Comparison of noninvasive devices for assessing central blood pressure parameters: what to compare, when and why

Vascular aging and hypertension: Implications for the clinical application of central blood pressure

Vascular aging may be responsible for the high residual lifetime risk for hypertension in the middle-aged and elderly individuals. Increased arterial stiffness and wave reflection has been recognized as the dominant hemodynamic manifestations of vascular aging, and both are major determinants of central blood pressure (BP) and independent predictors for incident hypertension. Because central BP is strongly linearly associated with age, it can be regarded as an integrated marker for vascular aging. Central BP can be measured noninvasively using various techniques, including the convenient cuff-based oscillometric central BP monitors. Noninvasive central BP is likely better than the conventional brachial BP in association with target organ damages and long term cardiovascular outcomes. Based on the analysis of the long-term events of derivation and validation cohorts, the central BP threshold of 130/90mmHg for defining hypertension has been proposed. Recent studies suggest that the central BP strategy for confirming a diagnosis of hypertension may be more cost-effective than the conventional brachial BP strategy, and guidance of hypertension management with central BP may result in less use of medications to achieve BP control. Vascular aging-related hypertension is expected to become the dominant phenotype in many countries, especially in the Asian regions. Although noninvasive measurement of brachial BP is inaccurate and central BP has been shown to carry superior prognostic value beyond brachial BP, the use of central BP should be justified by studies comparing central blood pressure-guided therapeutic strategies with classic guidelines-guided strategies for preventing cardiovascular events. Future randomized control trials are required to support that the diagnosis and monitoring of vascular aging-related hypertension is best managed with the central BP strategy.

Is Noninvasive Brachial Systolic Blood Pressure an Accurate Estimate of Central Aortic Systolic Blood Pressure?

OBJECTIVES

Noninvasive brachial systolic blood pressure (nSBP-B) usually approaches invasive central systolic blood pressure (iSBP-C) with a high correlation. Whether nSBP-B is an accurate estimate of iSBP-C remained to be investigated. Thus, this study aimed to compare the errors of nSBP-B and noninvasive central systolic blood pressure (nSBP-C) with different techniques in estimating iSBP-C.

METHODS

Simultaneous invasive high-fidelity central aortic pressure waveforms and the noninvasive left brachial pulse volume recording (PVR) waveform were recorded in a Generation group ( N = 40) and a Validation group ( N = 100). The accuracy of the noninvasive estimates of iSBP-C obtained from analysis of the calibrated PVR waveform using the generalized transfer function (GTF), pulse waveform analysis (PWA), and N-point moving average (NPMA) methods was examined in the Validation group by calculating the mean absolute error (MAE).

RESULTS

In Generation group, the MAE was 4.6±4.1mm Hg between nSBP-B and invasive brachial SBP, and 6.8±5.5mm Hg between nSBP-B and iSBP-C. In comparison, the MAE of between iSBP-C and nSBP-C with PWA, NPMA, and GTF were 5.5±4.5, 5.8±4.9, and 5.9±5.0mm Hg, respectively. In Validation group, the MAE of nSBP-B (6.9±4.6mm Hg) for estimating iSBP-C was significantly greater than that of PWA (5.0±3.4mm Hg) and NPMA (6.1±4.4mm Hg), and GTF (6.1±4.9mm Hg). The percentage of absolute band error ≤5mm Hg was 62% for nSBP-B, 69% for GTF, 83% for PWA, and 69% for NPMA.

CONCLUSIONS

The accuracy of nSBP-B was inferior to the n SBP-C measures in estimating iSBP-C.

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand-alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.

Brachial vs. central systolic pressure and pulse wave transmission indicators: a critical analysis

This critique is intended to provide background for the reader to evaluate the relative clinical utilities of brachial cuff systolic blood pressure (SBP) and its derivatives, including pulse pressure, central systolic pressure, central augmentation index (AI), and pulse pressure amplification (PPA). The critical question is whether the newer indicators add sufficient information to justify replacing or augmenting brachial cuff blood pressure (BP) data in research and patient care. Historical context, pathophysiology of variations in pulse wave transmission and reflection, issues related to measurement and model errors, statistical limitations, and clinical correlations are presented, along with new comparative data. Based on this overview, there is no compelling scientific or practical reason to replace cuff SBP with any of the newer indicators in the vast majority of clinical situations. Supplemental value for central SBP may exist in defining patients with exaggerated PPA ("spurious systolic hypertension"), managing cardiac and aortic diseases, and in studies of cardiovascular drugs, but there are no current standards for these possibilities.

Invasive validation of arteriograph estimates of central blood pressure in patients with type 2 diabetes

BACKGROUND

Central blood pressure (BP) has attracted increasing interest because of a potential superiority over brachial BP in predicting cardiovascular morbidity and mortality. Several devices estimating central BP noninvasively are now available. The aim of our study was to determine the validity of the Arteriograph, a brachial cuff-based, oscillometric device, in patients with type 2 diabetes.

METHODS

We measured central BP invasively and compared it with the Arteriograph-estimated values in 22 type 2 diabetic patients referred to elective coronary angiography.

RESULTS

The difference (invasively measured BP minus Arteriograph-estimated BP) in central systolic BP (SBP) was 4.4±8.7 mm Hg (P = 0.03). The limits of agreement were ±17.1 mm Hg.

CONCLUSIONS

Compared with invasively measured central SBP, we found a systematic underestimation by the Arteriograph. However, the limits of agreement were similar to the previous Arteriograph validation study and to the invasive validation studies of other brachial cuff-based, oscillometric devices. A limitation in our study was the large number of patients (n = 14 of 36) in which the Arteriograph was unable to analyze the pressure curves. In a research setting, the Arteriograph seems applicable in patients with type 2 diabetes.

CLINICAL TRAIL REGISTRATION

ClinicalTrials.gov ID NCT01538290.

The barriers to clinical application of non-invasively obtained central blood pressure

With the demonstration of superior prognostic value of central blood pressure (CBP) beyond traditionally used brachial BP, there have been increasing interest in the development of novel devices reporting parameters of CBP. The emerging devices for non-invasive estimation of CBP, based on either tonometry-based or cuff-based techniques, were evaluated with various validation studies. Therefore, the research community and clinicians have been faced with challenges regarding the conduction and interpretation of the validation studies for the non-invasively obtained CBP. We summarize here the barriers to the clinical application of the CBP concept, which provide research opportunities to further the subsequent translation.