Time to end a doubt: is pulse wave analysis a valid measure for central arterial blood pressure and arterial stiffness?

A cohort evaluation on arterial stiffness and hypertensive disorders in pregnancy

BACKGROUND

Hypertensive disorders in pregnancy are associated with systemic endothelial dysfunction leading to impaired physiological vasodilation. Recent evidence has shown central aortic pressures obtained through pulse wave analysis, at less than 14 weeks of gestation, to be predictive of pre-eclampsia. In light of this, we aimed to evaluate the role of central aortic stiffness in the prediction and discrimination of hypertensive disorders in pregnancy.

METHODS

A cohort study of women with viable, singleton pregnancies at less than 14 weeks of amenorrhoea, and without multiple pregnancies, autoimmune or renal disease, diagnosed with aneuploidy or fetal anomaly will be recruited from a single maternity hospital and followed up till delivery and puerperium. A targeted sample size of 1000 eligible pregnant women will be enrolled into the study from antenatal clinics. Main exposure under study is central aortic pulse pressure using radial pulse wave recording, and the outcomes under follow-up are gestational hypertension and pre-eclampsia. Other measures include lifestyle factors such as smoking, physical exercise, psychometric evaluations, vasoactive factors, uterine artery pulsatility index, height and weight measurements. These measures will be repeated over 4 antenatal visits at 11-14, 18-22, 28-32 and above 34 weeks of gestation. Double data entry will be performed on Microsoft Access, and analysis of data will include the use of random effect models and receiver operating characteristic curves on Stata 11.2.

DISCUSSION

The proposed study design will enable a longitudinal evaluation of the central aortic pressure changes as a marker for vascular compliance during pregnancy. As measures are repeated over time, the timing and severity of changes are detectable, and findings may yield important information on how aberrant vascular responses occur and its role in the early detection and prediction of hypertensive disorders.

Measurement accuracy of non-invasively obtained central blood pressure by applanation tonometry: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVES

Non-invasive methods based on applanation tonometry have been proposed to estimate central blood pressure. However, the accuracy of these methods hasn't been systematically examined.

METHODS

We performed a systematic review and meta-analysis of studies comparing estimated and invasively measured central BP.

RESULTS

Sufficient data were available in 22 studies for meta-analysis (857 subjects and 1167 measurements). Acquired arterial pressure waveforms in these studies were directly measured, calibrated to match invasive aortic mean BP and diastolic BP or calibrated to match brachial BP measured with a sphygmomanometer, cuff BP. Of the former 2 conditions, the errors of estimated central BP were small with a mean and standard deviation of difference -1.1 ± 4.1mm Hg (95% limits of agreement -9.1-6.9 mm Hg) for central systolic BP; -0.5 ± 2.1mm Hg (-4.6-3.6mm Hg) for central diastolic BP; and -0.8 ± 5.1mm Hg (-10.8-9.2mm Hg) for central pulse pressure. However, the errors inflated to -8.2 ± 10.3mm Hg (-28.4-12.0mm Hg) for central systolic BP, 7.6 ± 8.7 mm Hg (-9.5-24.6mm Hg) for central diastolic BP, and -12.2 ± 10.4mm Hg (-32.5-8.1mm Hg) for central pulse pressure, when calibrated to cuff BP. The findings were still evident in subgroup analysis conducted with different central BP estimating methods and validated cuff BP monitors.

CONCLUSION

Present tonometry-based central BP estimating methods are acceptable in theory, with small errors. However, based on current available evidence, there is substantial room for improvement in measurement accuracy of central BP when cuff BP is used to calibrate the peripheral waveforms.

Brachial blood pressure-independent relations between radial late systolic shoulder-derived aortic pressures and target organ changes

Central aortic blood pressure (BP; BPc) predicts outcomes beyond brachial BP. In this regard, the application of a generalized transfer function (GTF) to radial pulse waves for the derivation of BPc is an easy and reproducible measurement technique. However, the use of the GTF may not be appropriate in all circumstances. Although the peak of the second shoulder of the radial waveform (P2) is closely associated with BPc, and, hence, BPc may be assessed without the need for a GTF, whether P2-derived BPc is associated with adverse cardiovascular changes independent of brachial BP is uncertain. Thus, P2- and GTF-derived aortic BPs were assessed using applanation tonometry and SphygmoCor software. Left ventricular mass was indexed for height(1.7) (n=678) and carotid intima-media thickness (IMT; n=462) was determined using echocardiography and vascular ultrasound. With adjustments for nurse-derived brachial pulse pressure (PP), P2-derived central PP was independently associated with left ventricular mass indexed for height(1.7) (partial r=0.18; P<0.0001) and IMT (partial r=0.40; P<0.0001). These relations were similar to nurse-derived brachial PP-independent relations between GTF-derived central PP and target organ changes (left ventricular mass indexed for height(1.7): partial r=0.17, P<0.0001; IMT: partial r=0.37, P<0.0001). In contrast, with adjustments for central PP, nurse-derived brachial PP-target organ relations were eliminated (partial r=-0.21 to 0.05). Twenty-four-hour, day, and night PP-target organ relations did not survive adjustments for nurse-derived brachial BP. In conclusion, central PP derived from P2, which does not require a GTF, is associated with cardiovascular target organ changes independent of brachial BP. Thus, when assessing adverse cardiovascular effects of aortic BP independent of brachial BP, P2-derived measures may complement GTF-derived measures of aortic BP.

Measurement Accuracy of Non-invasively Obtained Central Blood Pressure: A Systematic Review and Meta-analysis

BACKGROUND

Blood pressures determined at different sites vary considerably. Non-invasive methods are available to estimate central aortic blood pressure, the blood pressure at the origin of all arterial pulses. These methods obtain estimated central blood pressure by calibration and/or mathematical calculations for peripheral pulse waveforms. However, the accuracy of these methods has not been systematically examined.

OBJECTIVES

The review aimed to synthesise the best evidence on the accuracy of non-invasive measurement methods for central blood pressure.

INCLUSION CRITERIA

Types of participantsStudies with adult patients receiving invasive and non-invasive measurements of central blood pressure were considered.

PHENOMENA OF INTEREST

Studies were considered for inclusion if the focus was accuracy of non-invasive central BP estimating methods compared to invasively obtained corresponding values.

TYPES OF STUDIES

Studies examining agreement between measurements using non-invasive central blood pressure estimating methods compared to invasive corresponding values were considered.

TYPES OF OUTCOMES

This review included the means and standard deviation of differences between estimated and invasively measured central blood pressure.

SEARCH STRATEGY

The search sought to identify any relevant published or unpublished studies with a three-step search strategy.

METHODOLOGICAL QUALITY

Two independent reviewers assessed methodological quality of studies by a critical appraisal tool modified from Cochrane Diagnostic Test Accuracy Working Group.

DATA COLLECTION

We used an original form to extract from included studies all study characteristics possibly related to agreement.

DATA SYNTHESIS

Inverse variance weighted approach and DerSimonian-Laird weights for the random effects model, which incorporates a between-study variance, were used to obtain pooled estimates of systematic and random error from individual study estimates of the mean and standard deviation of differences between the paired measurements. Heterogeneity was assessed using Cochran Q. All analyses were performed in Microsoft Excel 2003.

RESULTS

Twenty eight studies were eligible for inclusion and critically appraised in this review. Appropriate data for agreement were extracted from papers or authors in 20 studies, which were further included in meta-analysis. Acquired peripheral waveforms in these studies were directly measured, calibrated to match invasively obtained aortic mean blood pressure and diastolic blood pressure, or calibrated using brachial blood pressure measured by sphygomomanometer, the cuff blood pressure. Estimated central blood pressure of the studies using the last totally non-invasively methods (real world practices) were subject to meta-analysis separately from studies with the former two invasive methods (theoretical practice). Of the invasive methods, mean difference of the estimated central blood pressure was small (-1.2 ± 4.2mmHg for central systolic blood pressure, -0.6 ± 2.1mmHg for central diastolic blood pressure, and -1.1 ± 5.3 mmHg for central pulse pressure). However, the errors of the non-invasive method inflated considerably (-8.1 ± 10.7mmHg for central systolic blood pressure, 8.8 ± 9.5mmHg for central diastolic blood pressure, and -11.8 ± 13.3 mmHg for central pulse pressure). The findings were similar in subgroup analysis by different central blood pressure methods and by validated cuff monitors.

CONCLUSIONS

Current central blood pressure estimating methods are acceptable in theory with small systematic and random error. However, the error of these methods was evident when cuff blood pressure was used for calibration and probably made them clinically inapplicable.