac output, assessing autonomic function and also detecting peripheral vascular disease. The introductory sections of the topical review describe the basic principle of operation and interaction of light with tissue, early and recent history of PPG, instrumentation, measurement protocol, and pulse wave analysis. The review then focuses on the applications of PPG in clinical physiological measurements, including clinical physiological monitoring, vascular assessment and autonomic function.

https://iopscience.iop.org/article/10.1088/0967-3334/28/3/R01/pdf

Photoplethysmography and its application in clinical physiological measurement.

Background— Different blood pressure (BP)–lowering drugs could have different effects on central aortic pressures and thus cardiovascular outcome despite similar effects on brachial BP. The Conduit Artery Function Evaluation (CAFE) study, a substudy of the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT), examined the impact of 2 different BP lowering-regimens (atenolol±thiazide-based versus amlodipine±perindopril-based therapy) on derived central aortic pressures and hemodynamics. Methods and Results— The CAFE study recruited 2199 patients in 5 ASCOT centers. Radial artery applanation tonometry and pulse wave analysis were used to derive central aortic pressures and hemodynamic indexes on repeated visits for up to 4 years. Most patients received combination therapy throughout the study. Despite similar brachial systolic BPs between treatment groups (Δ0.7 mm Hg; 95% CI, −0.4 to 1.7; P=0.2), there were substantial reductions in central aortic pressures with the amlodipine regimen (central aortic systolic ...

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Differential impact of blood pressure-lowering drugs on central aortic pressure and clinical outcomes: principal results of the Conduit Artery Function Evaluation (CAFE) study.

Background— Arterial distensibility measures, generally from pulse-wave velocity (PWV), are widely used with little knowledge of relationships to patient outcome. We tested whether aortic PWV predicts cardiovascular and all-cause mortality in type 2 diabetes and glucose-tolerance–tested (GTT) multiethnic population samples. Methods and Results— Participants were randomly sampled from (1) a type 2 diabetes outpatient clinic and (2) primary care population registers, from which nondiabetic control subjects were given a GTT. Brachial blood pressures and Doppler-derived aortic PWV were measured. Mortality data over 10 years’ follow-up were obtained. At any level of systolic blood pressure (SBP), aortic PWV was greater in subjects with diabetes than in controls. Mortality risk doubled in subjects with diabetes (hazard ratio 2.34, 95% CI 1.5 to 3.74) and in those with glucose intolerance (2.12, 95% CI 1.11 to 4.0) compared with controls. For all groups combined, age, sex, and SBP predicted mortality; the additi...

Aortic pulse-wave velocity and its relationship to mortality in diabetes and glucose intolerance: an integrated index of vascular function?

The stiffness of the aorta can be determined by measuring carotid-femoral pulse wave velocity (PWV(cf)). PWV may also influence the contour of the peripheral pulse, suggesting that contour analysis might be used to assess large artery stiffness. An index of large artery stiffness (SI(DVP)) derived from the digital volume pulse (DVP) measured by transmission of IR light (photoplethysmography) was examined. SI(DVP) was obtained from subject height and from the time delay between direct and reflected waves in the DVP. The timing of these components of the DVP is determined by PWV in the aorta and large arteries. SI(DVP) was, therefore, expected to provide a measure of stiffness similar to PWV. SI(DVP) was compared with PWV(cf) obtained by applanation tonometry in 87 asymptomatic subjects (21-68 years; 29 women). The reproducibility of SI(DVP) and PWV(cf) and the response of SI(DVP) to glyceryl trinitrate were assessed in subsets of subjects. The mean within-subject coefficient of variation of SI(DVP), for measurements at weekly intervals, was 9.6%. SI(DVP) was correlated with PWV(cf) ( r =0.65, P <0.0001). SI(DVP) and PWV(cf) were each independently correlated with age and mean arterial blood pressure (MAP) with similar regression coefficients: SI(DVP)=0.63+0.086 x age+0.042 x MAP ( r =0.69, P <0.0001); PWV(cf)=0.76+0.080 x age+0.053 x MAP ( r =0.71, P <0.0001). Administration of glyceryl trinitrate (3, 30 and 300 microg/min intravenous; each dose for 15 min) in nine healthy men produced similar changes in SI(DVP) and PWV(cf). Thus contour analysis of the DVP provides a simple, reproducible, non-invasive measure of large artery stiffness.

Determination of age-related increases in large artery stiffness by digital pulse contour analysis.

Aortic augmentation index, a measure of central systolic blood pressure augmentation arising mainly from pressure-wave reflection, increases with vascular aging. The augmentation index is influenced by aortic pulse-wave velocity (related to aortic stiffness) and by the site and extent of wave reflection. To clarify the relative influence of pulse-wave velocity and wave reflection on the augmentation index, we studied the association between augmentation index, pulse-wave velocity, and age and examined the effects of vasoactive drugs to determine whether altering vascular tone has differential effects on pulse-wave velocity and the augmentation index. We made simultaneous measurements of the augmentation index and carotid-to-femoral pulse-wave velocity in 50 asymptomatic men aged 19 to 74 years at baseline and, in a subset, during the administration of nitroglycerin, angiotensin II, and saline vehicle. The aortic augmentation index was obtained by radial tonometry (Sphygmocor device, PWV Medical) with the use of an inbuilt radial to aortic transfer function. In multiple regression analysis, the aortic augmentation index was independently correlated only with age (R=0.58, P<0.0001). Nitroglycerin (3 to 300 microg/min IV) reduced the aortic augmentation index from 4.8+/-2.3% to -11.9+/-5.3% (n=10, P<0.002). Angiotensin II (75 to 300 ng/min IV) increased the aortic augmentation index from 9.3+/-2.4% to 18.3+/-2.9% (n=12, P<0.001). These drugs had small effects on aortic pulse-wave velocity, producing mean changes from baseline of <1 m/s (each P<0.05). In healthy men, vasoactive drugs may change aortic augmentation index independently from aortic pulse-wave velocity.

Vasoactive Drugs Influence Aortic Augmentation Index Independently of Pulse-Wave Velocity in Healthy Men

Photoplethysmographic assessment of pulse wave reflection: blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus.

The digital volume pulse can be recorded simply and noninvasively by photoplethysmography. The objective of the present study was to determine whether a generalized transfer function can be used to relate the digital volume pulse to the peripheral pressure pulse and, hence, to determine whether both volume and pressure pulse waveforms are influenced by the same mechanism. The digital volume pulse was recorded by photoplethysmography in 60 subjects (10 women, aged 24 to 80 years), including 20 subjects with previously diagnosed hypertension. Simultaneous recordings of the peripheral radial pulse and digital artery pulse were obtained by applanation tonometry and a servocontrolled pressure cuff (Finapres), respectively. In 20 normotensive subjects, measurements were obtained after the administration of nitroglycerin (NTG, 500 microgram sublingually). Transfer functions obtained by Fourier analysis of the waveforms were similar in normotensive and hypertensive subjects. In normotensive subjects, transfer functions were similar before and after NTG. By use of a single generalized transfer function for all subjects, the radial and digital artery pressure waveforms could be predicted from the volume pulse with an average root mean square error of 4.4+/-2.0 and 4.3+/-1.9 mm Hg (mean+/-SD) for radial and digital artery waveforms, respectively, similar to the error between the 2 pressure waveforms (4.4+/-1.4 mm Hg). The peripheral pressure pulse is related to the digital volume pulse by a transfer function, which is not influenced by effects of hypertension or NTG. Effects of NTG on the volume pulse and pressure pulse are likely to be determined by a similar mechanism.

R P Kelly

Papers

Determination of age-related increases in large artery stiffness by digital pulse contour analysis.

Vasoactive Drugs Influence Aortic Augmentation Index Independently of Pulse-Wave Velocity in Healthy Men

Photoplethysmographic assessment of pulse wave reflection: blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus.

Noninvasive assessment of the digital volume pulse. Comparison with the peripheral pressure pulse.

The vascular impact of aging and vasoactive drugs: comparison of two digital volume pulse measurements