Bernhard Hametner

Validation of a Brachial Cuff-Based Method for Estimating Central Systolic Blood Pressure

The prognostic value of central systolic blood pressure has been established recently. At present, its noninvasive assessment is limited by the need of dedicated equipment and trained operators. Moreover, ambulatory and home blood pressure monitoring of central pressures are not feasible. An algorithm enabling conventional automated oscillometric blood pressure monitors to assess central systolic pressure could be of value. We compared central systolic pressure, calculated with a transfer-function like method (ARCSolver algorithm), using waveforms recorded with a regular oscillometric cuff suitable for ambulatory measurements, with simultaneous high-fidelity invasive recordings, and with noninvasive estimations using a validated device, operating with radial tonometry and a generalized transfer function. Both studies revealed a good agreement between the oscillometric cuff-based central systolic pressure and the comparator. In the invasive study, composed of 30 patients, mean difference between oscillometric cuff/ARCSolver-based and invasive central systolic pressures was 3.0 mm Hg (SD: 6.0 mm Hg) with invasive calibration of brachial waveforms and −3.0 mm Hg (SD: 9.5 mm Hg) with noninvasive calibration of brachial waveforms. Results were similar when the reference method (radial tonometry/transfer function) was compared with invasive measurements. In the noninvasive study, composed of 111 patients, mean difference between oscillometric cuff/ARCSolver–derived and radial tonometry/transfer function–derived central systolic pressures was −0.5 mm Hg (SD: 4.7 mm Hg). In conclusion, a novel transfer function-like algorithm, using brachial cuff-based waveform recordings, is suited to provide a realistic estimation of central systolic pressure.

Wave Reflections, Assessed With a Novel Method for Pulse Wave Separation, Are Associated With End-Organ Damage and Clinical Outcomes

We recently developed a novel method for assessment of arterial wave reflections (ARCSolver method): based on adopted Windkessel methods, flow curves are estimated from pressure waveforms, and wave separation analysis is performed, yielding the amplitudes of the forward and backward waves. The aim of this study was to investigate their clinical correlates and prognostic impact. In 725 patients (417 men; mean age, 64 years) undergoing coronary angiography, we determined wave reflections from radial tonometry and transfer function-derived aortic waveforms using pulse wave analysis, as well as wave separation analysis. Measures of pulsatile arterial function were statistically significant, although moderately associated with markers of cardiac load and subclinic cardiac, renal, and aortic end-organ damage. After a median follow-up duration of 1399 days, 139 patients reached the combined cardiovascular end point (death, myocardial infarction, stroke, coronary, cerebrovascular, and peripheral revascularization). In univariate analysis, the relative risk of the combined end point increased with increasing levels of incident pressure wave height, augmented pressure, and forward and backward wave amplitude (hazard ratio for 1 SD was 1.302, 1.236, 1.226, and 1.276; P<0.01 for all, respectively). In multivariate analysis, backward wave amplitude was the most consistent predictor of the combined end point. Of note, its predictive value was independent of brachial systolic, diastolic, and mean blood pressures and was superior to brachial pulse pressure. In conclusion, the amplitude of the reflected wave, as assessed with a novel method for wave separation, is associated with hypertensive end organ damage and is an independent predictor of cardiovascular events in high-risk patients.

Oscillometric estimation of aortic pulse wave velocity: comparison with intra-aortic catheter measurements.

ObjectivesRecently, a novel method to estimate aortic pulse wave velocity (aPWV) noninvasively from an oscillometric single brachial cuff waveform reading has been introduced. We investigated whether this new approach provides acceptable estimates of aPWV compared with intra-aortic catheter measurements. MethodsEstimated values of aPWV obtained from brachial cuff readings were compared with those obtained using an intra-aortic catheter in 120 patients (mean age 61.8±10.8 years) suspected for coronary artery disease undergoing cardiac catheterization. Differences between aPWV values obtained from the test device and those obtained from catheter measurements were estimated using Bland–Altman analysis. ResultsThe mean difference±SD between brachial cuff-derived values and intra-aortic values was 0.43±1.24 m/s. Comparison of aPWV measured by the two methods showed a significant linear correlation (Pearson’s R=0.81, P<0.0001). The mean difference for repeated oscillometric measurements of aPWV was 0.05 m/s, with 95% confidence interval limits from −0.47 to 0.57 m/s. ConclusionaPWV can be obtained using an oscillometric device with brachial cuffs with acceptable accuracy compared with intra-aortic readings.

Wave reflection quantification based on pressure waveforms alone-Methods, comparison, and clinical covariates

Within the last decade the quantification of pulse wave reflections mainly focused on measures of central aortic systolic pressure and its augmentation through reflections based on pulse wave analysis (PWA). A complementary approach is the wave separation analysis (WSA), which quantifies the total amount of arterial wave reflection considering both aortic pulse and flow waves. The aim of this work is the introduction and comparison of aortic blood flow models for WSA assessment. To evaluate the performance of the proposed modeling approaches (Windkessel, triangular and averaged flow), comparisons against Doppler measurements are made for 148 patients with preserved ejection fraction. Stepwise regression analysis between WSA and PWA parameters are performed to provide determinants of methodological differences. Against Doppler measurement mean difference and standard deviation of the amplitudes of the decomposed forward and backward pressure waves are comparable for Windkessel and averaged flow models. Stepwise regression analysis shows similar determinants between Doppler and Windkessel model only. The results indicate that the Windkessel method provides accurate estimates of wave reflection in subjects with preserved ejection fraction. The comparison with waveforms derived from Doppler ultrasound as well as recently proposed simple triangular and averaged flow waves showed that this approach may reduce variability and provide realistic results.

Noninvasive methods to assess pulse wave velocity: comparison with the invasive gold standard and relationship with organ damage.

Objectives: To compare noninvasive methods to assess pulse wave velocity (PWV) with the invasive gold standard in terms of absolute values, age-related changes, and relationship with subclinical organ damage. Methods: Invasive aortic PWV (aoPWVinv) was measured in 915 patients undergoing cardiac catheterization (mean age 61 years, range 27–87 years). Carotid–femoral PWV (cfPWV) was measured with tonometry, using subtracted distance (cfPWVsub), body height-based estimated distance (cfPWVbh), direct distance × 0.8 (cfPWVdir0.8), and caliper-based distance (cfPWVcalip) for travel distance calculation. Aortic PWV was estimated (aoPWVestim) from single-point radial waveforms, age, and SBP. Results: Invasive and noninvasive transit times were strikingly similar (median values 60.8 versus 61.7 ms). In the entire group, median value of aoPWVinv was 8.3 m/s, of cfPWVsub and cfPWVbh 8.1 m/s, and of aoPWVest 8.5 m/s. CfPWVsub overestimated aoPWVinv in younger patients by 0.7 m/s and underestimated aoPWVinv in older patients by 1.7 m/s, with good agreement from 50 to 70 years of age. AoPWVestim differed from aoPWVinv by no more than 0.4 m/s across all age groups. CfPWVdir0.8, measured in 632 patients, overestimated aoPWVinv by 1.7 m/s in younger patients, with good agreement in middle-aged and older patients. CfPWVcalip, measured in 336 patients, underestimated aoPWVinv in all ages. In 536 patients with preserved systolic function, aoPWVinv and aoPWVestim were superior to cfPWVs in predicting coronary atherosclerosis, renal function impairment, left atrial enlargement, and diastolic dysfunction. Conclusion: CfPWVsub, cfPWVdir0.8, and aoPWVestim are reasonable surrogates for aoPWVinv. AoPWVinv predicts subclinical organ damage better than cfPWVs, and as good as aoPWVestim.

Assessment of central haemomodynamics from a brachial cuff in a community setting

BackgroundLarge artery stiffening and wave reflections are independent predictors of adverse events. To date, their assessment has been limited to specialised techniques and settings. A new, more practical method allowing assessment of central blood pressure from waveforms recorded using a conventional automated oscillometric monitor has recently been validated in laboratory settings. However, the feasibility of this method in a community based setting has not been assessed.MethodsOne-off peripheral and central haemodynamic (systolic and diastolic blood pressure (BP) and pulse pressure) and wave reflection parameters (augmentation pressure (AP) and index, AIx) were obtained from 1,903 volunteers in an Austrian community setting using a transfer-function like method (ARCSolver algorithm) and from waveforms recorded with a regular oscillometric cuff. We assessed these parameters for known differences and associations according to gender and age deciles from <30 years to >80 years in the whole population and a subset with a systolic BP < 140 mmHg.ResultsWe obtained 1,793 measures of peripheral and central BP, PP and augmentation parameters. Age and gender associations with central haemodynamic and augmentation parameters reflected those previously established from reference standard non-invasive techniques under specialised settings. Findings were the same for patients with a systolic BP below 140 mmHg (i.e. normotensive). Lower values for AIx in the current study are possibly due to differences in sampling rates, detection frequency and/or averaging procedures and to lower numbers of volunteers in younger age groups.ConclusionA novel transfer-function like algorithm, using brachial cuff-based waveform recordings, provides robust and feasible estimates of central systolic pressure and augmentation in community-based settings.

Effect of Monthly, High‐Dose, Long‐Term Vitamin D Supplementation on Central Blood Pressure Parameters: A Randomized Controlled Trial Substudy

Background The effects of monthly, high‐dose, long‐term (≥1‐year) vitamin D supplementation on central blood pressure (BP) parameters are unknown. Methods and Results A total of 517 adults (58% male, aged 50–84 years) were recruited into a double‐blinded, placebo‐controlled trial substudy and randomized to receive, for 1.1 years (median; range: 0.9–1.5 years), either (1) vitamin D3 200 000 IU (initial dose) followed 1 month later by monthly 100 000‐IU doses (n=256) or (2) placebo monthly (n=261). At baseline (n=517) and follow‐up (n=380), suprasystolic oscillometry was undertaken, yielding aortic BP waveforms and hemodynamic parameters. Mean deseasonalized 25‐hydroxyvitamin D increased from 66 nmol/L (SD: 24) at baseline to 122 nmol/L (SD: 42) at follow‐up in the vitamin D group, with no change in the placebo group. Despite small, nonsignificant changes in hemodynamic parameters in the total sample (primary outcome), we observed consistently favorable changes among the 150 participants with vitamin D deficiency (<50 nmol/L) at baseline. In this subgroup, mean changes in the vitamin D group (n=71) versus placebo group (n=79) were −5.3 mm Hg (95% confidence interval [CI], −11.8 to 1.3) for brachial systolic BP (P=0.11), −2.8 mm Hg (95% CI, −6.2 to 0.7) for brachial diastolic BP (P=0.12), −7.5 mm Hg (95% CI, −14.4 to −0.6) for aortic systolic BP (P=0.03), −5.7 mm Hg (95% CI, −10.8 to −0.6) for augmentation index (P=0.03), −0.3 m/s (95% CI, −0.6 to −0.1) for pulse wave velocity (P=0.02), −8.6 mm Hg (95% CI, −15.4 to −1.9) for peak reservoir pressure (P=0.01), and −3.6 mm Hg (95% CI, −6.3 to −0.8) for backward pressure amplitude (P=0.01). Conclusions Monthly, high‐dose, 1‐year vitamin D supplementation lowered central BP parameters among adults with vitamin D deficiency but not in the total sample. Clinical Trial Registration URL: http://www.anzctr.org.au. Unique identifier: ACTRN12611000402943.

Non-invasive wave reflection quantification in patients with reduced ejection fraction

The non-invasive quantification of arterial wave reflection is an increasingly important concept in cardiovascular research. It is commonly based on pulse wave analysis (PWA) of aortic pressure. Alternatively, wave separation analysis (WSA) considering both aortic pressure and flow waveforms can be applied. Necessary estimates of aortic flow can be measured by Doppler ultrasound or provided by mathematical models. However, this approach has not been investigated intensively up to now in subjects developing systolic heart failure characterized by highly reduced ejection fraction (EF). We used non-invasively generated aortic pressure waveforms and Doppler flow measurements to derive wave reflection parameters in 61 patients with highly reduced and 122 patients with normal EF. Additionally we compared these readings with estimates from three different flow models known from literature (triangular, averaged, Windkessel). After correction for confounding factors, all parameters of wave reflection (PWA and WSA) were comparable for patients with reduced and normal EF. Wave separations assessed with the Windkessel based model were similar to those derived from Doppler flow in both groups. The averaged waveform performed poorer in reduced than in normal EF, whereas triangular flow represented a better approximation for reduced EF. Overall, the non-invasive assessment of WSA parameters based on mathematical models compared to ultrasound seems feasible in patients with reduced EF.

Performance of pulse wave velocity measured using a brachial cuff in a community setting

BackgroundWe have previously reported that estimation of central blood pressure (BP) and augmentation using an automated oscillometric device are robust and feasible in a community setting. The same method has recently been validated for estimating aortic pulse wave velocity (aPWV) in laboratory settings, and its prognostic value has been confirmed in a prospective clinical trial. ObjectiveThe aim of this study was to assess the performance of aPWV estimates from an oscillometric device in a community-based setting. MethodsWe assessed estimates of aPWV for compatibility with data from reference noninvasive techniques. Estimates of aPWV were obtained in a community setting from a general population of 1903 volunteers (age range 14–99 years). Values of aPWV were analyzed according to sex and each age decile from less than 30 years to greater than 80 years and for a subset of patients with a peripheral systolic BP of less than 140 mmHg (n=1064). ResultsWe obtained valid measures of PWV from 1794 volunteers. Age (r=0.94, P<0.001) and BP category (r=0.63, P<0.001) were associated with aPWV, which was also statistically (P=0.002) but not clinically (<0.1 m/s) higher among female individuals after correction for quadratic age and mean BP. Known differences in and associations of aPWV with sex, age, and BP category mirrored those previously established from reference-standard noninvasive techniques in nonroutine clinical settings. ConclusionData presented here represent initial reference values for cuff-based estimates of aPWV, which can now be obtained in routine clinical practice (e.g. primary care).

Calculation of arterial characteristic impedance: a comparison using different blood flow models

Within the concept of pulse wave analysis, arterial pressure and flow curves over a whole cardiac cycle are analysed. Characteristic impedance is obtained as ratio of pressure to flow when waves are not influenced by reflections. The aim of this work is to evaluate the effects of different blood flow models on the determination of the characteristic impedance compared to flow curves gained from ultrasound measurements. Beside a simple triangular and an averaged flow, a new blood flow model based on Windkessel theory is used. In a study population of 148 patients for the evaluation of the different models, the characteristic impedance is calculated in the frequency domain. The results indicate that the characteristic impedance strongly depends on the accuracy of the used flow model. While the averaged and the ARCSolver flow provide good estimates for impedance, the triangular flow curve seems to be too simplistic for getting accurate values.